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MINERAL DEPOSITS AND GEOLOGY OF NORTHERN OMAN AS OF 1974
By R. G. Coleraan and E. H. Bailey
U. S. Geological Survey
Open-File Report 81 - /-^Sy
This report is preliminary and has not been
reviewed for confornjity with U. S. Geological
Survey editorial standards and stratigraphic
nomenclature. Any use of trade names is for
descriptive purposes only and does not imply
endorsement bv the USGS.
Pr'ep'ar'e-.'. oia 'behalf of the Directorate Genera], of Petroleum and Minerals,
•Ministry of Development, Sultanate of Oman.
1931

Frontispiece. Headquarters building of the Directorate of Petroleum
and Minerals, Ministry of Development, Muscat, Sultanate of Oman.

CONTENTS
Page
Suiiunary 1
Introduction la
Staff la
Methods of investigation and logistics. la
-Acknowledgements .....: 3
Geography. 3
(Oology. 5
Previous work ;........ 5
Geologic overview 9
Basement rocks (Autochthon) 10
Pre-Permian rocks 10
.Arabian Shelf Carbonates....... 10
Ophiolite and related rocks (Allochthon) 10
Semail ophiolite 10
Hawasina unit, exotics, melange, and metamorphics 14
Sedimentary rocks lying on Semail ophiolite 18
Shallow-water marine limestone ',.... 13
Pliocene-Holocene deposits.. • ••• 18
Structural history 19
Economic geology—metallic minerals . 21
Summary -1
Copper deposits of the Semail ophiolite. I'i
Dfescriptions of copper deposits in volcanic rocks 30
•-(1) Semda 30
(2) Lushil.. '. 33
(3) Zabin. 36
(4) Fizh .. 39
yS) Khabiyat .. 39
c (6) Bayda. 42
0 (7) Aarja 45
(8) Ghayth 48
^^ (9) Usail ..., 51
(10) Jabah. 54
(11) Rakah 54
Descriptions of copper deposits in gabbro and peridotite. 58
(12) Maydan I.. .*... '. . . 58
(13) Maydan II. . .... 58
(14) Bu Kathir 58
(15) Hawirdit... 62
(16) Tawi Ubaylah.' 62
(17) Ghayl.. 65
(18) Muden 65
(19)'L-azak 65
(20) Tabakhat '. 66
(21) Khafifah .......; 69
(22) .Masakivah.. 69
II

- . Page
(23) Inah ... 69
(24) Eedah I. 69
(25) Eedah il... .., " 70
(26) Hoowasi 70
(27) Khara.,-. 71
(28) Zahir. 71
(29) Shwayi. 72
Iron and nickel(?) deposits in laterite 75'
Summary. 75
Descriptions of laterice deposits... .^ ... .^.. 77
(30,31) Kalahay Niba I and II 77
(32) Salahc 77
(33) Wasic... 81
(34) Fanjah ,. 81
(Jhromlte deposits in Semail peridotite 83
Descriptions of chromite deposits 85
(35) Maaakirah 85
(36) Mudi 85
(37) Aka Keya 85
Manganese deposits in Hawasina chert 88
Descriptions of manganese deposits 88
(38) Hammah. .. . 88
(39) Jaramah . 88
(40) Wasit 92
Lead-zinc deposit 93
(41) Nujum ,. 93
Economic geology—nonmetallic minerals . 96
Limestone-dolomite. 96
Asbestos 96
Magnesite 96
Clay 98
Evaporites 98
Hot springs 98
Descriptions of hot springs 99
(42) Gallah 99
(43) Rustag... 99
(44) Al Khadra 99
Cold springs 101
Reconmendations 1 1^',
\j-*
Metallic ore deposits. J 105
Nonmetallic ore deposits 10
Water Resources .- 108
Mapping. 109
Open-aoor science policy .and Arab cocperation. 112
Selected references 113
Appendix 117
III
r
1/

: -LIST OF FIGURES .
Page
Figure i. Hap of Oman showing published geologic maps by 1974
and proposed mapping.... ^
2. Map of Oman showing area covered by gravity surveys
through 1973 .....' 7
3. Map of Oman showing area covered by aeroraagnetic
surveys through 1973. ,. 8
4. ERTS mosaic of northern Oman at 1:500,000 scale,
showing locations of mineral deposits and hot
springs. Deposits are numbered as in text and
on Table; 1. Also shown on mosaic is the UTM
grid by which the location of deposits is given in
the text .....4.. In. pocket
5. Diagram showing distribution of 29 copper-iron
sulfide deposits in the Semail ophiolite. 25
6. Geologic map of the "Bowling Alley" showing the
relation of copper-iron sulfide deposits to .
northwest-trending faults 29
\ .
7. Geologic map of the Semda copper deposit. 32.
8. Geologic map of. the Lushil deposit, . 34
9. . Geologic .map of the Zabin deposit.. .. 3%
10. Geologic map of the Fizh deposit 40
11. Geologic map cf the Bayda copper deposit...... 43
12. .Geologic map of the Aarja copper deposit .w..... 46
.13. Geologic map of the Ghayth deposit 49
14. Geiologic tnap of the Rakah copper deposit 55
15. Geologic map of the .Maydan I copper deposit 59
16. Geologic.map of the Maydan II copper deposit. 60
17. Geologic map of the Hawirdit copper deposit. .!. 63
18. Sketch map of'one of the underground workings at the
Tabakhat copper deposit. 67
IV

LIST OF FIGURES—Continued
Figure 19. Geologic map'of the Shwayi copper deposit
Page
73
20. Sketch map showing area of potential iron deposits in
lateritei 76
21. Map showing locations of the Kalahay Niba iron deposits
in latetite below Tertiary limestone 80
22. Map showing location and geologic setting of the
Masakirah chromite deposit.... 86
23. Measured section through one of the ore zones of the
Jaramah manganese deposit near Ras al Hadd 90

LIST OF PHOTOS
Frontispiece. Headquarters building of the Directorate of
Petroleum and Minerals, Muscat, Oman. Page
Photo 1. Land Rover caravan of U.S.G.S. team...... 2
2. Folded flanks of Jabal Akhdar showing Arabian Shelf
carbonates and overlying Hawasina chert, limestone,
and melange. • 11
3. Hawasina melange in "Bowling Alley" 12
4. Semail peridotite in mountains and calcium hydroxide
spring 13
5. Layered gabbro in Semail ophiolite 15
6. Diabase dike swarm in Semail ophiolite, 16
7. Pillow lavas in upper part of Semail ophiolite, 17
8. Semda gossan, showing depression due to collapse
owing to removal of copper and iron in solution.... 3d
9. Exposure of Lushil gossan 35
10. Zabin deposit viewed looking northwest...... 3 7
11. Gossan hills of the Wadi Fizh deposit., 41
12. Bayda copper deposit 44
13. Aarja copper deposit 47
14. Ghayth gossan zone 50
15. Lasail copper deposit as viewed from the air showing
surrounding ancient slag piles ... 52
16. Central part of gossan over the Lasail ore body...... 53
17. Rakah gossan zone viewed from the air 56
18. Northern part of the Ri-kah gossan zone 57
VI

LIST OF PHOTOS—Continued
Page
Photo 19. .Maydan II ore zone • 61
20. Mineralized shear zone of the Tawi Ubaylah copper
deposit...... • 64
21. Peridotite hillside containing underground workings
of the Tabakhat copper mine 68
22. Depression overlying the northern ore body of the
Shwayi copper deposit • • • • '^
23. Kalahay Niba I iron laterite deposit exposed under
Tertiary "limestone 78
24. Pisolitic iron ore at Kalahay Niba I deposit 79
25. Aka Keya chromite deposit in Semail dunite 87
26. Black chert containing pyrolusite in the Hawasina
Unit at the Jaramah manganese deposit 89
27. Ancient workings along the vein of the. Nujum
lead-zinc deposit • •. 94
28. Magnesite vein cutting serpentinized peridotite north
of Rustag 97
29. Khafifah calcium hydroxide spring, travertine, and
stream mortar beds. , 103
VII

List of Tables
Table 1. List cf deposits investigated in northern Oman 22
Page
Table 2. Chemical analyses of chromites from Oman and
, Trucial Oman 84
Table 3. Chemical and spectrographic analyses of
manganese samples from the Hawasina Unit..., 91
Table 4. Chemical analyses of Oman hot springs,
concentrations in mg/1. 100
Table 5. Chemical analyses of Oman calcium hydroxide
spring waters concentrations in mg/1. 102
Table 6. Chemical and spectrographic analyses of copper
prospects in Semail Ophiolite 118
Table 7. Spectrographic analyses of ancient sla.g from
Oman copper deposits 122
Table 8. Chemical and spectrographic analyses of
Kalahay Niba I and II iron deposits 123
Table 9. Chemical and spectrographic analyses of iron
laterite samples from Semail Ophiolite 124
Table 10. Chemical and spectrographic analyses of Chromites
from Semail Ophiolite, 125
Table 11. Chemical and spectrographic analyses of Nujum
lead-zinc depfosit 126
Table 12;. Chemical and spectrographic analyses of
miscellaneous samples from northern Oman 127
VIII

MINERAL DEPOSLTS AND GEOLOGY OF NORTHERN OMAN AS OF 1974
. by •
R. G. Coleman and E. H. Bailey
SUMMARY
An investigation of the mineral resources of northern Oman was
carried out under an agreement between the U. S. Geological Survey
and the Ministry of Development, Sultanate of Oman, during late 1973
and early 1974. The purpose of the investigation was to provide an
evaluation of the mineral potential of northern Oman and produce
recoiranendations- leading toward the utilization of any viable mineral
deposits that were found. The widespread copper deposits located
within the Semail volcanics. appear to be mineable, the ironnickel
laterites developed upon the weathered surface of the Semail
ophiolite have economic potential. Manganese and chromite deposits
investigated have only a marginal value and are not likely to be of
economic importance in the near future. Discovery of economic copper
and iroq deposits warrants further geologic mapping and mineral
exploration in northern Oman. In addition to this, recommendations
regarding the organization of a geological and minif;g group within
the Directorate of Petroleum and Minerals are presented.

' INTRODUCTION
Negotiations for this investigation were initiated early in 1971
by the Government of Oman in discussions with the U, S. Department of
State, and the final agreement was made in May 1973. The agreement
provided that a U. S. Geological Survey team would carry out field
investigations during the winter field season of 1973-1974 and would
produce a written report within six months of the completion of the
field work. This is the report so specified.
Staff
The U. S, Geological Survey team consisted pf Dr. R. G. Coleman
and Dr. E. H. Bailey. Dr. Coleman conducted the initial planning and
logistics of the operation beginning early in 1973 while in Menlo
Park, California. In late November 1973, Dr. Coleman arrived in Oman
and remained there until the end of February 1974. Dr. Bailey reached
Oman on January 15, 1974 and remained until February 23, 1974. The
U.S.G.S. team spent 125 man-days in Oman with 90 man-days in the field.
Writing, typing, drafting, and chemical analyses for the final report
entailed at least another 100 man-days during the period May-July
1974. Dr.,G. F. Brown of the U.S.G.S. also contributed considerable
time to the early phases of planning and organizing the Oman Project.
Our field work was facilitated by assistance given to us by
Mr. Mohammed Kasim of the Directorate of Petroleum and Minerals, and
by Dr. Ismail El Boushi, Geologic Advisor to the Directorate,
Methods of Investigation and Lo;^istics
To assess the mineral potential of Oman it was necessary to.
investigate the known ore occurrences and co also search for unrecorded
deposits. In addition, time had to be spent doing reconnaissance
mapping to learn the geologic relations where mineral deposits
were known in order to appraise what other areas were also favorable
for the discovery of new deposits. The most expeditious way to do
this was to work out of field camps, examining known deposits, mapping
the terrain within a limited distance from each camp, and inquiring
of the local inhabitants and wali's about the occurrence of ancient
mines or slag piles. We were assisted by .Mr. Salim Makki, Director
•General of Petroleum and Minerals, in these contacts with the local
wall's and the Omani people. These contacts provided valuable
information regarding sites of ancient mines and possible areas of
.mineral deposits.
The Directorate provided us with three Land Rover vehicles
(two staition wagons, and one p\':k-up), a driver-interpreter, a cook, j
and a watchman (photo I). Most of our camping equipment was sent to
Oman by the U.S.G.S.; however, some essential items were loaned to us ;
by the Directorate. In making our field examination.s approximately i
la

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8000 km (5000 miles)- were covered by Land Rover traverse, and
although no mileage figure was kept of traverses on foot, the distance
probably was in excess of 160 km (100 miles). In addition, we
had approximately four hours of helicopter time through the courtesy
of Prospection Limited.
Two series of maps that cover Oman were available, one at
1:500,000 and the other at 1:100,000, printed and distributed by the
Ministry of Defense, United Kingdom. We also were provided with
approximately 1000 RAF*aerial photographs (1:60,000) of the Oman
Mountains through the Directorate of Military Surveys, Ministry of
Defense, United Kingdom. Our field observations were recorded on
1:60,000 RAF photos, 1:100,000 maps, and on larger scale sKetch maps
we made ourselves. Rock and ore samples were collected from selected
areas, and some of these materials were chemically analyzed in order
to ascertain the amount of economic metals contained. Basic to such
an inyestigatipn is the acquisition of as much data as possible from
previous geologic studies. In this we were particularly fortunate
to have had the full cooperation of the Petroleum Development Company
(OMAN) Ltd. (PDO) , which has done most of the; geologic mapping in Oman.
Their maps were made available to us during our investigations.
Ack nowled^ements
We are indebted to Mr. Salim Makki, Direccor General of Petroleum
and Minerals, for the support and cooperation he freely provided. Dr.
Rudy JackLi, General Manager, PDO, generously provided us with much
valuable unpublished geologic and geophysical data, and other members of
the Ppp staff also helped with our geologic wcrk on numerous occasions.
Mr.C.C. Huston and Mr, Alan Hutchinson of Prospection Limited kindly
provided us with information on cheir operation as well as a copy of
their 1973 field investigations report. Mr. C. J. Quinlan and Mr. Fred
McEldowney of the American Embassy in Muscat '.vere a great help to us in
establishinj our field project in Oman. Mr. J.3. Townsend, Economic
Advisor to the Oman Government, provided encouragement and also greatly
facilitated our operation in Oman.
• ',••;. GEOGRAPHY-
The area covered in this agreement is wholly within northern Oman
and extends from Ras Al Hadd to the southern border of the Union of
Arab Emirates, an area of about 41,000 sq.'k.v, (16,000 sq. miles). Most
of the area is within the Oman Mountains, which form a crescent shaped
range extending 600 km (360 mil) parallel to the coast from Muscat to.
the northern tip of the Musandam Peninsula. Northwest of Muscat, a
narrow coastal plain 10-40 km (6-24 miles) wide, known as the Batinah,
separates the mountains from the Gulf of Oman, but to the east of
Muscat the coastal plain disappears and farther southeastward to
Ras Al Hadd the coast is rugged and 3tee? wit.i some parts drowned to
form in intricate shoreline. The Oman Mountains form a barrier
befrfeen the Batinah coast and the western interior of Oman. The
* ?.oyal Air Force '

highest part is in the mid-section of the mountains at Jabal Akhdar,
which rises to 2980 meters (9800 feet). Northward from Jabal Akhdar
the mountains become subdued, and in the United Emirates section the
average elevation in the mountains is less than 900 meters (2970
feet). Continuing northward to the Musandam Peninsula the elevations
rise to over 2000 meters (6600 feet) at Ruus Al Jibal. South of
Jabal Akhdar the mountain range is cleft by the Semail Gap providing a
natural passageway across the Oman Mountains. The mountains to the
south (Al Hajar Ash Shargi) are extremely rugged with many elevations
in excess of 2000 meters (6600 feet).
The Oman Mountains are dissected by numerous vadles that form deep
canyons cutting into the core of the mountain range. The wadies
flowing northeastward into the Gulf of Oman are steeper than those
wadies flowing south into the great Interior basin (Umm as Samim) at
the edge of the empty quarter (Rub Al Khali) and have locally
advanced their headwaters southwestward beyond the crest of the range.
The southwestern foothills of the Oman Mountains are marked by an almost
continuous pediment that forms extensive gravel plains cut only
locally by southwestem flowing wadies. South and east of the Oman
Mountains the Wahiba sands cover the southwestern slope and only a
narrow plain separates the mountains from the migrating sand dunes.
' , . ' • ' ' \ '
The positions of the main road syst;ems of Oman are strongly
influenced by the physiography. .-Uong the Coastal Plain a new paved
road extends northward from Muscat to Sohar allowing easy access Co
all coastal towns, but south of Muscat there is no coastal road nor,is
there any road crossing the kl Hajar Ash. Shargi. The main access road
to the interior is a graded gravel road across the mountains at Semail.
Gap. North of the Semail Gap road only two poor roads cross the Oman
Mountains: 1) Wadi Jizzi from Sohar to Buraimi; 2) Wadies Zallah
and Hawasina from Al Khabura to Ibri. The inaccessibility of much of
the Oman Mountains by road makes geologic work time consuming when
carried out by Land Rover and foot traverses, and access is particularly
difficult on the northeastern slope of the Oman.Mountains
where incised wadies produce deep canyons that cannot be traversed
by Land Rover. Because the accessibility of many parts of the Oman
Mountains' is so difficult, large areas remain unexplored geologically,
and this fact should be taken into account when making an evaluation
of their mineraFpotential.
The most important copper district of northern Oman has been,
called the "Bowling Alley" by Prospection Ltd. (see photo 3 and
figure 6) as it forms a narrow corridor (3 km x 17 km) on the east
side of.the Oman mcuntains approximately 32 km due east of Sohar.

^ ^^ .,.,.. .,.^, .,..„., , . -, ^ , —,.-_-^,- ••»ii»iii«M;iMjiKWWjg'''''-'°'«««fqsM
. .^ GEOLOGY
Previous Work
Geologic studies of northern Oman have been directed mainly
toward the search for petroleum and reflect that Influence. A3 a
proper background for this report a short review of previous work
is presented. The earliest geologic report on Oman was made by
Pilgrim (1908) as part of a larger study of the Persian Gulf area for
the Geological Survey of India. Pilgrim's report was mostly descriptive
and provided few details. During the winter field season of
1924-1925, G. M. Lees (1928a) carried out an extensive exploration
of northern Oman and the southeastern coast, and his observations
form the basis for some of the stratigraphic nomenclature now used.
Nearly 25 years later. Increased interest in the petroleum potential
of the Arabian peninsula brouRht forth a series of sumoiary papers on
Oman geology: Hudson, Browms and Chatton (1954), Hudson, McGugan, and
Morton (1954), Morton (1959), Hudson and Chatton (1959), Hudson (1960),
and Tschopp Q.967a). Much of this data was a distillation of work carried
out by oil companies, and very little basic data was published. The first
published geologic map of Oman, at the scale of 1:2,000,000 resulted from
a joint effort of the U. S. Geological Survey and Arabian .American Oil
Company (1963). ^'.
More recently Shell Research N.V.,^The Hague, and the Petroleum
Development (Oman) Ltd. have carried out extensive geological studies
of Oman, and summary reports have been published .by Wilson (1969),
Glennie and others (1973), and Reinhardt (1969). A summary detailed
report, including a geological map (1:500,000) of northern Oman
wilt fct published in the near futu-re (Glenhie and others, 1974,
Konink. Nederlandsch Geol. Mijnboukundig Genootschap Verh.). Besides
these reports on Oman generated by PDO, a few other publications:
that also discuss the geology of the Oman Mountains are Moseley (1969),
Allemann and Peters (1972), Greenwood and Loney (1968), and Beydoun
(1964). The mineral resources of the Oman Mountains are considered
''only in the published report by Greenwood and Loney (1968); however,
PDO has an. unpiiblished report oh mineral resources of Oman that was
an outgrowth of their geologic studies. Figure 1 shows the areas covered
by geologic mapping In Oman, along with mapping we propose.
Considerable unpublished geophysical work that has been done in
Oman is summarized in figures 2 and 3. .All the geophysical information
was obtained from PDO, who collated and synthesized the results
to delineate subsurface structures favorable for the accumulation
of petroleum. Release of this data could, however, provide information
of value in understanding the geologic history of Oman.
As mentioned earlier the only modern prospecting for metallic
and non-metallic deposits prior to 1971 was that carried out rather
incidentally by the JPDO team that mapped the Oman Mountains in 1963-
1969. These data were made available to us, but were
not generally encouraging regarding tha mineral potential. Beginning

Figure 1. Map of Oman showing by dotted pattern status
'...' of published geologic maps by 1974, ard by solid
pattern , the proposed mapping.

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rigur.e 2. Map of Oman ahowing by dotted pattern area'
covered by gravity surveys through 1973.

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Figure 3. Map of Oman .showing by dotted pattern area
covered by aeroraagnetic Surveys through 1973.
8

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Pre-Permian Rocks
Basement Rocks (Autochthon)
Within the Oman Mountains low-grade metamorphic rocks are
exposed in erosional window at Jabal Akhdar, Sayah Hatat, and Jabal
Ja'alan. .These rocks can be divided roughly into carbonate sedimentary
rocks and fine-grained clastic .sediments with minor amounts
of yolcanlc rocks. All have uiidergone greenschist facies metamorphism
and show at least two periods of deformation. Within the Sayah Hatat,
numerous quartz reefs have developed in the metasediments; however, as
shown by the analyses included in Table liX> in the appendix, these do
not contain economic concentrations of metals. There are.no crosscutting
leucocratic intrusions within this series, and the only
geologic event that could have produced mineral concentrations was
the metamprphic event dated at 327 m.y. by PDO.
Arabian Shelf Carbonates (Permian to Cretaceous autochthonous rocks)
Resting unconformably on the folded and metamorphosed Pre-Permian
basement are the Arabian Shelf carbonates, see photo 2. The rocks
consist mainly of limestone, dolomite, and mudstone whose fossils
indicate shallow water deposition. Near the top of the autochthonous
section the Late Cretaceous Mutl Formation is made up of marl, shale,
lenses of limestone, conglomerate, and sandstone flysch. The total
thickness of this section is approximately 2700 meters. These rocks
represent the source beds and traps that contain most Of the petroleum
in Oman; however, they are not known to contain metallic mineral
deposits. The pure limestones in the section afford an almost
unlimited;, supply for the manufacture of cement.
Semail ophiolitei
Ophiolite and Related Rocks (Allochthon)
Economically the most important rock unit in the Oman Mountains is
the Semail ophiolite, because nearly all of the ore deposits are associated
with it. We consider the ophiolite to be ancient oceanic crust
which has been thrust over the Hawasina, and we accept the hypothesis
of Reinhardt (1969) that it formed at a spreading center within the
Tethyan sea during Mesozoic time. The Semail is a classic example of
ophiolite, perhaps containing 30,000 cu. km, and offers the most
extensive exposure of this kind of rock to be found anywhere in the
wprld^pl^ofts i). .
The ophiolite is divided from base to top into the following
major rock units: (1) Peridotite, containing rocks composed chiefly
of olivine, orthopyroxene, and clinopyroxene. It crystallized in
the upper mantle, and now forms the thickest and most widespread part
of the ophiolite, see photo 4. Parts of the peridotite, particularly
near its base, have been converted to serpentinite by hydration;
10

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Photo 2. Folded flanks of Jabal Akhdar north of Izkl. Thick section
oftfAi^.>aiMo>Nub Arabian Shelf carbonate rocks forming dip slope In
background. Hawasina red cherts and gray limestones fortn melange
within ridge, of the foreground.
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^M Photo 3. Hawasina melange containing exotic blocks of Permlan-Trlassic
reefal limestone In middle distance. Exposure Is within "Bowling
Alley" a few kilometers north of Wadi Jizzi. Cloud-covered hills
In the background are composed of Semail ophiolites.
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Photo 4. Typical exposQre of Semail peridotites in the
mountainous part of northern Oman. Area of white
and blue along wadi is typical calcium hydroxide
spring with accompanying travertine apron.
13

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minerals of the peridotite plus plagioclase and hornblende. It
crystallized in shallow magma chambers above the peridotite, and
because of crystal settling may be strongly layered, see photo 5;
(3) Diabase, with the same minerals as the gabbro but a medium
grained texture. Most of the diabase crystallized as dikes formed by
magma Injection into fractures repeatedly opened at an active spreading
oceanic rift zone. , The resulting unit, conmonly referred to as a
sheeted complex, consists of nearly parallel dikes with little or no
intervening country rock, see photo 6. Diabase also occurs as dikes
in the upper part of the gabbro and in lava that overlies the sheeted
complex; (4) Plagiogranites, consisting of coarse to medlust-grained
quartz, plagioclase, and hornblende rocks, crystallized, as small
intrusives in the upper pa^rts of the gabbro or within the-.sheeted
complex; (5) Basalt, a fine-grained or aphanitic rock of gray to
black color, occurs as a thick uppermost unit in the ophiolite. It
represents voluminous and repeated submarine extrusioo of mafic lava
at the spreading rift zone, and much of it exhibits pillow structure,
see photo 7. This thick pile of igneous rocks, therefore, developed
at the spreading center within the ancient Tethyan sea prior to the
thrusting of the Semail ophiolite upon the Hawasina. During
emplacement, imbricate thrusting, folding, and overturning resulted
in complicating the structure and introducing local repetitions of
parts of the sequence. \^
Massive sulfide copper deposits are present within the pillow
basalts and diabase of the ophiolite sequence, and copper mineralization
also occurs along high-angle thrust faults and normal faults
in the gabbro and peridotite. Chromite deposits are present within
the peridotite and most often are concentrated in dunite. Asbestos
developed"locally in parts of the peridotite during late stage
serpentinization. Widespread weathering of the exposed surface of the
Semail ophiolite in early Tertiary time produced extensive laterites
that are rich in Fe, Ni, and Cr.
Hawasina unit, exotics, melange, and metamorphics (Permian to mid-
Cretaceous.
The Hawasina includes a series of six tectonically-bounded
units, each of which contains rocks which range in age
from Jurassic to raid-Cretaceous. The individual tectonic units rang*
from 60 to 900 meters (198 to 2970 feet) with a total tectonic
thickness of 1900 meters (8910 feet). The lower units of the
Hawasina are. mainly lithoclastlc lloiestones and quartz sand
turbidites. Thin-bedded red cherts with shales predominate in the
upper sections, and pillow lavas are commonly interbedded with chem.
The environments Indicated by the lithology and faunas of the
Hawasina allochthonous units suggest transgression from shallow to
deep water, seemingly contemporaneous with the shelf carbonates of
the autochthon. Deep ocean sedimentation below the carbonate
1^

t^
I'holo 'j. LLiymct n.il.loti within Sf-iiidll ophi oHte exposed along Wadi
Ji2?i I liilil li.iiul'. cunsisL mostly of plagioclase and dark bands
cont,

p;B;«3A,^*
Photo 6. Diabase dike sv;ara in Semail ophiolite near Ibra illustrating result of
repeated injection ot.Tiaqma alone 3dra)"iel ^ViCtures forming a >rj'".es o*
dikes with no interyenino country rock. At the time of
injection the dikes ooubtless wers nearly vertical.
16

jiSaSfss^-*?"'" "
Photo 7. Pillow lavas from the upper part of the Semail ophiolite.
Many of the best copper deposits are concentrated In similar
layers ,of pillow lava.
17

kt¥''S^''^^'^-^""d •
W¥
compensation level is indicated by manganese ore beds occurring
locally with the cherts. No mineralization has been detected within
the volcanics interlayered between the cherts.
In the highest structural units of the Hawasina occur isolated
exotic blocks of white recrystalllzed reefal limestones (Permian-
Triassic), ranging in size from small isolated hills to large
mountains resting on, or in, a melange, see photo 3. the melange
itself consists of a tectonic mixture of" Hawaslha chert, shale,
limestone and locally serpentine and amphibolite. Both the melange and
exotic blocks are considered to result from the tectonic emplacement
of Semail ophiolite on top of the highest units of the Hawasina.
Extensive mineral deposits are not expected to occur within the
melange, although silica-carbonate rock related to the low-angle
thrusts was observed in two places. This silica-carbonate rock shows
that some hydrothermal alteration was developed during thrusting or
perhaps shortly thereafter.
Sedimentary Rocks Lying On Semail Ophiolite
Shallow~water marine limestone (Late Cretaceous to Middle Tertiary).
During the Late Cretaceous (Maestrichtlan) both the autochthonous
Mesozoic carbonates and the,allochthonous Hawasina and Semail
ophiolite were covered by a transgriessive sea that deposited limestone
and tiarl. These limestones characteristically contain rudists
and orbitoid Foraminifera in the Late Cretaceous deposits and alveolinid
and nummulitid Foraminifera in the Lower Tertiary deposits.
They attain thicknesses up to 2500 m (8250 ft) in the eastern Oman
Mountains, and thicknesses up to 2000 m (6600 ft) are found west of
the northern Oman mountains. They provide a virtually unlimited
supply of nearly pure limestone that could,be utilized for the
manufacture of cement or other industrial products where an unusually
pure llmestpne is required. Miocene rocks resting on top of these
marine limestones in the vicinity of Sur are reported to contain
coal.' ' '
Pliocene-Holocene deposits.
Beginning In the Oligocene or early Miocene the eastern Arabian
continental margin was deformed. This resulted in folding and uplift
of the Oman Mountains, causing erosion and deposition of extensive
alluvial deposits on their northern and southern flanks. To the south
these deposits filled the large interior basin centered around Umm as
Samim, and to the north much of the alluvium deposited on the Batinah
coastal plain was derived in this period of erosion. Information from
drill sites 222 and 223 of the Glomar Challenger located near the
east coast of Oman Indicates that during the middle Miocene greatly
accelerated sedimentation rates coincide with the uplift and deformatioi
18

IA.
'^'-M^
m
A'
^ MhSL'
J
yfk
m
•.I
d.
4
J ''as
t •*'ti
Pp
r
' "Si
m
Mi
of the Oman Mountains (Whitmarsh and others,1974). Detrital minerals
characteristic of the Oman ophiolites were found in these offshore
sediments.-' •:-.'••.,.••
Recent tectonic movements have arched the Oman Mountains,
rejuvenating particularly the streams flowing northward. These
down-cutting streams have produced interfluve terraces containing
many boulders of peridotite and gabbro. Such terraces are very
resistant to erosion because they are generally cemented by calcium
carbonate, and chariacteriatically canyons cut into then develop
unusually steep walls. Placer deposits of chromite may possibly
exist within these sediments, and reworking along the coastlines could
perhaps develop black sand deposits. It is also possible that
evaporite deposits containing Li or K salts may be concentrated
within the large Interior playa of Umm as Samin.
Structural History
The Oman Mountains reveal five major tectonic events that can be
tied to their geologic evolution:' 1) Metamorphism and folding along
N-S axis is recorded within the Pre-Permian basement rocks of the
Sayah Hatat and Jabal Akhdar windows,. K-Ar ages of 327 m.y. Indicate
that this event was late Paleozoic and not Precambrian. 2) The late
Paleozoic breakup of Pangaea into Gondwanaland and Eurasia created
the Hawasina ocean (Tethys), and the production of the Semail ophiolite
at a spreading ridge within this ocean, the Arabian Peninsula is
considered to have drifted southward with Gondwanaland, and during the
period from late Paleozoic to late Mesozoic shelf carbonates of the
autochthon were deposited along the east margin of the Arabian shield •
and deep water chert and limestone of the Hawasina formed in the sea
Qortheast of the present coast line. 3) During the Campanian, the
Hawasina sea began to close as the Afro-Arabian continent moved
towards Eurasia,\and parts of the Hawasina and Semail ophiolite moved
southwestward over the Arabian shelf carbonates. This emplacement
was accompanied by gentle folding and imbricate thrusting within both
the Hawasina and Semail ophiolite. Metamorphics (85 m.y.) developed
at the. base of the Semail ophiolite* and during the final emplacement,
melange zones developed under the Semail ophiolite. 4) During the
middle Miocene, uplift and folding of the Oman Mountains formed the Nto
NV-trending fold belt that is characterized by the huge antifonus
of Jabal Akhdar, Sayah Hatat, and Musandam Peninsula. The middle
Miocene folding further complicated the Internal structures of the
ophiolite and perhaps also produced some gravity sliding away from the
crests of the antiforms. 5) After middle Miocene, normal faults
striking NE and NW have cut the northwesterly trending mou:.itain3.
Within the Batinah coastal plain and offshore, normal faults parallel
to the coast have dropped the Tertiary and Mesozoic sediments downward
to the north into the Gulf of Oman. During recent times the middle
portion of the Oman Mountains from Fujaira southward to the Semail Gap
has been gently arched. This uplift rejuvenated the north-flowing
streams whose increased sedimentary load soon covered most of the
block faults along the Batinah coast. During this period of arching
19

t m
y^3
m
¥1-
f "al
^^1
' Cf
III
y
'41
m
in the midsection of the Oman Mountains, the Musandam Peninsula sank
nearly 300 meters (1000 ft) forming its characteristic drowned
topography. Less intense subsidence is also recorded along the north
Oman coast from Muscat southward to Ras al Hadd.
In general, in this structural Interpretation, we agree with
the geologic .interpretation of Glennie and others (1973), even though
some seem to strongly oppose their views (Wilson, 1973; Moody, 1974).
Itich contrary discussion involves stratigrapTiic paleontology and is
beyond the scope of our studies. The crux of the controversy regarding
the geologic history is whether the Semail ophiolite and the
Hawasina rocks are in normal stratigraphic sequence or whether they are
separate thrust sheets (nappes) now Imbricated on top of the.carbonates
that make up the Arabian platform. Morton (1959), Tschopp (1967a),
Wilson (1969, 1973) and Moody (1974) all have stated that the Hawasina
Series and Semail ophiolite are autochthonous (remain at site of their
origin) and of Late Cretaceous age. Furthermore, they visualize that
the Semail ophiolite has formed as huge extrusions of mafic lava
in situ. Contrary to this, Glennie and others (1973) and Lees (1928a)
visualize that the Hawasina rocks represent deep water deposits
formed contemporaneously with the Arabian Shelf carbonates but deposited
within an ocean situated along the axis of the present Gulf of Oman.
At the same time, new oceanic crust constituting the Semail ophiolite
was being formed at a spreading ridge'wlthin the ocean. During the
Late Cretaceous southwesterly directed over-thrusting of the Hawasina
and Semail ophiolite onto the .Arabian continental ma.rgin produced the
present imbrication. As the Semail ophiolite contains most of the
potential ore deposits within the Oman Mountains, the present geologic
distribution of Its component rocks, and perhaps the faults within
them, is of overriding economic concern.
20

•^:.
p^ m
•% ^%
Mi
?«
m
m
^^A
mi
••"til
'.il^l
-0.
y
W
1
'%m
.t\yj
W'
r

fifSW'""
Tahlo 1. Ltjc of dopouica invesclfiit ed In iiort.hcr.n Oman
y y
Grid I.i>calluii r.vjlualion
Host kock
Cjoi'i^r Uf.-','i.-!i i t s
n...salc - di.-ibaiitf
ll;:salc - diabase
Basalc
CasalC
B^auait
Basalt
Basalc
Babalt
Basalc
Tuff '
Basalt
Cabbro - Peridotite
Cabbro - Perliiocicc
Cabbro - Pqrldoclce
Peridotite
Cabbro - Perltlodite
(Ubbro - Peridotite
Diabase - Cabbro
Cabbro
Peridotite
Cabbro
Cabbro
Peridotite
Cabbro
Gabbru
Peridotite
. Peridotite
Cabbru
. ua!; b L'o
Rafers co coordinates used on 1:100,000 oaps of Ministry of Defense,
1^ United Klngdon, and on fig. 4, this report
** > Probably useable
Possibly useable
Not useful 22
Type of Deposit: Foraer Acclvlcy
Pipe - Gossan
Pipe - Cossau
U:nscs - Cossan
Lens** - Gossan
Coasaa
Plp« - Gossan
Pipe.* Gossan
Lens - Gossan
Pipe - Gossan
Bed
Stockwork - Gossan
Vain Zone
V

J. i •^
fA.
J»J
AM
.w yn
Mmk'^
P4 diwii
'p ^i
1
If?'
Mr
iM%
mm
Ho.
JU
Jl
il
33
.4
Table X. List -Jt deposits investigated in northern 0*ea—Continued
2/
Naioe . Grid Location Evalvtetlos
Kalahay
Niba I
Kalahay 1
Niba II
Salaht • "
Wasit
Fanjah
FA 597
>A 787
FA 822
EA 589
FA 137
149
215
143
338
944
)5 .Hasakirah FA 597 U9
)6 Mudi FA 958 025
).' Aka ICeya OB 026 736
]B Kasansh FV 661 871
)• Jaramah CV 791 .141
.0 Wa«it ts 589 338
Nujua FA .205 itao
..• . .Cllah :, F3 ..n C2j
>] Xuatag t.K ^10 .46?
V. Ai Khadri • • EA 312 33y
V
.y
Host Bock
Iron Deposits
Lecerlte
Laterite
Sendeeone
Peridotite
Laterite
Chroaite Deposits
Typ« of OepoalC Fonser Aictivity
Keeorked laterite
Dunite Scrlogers
Perldotlta Layer
(Dunite Stringers
Kanganeea Ocgogics
CItsrt
Chert
Cherc
Lead-Zinc Deposit
Silica-carbonate
Hot Springs
Pods
Layer - Pods
Velne
Serpentine Spring
Lisestoae Spring
Llacston« Spring
Wafers to coordinates used on 1:100,000 naps of Ministry of Defense,
United Kingdom, and.on fig. 4, this report
>. Probably useable-
I Possibly useable
. Sot useful
23
?
Cue
Cut
Mine
Falag

'"^I
M
I i.
work will find other deposits that are either more remote, less well
exposed,, or entirely-covered by a shallow layer of aluvlum.
Copper Deposits in the Semail Ophiolite
Copper deposits occur throughout the vast thickness of the Semail
ophiolite, but those siliuated in the pillow lavas, especially those
aear the top of the pillow layas, have the greatest potential. The
position of the deposits within the ophiolite 13 shown dlagraimnatlcally
on figure 5, which also gives added data regarding features of
mineralization that vary according to their position and host rock.
The better copper deposits in the basaltic pillow layas are
accompanied by large amounts of iron sulfide (pyrite), which where
very concentrated may be a saleable product even without the copper.
Through oxidation, the pyrite has given rise to sulfuric acid
waters and colorful, extensively leached, gossan outcrops. These
gossan zones, and doubtless the underlying ore bodiesf, are small in
areal extent, being generally elliptical in plan with major axes
of from 30-150 m (100-500 ft). A downward extent for an ore body to
at least 225 meters (750 ft) has been proved by drilling at one
deposit, and it is likely others may,extend to comparable depths.
Some ore bodies, like Ghayth, are no^ elliptical but elongate and
obviously deposited along a fault, whereas others show by a straight
marginal segment partial fault control. Typically, little primary
alteration exists about the deposits in basalt, although there is some
evidence of zeolite alteration.
The bright orange, red, brown, or yellow colors of the gossan
makes the exposed deposits easy to find, especially if searched for
from the air, see photos 15 and 17. However, distinguishing gossans
over sulfide deposits containing copper from those containing just
pyrite can be difficult. Where there are secondary copper minerals
in the outcrop, the deposits have invariably been found and worked
in ancient times, perhaps more than 3000 years ago. Black slag piles
dot the landscape surrounding the deposits, and in some places there
are extensive ruins of old reduction furnaces. But, where the
leaching of the gossan has been most intense the original copper
sulfides have been dissolved and no secondary copper minerals are left
behind. As a result, in some promising deposits secondary copper
minerals can be seen in the less altered periphery but not in the
most mineralized core. For example, the intensely altered surface
gossan in the core of the Lasail deposit shows virtually no copper,
but drilling revealed the underlying sulfide zone contained several
percent of ccpper ore as chalcopyrite in veins and disseminated
crystals in massive pyrite. In some places, copper leached from a
gossan is redeposited at the base of the leached zone, but as far as
we are aware, no zone of secondary enrichment has been noted in the
Lasail deposit. Some other deposits, for:example, Ghayth, Zabin, and
Fizh, exhibit strong gossan with no secondary copper minerals showing
ZU

^ !
<
rf
:'^.
-1
-SS
'* -a?^*'''"''
.1
I
f
i
i
\
i
t
•,
I
%
W'^
Q-
O
LiJ
CO
O
CJ.
Oi
^
Chert
UV4
Qiabase.
Gabbro
Layered
2one
Peridotite
y
.serpent j„g
LASAIL j /\AH..iA lUrDA
Ghayth
Khabiyat
RAKAH
SEflDA
L Muden
Jabah
. Zabin
Lushil
Zahir Khafifzh } Masakivah j
I SHWAYI I Luzak £edah I Eedah II
L ^ Maydan V " Maydan 11 Bukathir Hawirdit
|\i TaMi Ubaylah | Ghay) ichara Koowasl
Tabakhat
Inah
l.MPORTANT. .
LESS IMPORTANT
Unpromi sing
MUCH
MUCH
EXPLANATION
I 1
I SOME J
SOME
}
Outlook
for
deposi ts
Amount of
Fe or Gossan
Amount of
copper
shown by
underlining
Figure 5. Diagram showing distribution and other l^^"l "^
29 copper-iron sulfide d.eposits In the Semail ophiolite.
25

ki^^'^^y"
either in core or periphery; we suspect these contain little or no
primary copper sulfide but one cannot be sure without drilling.
It can be safely preidicted that some of. the copper-bearing
massive pyrite deposits in the pillow lavas will prove to be of
sufficient grade and size to be mineable, even though all facilities
for mining and transport of ore to market must be installed. If it
proves to be as expected, the ore of the Lasail deposit alone seems
to be able to carry the cost of getting into operation. If some
of the other deposits in the "Bowling Alley" can also be proven to
be viable, as seems likely, mining them concurrently with the Lasail
deposit will of course result in significant lowering of the
Installation and operating costs on a per-ton basis. The.massive
sulfide deposits in the pillow lava in Oman are much like the
Intensively mined deposits in the Lower Pillow Lavas in the Troodos
ophiolite on Cyprus,'which also were mined in ancient times (2500
B.C.?) (Searle, 1972). The Cyprus deposits consist of several ore
bodies of,1-10,000,000 tons of massive pyrite containing 1-4 percent
copper occurring as chalcopyrite. Other deposits of similar type
occur in Greece, Turkey, and Newfoundland (Upadhyay and Strong, 1973).
The diabase dike, or "Sheeted Intrusive," part of the Semail
ophiolite lying below the pillow lavas contains at its top only two
known deposits, see figure 5. Both have well-developed gossan and
are in all respects like the previously described deposits in the
basaltic lavas.
The lower gabbro and peridotite parts of the Semail ophiolite
contain more than half of the copper deposits so far discovered In
Oman, figure 5. Many of these were mined in ancient times, but only
the Shwayi deposit seems to have any potential for modern mining,
yiost of the deposits are .along a contact, generally a steep fault
contact, between peridotite and gabbro. The mineralized zones are
narrow, usually less than 8m (26 ft) wide, have lengths of less than
300m (1,000 ft), and generally are poorly exposed. Primary
chalcopyrite was found in some places, but the usual ore in outcrop
contained only secondary copper minerals along shears and fractures.
In one deposit we found pieces of chalcocite in veins of apparently
primary origin. In contrast to the ores in the lavas, these deposits
typically contain minor amounts of pyrite, and they generally
exhibit only a little iron staining rather than heavy gossan. Their
surface exposures are not prpminent, but assays Indicate several
really contain copper ore as rich as found in the massive sulfide
deposits.
Most of these deposits in gabbro or peridotite are too small to
be mined today. However, the Shwayi deposit, containing two ore bodies
comparable in size to those in basalt, warrants some exploration to
determine if the mineralized rock Is of ore grade. We are not too
optimistic about it being mineable, however, as copper deposits in
26

1" SB??---;
Ml : gabbro and peridotite In othier parts of the world generally have not
hi h
'Ai-^
J '»
been economic.
The origin of the copper deposits in the Semail ophiolite deserves
further study, both as a guide to where to search for additional ore
aad as a scientific contribution. At this state in their exploration,
with almost ho knowledge of the primary ore mineralogy or paragenesls,
tentative conclusions are best-drawn from*what is known of their
localization and comparison with better explored ore bodies of similar
type found elsewhere.
As mentioned before, the mineable massive sulfide ores in the
lavas in the upper part of the ophiolite are much like Cypriis ores,
whose genesis has been studied by several geologists (Bear, 1963;
Klnkel, 1966; Constantinou and Govett, 1972; Searle, 1972). However,
the less promising chalcopyrite vein deposits found lower in the
ophiolite are not well represented in Cyprus. There is general agreement
that the Cyprus ores are ultimately derived from the ophiolite itself,
but processes leading to their formation are debatable. The most
generally accepted theory postulates that the sulfide deposits are
formed at an oceanic spreading center about submarine springs, with
deposition at the lava-water interface \and also in the underlying
channelways by fracture filling and some replacement. The source
of the copper, and generally also the iron, is believed to be either
from leaching of underlying basalt, differentiation in a gabbroic magma
chamber within the ophiolite sequence, or "exhalations" from the
mantle itself. In some deposits of the Cyprus type, post-mineral
faulting and remobllization of the sulfides has be;en proposed.
In Oman, the massive iron sulfides occur only in the upper part
of the ophiolite, mostly in the basalt, and it seems likely that the
Iron was extracted from the iron-bearing rocks lower in the pile but
above the peridotite. As copper mineralization is found throughout
the ophiolite, the copper seems to have had a mantle origin. However,
its greatest concentration is near the very top of the ophiolite, and
the search for mineable copper deposits should give greatest priority
to the examination of the pillow lavas, especially those at the very
top of the lava pile. Overlying copper-rich sedimentary umbers, such
as occur at Cyprus, have not been found; however, in the "Bowling
Alley" somewhat similar sedimentary Ironstones occur interlayered
with the uppermost pillow lavas. These ironstones are discontinuous
and are nowhere more than 1 meter (3.3 feet) thick. Spectograjphic
analysis show they contain high iron and manganese contents with only
a little copper and nickel. Somewhat similar appearing Ironstones
have been dredged from the Red Sea hot brine areas, but the Oman
ironstones contain much less copper, lead, zinc, a-nd silver.
The time of mineralization is unknown, and some evidence suggests
that the final emplacement of the ore did not coincide with the
period of volcanism and sea-floor spreading but came later. Some
deposits in the "Bowling Alley" by their shape indicate fault control
27

m
t •
in II
*
to the mineralization,- for example, the Ghayth and Semda deposits
(figure 6). Others seem to lie along northwest-trending faults
related to younger tectonics, for example, the Lushil, Fizh, Bayda,
and Ghayth deposits. In addition, the northern trend of the "Bowling
Alley" projected southward coincides exactly with the Maydan, Bukathir,
and Hawirdit deposits in the peridotite, suggesting perhaps some
deep-seated, fracture is responsible for the gross distribution of
most of the better copper deposits. Curiously,-far to the north
in Iran, the spectacular Sher Cheshmeh porphyry copper deposit is
* also along the extension of this line. While not enough is known
J about why the ore is related to these .structural trands they can be
J used as guides in exploration.
«.
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28
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CONTACT
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k Cof>p«

Descriptions of copper deposits in volcanic rocks
(1) Semda (DC 418-193 Fizh)
The Semda deposit is located on isolated Interfluve between
two wadies within low hills of Semail ophiolites 9.5 km (6 mi)
north of the, village of Fizh. Part of the ore is clearly developed
in diabase dikes, and the occurrence of pillow lavas nearby
suggests that the deposit may be in the transition zone between
pillows and sheeted dikes. A thick mantle of pediment gravels
whose level upper surface is about 90 ra (300 ft) above the valley
floor surrounds the mineralized of area on three sides and could
be concealing other similar deposits. ^
The mineralized zone is very conspicuous because of the bright
yellow and redish brown colors of its intensely altered gossan,
see photo 8. It is elliptical in shape with a long axis of 150 m
(500 ft) and a short axis of 115, m (375 ft), as shown in figure 7.
Its southern limit is partly covered by alluvium, but we believe
the float here is adequate to permit an accurate estimate of its
extent. Its northeastern boundary is locally straight and includes
a tail-like extension, perhaps suggesting some fault control for
the mineralization. Centrally located in the gossan is a nearly
circular depression about 60 m (200 ft)' in diameter whose flat floor
is 2 m (7 ft) below the level of the surrounding alluvial plain.
Within this area all the material is a copper-free (?) powder of
secondary iron oxides, sulfates, and gypsum, which forms a thin mud
when wet. Perhaps the level here has been lowered somewhat by
mining in ancient times, but small step faults visible in the walls
indicate that the depression of the central area is mostly due to
subsidence. This is doubtless the result of removal of material
in solution, which indicates that the underlying fresh material is
chiefly soluble sulfides with a minimum of insoluble silicates.
Surrounding the central core is a slightly less altered area pock
marked by shafts or pits only a few feet deep and connecting short
tunnels. Much green and blue copper "stain," in the form of both
hydrated oxides and sulfates, is still visible in the walls, and
it was doubtless from this less leached zone that the ancients
obtained most of,the ore now represented by the extensive piles of
slag found all about the mine area.
We believe the surface indications at the Semda deposit reflect
a buried massive sulfide pipe with slightly less, but still Intense,
mineralization extending out from it for a distance of several
hundred feet. Althcu^h at che surface the leached gossan over the
central core is virtually copper free, the presence of considerable
copper in the less leached periphery suggests the core also may have
a high copper content, and perhaps even a zone of secondary enrichment.
There is no way to be sure, however, without drilling to
obtain samples for analysis. To us this'appears to be the most
promising deposit we examined, and it should be promptly explored
JO

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Photo 0. Semda gossan viewed looking northeast. Central depression
is in area of complete oxidation and has collapsed owing to
removal of copper and iron in solution. Foreground area covered
by pits from which copper ore was mined in ancient time. Flat
skyline is on surface of old, elevated pediment gravel.
3/

ly^s^'.-"'-
O
EXPLANATIOf^
Slag
Alluviup, and
colluvium
Gossan
Pillov/ lava and
diabase
SEMDA COPPER DEPPSIT>
i OMAN
N
Area of complete
oxi elation
.''>r{;a cf ir.coiuplete
oxidation and
pit mining
^. Limit of gossan
; "^ outcroo and
•_-/• concentrated float
W^^^r Copper oxides in fracturci
I^fe«*r^n fre5h diabase.
M Iron oxide-s.
SCALE
.300 13* 1^^.
Figure 7. Geologic map of the Semda copper deposit,
31.
Pit IS 7feet lower
than surface of
surrounding, crfluv iutr<
Cor.nass ar.d pac
E;'. H. Bailey
1?74

%
Wt'
by drilling. If it comes up to our expectations it is quite likely
to be a mineable deposit.
About 120 m (400 ft) north of the main gossan is a low hill
of fresh diabase traversed by a shear zone containing copper "stain"
along fractures. Still farther north is another weakly mineralized
parallel zone. No iron mineralization seems to have been present
in either of, these places. The direction of the mineralized
fractures parallels the northeastern boundary of-the main gossan,
and reinforces our belief that the main ore body is at least in .
part fault controlled. Although a little digging has been done,
these occurrences north of the main pit seem to offer no chance
for serious mining.
(2) Lushil (DC 404-115 Fizh)
The Lushil deposit lies in a small flat at the intersection of
two minor valleys 1.7 km (1 mi) east of the village of Lushil and
near the road from the village to Fizh. It is in an area of rather
subdued topography west of a bold outcrop of diabase dikes that
are vertical and trend northerly. Just west of the deposit are
low hills of mafic pillow lava. Although the diabase nearby is cut
by northwest-trending faults, we have no evidence suggesting a
fault between the diabase and lavas that'mighty have aided in
localization of the ore deposit.
The exposure of the deposit consists of a ground-level circular
area about 30 m (100 ft) in diameter of strongly oxidized gossan,
see photo 9 and figure 8. We saw no copper minerals or "stain" in
the gossan, and no piles of slag indicating it had ever been mined.
The surrounding rocks are unmineralized and surprisingly unaltered.
The gossan probably has developed over a small pipe of massive iron
sulfides, but its small size and lack of any sign of copper
mineralization indicates further exploration is unwarranted.
The area about the deposit also seems unfavorable because of
the lack of alteration or mineralization in the exposed rocks.
In the valley a few hundred feet northeast of the gossan, however,
there is an area of powdery soil containing some gypsum in which
the geophysicists for Prospection Ltd. report a slight geophysical
response. We believe the lack of surface alteration or the
development of a good iron-stained gossan indicates little chance
for the discovery of covered ore in this area.
33
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I M
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EXPLANATION
Alluvium
Gossan
[jsT^ Mafic lava, with
^ pillows
[^ Oiabase
Edge of shallow wadi
•--''Drainage
LUSHIL COPPER DEPOSIT.
OHM
ra
••.Trv"-^./
too 2O0 300 >400 fjoo P4.
SCALE
Figure 8. Geologic map of the Lushil deposit,
34:
CoiTipass and pace
I. H. Bailey
1974

X
Photo 9. Entire area of exposure of Lushil gossan^ viewed looking north
35^

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(3) Zabin (DC 358-098 Fizh)
The Zabin deposit is 1.1 km (0.6 mi) S22''E of Zabin village
and 8 km nearly due west of Fizh. It is exposed as several hills
of iron-stained gossan and an lnterve.ning low area of bleached
rock, see photo 10. The deposit is at the erosional boundary
between an upper tableland floored by old gravels at least 9 m
(30 ft) thick and a new pediment being established at a level
that is 75 m (250 ft) or so lower. Small hills xit mafic volcanic
rock exposed on the flank of the erosional scarp contain the main
deoosit. and other minor shows of mineralized volcanics can be seen
through the riew pediment along the edge of incised wadies
to the north. On the north side of a major wadi 500 feet north of
the main deposit is exposed a contact between the volcanic rocks
and underlying diabase dikes, suggesting that the deposit is nea.r
the base of the volcanic flows. The attitude of the dikes suggests
backward rotation of this part of the Semail ophiolite.
Three main areas of mineralized rock exposed at the Zabin
deposit are nearly surrounded by alluvium, see figure 9. The
southern two, separated only by alluvial cover, could be parts of
one continuous mineralized mass, and the main northern exposure
also might extend northwestward beneath cover to the small
exposures shown along the wadi bank on\figure 9. Between these
two clusters of mineralized rock is fresh volcanic rock, which
niakes it improbable that the north and south deposits are exposures
of a single ore body. .^ projection of the S. 49° E. trend of the
mineralized zone to the southeast reaches fresh volcanics in the
next wadi to the south, indicating the mineralization does not
extend far beneath cover in that direction.
The most intense mineralization, as indicated by a well-developed
deep-red gossan of iron oxides in a silicate framework, comprises
the most southerly gossari mass shown on the map. It forms the
western part of a prominent hill, which has little-altered pillow
lava in its eastern part. Although the gossan is striking because
of its color, much initial silicate remains, indicating the
unoxidized rock below is only partially replaced by sulfides.
Neither here nor elsewhere in this area did we observe any copper
mineralization, and there is no slag or other evidence of ancient
mining about these prominent exposures. The gossans probably overlie
pyrite mineralization with little or no copper. The surface showings
are not encouraging enough to warrant further exploration.
36

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ill
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Photo 10. Area of Zabin deposit viewed looking northwest. Intense
alteration extends from colorful hill tliis side of Land Rover
to bleached zone just this side of broad, alluvial-filled wadi,
Hov/ever, a little alteration is found along the trend of the
zone on the far side of the wadi.
37

^•^ %^4
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EXPLANATION
Alluvium and
colluyium
N
Strongly mineralized
volcanic rock,
gossan
Weakly mineralized
volcanic rock
Mafic volcanic rock;
local pillows
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(4) Fizh (DC.345-068 Fizh)
The Fizh deposit Is 0-3 km south of wadi Fizh and 1.8 km (1.1
ai) east of the village of Mahjal. It is easily found as it
consists of two unusually dark hills rising from a broad pediment
surface, which is cut down about 3 m (10 ft) into an older alluvial
terrace, see photo 11. A mountain front nearby consists of northerly
trending diabase dikes, but the deposit itself ts in altered mafic
pillow lava.. The lava appears to lie about 45 m (150 ft) above
the contact with the zone of dikes; thus,"the geological setting
here is identical with that of the Zabin deposit.
The deposit forms two parallel mounds having a narrow connecting
band at their northern end, see figure 10. The mounds consist of
gossan made up chiefly of deep brown, locally black, goethite,
yellowish brown limonite, and deeply stained silica. Some very black
siliceous material Is thinly layered and perhaps is mineralized
chert. There is a vague suggestion that the hard gossan is a cap
extending little below the pediment level. No copper minerals were
seen, and no evidence of former mining was observed.
The pair of mineralized hills is surrounded by alluvium, but
there are enough small patches of unaltered volcanic rock sticking
up through the alluvium on all sides to eliminate any speculation
about the area of mineralization extending much farther beneath the
cover. Also, the small exposure of volcanic rock on the inside
edge of the eastern lobe, see figure 10, suggests the mineralization
is not continuous between the two lobes beneath the intervening cover.
The Fizh deposit does not appear to us to warrant further exploration.
(5) Khabiyat (DC 397-013 Fizh)
The Khabiyat deposit is 4.5 km (2.8 mi) S. 29" W of Jabal Shaykh
and 0.3 km (CIS ml) west of the main road up the east side of the
"Bowling Alley". It lies on a flat alluvial surface between the main
Oman Mountains and a smaller range of hills comprised of Semail gabbro
and diabase. The only exposures in the mineralized area are seven
small Isolated patches of gossan that protrude above the alluviated
plain. The gossans are strongly leached and consist mostly of
residual silica with some yellow and brown iron oxides. They contain
no visible copper minerals, and apparently were not mined in ancient
times. Owing to the advanced degree of alteration of the rocks in
these few exposures we are uncertain about the nature of the host
rock, but it probably was a mafic volcanic rock. The limited showings
do not appear to us co merit further exploration.
k
&m 39

mM'~
EXPLANATION
hJ
mineratiied
Alluvium and colluvium
Tfirrace deposit
OTM Gossan, ir.ineralized
^ volcanics and chert
^ Diabase dike
^tafic volcanic rock
y*^ Edge of wadi
FIZH COPPER DEPOSIT.
OMAN
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p^pd^ m.
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Photo 11. Gossan hills of the Wadi Fizh deposit, viewed looking southeast
Rock in right foreground is nearly fresh basalt.
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41
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(6) Bayda (DB 408-939 Fizh)
The Bayda copper deposit is on the east side of the "Bowling
Alley" about 1.1 km (0.6 ral) S. 54" E of the village of Bayda.
It occupies a slope leading up from an area of low hills of mafic
volcanic rocks to a high-level flat blanket of old gravels. The
mineralized zone is intermittently exposed through a mantle of talus
broken from the gravel above, see photo 12.
The ore deposit is a zone of slightly to intensely altered
volcanic rock extending for about 180 m (600 ft) in a northerly
direction and having an average width of about 45 m (150 ft), see
figure 11. The alteration is the most intense along the west side
of the zone, where some local areas are so leached that only white
silica remains. In other parts there has been less acid leaching
and the rocks are deep brown to yellow in color owing to the
abundance of iron oxides and sulfates. A little copper "stain"
can be seen throughout but is most common along the western margin
where some mining was done in open cuts and perhaps through a
shallow shaft. Jasper is exposed above the west edge of the ore
zone, and a hill on its southern end is mostly jasper. We are not
certain if the jasper is a cherty sediment or is the result of
silicification related to the ore genesis; however, local layering
suggests at least part is primary.
The deposit contains some copper and has been mined on a
small scale. We saw no slag, but perhaps some of the slag about
the nearby Aarja deposit represents ore carried from here.
Although the sulfide mineralization does not seem to be intense
through the entire width of the altered zone, we believe the showing
is of sufficient size and merit to warrant at least a couple of
exploratory drill holes. We also noted some iron staining in the
hills across the wadi about 1 km (0.6 mi) to the north, but did
not have time to inspect it closely.
f2

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m
I
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:.l.l-..:-SK"-J
rsi
•f ^ « Alluvium and colluvi I urn
Ai
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dm
iM
md 'crrace deposit
y .'(ineralized volcanic rock
J?f«
.^ Jasper (silicified tuff?)
^ ."tdfic volcanic rock,
soma pillows
f ('"') Probable limit of
% '^-' mineralized rock
f ^.y Drainage
Figure 11. Geologic map of the
BAYDA COPPER DEPOSIT.
H3
O.IA:I
..>
Compass and pace
f-;. H. Bailev
1974
lOO too ^oo
SCALE
Bayda copper deposit.

Photo 12. Bayda copper deposit viewed looking north. In upper left
arc old workings in area of gossan and bleached volcanic rock.-
Ccntor skyline is cap of older alluvium. Low hills to right of
central area of white beached rock are composed of unmineralized
pillow basalt.
4'f

(7) Aarja (DB 402-925 Fizh)
The Aarja deposit lies among low rolling hills surrounded by
alluvium in an interfluve between two large wadies 2 km (1.2 mi)
south of the village of Bayda and 1 km west of the "Bowling Alley"
road. The country rocks are mafic pillow lavas, locally cut by
a few diabase dikes. The deposit is probably near the top of thtf"
Semail ophiolite as beds of cherty ironstone 0.5-1 m (2-3 ft) thick
occur with the ore, and some silicified tuffs were'also noted
nearby.
The deposit is expo sed as a brightly colored hill about 25 m
(85 ft) high composed of intensively altered gossan of iron-stained
silicates, white silica, limonite, geothite, and other typical
products of intense sulf ide mineralization and subsequent acid
leaching, see photo 13. Secondary copper minerals are fairly common,
especially near the top o f the hill and along the base of its western
slope, where there has b een considerable mining. The extent of
mining is indicated by t he widespread piles of slag, which in the
aggregate amount to more than 25,000 tons.
The prominent gossan exposure measures 120 by 60 m (400 by
200 ft), but abundant float suggests that the ore body is larger
Chan this, see figure 12. We believe it is elliptical in shape
with lengths of major and minor axes of 165 and 100 m (550 and
350 ft). It is elongated in a northwesterly direction, parallel
CO the prevalent direction of faulting in the "Bowling Alley" area.
However, we saw no surface expression of a fault here, and are not
able to relate the structure to the fault along which is developed
Che nearby Bayda deposit.
Because of the size of the gossan and its copper content it
may represent a mlnable deposit, although the sulfide replacement
does not appear to have been as complete as at the Lasail or Semda
deposit. We recommend that it be further explored by at least
three drill holes to determine the grade of the primary ore and
its extent beneath the alluvial cover.
45

• I.
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[XPLANATIOi-l
Slag; number
shows averagt
depth in feet
Alluvium and
colluvium
_ Gossan; mineralized
1^ volcanic rocks and
cliert
_] Possible gossan, as
labelled
i^ ."'".afic volcanic rocks
^ Edge of wadi
t^\ f i»*:w^:
-. .. V

-~wrr^-
Rfp-"'''"
Photo 13. Aarja copper deposit, viewed looking southeast. The highest
parts of the prominent gossan hill contain mineralized chert.
Flat skyline on left is surface of overlying old alluvium deposited
in a prior cycle of erosion.
hi

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i!
(8) Ghayth (DB 428-905 Wadi Al Jizzi)
The Ghaych depo.sit extends along a narrcv/ alluviated valley
between low hills about 4 km (2.5 mi) N. 23° E. of ruins of
Mulayyinah on the bank of Wadi Jizzi. The valley is bordered by
hills of mafic volcanic rock, locally showing pillow structure,
and to the southwest other hills contain cherty ironstone beds
0.6 to 1 ra (2 to 3 ft) thick.
The exposure of the deposit consists of brick-red, orange,
and locally black gossan cropping out as lov; mounds or as nearground-level
patches along a zone extending N. 14" W., see photo
IA and figure 13. This zone developed along a vertical fault
Chat may be the southern extension of the fault on which occurs
the Bayda deposit.
The Ghayth deposit is exposed over s length of a little
more than 400 m (1,400 ft). Its northern end is about at the
limit of exposure, as a short distance farther north along the
strike of the fault fresh volcanic rock can be seen. To the.
south, the deposit might extend farther under coyer, as its
projection goes under a capping of thick terrace gravels. The
northern part of the gossan zone has an exposed width of about
30 ra (100 ft), but the southern part, which is less well exposed,
appears to be less than 15 m (50 ft) wide.
The gossan has not been mined and we saw no copper minerals
in it. From the leached surface exposures we judge that it
overlies a narrow vein of massive pyrite with borders of volcanic
rock containing varying amounts of disseminated pyrite. Owing
Co the total absence of copper "stain" it appears to have no
economic potential, but its extent is sufficient to warrant a
single exploratory drill hole to obtain samples of the unoxidized
ore. Mineralized areas shown on figure 13 to the east of the
main ore zone represent weak alteration and are not worth further
attention.
Uft

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N
Mineralized rock is
resistant and tends
to crop out; probab
little lies beneath
cover.
Compass and pace
E. H. Bailey
1974
liiiwwiiiWWPWIIWiiiii
GHAYTH DEPOSIT.
OMAN .
EXPLAM/MION
Alluvium, colluvium,
and terrace deposits
Gossan and mineralized
volcdnic rock
Mafic volcanic rock,
some pillows
yy^ fdge of wadi
Drainage
Figure 13. Geologic map of the Ghayth deposit.
SCALE

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Photo 14. Ghciyth gossan zone viewed from southern ona looking north.
Virtually the full extent of the minor.il ized 7oiir is shown in the
photo. Rordering rocks are mafic pillow lava ana hills beyond
are gabbro.
50

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(9) Lasail (DB 422-843 Wadi Jizzi)
The Lasail deposit occupies a depression within low hills of
pillow lavas, d.Lkes, and sills 2.7 km (1.7 mi) S. 14° E. of the
ruins of Hulay/inah. on Wadi Jizzi. The area appears to be synclinal,
and the occurretnce of dark, iron-rich sedLT.ants overlying pillov/
lavas suggests that the ore body lies at the top of the Semail
ophiolite pile. Local diabase dikes trend northward and dip at
moderate angles westerly. Because of the advanced study made her.e
by Prospection Ltd., who believe this to be'the most promising ore
body yet discovered in Oman, we made no attempt to map the deposit.
The exposure of the ore body consists of a flat low area of
striking orange, red, and brown powdery gossan said to measure
270 m (900 ft) by 135 m (450 ft), see photo 15 and 16. Diamond
drilling by Prospection Ltd. has shown that the gossan has formed
over a pipe of massive sulfide ore having a vertical extent of
at least 210 ta (700 ft), the depth of penetration by the equipment
available. Little data on the content of copper in the drill core
is available to us. But substantial sections are said to assay
2-3 percent copper, occurring as chalcopyrite veins and crystals
in massive pyrite. With only partial knowledge of -the preliminary
drill data we estimate the known amount of ore may be between 5
and 10 million tons of massive pyrite ore containing 2 1/2 percent
copper. Cost calculations indicate this deposit can be mined at
a profit under present conditions if the potential tonnage and
grade are as indicated.
Copper "stain" and relics of copper in vesicles in the lava
can be seen at the deposit. This was the site of the most extensive
ancient mining we saw, and the slag heaps lying all about the
gossan liave been estimated to contain 100,000 t* of roasted ore.
*t, metric tons
'Pi

y.
At
5
?itoto 15. Lasail copper deposit
as viewed from the air looking due
north. Black, pock-marked., a reas surrounding gossan are ancient
slag piles, which are estimated to contai'n'at least"l
Drill rig in center of
00,000 tons,
photo to right of wet area is set
Prospection Ltd. DDH-2
up at
'^•m;yp
wmm^i

Photo 16. Central ptirt of gossan o\/er the Ltisai^ ore. oody lOOKing
west. Conical piles of various colors to left of Land Rover
represent material from pits at 0,5 (l,b3 feet)-iiiot

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(10) Jabah (FB 247-002 Udhaybah)
,~,.««w-.mimmmamimmmimmiimmmS9SSll&.
The Jabah occurrence lies among low rolling hills along Wadi
Jalsa approximately 5 km (3 mi) S. 43* E. from the village of
Rusayl on the main road to Muscat. The area is underlain by pillow
lava which is capped by 1 m (3.3 ft) of silicified leucocratic
tuff containing plagioclase phenocrysts. At the contact a thin
bed of chert separates the tuff and pillow lava,and secondary
copper minerals occur sporadically at the-chert-tuff interface.
.Uthough an analysis of tuff in the mineralized zone shows 2.9Z
copper (see table 6 in Appendix), we recommend no further work here.
(11) Rakah (DB 570-182 Mlskin)
The Rakah copper deposit is exposed as a group of low hills
partly covered by alluvium 11.2 km (7 ml) N. 21' E. of Yanqual
Fort, from which it is readily accessible. The main mineralization
is in mafic volcanic rocks, but in adjacent diabase and nearby
gabbro there has also been some mineralization along fractures.
Boundaries between the different kinds of rock are apparently
northeasterly trending faults, and it is likely that here the
Semail ophiolite is also overturned.
The deposit is exposed as a colorful gossan of brown, yellow,
and orange iron oxides and white silica, with other products of
secondary alteration and acid leaching, see phcto 17 and 18.
Locally, however, a little pyrite still remains in the outcrops.
The surface area of the mineralized zone is rectangular in shape
and about 240 m by 120 m (800 by 400 ft) in dimension, see figure
14. Secondary copper minerals can be seen in several parts of the
gossan, and mineralization is particularly Intense along northeasttrending
shear zones in the central area and near the northwestern
margin where cuts, and some underground workings, attest to ancient
mining. Scattered about the deposit are many piles of slag which
in the aggregate are estimated to contain about 20,000 tons. Also
in the area are several well-preserved fire pits where the copper
was roasted out of the ore.
The size of the Rakah deposit and the prevalence of some copper
minerals in its gossan requires that it be explored by a few.drill
holes. However, the surface showings do not appear as in some of
the deposits in the "Bowling Alley", and the remoteness of this
deposit from all others of merit would make it difficult to operate
it as one of several supplying a single concentrating plant.
t-ii

N
EVPL/IWATIOW
Slag, number .shows depth in feel
asB Alluvium and colluvi
Idfyj Terrace cieposlt
^ ^ Mafic volcanic root;
rli^ Oiabase
^ fioscah
RAKAH COPPER DEPOSIT.
« ^
OMAN
Comoass ar.d pace
r;'. ii. Bailey
1974
Figure 14. Geologic map of the Rakah copper deposit.

i-'W".*^

?iwio 18. Northern part of the Rakah gossan zone where a little underground
mining has l)een done, viewed looking west Low greenishgray
slope beyond ore zone is composed of diabase dikes; high
range beyond is chiefly gabbro.
5 7

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>fd Description of copper deposits in gabbro and peridotite
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(12) Maydan I (D3 390-334 Qii..ayrah)
The Maydan I deposit is in a narrow wadi about 1.5 km (1 rai)
east of Tawi Salaraah, which is in VJadi Ahin. Here for 450 m (1,500 ft)
along an easterly trending shear zone in a peridotite screen in gabbro
occur scattered veinlets of malachite, see figure 15. The mineralization
is most intense in two zones near tlie margins of the peridotite, and
in thsm generally copper stains v/ere seen over widths of only a few
feet. Although small slag piles indicate some ancient mining here,
the deposit seems to have no potential for modern mining. •.-
(13) Maydan II (DS 380-343 Ouniavrch)
This deposit, which is also knovm as the Salama deposit, is less
than 1 km (0.6 mi) west of the village of Maydan in Wadi Ahin and about
2 km (1.6 ni) northwest of the Maydan I deposit. As' shown in photo 19
and figure 16, copper mineralization occurs in a shear zone separating
cumulate peridotite from coarse-grained, locally pegmatitic gabbro.
Across a small wadi 210 m (700 ft) to the south are prominent exposures
of diabase dikes v;hich strike almost due north and dip steeply eastward.
The mineralized shear zone forms a bench 6-9 m (20-30 ft) wide on a
scutht^est-facing slope and is in most places covered with talus. At
its east end is a good exposure of the ore zone, but here chalcopyrite
and secondary copper minerals are confined to a zone only 1 foot v/ide.
The debris-covered bench is largely the result of ancient mining, and
perhaps the ore zone was somewhat wider in this part. The scale of
ancient mining is indicated by the size of the slag piles found on
each side of the wadi and estimated to contain about 7,000 t. The
deposit ia too small to be of interest today.
(14) Bu Kathir (DB 374-149 Dank)
The Bu Kathir deposit is about 16 km (10 mi) west of Yanqul and
2.1 km (1.3 mi) south of the village of Bu Kathir in a small canyon
that can be reached only on foot. Most of the rocks in the canyon wall
are layered gabbro, but the ore shoxjings occur in a fault-bounded screen
of serpentinized peridotite. Secondary copper minerals are scattered on
shear surfaces in a zone trending N. 60 W. and dipping 70 S. Copper
"stain" occurs erratically over,a width of generally less than 2 feet
for a length of about 5GG feet, and there are minor shows even beyond
this. Selected pieces of mineralized rock from the ore zone gave 11.0
percent copper. The zone was formerly mined through one adit near its
center and several small open cuts, but two slag piles noted in the area
contain probably less than 1,000 t of roasted ore. In spite of the
richness of the selected pieces, the showings do not warrant additional
work.

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^ Peridotite, mostly
^^^ serpentinized ccr;r»c-.-: ?.nd pact:
Collu.T Grar.t end £. H. cailc---
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Figure 15. Geologic map of the Maydan I copper deposit,
53
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EXPLA^iATION
Slag; number shows
«^ average depth in
[i3 Alluvium and
**^ colluvium
Mineralized shear
zone •
Diabasvi dikes
iiiil Gabbro
j ^ Cumulate peridotite;
serpentinized
^ Edge of i vadi
.y
Small canyon
•^AYD,AN II COPPER DEPOSIT
OMAN
SCALE
One foof of sheared
ond mmeralized '"ock
Compass and Dace
E. H. Bailey
1974
if: is» Ft
Figure 16. Geologic map of the Maydan IL copper d leposit.
60

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(15) H;..wirdit (DB 334-169 Dank)
The Hawirdit deposit is 3 Ian (2 mi) south of the small village of
Ahdyah, from which it is accessible only by foot trail. Near the base
cf a south-facing hill are several durtpe, eroded ancient cuts, and a
small cave, see figure 17. The low ground is serpentinized peridotite
but the upper parts of the surrounding hills are gabbro. In the east
edge of the mineralized area the gabbro appears to be separated from
the underlying peridotite by a,more or less flat fault.
At the'Hawirdit deposit we saw no real exposures of ore in place,
but the material on the dumps, as well as the,locations of the pits,
indicate that the ore consists of secondary copper minerals in sheared
peridotite. Some of the sorted ore on the dump is of good grade, but
the quantity available is small. Extensive ruins of ancient buildings
and slag heaps attest to former copper recovery; however, the deposit
has no potential for mining today.
(16) Tawi Ubavlah (DB 147-776 Wadi Jizzi)
The Tawi Ubaylah copper deposit is 0.7. km (0.4 mi) southeast of the
village of Tawi Ubaylah, a short distance south of the drainage divide
of the Oman Mountains and east of the road between Wadi Jizzi and Buraimi.
The ore zone extends along the side of^ a south-facing ridge about 25 m
(80 ft) above the wadi at its base for a length of at least 210 m (700 ft),
see photo 20. The upper part of the hill is gabbro and the lower part is
highly sheared serpentinized peridotite containing blocks of gabbro.
The contact is a steep fault trending N. 75 E. Ancient dumps and diggings
form a narrow bench along the faulted contact, and although a
gossan zone is locally exposed we could find no good exposure showing
copper minerals in place. Pieces of sheared serpentine containing secondary
copper minerals, azurite and malachite, are common as float or in dumps,
and we found one piece showing a 1-inch vein of chalcocite. Samples of the
gossan analyzed by Prospection Ltd. contained about 1 percent copper, and
a grab sample from a gossan pile gave us a value of 3.0 percent copper
(^ee table 6 in A^jpeindlx). Ia the wadi at the foot of the hill sheared
peridotite is entirely "n^ineralized.
, Across the wadi are extensive slag piles, at least 20 old furnaces,
and ruins of numerous ancient rock buildings. This is the only place in
Oman where we found pieces of copper matte and bowl-shaped chunks of -slag,
indicating the use of an advanced copper recovery process. Probably the
ore zone at the Tawi Ubaylah deposit is too small to be mined today, but
if the chalcocite zone is well developed it might have some potential.
A drill hole or two into the ore zone would be interesting.
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3 Alluvium and colluviuo}
^ Slag, number is averagfi-
,depth in-feet
S3 Gabbro
Peridotite
Di'ainage
H.AWIRDIT COPPER DEPOSIT.
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Figure 17. Geologic map of the Hawirdit copper deposit.
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20. Mineralized shear zone of the Tawi Ubaylah copper deposit,
viewed looking north. Rock lying above the ore zone is gabbro,
and below Is mostly serpentinized peridotite. Thin reddish-brown
gossan cover on the slope below the ore zone Is largely dumps
resulting from ancient mining along the zone.
GH

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(17) Ghayl (DE 0.?:2-7S3 Wa.U Al Ji^zi)
The Ghayl copper deposit lies in an open valley about 13 km
(8 .mi).west of the Tawi Ubaylah deposit and 7.2 kr. (4.3 rai) southeast
of Jabul Umm Dhawan. The ore aone is poorly exposed in a few low hills
surrounded by alluvium and locally overlain by higher level terrace
gravel, The deposit is in peridotite, but local gabbro dikes and layers
near the deposit suggest that it is in the transition zone between peridotite
and gabbro. Secondary copper minerals occur in sheared peridotite
in an area 50 m (165 ft) long in a N. 20 1^. direction over a maximum
local width of 20 m (66 ft). The area contains some spots of good ore
but is so churned by digging and covered v.rith waste that it is impossible
to tell how much of the zone shows significant mineralization. A grab
sample of better ore in a waste pile assayed 3.2 percent copper.
Because of the alluvial cover it is difficult to estimate the total
length of the mineralized zone. It may go farther to the south, but
along strike to the north of the deposit about 30 a (100 ft) are exposures
of unmineralized peridotite.' In the mined area are the ruins of
at least 10 furnaces, and less tha^ 1,000 t of slag is piled in the
valley below. In,spite of ancient mining the deposit does not appear
worthy of additional exploration or sampling.
(18) Muden (EA 513-955 Nakhl)
\
The Miiden occurrence of copper mineralization is on the north edge
of the Oman Mountains 11.4 km (6.8 mi) S. 30°.W. of Jaramah. It consists
of a mineralized shear zone between layered gabbro and diabase dikes
along the north side of Wadi Muden. Dissemii\ated copper sulfides and
secondary copper minerals occur over a width of about 40 cm (16 in.), and
the mineralized zone can be traced 90 m (300 ft) northwest of the wadi bank
An assay of a selected piece from the mineralized zone shows 12.2 percent
copper (see table 6 in Appendix). No mining was done here in ancient times,
and the occurrence is too limited to be of interest today.
(19) Luzak (FA 155-782 TayinV
The Luzak deposit borders a wadi cutting gabbro hills about 5 km
(3 mi) south of the village of Luzak. The site is by ruins of at least
25 houses and a shallow slag pile extending along the north side of the
wadi for about 45 m (150 ft). At the east edge of the pile are pieces of
gabbro containing a little chalcopyrite and secondary copper minerals
along fractures. The source of the mineralized gabbro is uncertain, but
about 300 m (1,000 ft) up the canyon northwest of the slag pile there is
a possible cut in.sheared and bler.ched gabbrs. On, tne ridge above are'
other bands of bleached rock follovring shear zones trending a. few degress
east of north. We are not sure we found the deposit from which the ore
for smelting was originally mined, but there seem to be no promising
outcrops in the area.
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(20) Tabalchat (EA 4G0-340 Bahla)
The Tabkhat deposits are 6 km (3.5 mi) v/est-southwest of Nizwa,
from which thay Ciin be reached by driving up a v/adi for 5 km (3 ni)
then parking and hiking southvjestward up' through a saddle some 60 m
(200 ft) higher to reach the south slope of the ridge. The deposits
consist of chalcopyrite and secondary copper minerals occurring in
shear zones in peridotite, see photo 21. Locally, the peridotite
contains veins of magnesite, but those are unrelated to the copper
mineralization. The greatest mining was done in the undeirground
workings shoum in figure 18. Here there were two parallel zones,
trending nearly east and dipping 65° N., that were rained to a known
depth of at least 18 m (60 ft), and one shaft is reported to have
reached a depth of nearly 60 ra (200 ft). The mine is .difficult to .
enter because of its steepness, and it is quite hot owing to the
oxidation of the sulfides and lack of through circulation. T\i,'o chip
samples taken in these workings by Prospection Ltd. gave 2.86 and
5.21 percent copper. Sample 621, taken by the writers across 1 foot
of the ore zone underground as shown on figure 18 contained 2.1 percent
copper. A grab sample from the dump gave 1.1 percent copper (see table
6 in Appendix).,
• ;, ', - • - ' " \ . • • '
High on the ridge to the south of the mapped nine is another
tunnel which extends more than 50 m through the ridge. It is driven
in peridotite and follows a mineralized shear zone about 1 foot wide
along a fault trending N. 80° W. and dipping 80° W. Slickensides on
the fault plunge 43 to the east. Twenty feet below the tunnel portal
on the west.end is another adit following the same zone, and in the
general area are still other minor cuts and short underground workings.
In spite of the widespread mineralization and extensive underground
workings, we found no slag in the area and none was known to
our Omani guides. Possibly the ore was hauled to Nizwa for processing.
The mineralized zones are too narrow and too inaccessible to be
potentially minable now.

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Photo 21. Peridotite hillside containing the main underground workings
at the Tabakhat mine. Area in lower left of photo is the ancient
dump which was sampled. The upper portal of the workings shown
on figure 18 is a little more than one inch from the right margin
of the photo .and a little above the middle. The lower portal is
in the shadow area directly below. Other workings are over the
ridge beyond the figure on the skyline.
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(21) Khafifah (FA 464-320 Samad)
Next to several houses on the edge of the village of Khafifah
just before the road "crosses Wadi Khafifah into the main part of the
village is a slag pile in excess of 5,000 tons. The area is one of
layered gabbro that is in fault contact with peridotite. No zone of
minera.lization was found, but in the gabbro west of the road a zone of
hydrothermal alteration was seen. Assay of slag from this locality
shows about .5 percent copper and a trace of silver (see table 7 in
Appendix). We recommend no further work on this occurrence.
(22) Masakivah (FA 454-125 Samad)
The Masakivah occurrence is in the foothills of Jabal Haymah
about 12 km (7.2 mi) N. 80 W. of Ibra. Here layered gabbro strikes
northwest and dips 60 SW. near a contact with pendolite. In the gabbro
a mineralized zone containing secondary copper minerals in shear planes
extends less than 2 m (6.6 ft) and Is not more than 10 cm (4 in.) wide.
The occurrence is too small to deserve further attention.
(23) Inah (FA 700-337 Ibra)
The Inah deposit, which is 14.2 tan (8.5 ml) N. 8 W. of Batin at
the headwaters of Wadi Batin, can be reached only on foot after crossing
the plain north of Batin. At the divide between Wadi Batin and Tayin
numerous small adits have been driven into serpentinized pendolite. The
mineralization appears to be disseminated chalcocite in sheared serpentine
along a large northwest-trending fault. Numerous slag heaps totalling
perhaps 5,000 t indicate it was a fairly active mine in ancient time-.
The showings are too small and scattered to warrant further work on this
prospect. .
(24) Eedah I (FA 173-446 Wadi Tayan)
The Eedah I deposit is reached by driving 12.8 km (8 mi) north up
Wadi Andam northeast of Mahaliyah and turning off eastward to go up a
ravine 1 km (.6 mi). It also can be reached from the Ibra-Muscat road at
the Wadi Andam crossing by driving southwest for 7 km (4 mi). Here in
the foothills of a gabbro range are prominent slag dumps containing a
little less than 5,000 t and several old ruins. Bleached gabbro up
the canyon to the east contains local copper "stain" but we found no
definite excavation. The feeble showings do not warrant additional
investigation.
"'I G9

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(25) Eedah II (FA 171-439 Wadi Tayin)
The Eedah II deposit is east of Wadi Andara, and about 0.8 km
(0.5 rai) southwest of the Eedah I deposit but in the next wadi to the
south. The rocks on both pldes of the canyon are gabbro v.'hich for
300 m (1,000 ft) along the wadi bank has been hydrothermally altered
to a snov;ry white clay. A sample of an 8-cra (3-in.) iron-stained zone
cutting the clay contained less than 0.05 percent ccpper (see table 6
in Appendix). On the hillside above, gabbro overlies the bleached rock
with an abrupt, though apparently unfaulted, contact. It shows good
cumulate texture and prominent N. 85° W., 45° N. layering. Although,,
on a bench by the Wadi there is a slag measuring 60 m x 9 m (200 x
30 ft), we could' find no copper mineralization in place.
(26) Hoowasi (FA 090-378 Samad)
On a west-side bench above Wadi Andan less than 3 km (2 mi) north
of Mahaliyah are two small piles of slag containing only a few hundred
tons. Some of the slag contains copper staining, but no pieces of ore
were found. Across the wadi, on a sharp, point between it and a tributary,
is what is apparently an ancient cut, now much caved and eroded, about
25 m (80 ft) long and 2.5 m (8 ft) wide. The cut is in peridotite, and
the presence of gabbro a short distance up the wadi indicates it is
near the contact. Although there is considerable iron oxide along
fractures, we foimd no copper mineralization here.
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(27) Khara (FA 772-108 Ibra)
The Kliara copper-deposit is 5.5 km (3.3 mi) southeast of the
village of An Niba and 19 km (12 mi) east-northeast of Ibra near the
head of a northwe.stward-draiiiing wadi. The surrounding hills have
gabbrO; in their upper half with serpentinized peridotite containing
some large blocks of gabbro below. The contact in a regional sense is
nearly horizontal although undulatory, but in the mineralized area is
a nearly vertical fault trending northwestward. Locally along the
fault are ancient cuts in sheared peridotite containing thin veinlets
of secondary copper minerals, and on dumps we also found some scattered
chalcopyrite, The largest cut, which in its present eroded condition
is about 9 m,(30 ft) wide and 18 m (60 ft) long, follows K. 10° E.
fractures up into the gabbro. By this cut is a pile of mineralized
rock, presumed to be unprocessed ore rather than ore rejects, v;hich
yielded a grab sample that analyzed 4 percent copper (see table 6 in
Appendix). .^At the base of the hill is an extensive slag pile and the
ruins of at .least 16 houses. An assay of the slag shows 5.9 percent
copper, The antiquity of the mining is suggested by erosion of the miners'
hillside-tra^khy a gully: that has cut into it to a depth of 8 feet.
In a canyon about half a kilometer to the northeast we also
observed some copper "stain" along a northwest-trending shear zone in
peridotite.^ \-
'"These deposits are not rich enough or extensive enough to have
present-day mining potential. -
(28) Zahir (FY 866-986 Al Mintlrib)
The Zahir deposit is 1.8 km (1.1 mi) S. 52°,W. from the village
of As Zahir and can be reached easily by crossing the wadi and approaching
the southern tip of Jabal Suwadiyah. The mineralized zone is in a saddle
on top' of a hill consisting mainly of Semail gabbro. A shear zone 1-3 m
(3-10 ft) wide contains primary copper sulfides along with extensive
gossan consisting of secondary silicates, sulfates, and iron oxides. ' The
mineralized zone trends northwest and has an exposed length of 42 m
(142 ft).,. An analysis of mineralized gabbro within the ore zone gave
1.2 percent copper, and iron-rich gossan material had 1.7 percent copper
(see table 6 in Appendix). Ancient mining produced a single dump near the
mineralized zone and numerous slag heaps that would aggregate less than
1,000 t. The small number of ancient building foundations and the small
smount of slag indicates the production of this mine was small. We
recommend no further.work on this deposit. ,
71

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(29) Shv7ayi (FA 075r-188 Samad)
The Shv/ayi copper deposit is about 4.5 1cm (2.7 mi) east of the
village of Majazah in the Wadi Andam, or about 32 km east of Izki.
The main mineralization is in an area of very low hills nearly engulfed
in alluvium, and as there is no prominent development of colored gossan,
the deposit would be difficult to locate were it not for the extensive
piles of black .slag bordeir.ing it. • ' '
The deposit consists of two separate ore bodies developed in gabbro,
see figure 19. The northern ore body, which is very poorly exposed, is
elliptical in shape with a length of 210 ra (700 ft) and a width of about
60 ra (200 ft), see photo 22. In its western half is an uhidrained
depression Ira (3 ft) lov.'er than the general ground level and blanketed
with washed-in detritus. Probably its depressed level is a result of
ancient mining, but no evidence of this other than the depression itself
remains.; In its eastern part, small irregular pits are cut into leached
and iron-stained gabbro locally containing secondary copper minerals.
On a small hill at its southern margin is an inclined shaft, which is
now inaccessible but probably not very deep.
The second ore body is a few hundred feet south of the first, see
figure 19. It is roughly circular with^diameter of about 75 m (250 ft),
but because the western limit is an alluvium boundary it might extend
farther west. The mineralization is less intense than in the northern
ore body, and the gossan area as mapped includes some v;eakly mineralized
gabbro.
About a kilometer north of these deposits along the foothills of
a low range is a prominent steep eastward-trending fault separating
serpentinized peridotite on the north from gabbro on the south. The
path of the fault is marked by extensive terraces of white aragonitic
tufa deposited by calcium hydroxide springs having a pH of 11.2.
Along the fault are several dumps containing secondary copper minerals,
but the mineralization does not anywhere seem to be extensive. Analysis
of mineralized gabbro from one of the dumps yielded,2.0 percent copper
(see table 6 in Appendix),
The main Shwayi deposit cannot be properly evaluated, as surface
leaching makes it impossible to ascertain tlic copper content of the
primary ore. Because oxidation at the surface is incomplete, we assume
the depth to primary ore is not great, and deep trenching or bulldozing
across the largest ore body might be adequate to determine its grade.
Drilling would be more satisfactory but also more costly. It is probable
that the depc3it is not of com-Tiercial grade, as deposits of this type in
gabbro generally are not, but it cannot be entirely dismissed without
further physical exploration.
o'>4i 72

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Slag, number shaw
depth in |eeL '
^ Alluvia© aho! Col,luYi.v4rf
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(josssr. altered a:id
mineralized rock
^.•^ Dr»inaj.e •
SH'rJAYI COPPER DEPOSIT.
OMAN
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Figure 19. Geologic map of the Shwayi copper deposit.
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i. H. Bdiley
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Photo 22. Shallow depression believed to overlie the northern ore body
of the Shwayi copper deposit. Ipoking east. Toward the far end
of the.depression to the right of the trees colors due to Iron
staining can be seen, in some of the less altered gabbro.
Ih

. fTI
H Iron And Nickel(?) Deposits In Laterite
Summary
Ancient residual and reworked laterites lie on the Semail ophiolite
in several places throughout Oman. They have been found at Jabal
i'anjah where, Wadi Semail enters a narrow gorge before flowing
onto the Batinah coast, and extensive laterites underlie protecting
bluffs of shallow marine limestones in the uiclnity-of Kalahay
Niba northeast of Batin in the Ash Shargiyah country. The laterite
is believed to havie formed as a result of tropical, or perhaps
submarine, weathering of the ophiolite and, as the surface on
which it formed cuts at low angles across the sequence, in some
places it was derived from peridotite and elsewhere from gabbro
or volcanic rock. Because the Semail ophiolite contains
particularly high contents of iron, nickel, and chromium, the
weathering process has concentrated these elements In the
residual laterite, and locally further concentration has been
brought about by reworking. One can expect the laterites formed
on the different rocks to have ;different mineral potential; for
example, laterites formed on peridotite might be rich in nickel
or even chromium^but are less likely to have as high content of
iron as those formed from gabbro. However', we have not had time
to make a study..of their variations in rela,tion to the parent
rock. ' ' ' P - ' • ' . • - ' " ' ' • •
. As compared to vein or lode deposits, laterite deposits are
generally widespread and have the potential to yield very large
tonnages of ore. * Many of the large iron-nickel laterite deposits
of the world have developed on peridotite similar to those in the
Semail ophiolite, so it Is possible major deposits exist in Oman.
However, the Oman deposits in most places are overlain by massive
limestone which presents a formidable barrier to mining unless
places can be located where the limestone is thin or stripped
off by erosion.:
The laterite formed during latest Cretaceous time (Maestrichtlan),
soon after the generation of the Semail ophiolite, probably in late
Campanian time, and before the deposition of the Paleocene shallowwater
marine limestone that overlies the laterite in the Kalahay
Niba area. Laterite in southwestern Saudi Arabia (Overstreet and
others, 1973), and also those in Ethiopia (Mphr, 1962), are considered
to have formed during the same time period, suggesting that a large
area of tropical weathering then extended across the' southern Arabian
Peninsula and eastern Africa. The oolitic iron deposits within
the Shumaysi Formation east of Jeddah, Saudi .'.rabia, are considered
to be Late Cretaceous or Paleocene in age, and conceivably they
aay also be reworked laterica similar to the Oman laterite (Shanti,
1966).
75

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The section following provides more detailed descriptions of
the laterite deposits we have examined, but there are many miles
of contact between the Paleocene limestone and ophiolite that we
have not had time to examine, see figure 20. To properly assess
the iron and nickel potential of the laterite In Oman, all of
these areas should be carefully insRected, and sampled where the
outcrops warrant this. ' .- .
SS'

Description of laterite deposits
(30. 31) Kalahay Niba I (FA 597-149) and II (FA 787-215 Ibra)
The Kalahay Niba iron-rich laterite deposits are 7-9 km (4-5.5
mi) northeast of the village of Batin and easily reached from it by
following up the drainage of Wadi Batin to the limestone bluffs.
The deposits occur directly under the limestone cliffs that here
have a thickness of 25-30m (83-100 ft), as shown in photo 23. We
I found no exposures of laterite without the protective capping of
limestone. The laterite is quite variable.io thickness 15-30 m
(50-100 ft) as| it appears to follow channels, and sedimentary bedding
within it. also suggests some reworking. The iron-rich laterite is
locally pisolitic and reddish-brown in color, as shown in photo 24.
Some layers appear to be nearly pure hematite and geothite with
only minor amounts of residual silicates. Chemical and spectrographic
analyses of eight selected samples reveals a range from 30 to 51
weight percent iron, with surprisingly high chromium values of 1.18
to 12.53 percent (see table 8 in Appeiflx).
i
The distribution of the iron laterite faithfully following the
expo.sed cliff-forming contact of the marine limestone is shown in
figure 21. Assuming that the now known exposed laterite has an
average thickness of 15 m (50 ft) and extends at least 150 m (500 ft)
behind the limestone bluff with a total outcrop distance of 5.5 km
(3.3 ml), a value of approximately 50 million metric tons of an
average grade of 40 percent iron has been calculated. However,
considerable more wprk is required to fully characterize the grade
and tonnage of the actual reserves available. During our investigation
we were not able to Inspect all of the contacts between the limestone
and Semail ophiolite, and so all of these contacts should be considered
as having a possible laterite preserved under the limestone.
(32) Salaht (FA 822-143 Ibra)
The Salaht iron occurrences are 9 km (5.4 mi) east of the village
of An Niba. Here resting on top of the Tertiary limestone of Jabal
Salaht is a 60 m (200 ft) section of icross-bedded sandstone
interlayered with thin beds of shale. Within the sandstones are
several lenses up to 15 cm (6 in) thick of sandstone tn which
hematite forms an .interstitial cement. These lenses are continuous,
and within the section there are five separate iron-rich beds.
Analyses at one layer shows> \0 percent iron and 0.3 percent
chromium. The high chromium Indicates that the iron in these
sediments maybe reworked from the laterite produced on the Semail
ophiolite. As the exposure of this iron-bearing sandstone is less
than 3 sq km and the volume of the iron-bearing lenses very small,
we recommend no further work on this occurrence.
77

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Photo 23. Kalahay Niba I iron laterite exposed directly under Tertiary
limestone. Material in foreground is Semail volcanics. Viewed
looking southwest toward OM-114 where channel samples were
obtained.
78

o^ rvno^.irp of oisolitic iron ore at Kalahay Niba I
Vepresen?atlve Material fro. this ledge Is 44.6% Iron.
79
Assay of

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Figure 21.
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x^-int ' ,'
@ 1
^i^«. Jl^iw!-''^
* -—'———"T"^ rv.i.o»««t««>
-L-—^i ^ — ' ' , laterite below Tertiary
li.ii."
I r,,.isi- Jv.r*4S^=

't
•Il
\
'•3
(33) Wasit (EA 589-338 Birkat Al Mawz)
About 5 km (3 rai) east of Nazwa on the east side of Ja:bal
Al Hawrah, and reached by driving north from Nazwa road near Wasit,
is what appears to be an ancient open pit or quarry. It is cut
into a deeply weathered peridotite, and much secondary carbonate
occurs in the upper part of the weathered profile. It may have
been dug to extract the carbonate for use in making a form of mortar,
but no direct evidence for this was found. ' Spectrographic analysis
of material from the top part of the laterite showed 0.07 percent
nickel, 0.15 percent chromium and less than 5 percent iron. This
mysterious ancient cut warrants no further attention as a potential
source of ore.'
(34) Fanlah (FA 137-944 Ibra)^
I
^^ Along the high ridge of Jabal Fanjah 2 km (1.2 mi) S. 76' E.
of the village of Fanjah is a red laterite developed on Semail
peridotite and exposed over an area of approximately 18 sq km (7 sq
mi). Middle Miocene folding has steeply tilted both the laterite
and an overlying protective limestone,\and rapid erosion has
removed miich of the exposed soft, rich upper part of the laterite.
The weathering profile within the peridotite consists of approximately
'I 30 m (100 ft) of massive brown-weathered peridotite, containing iron
oxide accumulations on fracture surfaces at the base, overlain by
laterite approximately 18 m (60 ft) thick. The basal part of the
red altered peridotite is cut by silica-rich cross-cutting veins,
and this grades upward into a red jasper and hematite zone having
hard parts that form the ragged outcrops of the upper reaches of
Jabal Fanjah. Hematite-rich areas 15 x 30 m (50 x 100 ft) are
present as pockets within the jasper, and at the top of the section,
^ we found a small pit in soft, bright red, ochreous material that
'^' suggested this may have been the site of an ancient mine.
I •• • " • • •• • •
,
I*
1
d\

V.
I
i
?
Analyses of a sequence of samples from the unaltered peridotite
into the laterite are given below-(see also table 9 in the Appendix):
fJ.nnpl".-
Niit>i)ir'r>i
Ot^-2^(b
OM-27*C
0.'1-2;H3
0M-274A
0M-27J
OM-271
OM-270
HclRht
,. .ibo>»e "Rase
. , In f,

1
/Chromite Deposits in Semail Peridotite ' "
• • • , ( • • " ~ " " " ^ ' : ' ~ ~ ~ ~ - • •
ChromitS; is a cocunon accessory mineral in the Semail peridotites,
and although the crystals are commonly small it can be detected in
almost a-ay specimen by using a hand lens. Two representative samples .
•. of Semail'enstatite peridotite analyzed by PDO-contained between 0.4 and
0.45 percent Cr203. However, cnly locally within the great expanse of
the Seicail peridotite is chromite found in masses large enough to be of
potential economic significance. All the concentrations of chromite we
^ saw in the peridotite were in dunite rather than in the more abundant
•harzburgite, which is also generally true in other parts of the world.
The chromite. occurs as layers or stringers', and"in some places it exhibits'
cumulate te::ture, such as is normally associated v^ith direct crystallization,
from an igneous meit. Previous xrorkers (Greenwood and Loney, 1968;
Peters and Kramers, 1974) have noted for the chromites in Trucial Oman
habitats different than we describe above. They refer to,podlike bodies
extending up to 100 ra in length and containing up to 100,000 metric tons
of ore. Smaller sacklike bodies of less than 1,000 metric tons are described
as generally parallel to primary igneous layers. The chromite
*t
^ .prospects in Northern Oman appear to be concentrated in a layered zone
in peridotite 100-200 m below the contact with the overlying gabbro.
Those we have seen are cut by abundant faults and "pull-aparts" which
...disrupt the continuity of the ore layers and make both mining and
tonnage estimates difficult.
, The value of chromite ore depends on both the quantity of chromite
present and the ratio,of chromium, irori, and aluminum in the chromite
mineral itself. Compositionally, three general kinds of chromite ore arc
recognized: (1) high-chromium, which contains 46 percent or more Cr203
, and has a chromium/iron ratio of 2:1 or more; (2) high-iron, which contains
40-46 percent Cr203 and has a chromium/iron ratio of less than 2:1; and
(3) high-aluminum, which contains more than 20 percent AI2O3, and more
1 than 60 percent AI2O3 and Cr203 combined. High-chromium ores are used
4
- ' for metallurgy, and high-aluminum ores are used mostly for refractories.
«| Only high-iron ores are used for making chemicals, and-they are also of
major Importance for making alloys and refractories (Thayer, 1973).
Chemical analyses of the Oman chromites, together with some previously
published for Trucial Oman, are given in table 2 and additional
chemical data is given in table 10 of the Appendix. The Oman samples
represent chips across the ore zone and are not pure chromites. The
Cr203 values on our samples are less than 37 percent Cr203 and the
chromium/iron ratios are below the minimum generally required for metallurgical
grade which brings a price about twice that for refractory-grade
ore. However, the samples from Trucial Oman have a higher chromium
content and more suitable chromium/iron ratio. Considering the similarity
5] . of geology, it is likely that in central Oman specimens and even small
,i
lenses of commercial-grade chromite ore also a^-u be fcund. However, we
do not recommend a specific search be made in the peridotite for chroiiiite
• . deposits, as the chances of finding an overlooked deposit of commercial
size and grade seem to be too small to justify such a search.
n . ' ••'• ' " ' . ' .•• ' ' - . • " •.-• . : d ' •
>
B3

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;5
f,
c
I
4*
Table 2..—:Chemical analyses of chromites from Oman and Trucial Oman
• CtzOi ,Al203 . FeO MgO Cr/Fe
''• '-Oman* . . ..'•2 . Fujai
K •
'.. •
-
52.52
56.5
48.25
.54.4 ..
45.01-
;48.77
50.7
46.43 •
47.64
51.99
34.70
ind Kraners , 1974)
45.1
47.9
38.5
45.2
40.6
61.3 .,
53.3
59.0
51.0
11.22
11.9
10.45
10.8
17.93
18 .'75
19.4
"" \
—
~
18 ..2 .
19.4.
22.8
18.2 -
21.7
S .0
10.3
11.4
16.0
17.91
18.9 .
. 16.59
16.9
15.01
15.32
15.7
14.39
16.59
16:08
15.44
13.7
13.7
14.2
13.7
17.0
13.5
1^,4
15. i
15.4
14.11-.,
12.9
16.65
14.0
16.82
15.30
14.2
. — . .
—
—
—
15.2
14.0
14.4
14.7
13.5
13.0
13.4 .
13.0
13.3
—
2.63
2.56
2.3
—
—
2.84
2.84
2,53
2,85
1.98
2.91
3.09
2.39
2.91
2.10
4.01
3.38
3.37
2.90
*Analyses by Sarah T. i.'eil, U.S. '-eologicai Survey, Menlo Park, Cali.-f:
BU

%
4
i!
^ > Descriptions of chromite deposits
, (35) Masakirah (FA 597-149 Ibra)
The small Masakirah chromite deposit is exposed on an open low
surface 6 km (3.6 mi) N. 23 E. of Ibra. The chromite ore occurs as
discontinuous elongate stringers, some measuring 7 x 3 m (23 x 6.6 ft)
within dunite surrounded by harzburgite, see figure 22. The contact
between the chromite stringers and dunite is diffuse as the chromite
occurs as a cloud of Individual grains imbedded "in the olivine rock.
The area of chromite occurrences extends through a narrow elongate lens
of dunite and a rough estimate of the quantity available is about 5,000
tons. Analyses of the chromite ore given in table 2 Indicate it to
be only of refractory grade, and we recommend no further.wprk on this
deposit.- •-
(36) Mudi (FA 958-025 Al Mintlrib)
The Mudi deposit is 8.5 km (5.1 mi) N. 71° E. from the village of
.\z Zahir. It consists of a vertical layer of chromite about 1 m wide
and extending approximately 15 m along a very steep inaccessible gully
in harzburgite. The abundance of float in the gully suggests that a
much larger body previously exposed has been largely washed away. The
texture within the layer indicates primary cumulus origin; however,
no other layered rock or gabbro was seen near this occurrence. The
chemical analysis of chromite from this deposit is given in table 2.
We estimate only about 900 metric tons of chromite ore could be obtained
here and recommend no further work.
-. - • •'*^ - • . ' •
(37) Aka Keya (DB 026-786 Wadi Al Jizzi)
^0
At the Aka Keya locality, which is 6.4 km (3.8 mi) S. 32 E. from
J . jabal Umm Dhawan, chromite stringers follow a dunite zone in Semail
peridotite for a distance of.700m (2,310 ft), see photo 25. They show
I some cumulate texture but are discontinuous and pinch out over distances
as short as 10 m. As the entire dunite zone has undergone folding and
faulting it..^ls difficult to estimate the possible amount of chromite ore
. available, but it is believed to be less than 1,000 metric tons. A chemical
analysis of chromite from this deposit is given in table 2. Owing
"to the small size and broken nature of the deoosit we recommend no
further,, work be done on i:
85

ff&&U^iS^.4isS3S£r;i?l^j^m:isiMMBs^^ 'M^^^i^isSmm^smssiMgi^shmmmM!^
CO
CO
J«*V*'
'fi-'jJ
EXPLANATION
2hil
Qa 1 ' > «
3
o
> » o
louj wafer riarine ? —
• 1 J. -f "
-Oman Mtlange.
SEMAIL OPHIOLITE
Pillow L(trtd Gabbro
Pe.r.dotit«
Hav~.*ina Allochthonous
t)cd i men-t-ar-j RotK»
_»—1 k_
Thrujt Fault Con-t act
Figure 22. Map showing location and geologic setting of the Masakirah chromite deposit,
"Tic
t 3
c o
I
c
(?
4-
. *)
V
u
I- 1.
•J
U)» J. Li mi f s ^ .* J .. J
Oxtvtvai-ntd beds
—O-
Vtrlital bed*
° . 1 3 4- I
Ki lom«ter4
J

5
I
Photo 25. Aka Keya chromite deposit showing light brown dunite zone
within darker brown peridotite Dark material in foreground is
chromite rubble derived from a single stringer Orthopyroxenite
forms ribs crosscutting the dunite.
87

•>•• ..|
•i
.'i
.,.;Si
I
-•I
-I
. ,.s
d-M
•"'-. yn
• " - ' Manf;anese Deposits in Hawasina chert
Scatterad manganese deposits have been found in the Hawasina cherts
in several areas. These deposits represent direct accumulation of
manganese oxides on the ocean floor during the deposition of deep-water
cherts that cliaracterize tha Hawasina Formation. As a general rule, the
manganese ore forms thin lenticular beds, bl.^bs, or pods v/hich as
deposited have limited continuity. In addition, local disharmonic
folds and minor faults interrupt the ore beds. We believe the Jaraniah
deposits near Ras al Hadd might be mined bn'a small scale, but all the
other occurrences we saw were too small to be of interest.
. • - . . • ^ . • , , . - , ' , - . ' . • - • • • .
Descriptions of manganese deposits .
(38) Hammah (FV 681-871, Al Mintlrib) .,,
The Hammah deposit lies in low rolling hills 5.7 km (3.4 mi)
S. 38 W. from Tawi Silaira, which is situated on Wadi al Batha. Tha
manganese ore, consisting of fine-grained pyrolusite, forms small pcds
and lenses within gentlj' folded beds of Hawasina chert. All the lenses
we saw were very small, and nom extended for more than 1 m or had a v/idth
of more than 30 cm (1 ft). We did not have time for an extended search
for additional manganese occurrences In i^his area, but no further work
is warranted. . ; '• '^ '
(39) Jaramah (GV 791-841 Sur)
The major Jaramah manganese deposits are in low rolling hills
11.8 km, (7 mi), S. 41. W. from the fort at Ras al Hadd in the northeastern
tip of. Oraan., The manganese ore forms prominent black outcrops
along several lOr-meter-high ridges where it is interbedded with red and
tan Hawasina phert, see photp 26. The mangatiiferous horizon can be
easily followed as discontinuous outcrops for more than 7 km (4.2 ai),
and because of its color shows up prominently on airphotos. Locally the
ore beds exhibit some minor folds, but the regional strike is northwesterly.
Results of an examination made in 1973 by L. E. Carlson for Granges
International Mining of Stockholm were made available to us. Our work
chiefly corroborates hi.s findings and adds additional analytical data.
88

•••-I
*
•••«fi^..
r
"J^-^ ,-*?^.-7t...
^!^^^^p:^rfd:^^dffr.. .-• ..,,>:i;y?t::3ii;^^^;v'':-'•••• '-.c-'"- ';'• -*3 .?- .^-..
.'."v^'t.!
••;^pi^p .'dp::' ^ ^•-•:^Ll
•.--. - ••ir.- 1 -ii.',-. '.-...':N».C , - ^
d::t^ • - ' ^ ^ • * ; *
: .TS-..
5 Photo 26. Exposure of black chert containing pyrolusite within red
cherts and shales of the Hawasina Unit at the Jarairiah manganese
deposit. This is one of the least Interrupted beds but it shows
some local folds and breaks due to minor faults.
y '•
OJ
.^y '

3
I
r
i
}
The main ore mineral is pyrolusite. It occurs as apparently
nearly pure beds . 3, cm to 50 cm thick and in places as much as
330 m (1,000 ft) long. It also impregnates even more extensive chart
beds coloring them jet black. The rich, ore, which is heavy and partly
crystalline, in places contains 50 percent manganese; but the equally
black chert beds aire deceptive, as they may contain less than 10 percent
manganese. "In places in the black chert there are pods of rich crystalline
pyrolusite.less than a meter long. Beds and pods are scattered through
parts of a Hawasina red chert sequence locally as much as 30 m thick, and
in most places dipping steeply into the low ridges. The rich ore comprises
only a few percent of the width of tlie entiire ore zone. A -
columnar section of one of the .richest zones is given in figure 23.
—a.j jsr .J »» ,
: —..£s=r
DlocU chcvf yciMct* of ^^»^.
BlacK Co7. JnJ C«d 0*% Cheirt 5-ioX tAn O'fC.
BUct: 4o% 3n«l Cej4o*.i Chc-tlectin
pois of rAn ort.
StreslCy ore, sviiti poJt'ofKn
IS Cm M*\ ore poi \
• '• • " •• . . • • \ -
BlictC -io by{{chevV hUV\r| Noviabl*.
A {cvg acm (An ovtpoAs
2 » 4 em {An ?oJi,
9\icK t«\a ehevf
5ec+von hi- ^ acvoss sec^uoacc
5 /• « V
U-J-Ki
o • I 2. me-lers
V«r4-ical "icllc.
• lAn Concern+

i
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AI
Table 3.^rChemical and spectrographic analyses of manganese samples
from the Hawasina Unit ',
Map No.
Field No.
Mn %•
S i %•••'
•Ai'-- ••-
Fe •' -. '
Mg
Ca ,;,
Na.: •,
Ti •
Mn ppm
3 • • -
3a "
Be
Co
Cr
Cu
Ga
Mo
Ni .
Sr
V
39
OM-193
Chemical Analyses'
39
OM-198
49.89 ^ 11.33
Spectrographic Analyses
7 . •-.•
.3
.05 •
.03
.3
.15
.003
50000
20
2000
3
100
50
1000
500
200
• 700
200
>10.
.3
.15
.07
.2
.15
. 015
\ 50000
50
2000
20
7
70
200
30
70
70
40
OM-250
7.
.7
.1
.2
.5
.7
.003
>150000
1500
3000
15
15
100
500
70
700
150
Chemical analyses by Sarah T. Neil and
Spectrographic analyses by R. E. Mays, U. S. Geological Survey, Menlo Park
OM-193 Small pod of pre from interbedded black and red cherc, Jaramah.
OM-198 Channel sample 1.3m (4.3ft) of manganese ore zone in chert,
Jaramah
OM-250 Manganese bpulder from Hawasina cherts near Wasit.
SI

:%P:M
.a
-fl
'•is
"M
^•--1
:f
We located at least four main manganese ore zones, which nay be
unrelated or may be outcrop belts of fev/cr horizons that have been
folded.. Other belts probably exist, as we found manganese float in
wadis oyer a very extensive area but had insufficient time to follov; up .
on the discoveries. We believe, however, we saw the best areas, as did
also the geologist for Granges International Mining.
It is our opinion that the Jaramah manganese deposits are marginal,
and it is unlikely that better manganese deposits in the area have
escaped notice. Chemical-grade (50% Mn)'and battary-grade (45% Mn) ore
occurs in the deposits and probably could be recognized and removed by
hand sorting. The deposits appear to us' to have nc potential for
large-scale mining, but perhaps could be operated on a small scale to
provide income for local residents of a relatively unprodu.ctive part of
Oman. The occurrence of the ore is such that it could be dug up in the
low hills, at least down to valley level, at low coist by a bulldozer
and this could be followed by recovery of the rich ore by hand sorting.
However, the total tonnage available seems to be barely adequate to
justify the cost Pf bulldozer, truck, and storage facilities.
(40) Wasit (EA 589^338 Birkat Al !4awh)
> About 5 km (3 mi) east of Nazwa on the east side of Jabal Al Hamrah
we found in an exposure of Hawasina chert several loose boulders of
nearly pure pyrolusite. The Hawasina here is mostly covered by terraca
gravel and we were unable to find the ore in place. A spectrographic
analysis of one of the loose pieces of ore is given in table 3.
I -. •-• -., •'•',> ' • ' ' ( •
92

I
1
i
¥
I
1
i
I
(41) Nujum (FA 205-830 Udhayban)
Lead-Zinc Deposit
The. Nujum deposit is the only lead-zinc deposit we found in
Oman. It is about 13 km (8 mi) southeast of Hadadibah, and is
reached from a point near Bidbid by driving eastward from the PDO
pipeline road up Wadi Nujum about 5 km, parking, and walking half
a kilometer.., V';,v '.' "
The deppsit consists pf a single long vein zone that parallels
the wadi near the base of the mountains on the southwestern Eide.
The vein is in hard silica-carbonate rock formed by the hydrothermal
- ialteration of serpentine, which comprises a rather thin zone at the
base of the Semail. ophiolite. Underlying Hawasina rocks, here
metamorpho.sed to a schist, are exposed in several places only a few
tens of meters belpv the mineralized silica-carbonate rock. Where
exposed, the Hawa.sina is entirely unmineralized.
The vein zpne containing the lead-zinc ore trends N. 10' W. and
dips steeply to the east. It is intermittently exposed over a
length of about 300 n (1,000 ft) and has been explored or mined
in three main workings. Near its center it was mined in an open
cut 36 m (120 ft) long and in places 9 m (30 ft) deep, see photo
, 27. From the deepest part of the cut, level workings have been
driven, but they are now inaccessible. The main vein was variable
in width but Ideally it was over 1.5 m (5 ft) wide, and with a
parallel vetin was rained over a width of 5 ra (16 ft). The mineralized
zone has vague margins, as it consists chiefly of hard siliceous
rock fprmed by replacement of the rather similar silica-carbonate
—rock. It is stained brown by oxidation of iron sulfides, and
contains Ipcal pods and disseminated crystals of galena, sphalerite,
anglesite-^cerussite, mimetite, and the rare, bright red, lead
oxide, minium - An analysis of a chip sample acrpss a 1.35 m
(4 1/2 ft) .yidth gave the following percents:
Copper.
Lead;
.Zinc
Arsenic
3.8
/S-O
7.5
3.0
Another sample representative of a dump below the mine contained
4&/i lead, 4T/'. zinc, ).8/^percent copper. Fire assays of two
samples gave silver values of .004 and .01 percent or 1-3 oz/ton.
Additional semiquantitative spectrographic data on ore samples from
the Nujum deposit is g.lven in Table 11 in the Appendix of this
report.
93
X

. 0
4
-I
rl
I
-I
•I
•••'P
• 1
•A
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...I
I
Photo 27. Ancient workings in the central part of a v

'. 4
.t
I
{<
North of the cut a little less than 150 m (500 ft) is a narrow
inclined working, following .dpvmward along the vein, which here is
only about 5 cm. (2, in) wide. . The working is so small one must, lie
flat and go headfirst into it, and after going in about 9 m (30 ft)
we gave up because pf ,the lack of ventilation. It appeared to go
down at least jaupther. 9 m (30 ft), "put seems to have been driven
only for exploration.
About 150 ra (500 ft) south of the main-cut is another adit
driven northward along the mineralized zone. Here there are two
adits with a common portal; one going slightly upward and the other
inclined dovmward. The lower follows the vein, which here, trends
N. 25° W., fora distance of 27 m (90 ft). The upper level was
penetrated almost as far to where it was partly filled with-rubble.
Both adits were.unusually tall and doubtless they were used for
removal of ore as well as exploration. At the portal here, as well
as below the main cut, were piles of ore that had been sorted out
from other rock removed in mining. However, we saw no slag in
this area, and can only surmise from the extent of the work done
that probably metals were recovered from this ore. Also unknown,
is whether lead or zinc was extracted, or whether all the mining
was done solely to recover the silver present in the lea:d ore.
The vein although mineralized over a reasonable length and
width probably has no potential for modern mining. It occurs in
the silica-rearbonate rock, and probably does not penetrate into
the Hawasina schists believed to lie less than 10 m (33 ft) below
the old workings. However, without a drill hole or winze into this
area immediately below the mined portion of the vein, deeper
mineralization cannot be positively ruled out. The relations here
J^eera to indicate that the formation of the silica-carbonate rock
from the serpentine came later than the emplacement of the ophiolite
by thrusting, and certainly the lead-zinc mineralization post-dates
the silica-carbonate rock. The lead mineralization is thus younger
than the Late Cretaceous deformation, and perhaps much younger.
95

ECONOMIC GEOLOGY,- NONMETALLIC MINERALS
Insufficient time was available for the proper evaluation of nonmetallic
mineral deposits. We record here some of our observations
and ideas as a guide to future work, but this report should not be considered
as a final word regarding the real potential of these less
glamorous, but often .very lucrative, deposits.,:
'"'':'•- Limestone-Dolomite ,
A considerable part of the Oman Mountains is made up of limestone
and dolomite, some of which certainly can be utilized domestically
and, where favorably located, might be exported. Examples of carbonates
that might be used are mentioned here only briefly. A large supply of
low-magnesium limestone is necessary for the establishment or expansion
of the cement industry. Certain limestones within the Hawasina develop
II excellent flagstones that might be used as ornamental stone. Tertiary
shallow-water limestones may locally be pure enough to be used as metallurgical-grade
material. Certain parts of the recrystalllzed limestones
that make up the';huge exotic blocks in the melange have the potential of
being excellent sources of polished marble. Tp assess the usefulness of
these rocks, we r.ecommend that a careful study be made of the chemical
and mecha,nical p.rpperties of the various types of carbonate sediments.
•1
','S
d'-.'P'^'l;' 'y Asbestos ' \ '•
The large area of serpentinized Semail peridotite may contain
potential sources for asbestos fibers, as chrysotile, the main source
of fibrous or spinning-grade asbestos, is one oif the common constituents
in peridotite. We were shown some specimens of ore-grade cross-fiber
crysotile from near Rustag; however, during our limited traverses
within the peridotite we saw no zones of asbestos large enough to be of
commercial interest. The short-^-fiber (Grade #7) asbestos commonly
occurs in highly,sheared serpentine, and the unusual lack of shearing
in the serpentine of Oman is a discouraging feature. Early work by
Greenwood and Lpney (1968) in Trucial Oman has revealed no conmercial
;m -asbes.tos depo.sits.,-^;; v"' "'• ^.,..-..• •
Magnesite
Veins pf magnesite (MgCOs) are abundant within the serpentinized
peridotites of Oman. 'Some veins reach thicknesses up to 1 m (3.3 ft)
and may extend up to 100 m (330 ft), see photo 28. All the veins,
however, are too small to be considered as a deposit of magnesite, which
now is not greatly in demand. Should there be an increased interest
in the mining of magnesite, Oman has the potential of becoming an
important producer.
96

• • • $
•'ii
i
M
•M
J!
•I
..ft
".•A
•I
•4
Photo ?n. Magnesite vein cuttini) p.irtia i ly seroentini zpd nendotitr
along wadi H

.:•.:, ;-•.-•....;'. Clay ,:;,
The use of clay in Oman has been restricted mainly to small
potteries turning out utilitarian utensils used mainly for the storage
of water. However, utilizing excess natural gas now being flared-off
at the wellheads within the Interior of Oman, a ceramic industry racking
products for both domestic use and export may be feasible where an
adequate Supply of natural clay is available. In the area north of
Bahala there is a surface, or near-surface, layer of clay, perhaps
deposited in a Pleistocene lake, which has provided an adequate supply
of clay for adobe bricks and a local pottery industry. A detailed study
of these clay beds should be attempted to ascertain the clay reserves
of this deposit, and their feasibility for greater use.
'''' P' Evaporites
The large interior drainage area centered around Umm As Samin has
been an area of deposition of evaporites over a long period of time. It
is possible that .economic concentrations of alkali salts and alkaline
earths (including lithium) may have been concentrated within this interior
basin. Chum drilling accompanied by assays is necessary to establish
the nature of the evaporites in this basin.
: \..>'^c. ;.v .•.-•,. Hot Springs „ . -. \
: • • ' t.-: •• \. ; ' • . ' . • ' • \
Three major hot springs investigated during this study issue along
normal faults in carbonate rocks on the north.side of the Jabal Akhdar
antiform. Their.positions are marked by ancient traviertine aprons at the
Gallah and Rustag Springs, but no travertine was found at Al Khadra.
Chemical analyses show these waters to be normal bicarbonate waters of
very high quality. They have surface temperature ranges from 44 to 51 C.
The possible maximum.subsurface temperatures for the springs, estimated
by using the Na/K ratios, are 123° C, see table 4. This value suggests
that the water issuing from the hot springs is normal meteoric water that
has percolated down along normal faults, has been heated up several
kilometers below the surface, and has risen again to the surface as hot
water. .iThe data indicate, they have no potential for geothermal power,
but the steady supply of water of high quality could be utilized as an
excellent source for bottled water. Further facilities constructed at
the siteis of these hot springs could provide the basis for health spas.
Individual descriptions of the hot springs we examined follow .
38

.. '-Descriptipns,of hot spring .
(42) Gallah (FB 413-0Z5 Udhavbah)
The springs are located at the foot of the mountain just south of
the village of Gallah, which is 5.8 km (3.5 mi) south of the main blacktop
highway near Azalba. The series of four springs Issuing here have a total
flow estimated as J^O gal/min. They, are alined along a low-angle thrust
fault between overlying carbonate rocks and underlying serpentine melange,
but on both sides of the spring area normal faults displace the thrust
plane. Locally developed silica-carbonate rock formed from the serpentine
in the melange suggests that the hydrothermal alteration here is clearly
related to the hot springs. An extensive travertine apron, up to 4 m
(13 ft) thick, has developed along the spring line forming a prominent
terrace; however, the water is not now depositing calcium carbonate. An
analysis of the water is given in table 4.
(43) Rustag (EA 420-867 Rustag)
The Important Rustaq hot spring is located 1.7 km (1 mi) west of
Rustag castle and can be reached by a road that starts at the west entrance
of the village market place. Geologically the spring lies along a normal
fault that extends southward into the Jabal Akhdar antiform. It is a
large spring supplying a surface pool that is approximately 14 m in diameter
and 10 m deep. The pool has a manmade protective wall around it, and the
overflow water is diverted along an open canal to be used for household
and irrigation purposes. According to the local people this hot spring
maintains a steady flow the year round. At the time of collection the
estimated flow was about 400 gal/min. A well-developed travertine apron
is exposed around the spring, but no CaC03 is being deposited now. Analyses
of the water are given in table 4. ^
(44) Al Khadra (EA 312-839 Rustag)
On Wadi Sahtan 4 km (2.4 mi) south of the village of Tabaqah, and
reached by driving up the.wadi from Tabaqah, is a single spring issuing
from a horizontal cleft in carbonate rocks. No travertine was found at
this locality, however, rapid erosion within Wadi Sahta,n may prevent the
accuiaulation of such deposits. It was estimated that the flow at this
spring was approximately 100-200 gal/min, and local residents indicate
that the flpw is ste'ady throughout the year. A chemical analysis is
presented in table 4. .
33

»^1i
Table 4.—c"p*»mical analyses of Oman hc-t springs, concentrations
in m g / 1 . ••-•;-. • . _ . , .
•' p: : "P:.d-''''
?H .•^.•••••..d,K;''.
.Temperature *C
Ca+2-':.. • • ^'-'.•••'••
•Mg+-::'. ;••/•'-•• ^•
r-a+V--.: ,•.'.. . '
•jH-i_ .
ci-^ •'.••••.:,;;:".
SQ^-2' •••-:•>''• ' - y d
HCOs"^ .
Li+i ' /, .••:\
SiOr
, 1 • ,
' Gailah*
" ' 48
,84.
8,0 .
• 38
.. 94. .
•^'^•-•'3.8 _
130
170
220
:.03
23.5
. 2
Rustag
51
66
26
97
150
7.8
4.2
85
230
24
.17
Calc. max sub- '_ ,
3
Al Khadra
' ' 44
7.9
70
27
80
3
130
91
220
surface Temp. ''C 118.2 123 114
.08
26.5
J Analyst ; T. S.P.resser , u. S.G. S. , Menlo Park, Calif,
1. Sample OM-80A hot spring near village of Gallah, grid location
FB 412 029. '
2. Sample OM-170 hot spring near village at Rustag grid location
'^ EA 420 867.
3. Sample CM-171 hot spring on Wadi Sahtan, grid location EA 312 839.
100

m
• : "il
'-..••. u
d.:%
.-•• '''I
-••• ' %
;l
1
^1
;.:'.^,y-:-:: •-,;.;.-: ,.;•-, '•.• Cold Springs
Cold springs with extensive white travertine aprons are conspicuous
along normal faults within the dark-colored Semail
peridotite, see i>hoto 4. None of these springs has a large volume
of flow, and most are small seeps whose restricted pools aret
coated with a thin scum of newly precipitated aragonite. In spite
of their limited flow, similar travertine-depositing springs in
partly serpentinized alpine-type ultramafic bodies in the western
United States have been extensively studied (Barnes and O'Neil,
1969).' Their waters are characterized by high pH, usually greater
than 11, and their analyses are similar to the three new analyses
of Oman spring waters given in table 5. Their unusual character
is believed to result from low-temperature near-surface serpentinization
of peridotite by meteoric waters.
J 01

"wm
-«
••ij
-vi
1
I
' -I
Table 5. Chemical analyses of Oman calcium hydroxide spring waters
concentrations in mg/1.
.pH .
Temperature, °C
''d:"-Capdd-p.
.\yhg*dyd
. . ' -'Na+^ -^ •
;''- uS0u^,^v:^
. • ./ Si02•'.^'-
(Calc) OH-i . '
.•.4-t.dlr'}-
1 ,'
Kafifah .
11.2 •
; 28
:p(>^P
^'"••';0-.2 . .;.,„- .
'110 :
. M.Q
,140 ^
'••r 2 , . 9 . : •.:.••;-••
••..•:-i.^-''-'--..-
, J?.}'- c-:.';
.03
• 2
Hahwalah
11.5
,25
60
0.1
. 230 /
280
8 '
d- B.S
• • • . - - ' • . 1 , , . .•
'••:•

I
I
f
i I
%
Photo 29. Kafifah calcniin hydroxide spring along fault zone separating
gabbro in background and peridotite of foreground White travertine
apron consists of aragonlte (CaCOa) which also cements stream mortar
beds in foreground.
V •J

m
i
:-i
:,,,,RECOMMENDATIONS •.
Our conclusions resulting from the field investigation of the
geology and mineral resources of Oman are summarized in a series ,
of recommendations. They are made chiefly to provide guidelines
for the orderly and full development of the mineral potential within
the economy of the Sultanate of Oman. For some resources, such as
copper, recommendations regarding imoiedlate utilization of known
deposits can be made. For the development of other resources
additional short-term investiga.tion is required, either to learn
more about, the grade and extent of known deposits, pr to search
further fpr similar deposits more amenable to use. To achieve the
ultimate utilization of the Oman resources requires longer term
geologic, geophysical, and geochemical investigations aimed primarily
at the discovery of accessible deposits that are not now exposed
at the surface, chiefly because they are blanketed by alluvium or
other surficial material. Their discovery generally requires years
of study by teams of specialists, and, although perhaps only partly
within the capability of present-day Oman, some suggestions
preparing the_way for this type of wprk in the future are included.
1.04^

: • ' »
•:1
'pi
4
Metallic Ore Deposits
The combined result of the Prospection Ltd. and U.S.G.S.
investigations in the mountainous pprtion of Oman during 1972-1974
clearly reveals that this area does have economic deposits of
copper, potentially econpmic iron deposits, and less encouraging
occurrences of chromium, lead-zinc, and manganese. Of these, the
copper deppsits are the mpst promising, and exploration of some
of them is in an advanced stage. We recommend that continued
effort should be made to determine the real ore potential of each
known copper prpspect by diamond drilling and geophysical investigation
where warranted. This Investigation of known deposits is
now in the hands of Prospection Ltd., and we feel that they are
doing a very competent and professional job. However, because of
their requirement to be rigidly cost conscious, they may not
adequately explore some of the more promising deposits in gabbro
or peridptite.or the more remote Rakah deppsit.
All of the most, promising copper deposits are In the "Bowling
Alley" and southern extension in Wadi Jizzi, and detailed geologic
mapping of the area is a necessary adjunct to the work now being
carried out by Prospection Ltd. Such mapping will provide answers
to the genesis of the ore and nature of features, responsible for
its localization, from which one develops control for use in
mining of these deposits and search for new ones.\ Prospection Ltd.
is not doing this kind of detailed mapping, nor do they have geologists
experienced in such studies. We recopnend that modest, scale geologic
mapping of the entire "Bowling Alley" ore zone be started as soon
as ppssible to assist in the most orderly development of this
important mineralised.area.
The laterite deposits discovered in Oman during this study may
have a potential to produce significant quantities of iron, and
perhaps also nickel and chromium, but they are so little known that
the potential cannot be properly assessed. To provide the basis
for a steel industry they must satisfy several major requirements,
which the deposits as now known cannot do though perhaps they have
the potential. To be useful, iron ore must be available in large
amounts, reasonably, accessible, preferably amenable to low-cost
open-cut mining, and of proper metallurgical content and grade.
The richest deposit is nox uessarily the best for exploitation.
For proper evaluation detailed maps depicting topography, geology,
structure, and sample locations with assay values are a basic
necessity.
105

•Jl
SI
We recommend that a detailed study of the area containing the
laterite deposit be made in order to ascertain If any deposits are
mineable, to locate the deposits most suitable for mining, to
determine their tonnage.and grade, and to prepare adequate maps to
permit evaluation and proper development of this resource. This
will require examination of an area of 625 sq km, followed by
large-scale mapping accompanied by the collection and analysis of
numerous channel or larger samples^ If deposits of commercial .
promise are locate, further metallurgical tests and feasibility
studies will be required. ' ^ ' • • '• --
• • ' • • ' ' • -• - • ' • ; ' • • . • ' . r " • ' ! .- , • . ; . . - • • ' .. . - ; • ,- . • • ,.
Prpspectlng for chromite should be continued in the ultramafic
parts of the Semail peridptite. Only small unmineable deposits have
been found, but thie geologic setting is the same as in parts of
Turkey, Iran, and Russia where chromite is being mined* Chromite
deposits are most likely to occur in masses of dunite, but this
mineral is perhaps' best Sought by observing the stream pebbles or
concentrations of black sands in the drainage areas in the peridotite,
which encloses local masses of dunite. The chances for success do
not warrant the cost of a geologist searching specifically only for
chromite, but if mapping is being done for other purposes he should
be watching for its occurrence. The search for chromite could best
be done by prospectors, goatherders, villagers, or wandering
bedouins if they could be shpwn pieces of the distinctive black ore
and told of its value. , \
Known deposits of manganese ore in the Hawasina cherts are
marginal. It is possible that the Jaramah deposit might be mined
by,local villagers on a small scale to provide income in an area
with almost no other resources. The ore, however, is too limited
and too difficult to mine on a large scale to warrant major development.
If a market is available, we recommend mining by bulldozing
across the ore zone to yield broken rock from which pieces of very
high-g;rade ore could be readily sorted by unskilled laborers. Cost
of such an operation could be kept very low as the only requirement
in addition to local labor would be an informed director for the
operation,-'a.bulldozer, a single truck for mining and haulage, and
construction of ore bins for storage, perhaps at Sur.
Elsewhere in the Hawasina we found loose, out-of-place pieces
of high-grade manganese ore, and geologists working in the area
should be alerted to", possilJility pf discovery of other manganese
deposits..'
106

I
-.4
^4
, Nonmetallic Ore Deposits
The main emphasis of pur field study was metallic ore deposits, and
we had neither the time or competence to make a valid appraisal of
the nonmetallic deposits of potential value. In most
countries the value of nonmetallic prpduction greatly exceeds that
of metallic ore deposits, and a study of Oman's nonmetallic resources
is likely to be worthwhile in; planning for its expanded economic
development. Potentially useful nonmetallic mineral resources
include: carbonate rocks as sources for cement, metallurgical limestone,
and building or.ornamental stone; clay deposits for building
and ceramic products; evaporites as sources of potash and lithium;
and possible sedimentary phosphates. As Oman is now constructing
roads at a rapid pace, some effort might also be directed toward
studies of sources and properties of major road building materials.
We recoinnend that the Oman Government have a knowledgeable geologic
group make a survey of the nonmetallic mineral potential of Oman. This
should be initiated as a limited appraisal carried out by a small team
of geologists, as was done during this U.S.G.S. investigation of the
metallic mineral potential.
107

'WW
Water Resources
Our investigation did not touch on the larger problems of
water resources in Oman and we did not collect enough field data
to make specific recommendations except for the hot springs. We
did however sense the need fpr one central governmental agency
tc have authority over the use and development of the water
resources in Oman. The development should start with a ssurvey of
the water potential within Oman by a competent group which has
had experience.bpth in surface and ground water geology. The
government agency that contrpls the use of water should be made
aware of the results of such a study aiid also retain a
professional groundvfater,; geologist on its staff.
. . . . . ^ • : . ' • -. . •'' . .
108

.$
.^
Mapping
The basis for most geologic decisions regarding mineral
resources, civil engineering for roads and dams, and water resources
is a proper geologic map. For the consideration of different
problems, maps of different scales are needed so, that each.problem
is properly focused. A map of the Arabian peninsula (1:2,000,000)
which included,Oman was published by the U.S.G.S. in 1963. More
recently northern Oman has been mapped geologically at a scale of
1:250,000 by P.D.O. as part of their oil-related studies, and this
map will soon be published and available to the Oman Government.
The P.D.O. map is an excellent start as it provides a broad overview
of the geology, and it was used by our investigative team to great
advantage. However, for detailed knowledge of specific areas, such
as the "Bowling Alley" copper district near Wadi Jizzi, the P.D.O.
map scale is much too small and the geology too generalized. We
recommend that the Oman government suppoirt geologic mapping of the
"Bowling Alley Copper District" at a scale of 1:50,000 and mapping
of the Kalahay Niba laterite Iron deposits at a similar scale.
The; 1:100,000 British military maps which are available could
be used as a basis for the above mapping, and for a countrywide
geologic mapping program at a scale useful for most purposes.
Approximately fifty 1:100,000 sheets co'y^er northern Oman, and
twelve cover the coastal area of Dohfar,^ As a basic long-term
geologic project for Oman, we recommend geologic mapping of all
these areas, with priority of mapping given to those areas that
would most benefit the economic development of the country. An
experienced geologist (5-6 years) with proper support can map one
1:100,000-sheet in one field season of 3-4 months, and with proper
office and laboratory facilities could write a report and finish
compiling the map in the remainder of the year. Therefore to
carry out such a project would entail 62 man-years, and with a staff
of 5 field geologists the task could be completed in approximately
12 years. This admittedly is a very ambitious program,, but it
coul^d be started on a modest scale with outside cooperation until
Oman had developed a geological staff capable of doing this work.
In addition, it is likely that some areas are of sufficient
interest that foreign geologists might map them, without pay, as
a scientific study if provided some logistic support. The benefits
of such work would be in development of ore deposits; help in
large civil engineering projects; development of additional water
supply; and woyld provide a geologic basis where needed for planning
the economy of Oman.
109 - 111

Open-Door Science Policy And Arab Cooperation
. ^ k • •• .'^ •;•"•• ' " • . ' • . • ' . ,
, . Lastly, we recommend that the Oman Government actively encourage
;| scientific investigations within" the country. As shown earlier,
Oman has within its borders one of the best exposed areas of on-land
ancient pceanic crust to be found anywhere in the world. At the
present time, there is much interest in these rocks, and many
geoscience groups would like to have the opportunity to fully
\ investigate this ancient oceanic crust. Generally such work would
entail no expense to the Oman Government but would be an important
prestige item to the country. Most visiting geologists wpuld
require help in the form of interpreters and transportation, but
they could pay for this assistance. If an open-door policy prevails,
there is no doubt that results of such scientific expeditions would
benefit the country from several standpoints. Added scientific
information will lead to a better understanding of the geology of
Oman, and perhaps lead to the discovery of additional mineral resources.
Exchange pf ideas between visiting scientists and Omani government
representatives could also provide guidance in developing these
resources. In,additipn, there wpuld be a small inflow of capital.
• Ih :.-
in

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\ Cove copper deposits, Newfoundland: An exasiple of ophiolite sulfide
j mineralization: Econ. Geology, yol. 68, pp. 161-167.
U. S. Geological Survey and Arabian American Oil Co., compilers, 1963. Ma?
of the Arabian Peninsula 1:2,000,000: U. S. Geol. Surv. Misc. Geol. Inv.
i Map 1-270, B-2. '
j U. S. Geological Survey and Arabian American Oil Co., compilers, 1963. Geologic
•

w
APPENDIX
Chemical and Spectrographic Analyses
117
\

Table 6.--Chemical and spectrpgraphic analyses of copper prospects
; in the Sernail Ophiolite.
Map No. - 10 :-: 10 11 13 13 14 15
Sample No;. ; ,0M-13A : 0M-13B OM-287 OM-291A OM-291B OM-63i OM-304
I I'I — • •••• I .1 11 I •••IM.I— I ^ ;il " ._ ^ ^ — — ^ — • I ,1 ||,.,,I|. ^ I, I I I .1111 ..I.I ,11 „.• I •• IIM I I IM—^M^^^I— • !• I • M^l
Chemical Analyses
Cu Z 2.9, ; — ' 0.05 1.1 — 11.0 3.4
Ag., ppm; J-;..-.. •^. •—.,.- •;^—-,,.: -— — —, ' —: ^ ^
Au ppm' --.; • —7. .— — .-,--. — "- —
Ni %' ;,* 10.
'; , 5. •
10.
- :.2.-"
1:5
:- ^2.;,
-•:•;.• 1 - ' "
2000 •
10
50
-,• 3 ' ;
20000
20
50
100
200 .
50
. 100 .,
Spectrographic Analyses
>10.
.3
10.
.03.
.15
- — •
. 50 .
15
7
.03
• 5 ' . • ' :.
200
.. ^ ......
——
30
100
—
—
>10.
.3
1.5
- ' • : . - -
70
15
—
20
700
• . 1
.5
15
50
—
—
1000
15
.03
118
>10. "
5.
3.
: 5.''-
'1.
1.
.1
700
— .
30
700
1000
. 7' -•
200
50
100
100
__
7.
1.5
2.
2.
7.
—
• .01
1500
3
300
700
>20000
1000
15
20
30
700
— ' '
10.
2.
5.
7.
7.
.07
.01
1000
7
200
3000
>20000
1500
. _—
300
—
1000
7
>10.
.5
7.
>10.
1.5
—
.005
500
—
300 •
3000
>20000
1500
_—
_
20

Table 6.--(cont'd)
Map No.
Sample No.
••" • ,
Cu %
.\g ppm
Au ppm
Ni.
Si z
Al .
Fe .
Mg^
Ca
Na
K •
Ti
Mn ppm
Ba •'.•..
Co
Cr .
Cu
Ga
Ni'
Pb
Sc
Sr .
V
Y
Zn .
Zr
A g :•'.. •.: •
Mo;
.. ,16:
V 0^t-632
; • : " ' . . -
( ^ ,• 'If:
•, -rr .
'. - . • - - • . . :
. 7 .
• „ : • • - - - . 3 .
>10.
1.5
' ... • • 3 . ,
- .3
1.5;
.05
- " ' : • ••
500
20
1500
150
>20000,
300
— -
15
1500
' 'rrr
• d " 30 •
3000
• •" ^ T : -
' -.—
20
: 16; 18
OM-634 OM-60
Chemical .\naly ses
3.0 12.2
• . - - -

Table 6. —(cont'd)
Map No. .. 25 , 2 7 27 28 28 29
Sample No. . OM-630 0M-18U 0M-181C OM-133A OM-133B OM-256
-'..-.-•^ ;;•.•'.''-. -Chemical-Analyses^- • - _ " ^
Cu % ; ; " - - , 4.0 : 5.9 1.2 1.7 2.0
Ag ppm-.:;•:,-•'.-• — - • • , — • - . . • — • . . . — — —
Au ppm' •-.;.:---.; ,',,' ~ •'• • — — — —
Ni :•,.,,_-;;; 0.17-0.04 0.09-0.04 ' .—
Si %
Al
Fe •
Mg
Ca
Na - -^
K
T l -• •
Mn ppm
Ba *
Co
Cr
Cu
Ga
Ni
Pb
Sc
Sr
V
Y
Zn
Zr
Ag
>10.
- • 3.-'
; 10. ,
10.
•> 2.-- -
..' - 2 • •
-. ..•i;/.03--'-
• • 1500
30
:• 150
; 500
'150
- • ; ' . - . - •
' 700
, 150
15
100
V " 30
Spectrographic;Analyses
>10.
.3
7.
10.
-•- -.5 -
. - • -
.007
700
5
300
2000
>20000
.—^
1500
• • _ - •
15
15
3.
3.
7.
2.
>10.
-'-
.02
1500
—
150
1000
>20000
5
300
—
30
70
30
>10.
7.
10.
10.'
.07
'. —
Ul-:
— •
500.
200
1000
10000
20
500
50
. • —
100
1.5
1.5 •.
>10.
.15
.5
.15
.05
100
3
300
1000
15000
—
300
—
50
30
300
>10.
7.
>10.
5.
.7
.3
.05
1500
5
150
200
15000
15
150
-.-
15
20
70
Chemical analyses by Sarah T. Neil and
Spectrographic analyses by R. E. Mays, U. S. Geological Survey, Henlo I-ark
120

Table 6.--;(Cont.'d)V ,! 1,-.
Explanation
0M-13A Copper mineralization in silicified tuff at contact with
Semail pillow lava, Wadi Jabah.
0M-13B Mineralized chert resting on top pf Semail pillow lavas, Wadi
'.'•••. Jabah.' •"''""'
pM-287 Silicified sulfide-bearlng rock in gassan," Rakah.
0M-291.V Chalcopyrite in altered gabbro, JIaydan II.
0M-291B Malachite-rich gossan material, Maydan II.
OM-631 Selected pieces of mineralized rock, Bu Kathir.
pMr-304 Selected pieces from dump, Hawirdit.
OM-632 Chalcocite ore from dump, Tawi Ubaylah.
OM-634 Gossan from dump, Tawi Ubaylah.
I OM-60 Copper mineralization in shear zone, Wadi Muden
: OM-621 Chip samples of mineralized rock, Tabakhat (Pb«05%, 2n".04Z)
\ OM-622 Dump sample, Tabakhat (Pb-.072, 'in-.027,).
; OM-629 Altered zone 7.5 cm (3 in), iron stained, Eedah II
\ .OM-630 Altered and bleached, rock. Eedah II.
: 0M-181A High grade dump material, Khara mine.
;i 0M-181C Ore from mineralized zone, Khara mine.
i- OM-133A Mineralized gabbro with malachite, Zahir mine.
;i
OM-133B Gossan, Zahir mine. \
OM-256,. Mineralized gabbro from dump, Shwayi mine.
'H'I...'V"
121

w
Table 7.-r.Spectrographic analyses of ancient slag from Oman
copper deposits.*
Map No..
Sample No.
SI % • •:.';
Al
F e - - • ••^.- ^••••-
Mg
Ca
Na •'
T l •• •'..-'^ ••'":.
Mn ppm
Ag. •;•;, P
.Ba
Co''' ' ':'•
Cr
C a . .- •..••• d ' ' : ^
G a •• . . •'••
Ni
Sc' .
S r ••.•'
V • v^ /• ,. '
Zn
Zr
',. 21 .
PMT165
^••

3 ..
,•'.-:•;& "'
^y.:
Table 8. -r-Chemical and spectrographic analyses pf Kalahay
Nib^ I and. H iron deposits..
Map No. : -
Sample No.
;ai4;A-
Fe % • ' •''
Cr
Ni
Si z
Al
Mg
Ca
Ti
Na
.h, •.^.,;d' ';'Pd\p
y''(MP-':
':-^':d
.30.80
12.53
—
l
• 10
3
1.5
•15
—
" • > ' • " . • • • '
'^••;.30:,-:-;
dOM. /
114 B
51.43
1.53
—
5..
3.
• .3
2.
.15
.1
Sr\"' ••"•;'
^30 ; ' 30 - 30
OM- ; OM OM
;114.C 114 P 114 E
Chemical Analyses
44.62 39.1 30.1
2.61 .2.6 2.8
~ ;0.33 0.36
Spectrographic Analyses
5.
7.
.5
1.5
.3
.15
:^5...
•• 5 . •'
: .5 -•
'•:2.
•c .l"..
"••-^2.-"' -•
• 5.,.-- •
.5.'
'•..7
2.
:'._.15.
Mn ppm ' 700' 3000 700 500 200 .
Ba' '". ..P'' -;• 5'-. { 100 20 ; : 7 . 10
Co • •;^; 300 : 150 200 150;: 150
Cu ;
Ni
:' 150
'/ -2000
•;i5o;-
3000
100 . - 300
5000 2000
300
2000
Pb ;
.15 30 "- —. 20 —
S c ' •• - . • ' ^•- ' • -50 -• 70 : 100 ' 70 70
Sv.^-p-d" -y-A 20--:. ;? 100: 70
V ^ :y--'-- 500 y 20O '500
. 500
150
500
150
zd:P'- •.•'•••• 'y.
.zr•.^'•:••
7po. d : r— , 30.0
'•' - - • ' ;
. 30^ :- 70:.
—
100
30
, OM
':ll^ F
.38.4;
.87
1.1
10..
3.
• .7
. 3
. .1
.15
1000
7
500
100
7000
—
70
50
150,
• — '
' . •
30
OM
"117 A
45.52
1.18
.- .—
1.5
2..
.15
5.
.03
.05,
15000
3
700
300
3000
!>
100
1000
300
, 200
30
OM
117 B
43.95
2.94
• — —
1
15
.2
1. :
.2
.03
2000
30
500
100
3000
— • • -
100
150
300
200
• • ~ ~ . ••
Chemical a.nalyses by Sarah T. Neil and semiquantitative spectrographic
analyses,by Chris Heropoulus and ;?..£. Mays, U.S.G.S., Henlo Park
- Kalahay Niba .^i'";......:';••
0M-114-A ; High grade Irpn ore
pM-114-3;; Medium grade iron ore
0M-114-C."' Low grade iron ore
0M-114-D', Channel sample (9 feet) of iron ore
0M-114-E 'Average sample froa csius 1.- iron ore
0M-^4-?- .Channel smaple (2 feet) of iron ore 100 feet east of D & E.
ifialahay'Nifaa"il-; ;:^•'••'-
0M-117-A 7; ;High grade iron ore
0M-il7-3-^;;-.Medium grade Iron ore
-•;T; ';;;-..,-..>,::• . y':.:dd'y'''\' y d •- i >-. o

vj)
4=-
Hap No.
Sample No.
NI Z
Fe Z
Si X
Sl z
Al
Fe
MB
Ca
No
11
Mn p|Hii
B
Bu '•• -*:
Be
Co ,
Cr
Cu
Ca
HI
Pb
Sc
.Sc
V
W
Table 9. Chemical and Speclrogru|>liic aiiulystia uf Iron laterite saoples fruia Seiaall ophiolite
33
OM 27U
0.24
4.9
16.8
33
OH 271
0.24
5.2
17.8
33
«)M 272
- - • . - • - • • ' - .
0.27
5.0
15.1
33 33
OH 274 A l)M 274
-Ohoulcal Analyses
0.16 0.09
13.9 11.7
.51 37.1
Spcctrnuraplilc Analyses
. . , • ' '
>10
.15
•10
.15
10
.07 .3
>10
.3
3.
10
5.
>10
.,"•5.
>10
>I0
5.
>10
.07
1.5
-
.001
.1
.15
.001
-:"-2.' : •
- , 1 •- •
:ooi)7
>10
, .003
.1
.003
700 700 500 2000
200
- • - 50
' - ' •
, • • -
7 -• .
70 150
70
-
70
-
70
- ...
70
•-•' 2
70
7
10
2000
100
- •
.2000
50
-.
2000
30
-
2000
50
10
1000
50
10
1500
- '
1500
.
1500 1500
• ' _
700
7
100 -
10
10
30
20
150
30 . 30
20 50
200
B
33
OM 274 C
0.23
55.0
6.3
.5
>10 )
.1
.5
.005
200
,500
7
50
1000
70
3000
' 10
30
' 30
500
33
OH 275
-.04
1.9
37.7
>I0
5.
1.5
.2
.3
.05
100
100
5
1000
30
7
200
70
15
15
50
33
CM 276 .
0.11
31.6
22.5
>10
32
OM 247
10
-
-
>10 1
2.
.15 7.
.5 >10
- > 5
;007 ; ;001
200 .: 500
70 15
150 ; ,30
2 , - -
50 . 30
2000 1500
50
10
50
1000 700
20 ---
20
. - . •
700 700
50 , 15
500 • - . -
ChkiBlcal analyses by Sarah T. Nell and eeraiquantltatlve spectrographic analyses by R. E. Mays and Chris iieropuulos,
U.S. GuoloKtcnl Survey, Menlo Park
Fanjah
OM 270 Base of laterite section, slightly weuthered peridotite
OH 271 70 feet above baBc, mSHslve brown weathered peridotite Iron oxide nn surface
OM 272 120 feet above base, completely weathered perldotlta original textures preserved
OM 274 A 165 feet above base, completely weathered Iron-rich peridotite
OM 274 U 165 feet above biise, red Jaspar with hematite veins cutting peridotite
UM 274 C 165 feet above base, lenu of iron ore in red Jaspar
(JH 275 Sliear zone wltliln laterite containing green material
OM 276 Tup of laterite uoft Iron ore from ancient mining pit
Wasit
OM 24/ Weuthered surface of peridotite near Wasit

Table 10. Chemical and spectrographic analyses of chromites
from Semail Ophiolite
Map No..-:. -:-_;.. '„.•.,.35 ;.'•, ,^ , 36- 37
Sample No. - OM 110 . OM 138 OM 356
Zn,
Zr
Chemical Analyses
Cr ,% 24.98 22.80 26.0
Fe 12.16 ;• 9.70 11.0
Al 11.3 12.0
Spectrographic Analyses
'Sl'.Z • P'.^^'' / •'. • 2. '-'. 5. 3.
Al ;15. > 15. >10.
Fe 15 ; ; \ 10. >10.
M g - -•' •'•;• -J-:'--' •''!..' :•• '• . \ 10. • • 10.
Ca. - ,1.5 • .15 .3
Ti-' •'•.'•" •:;''••; ;; .2 ' - . - -• ' .1 •:' .05
Mn ppm ",' 700 700 1500
Ba- • -, •'.-..:.-' '\ • 5 , .:'' .7 7
Co ' ' 150 . 150 150
Cu 50 15 20
Ni ,' 2000 200 1000
Sc •••-•.':" • • 10. 7' • • 7
Sr .. , d • •; 10 - 20
V ' 1000 700 1500
•\y
Chemical analyses by Sarah T. Neil and spectrographic analyses by Chris
Heropoulos and R. E. Mays, U.S. Geological Survey, Menlo Park.
OM 110 Chromite ore from MasaKlrah deposit
OM 138, .Chrpmlte ore from Mudi deposit
OM- 356 iChromite ore from Aka Keya deposit
125

Table 11. Chemical and spectrographic analyses of Nujum lead-zinc deposit
Map No.
Sample Np.
Pb Z
Zn %
Cu Z
Ag ppm
Au ppm
Si z ,
Al
Fe ......i--.
M g • •• . .
Ca
Tl
Mn ppm
Ag
As
B
Ba
Cd
Co
Cr
Cu
Ni
Pb
Sb
Sc
Sr
Zn
41-
OM 615
15.0
-7.5
3.8
. 120
io- •
• • ' - " ' • • a •
•' s'y '
•••.•-;-^-"1.5'-.,'
. '.,3;
.002
- 2000
200
30000
•' • ' ' " ' ' ' ' • 7 '
300
1000
1000
P - •'•• 700
>;2oooo
•' •: 5000
>50000
- 1500
•' ..5 ---^
' v'' 200
>50000
• . ; . • ' " • ' , • • • • ' ' ' • ;
41
OM 617
Cheimical Analyses
4.8
4:7
1.8
40
0.05
Spectrographic Analyses
>10
.• ••• . 5
5.
1.5
3.
.007
2000
70
>5000
10 :
200
500
1500
700
15000
10000
50000
700
-
100
50000
41
OM 618
>10
.2
V 2. •
'\ .2
•^ . - 1 - :
.001
200
100
>5000
10
100
150
500
700
10000
2000
>50000
700
7 '
10
1000 .
41
OM 619
>10
.3
5.
3.
5.
.002
1500
100
7000
7
50
200
500
700
1500
1500 .
>50000
-
—,
200
15000
41
OM 620
. >10
.3
3.
.5
.7
.003
2000
15
2000
10
50
500
500
1000
300
3000
2000
—
10
20
>50000
Spectrographic analysis by R. E. May. Chemical analyses by Sarah T. Neal and
Claude Huffman, Jr., U.S. Geological Survey, Menlo Park and Denver.
OM 615 Chi? sample of average ore
OM 617 Dump material
OM 618 Picked sample with visible galena
OM 619 Picked sample with visible galena
PM 620 Picked sam^ple with secondary lead minerals
126

Map No.
Table 12. Chemical and spectrographic analyses of miscellaneous samples
Sample Np. OM 321
Si Z
.A,l
Fe
Mg
Ca
Na •
Ti
Mn ppm
B
Ba
Co
Cr
Cu
Ni
Pb
Sc
Sr
V
Y
Zr
10
.7
>10 1 . •
1, •,
.3 '••:;:
- - -
.015 •
300
- ••' • • ' ' . .
20 A
50 ,
30
1000;
50..
-
30
200
V 15
- -
from northern Oman
.'-•.8 .:.-,
OM 324 A OM 2
>10.
3.
>10.
.7
'• .7.
. ^ - •• .'5 •
.07
>'.-• 50000
50
70
30
20
500
300
:..: 200
-»
Spectrographic Anayses
200
150
50
50
2.
1.5
>10.
2.
7.
.05 •
200
—
100
20\
10
150
-
30
150
32
OM 185 OM 1 OM 4
>10.
' 1.
>10.
.2
.5
.7
150
70
10
3000
200
50
-
15
50
200
70 100
>10.
.3
3.
.7
3.
Spectrographic analyses by R. E. Mays, U.S. Geological Survey, Menlo Park
.0015
2000
30
20
; OM 321 Iron-rich sediment Interlayered with pillow lavas, Lasail deposit
OM 324 A Iron-rich sediment interlayered with pillow lavas, Ghatyh deposit
OM 2 Iron-rich dolomite from the Hljam dolomite, Sayah Hatat
OM 185 Iron-rich Tertiary sandstpne^. Jabal Salaht
OM 1 Quartz vein with spme mineralization, Sayah Hatat metamorphic rock
OM 4 Sideritercalclte in quartz vein, Sayah Hatat metamorphic rock
127
-
7
30
7
70
20
.7
.1
1.5
.3
10.
.003
7000
-
10
-»
7
15
150
50
1000
200

5 1^-'-.
\ IA?
'•I

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J .. '^"•"'
SUHAIL & SAUD BAHWAN
P.O.BOX 169. MUSCAT, SULTANATE OF OMAN --
Ref.PRO/r.84/2182/RJN
September 12, 1983.
USS Engineers & Consultants, Inc
600 Grant Street ^
Pittsburgh, Pa 15230
U.S.A.
-»t A-
Attention; Mr. Monro B. Lanler/Mr. Scanlon
Dear Sirs,
Re: Tender No.102/83 for Copper Exploration in Northern
Part of Oraan. ^
-r—r——I ::
BY DHL COURIER SERVICE
In response to your telex dated September 8, 1983, we have purchased
a tender bid documents in your name which is attached hereto.
Please acknowledge on receipt.
Thanking you, we are.
Yours very truly,
for dbHAIL AMD SAUD BAHWAN
Alex j ^ / ^ '
Commetb'ial Managei/ (Projects)
end: asstated
anf.
Cable BAHWAN Telex 3274 MB Telephone: 734201, 734202, 734203 vrt,.r.vrtT...vr(».\ lOyXii > rrst 0.^^ -..r^ ' '^^J*'. -.^Ji
C R, No; 8740
A V < . Cu'

Min./Dept.
RECEIPT
^roo£Y^-
Received From \ . rJ> ir^'^
The Sum of
In Words
R.O. t'^
CL.^,
Bz8. *-r
—
d\'d\sy^.
On Account of u.\ ••>-'^'-
Account No. .\ yp
«r ''^'^^^^rrr;:
V
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' d
MINISTRY OF PETROLEUM AND MINERALS
DEPARTMENT OF MINERALS
SULTANATE OF OMAN
SPECIFICATIONS FOR A COPPER EXPLORATION
PROGRAMME IN THE NORTHERN PART OF THE
OMAN MOUNTAINS
26 SEPTEMBER 1982

1.
2.
10.
11.
12.
13.
1*.
INTRODUCTION
GENERAL
CONTENTS
OBJECTIVES OF THE PROGRAMME
PREVIOUS WORK
REVIEW OF COPPER EXPLORATION/EXPLOITATION
PR03ECT AREA AND ITS GEOLOGICAL SETTING
EXPLORATION APPROACH
GENERAL
PHOTOCEOLOGY/LANDSAT IMAGERY
GEOLOGY - GENERAL
GEOLOGY / PRESENTATION OF RESULTS
GEOCHEMISTRY
GEOPHYSICS
DRILLING
STAFFING
APPENDIX NO. I
SUPPORT FACILITIES
TRAINING AND EMPLOYMENT OF OMANIS
REPORTING
PROGRAMME MANAGEMENT
SPONSORSHIP
CONTRACT
ILLUSTRATION NO. 1
Page Nos.
1
1
1
2
3
4
5
6
7
7
8
9
IC
11
11
12
12
12
13
13
13

V
SPECIFICATIONS FOR MINERAL EXPLORATION PROGRAMME WITHIN
1. INTRODUCTION
THE MINING LEASE AREAS OF OMCO
The Government of the Sultanate of Oman wishes to implement
a mineral exploration programme for Copper as part of its 5 year Develop­
ment Plan 0981-1985).
You are invited to tender for this work as per the specifications
and information given below.
Tenders should be submitted to H.E. The Chairman, The
Tender Board, P.O. Box 787, Muscat By and
should incude details of cost, personnel requirements, programme schedule
and training of local staff.
2. GENERAL
The area(- 1000 km') to be explored occupies an approximate
north-south band along the eastern foothills of the Northern Oman Mountains.
Within the area two underground copper mines are being developed while a
third is planned. Metallurgical and process plant is under construction and
the aim is to produce electro-refined copper at a rate of approximately
20,000 tonnes per year..
The attached map (Illustration No.l) shows the location and
boundaries of the area to be explored.
3. OBJECTIVE OF THE EXPLORATION PROGRAMME
The main objective of this exploration programme is to:
1. Investigate eight specific prospects having immediate ore potential to
bring them to the development or rejection stage
and simultaneously
2. Explore and prospect in detail within the local- 1000 km' area to generate
additional prospects with ore potential.
period and start in 1983.
The exploration programme will extend over a three year
Fbllow up work, may continue beyond 1986 dependent upon
the results obtained during the initial programme.

0. PREVIOUS WORK
The Oman Mountains were mapped by a team of Shell
Exploration Geologists (K.W. Glennie et al) between 1966 and 1968.
Earlier work by Lees of D'Arcy Exploration Co. Ltd. in 1924 and 1925,
and geologists of the Iraq Petroleum Co. between I9(>9 and 1960 provided
a basis for the Shell Exploration Project.
During 1973 and 1974 a brief investigation of the known
mineral deposits of Northern Oman was done by the U.S.G.S.
From 1973 to 1978 Prospection Limited carried put mineral
exploration within the Oman Mountains. Initially Prospection Limited
held an exploration licence covering the whole of the Oman Mountains.
Subsequently this was reduced to four exploration licences in May 1975.
These four licence areas were reduced early in 1978 to 10 Mining Licences
and 15 Prospecting licence areas, each of 225 km'. The 10 Mining
Licences essentially covered the most prospective areas for copper,
where ancient workings are concentrated and outcrop more substantial
than elsewhere.
Recent (1978-1981), detailed mapping at a scale of
1 : 100,000 by Open University staff has greatly advanced the knowledge
of the geology of the Sumail Ophiolite. This work covered the area from
latitude 23''30' ,N' northwards to the boundary with the United Arab
Emirates.
In 1978 - 79 a U.S.G.S. team mapped in detail (1:100,000)
a 40 X 130 kilometre N -S belt from Muscat, Southwards. The belt
included Pre Permian basement upwards through autochthonous and
allochthonous Permian to Cretaceous/Jurassic sediments and Sumail
Ophiolite.
With the formation of OMCO in late 1978 efforts have
been directed towards the development of the Lasail, Aarjah and Bayda
orebodies. Since 1979 regional mapping, local ground geophysics and

exploratory diamond drilling have been done by OMCO within their con-,
cession area. A better understanding of local host rock environment and
control of mineralisation in the Lasail area has been gained as mining has
advanced.
5. REVIEW OF COPPER EXPLORATION/EXPLOITATION
Prospection Limited concentrated their exploration effort
in the search for cupriferous massive sulphide mineralisation. The opera­
tion of this exploraion campaign was well organised, logically staged,
completely and well conducted and well documented. As a result it is
unlikely that any major sulphide deposit with a surface expression gossan
remains to be evaluated. Regional geochemical wadi sediment sampling
results obtained during this exploration campaign were doubtfully effec­
tive, possibly due to the use of the -80 fraction. Modern arid environ-
ntents techniques as developed in Saudi Arabia, Australia and the United
Arab Emirates suggest that the coarse -30 fraction is a more responsive
indicator as mechanical dispersion is more active than chemical desper-
sion in such environments.
Following an EM (INPUT) Survey in late 1974. follow up
work beyond the ancient mine workings intensified after 1975 and was
almost exclusively based on the results of the airborne Em Survey. Air­
borne EM anomalies were investigated by surface mapping ground geo­
physics (EM) to screen them prior to a decision whether to drill or not.
Possible difficulties which may have limited the effectiveness of the EM
(INPUT) Siffvey are:
1. Conductive overburden which masks responses and limits effective
depth pertetration.
2. Conductive country rock, alteration zones and numerous faults are
as responsive as mineralisation and identify a large number of anoma­
lies not related to mineralisation.
Mining started at Lasail in 1980 and at present primary
development has reached the 100 metre level. The first production
level (62.5m) has been fully developed and test stope mining is in progress.

Bayda mine was started in 1980 and primary development
has reached the 70 metre level.
Mining has not yet started at Aarjah.
6. PROJECT AREA AND ITS GEOLOGICAL SETTING
J
The area to be investigated occupies a belt along the eastern
foothills of the Northern Oman Mountains centred on Sohar approximately
y"
\'l- \^ ^ 240 kilometres northwest of Muscat. Within this area three copper ore-
\d d^
'1, bodies Lasail, Aarjah and Bayda have been evaluated and mining develop­
ment of Lasail and Bayda is in progress.
Outcrop within the project area is mainly Sumail Ophiolite
of mafic and ultramafic composition and is part of the Sumail thrust
sheet.
The Sumail Ophiolite is a stratified igneous sequence of
tectonised peridotite at the base, followed upwards by peridotite, layered
gabbro, sheeted dike swarm, pillow lava and pelagic sediments.
These rocks represent a slab of ocean crust and mantle
formed at or close to a mid ocean ridge spreading centre, which lay to
the northeast of the present coastline of Oman and which was emplaced
as a thrust sheet to the southwest during late Cretaceous, to overlie
Permian to Upper Cretaceous sedimentary and volcanic rocks on the
northeast Arabian Continental margin.
In the project area the ophiolite dips to the east at a low
angle and is cut by a number of faults.
The pillow lavas of the, Ophiolite host the known copper
deposits which are Cyprus type massive sulphides.
The volcanic stratigraphy of the Ophiolite consists of
three units, the Geotimes, Lasail and Alley units in order of eruption,
each occuring within different tectonic environments.
The Geotimes unit of basalt pillow lavas which is of
regional extent erupted at a spreading ridge crest. The Lasail Unit

consists of an areally restricted basalt - andesite - rhyolite fractionation
series formed off axis as discrete volcanic seamounts. The Alley unit
comprises a basalt - andesite- rhyolite fractionation series of regional
extent formed in a submarine graben. These uniu are intruded by feeder
dykes of andesite and felsite. The pillow lava units can generally be dis­
tinguished in the field but are more precisely defined by geochemical
methods.
The Lasail and Aarjah deposiu occur on top of the geo­
times, basalt pillow lavas which forms the footwall and are overlain by
Lasail basalt pillow lavas which forms the hanging wall.
Major significant deposits tend to occur in clusters with
a degree of structural control and are associated with volcanic centres
which have been interpreted as originally being a series of seamounts.
Mineralisation is related to hydrothermal activity post extrusion of the
Geotimes pillow lavas, but pre extrusion of the capping pillow lavas.
Associated with these volcanic centres granodiorite and plagiogranite
intrusive complexes are considered to be late stage fractionation products
of the seamount volcanic centres.
Mineralisation also appears to be related to major cross
cutting structures which traverse the Sumail Ophiolite complex. It
has been suggested that these cross cutting structures represent old lines
of weakness in the Mesozoic ocean floor i.e. transcurrent fracture zones
along which volcanic activity was concentrated. Local favourable envi­
ronments for mineralisation so far identified are:
a. The associated of mineralisation with local basin
shaped depressions and fault structures in the cort-
temporary sea floor.
b. Stratigraphic and possible genetic relationships between
mineralisation and umbers.
7. EXPLORATION APPROACH

I •
7.1 GENERAL
In general terms copper prospecting in Oman has been ex­
tensive and includes the use of geology. Geophysics, Geochemistry,
diamond drilling, photogeology and- remote sensing. The point has now \
been reached where there is justification for the use of improved, more
sophisticated, and more detailed methods in the continuining search for
undiscovered economic deposits. /
Appendix No. 1 contair\s an outline programme indicating
the exploration approach and work requirements for this proposed project.
general guide.
The time span of three years given for this work is as a
Tenderers should submit quotations giving:
1. A lump sum price for the programme.
2. The break down of the lump sum into elements
e.g. Cost per line kilometre for geophysical
work and the basis for quoting (cost plus or Unit
Rate).
9. All quotations in U.S. Dollars (US$'s).
Xk Impact of Currency Exchange rate fluctuations
5. Payment Terms.
6. Liabilities • Insurance and Guarantees
- Impoct: of equipment etc.
7. Detailed work schedules for the programme
as outlined.

,-,.6
0
M^ No.' i shows the boundaries of the area and the location of the
prospects to be investigated.
7.2 PHOTOGEOLOGY/ LANDSAT IMAGERY
Although much of Northern Oman is covered by 1 t 20,000
scale recent aerial photography some of it in colour, the present explo­
ration area is not. The use of colour aerial photograph has not been
utilised in prospecting for copper in Oman and it now felt that this has
been a seious ommission.
Therefore additional colour aerial photography will be
required over the exploration area with the principal objectives being
structural and alteration interpretation over the total area at a scale
of 1 : 20,000 and over some of the eight known prospects at a larger
scale where recent 1 : 5000 aerial photography is available.
This photo-interpretation should be conducted in conjuc-
tion with the application of Landsat Imagery. The scale and computer
treatment of the Landsat Imagery will be agreed between contractor
and client beforehand.
7.3 GEOLOGY - GENERAL
A study of similarities in the geological setting, mineralogy
and structural control between the Cyprus Type massive s)^'ulphides and
those of northern Oman, familiarisation with the Cyprus type massive
sulphides and a knowledge of the exploration methods used in Cyprus
could prove useful as a preliminary step in any copper exploration
programme in Northern Oman.
The delineation of volcanic centres, and the relationship
between volcanic units using plate tectonics and modern volcano­
genic concepts should be applied and may prove of value in this
programme.
V

Within the exploration area, outcrop is extensive.
Detailed geological mapping, paying close attention to the host rock
environment the location, grouping, spacing and overall geometry of
volcanic centres and individual deposits should constitute the primary
exploration approach.
The relationships or differences between gossans,
ironstones, ochres and umbers and their possible use as ore indicators
should be studied and applied.
Up to date techniques of gossan evaluation to deter­
mine their economic significance should be used. The use of multivariate
discriminant analysis of chemical data supported by field and Laboratory
observations such as microtexture analysis should be considered and
applied.
7.4 GEOLOGY - PRESENTATION OF RESULTS
A detailed geological base map at a scale of 1 : 50>000
(or 1 : 25,000) of the total area will be required. Geological maps at a
scale of I : 100,000 prepared by the Open University are available and
should be used and updated as required.
Superimposable maps at the same scale as the detailed
geological base map should be prepared for:
1. The location of all showings gossans, umbers etc !
2. The location of all work carried out, eg. trench­
ing, drilling, mining.
3. The location of geochemical sampling and geo­
physics surveys.
4. The location of geochemical and geophysical y
anomalies.
•or-d

5. The location of areas where more detailed work such as
mapping has been done.
Where mineralisation is known or is discovered during the
project, this will be mapped at large scale (around 1 : 10,000). These
scales will be chosen by the contractor case by case and agreed by the
Department of Minerals.
7.5 GEOCHEMISTRY
Wadi-sediment geochemistry used by Prospection Limited
proved disappointing, possibly due to the fact that the granulometric
fraction used was not the best. It is expected that orientation surveys
would be carried out, around and over known deposits and elsewhere to
determine the best approach and method for wadi-sediment sampling.
The orientation geochemistry survey should be started at
the beginning of the field work and detailed scheduling of this^survey
is required.
The number of samples will depend on the drainage pattern
but should be of as high a density as practical. These samples should be
analysed for between 20 and 30 elements in order to determine heavy . ^
metals, path finder and trace elements.
In order to screen significant anomalies from anomalous
amounts of metal related to lithology, processing by computer of the
geochemical results is required.
The results of the geochemical orientation survey, (types
of samples, spacing of samples, elements to be analysed in future ope­
rations ,analytical methocb, data processing) should be presented as a
separate report and discussed with Department of Minerals technical
staff before further geochemical work is started.
The usefullness of rock geochemistry should be investi- /
gated and if proved successful applied where applicable. / V^'
9
U--

7.6 GEOPHYSICS
A systematic and detailed reassessment of all the existing,
airborne E.M. (INPUT) and magnetic data, particularly that over alluvial
areas should be carried out.
The reassessment should be followed by a fast geophysics
survey over known orebodies using:
1. Ground E.M.
2. I.P.
3. Magnetometer
4. Geophysical Hole Logging of existing drill holes where
possible.
A separate report on this work should be submitted and
discussed with Department of Minerals Technical Staff.
orientation survey.
The following remarks should be considered during this
If ground E.M. follow up work is used on gossans or
input anomalies this should be selected with care in order to overcome
the difficulties experienced in the earlier use of this method.
Modern EM systems of the SIROTEM or Pulse EM type
should be used after proving its effectiveness over known ore deposits.
Consideration should also be given to the use of Induced
Polarisation (IP) Techniques and effectiveness of this method as used in
Cyprus checked. (G. Maliotis and A. Khan. Proc. Int. Ophiolite Symp.
Cyprus 1979J.
Magnetic surveys should be used where applicable to
check or confirm geochemical of geophysical anomalies which have no
apparent explanation.
Geophysical hole logging may be of value during a drilling
programme and this should be considered when preparing tenders.
10

7.7 DRILLING ,
Exploratory percussion and diamond drilling required to define
targets will be agreed between Dept. of Minerals geological staff and the
• • 1 1
Contractor. The Contractor will be required to use percussion and wireline t
drilling equipment available in the Dept. of Minerals and train Omani staff
in the use of thisdrilling equipment. The numbering of diamond drill holes
and the method of locating and recording drill collar elevations and co-ordi­
nates will be defined and agreed between the contractor and Dept. of Minerals
geological staff.
All diamond drill cores and percussion drilling cuttings will be
logged by a geologist, and geological logs and sections prepared and inter­
preted.
All mineralised core will be systematically analysed. The
following will be agreed between contractor and the Dept. of Minerals:
1. The analytical methods which will be used.
2. The length of core which will constitute one, sample to be analysed.
3. The analysis will be ntade on half longitudinal sections of the cores.
The remaining half core will be cut into two quarter longtitudinal sections
and stored. .
Core recovery in this drilling would be of a sufficiently high percentage to
be acceptable to geological staff of the Department of Minerals.
Core boxes and all other ancillary requirements would be supplied by the
Contractor.
8. STAFFING
The Tenderer should furnish detailed data on the staff to be
assigned to this programme. Viz.
1. Number aruj Discipline of Experts,
2. Education and technical training of each expert.
3. Relevant Technical experience and background in mineral exploration.
Details of local staff requirements and a programme showing
the application of all staff throughout the exploration programme should be
included.

\'\ {
9. SUPPORT FACILITIES
The contractor will require to obtain or set up and operate his
own support facilities such as: '
1. AccomiTDdationfor Personnel, base and field.
2. Office Accommodation.
3. Draughting office with reprographic facilities
4. Sample preparation, store and laboratory facilities
5. Stores
6. Motorpool and vehicle workshops
7. Equipment pool and Workshops.
As the exploration area is centred on Sohar these facilities would be best
established in the Sohar/Saham area, although a small office in Muscat '
might be required.
Consideration should also be given to the need for Airborne
Services and Computer Application facilities. The latter may be available
at the Ministry Building in Muscat.
10. TRAINING AND EMPLOYMENT OF OMANIS
The contractor will be required to train a minimum of four
Omani geoscience graduates who may be secondees from Ministry or
Commercial groups. Employment and training of Oman tiechnicians will
also be required of the contractor. Details of the training programme or •
modules should be included in the tender.
11. REPORTING
This would be a matter for discussion but at the minimum
monthly, quarterly, annual and final reports will be required.
The monthly report would give statistics such as number of
samples collected, number of assays completed and number of metres
drilled.
The quarterly report should include a summary of activities
showing the location and extent of the survey areas investigated, the ex­
ploration techniques employed and the results of the investigations.
The annual report will present a compreheruive account of
the years work and an outline of the followingyears proposed programmes.
12
/
\/

A final report would give comprehensive details of work done
and results achieved with proposals for future work.
12. PROGRAMME MANAGEMENT
Throughout the programme, exploration will be carried out to
the satisfaction of a programme co-ordinator from the Department of
minerals. The contractor will be required to maintain close contact with
the programme coordinator and with the Chief Geologist of Oman Mining
Company L.L.C.
13. SPONSORSHIP
The Non-Omani Tenderer must be represented in the Sultanate
Oman by a local agent authorized as such in accordance with the Law of
Commercial Agencies. The tenderer shall state the name and address of
his Omani agent and confirm that his agent has been duly authorised by
and duly registered at the Ministry of Commerce and Industry of the
Sultanate of Oman. >
14. CONTRACT
The successful tenderer . will be required to sign a contract
with the Ministry of Petroleum and Minerals. Details of the contract will
be negotiated between the Ministry of Petrojeum & Minerals and the
successful tenderer.
13

APPENDIX NO.l
OUTLINE PROGRAMME,
FOR
COPPER EXPLORATION WITHIN 30 KM RADIUS AREA
OF
PLANTSITE
INTRODUCTION
The 25 km (now extended to 30 km) radius area from the central plant
site was established in 1976 as being the distance over which run-of-mine
ore could be hauled economically to the plant site.
Regional photogeological mapping, showing the areal distribution and
extent of extrusive, volcanic units, was completed in 1982. Regional
detailed mapping carried out along regularly spaced east-west traverses
with aerial photographs as base maps, is now required to locate \^
gossans, umbers and other geological features. The 30 km radius area
is sub-divided into four areas for this regional detailed mapping.
Eight individual prospects are thought to have immediate potential and
require further investigations to advance beyond the prospect stage.
Chart I lists those prospects, summarizes work performed and gives \,^
additional work required.
ii-EEIMxED„MAEEING
1.1. GEOLOGICAL SETTING AND AIM
The photogeological index mapping (areal extent and
distribution of extrusive volcanic units) completed early
in 1982 will be followed by line traverse mapping; based |
on aerial photographs of 1 : 5000, to locate previously [ '-''
undetected gossans, geological features and delineate
more accurately rock units, their stratigraphic relationship
and structu-al settings.
1.2 AREAS OF INTEREST
The 30 km radius area is subdivided into four segments:

1.2.1 SEMDAH - KHABIYAT:
The extrusive volcanic belt extending to Khabiyat consists
prinwrily of Alley volcanics. In the upper reaches of Wadi
Zabin a large mass of Lasail pillow lavas deserves closer
attention.
1.2.2 KHABIYAT - BAYDA
North Bayda and Umar are located in high level Geotimes
and Alley volcanincs.
1.2.3 LASAIL - AARJA - BAYDA
The large mining area will be investigated.
1.2.4 ZUHA - MAQAIL
The east - west succession of Exotic Melange - Alley
volcanics - Gabbro - Geotimes units will be further prospected.
2. PROSPECTS FOR DETAILED INVESTIGATION
Chart I summarizes the exploration status of the eight
prospects selected for fwther investigation and showsr
additional work required to make a decision on the merit
of each prospect.
2.1 THE SALAHI PROSPECTS NO. 53 AND NO. 72
2.1.1. GEOLOGICAL SETTING - AIM OF EXPLORATION
Salahi Prospect No. 53: a north - south trending gossan -
umber horizon of approximately 200 metres strike length
occurs within Alley volcanics and corresponds to an
airborne E.M. INPUT anomaly (C 6-2) with a third priority
rating. Gabbro intrusives to the east are associated with '
it. Ground geophysics indicated a well developed narrow
conductor of 600 metres strike length thought to be indicative
of a small narrow sulphide body.
Salahi Prospect No. 72; mudstone cappir^s (umber ?),
underlain by pillow lavas, crop out along the western flank
of a limestone ridge and correspond to an airborne E.M.
INPUT anomaly (C 6T4), given a first priority rating.
Ground geophysics indicate numerous, narrow conductors
with good strike continuity. Beside clays filling fractures.

narrow sulphide mineralization could cause these conductors.
Geological and structural settings will be determined by
detailed geological mapping using a grid established over the
adjoining prospects. Geochemical and geophysical investi- ^
gations will determine possible drilling targets for initial
percussion drilling to be followed by diamond drilling, if
warranted.
2.2 WADI FORREST GOSSANS PROSPECT NO . 362
2.2.1 GEOLOGICAL SETTING - AIM OF EXPLORATION
Two large silicious gossan outcrops, in alluvial flats and
surrounded by Alley volcanics were discovered diring regional
photogeological mapping. The silicious nature of the gossans
warrants firther investigations as they are located on a -
north-south trend with which are associated the Salahi prospects
and the Maqail prospect (2.1 and 2.3 of this segment)
After establishing a grid detailed mapping will show the
geological setting of gossans and extrusive volcanics. Per- y^cussion
jcfa-illing of the gossans will give information on the
underlying formations and indicate whether a geophysical
evaluation is warranted prior to further drilling.
2.3 MAQAIL SULPHIDE OCCURRENCE PROSPECT NO. 361
2.3.1 GEOLOGICAL SETTING - AIM OF EXPLORATION
West of a line of gossanous outcrops in Alley volcanics
sulphide boulders were encountered in a bedouin water
well.
The sulphides are massive pyrite with very finely disseminated
chalcopyrite and a sample assayed 2.16 % copper. The
sulphide boulders are embedded in sheared and highly altered
, volcanics containing fragments of sediments, indicating the
presence of a fault or shear zone.
Geological mapping will determine the setting of this
prospect, extent of gossans and the need for geophysical ^^
evaluation, percussion drilling and diamond drilling if
warranted.
2.4 SEMDAH AREA NO. 7

2.4.1 GEOLOGICAL SETTING
Regional photogeological mapping indicated an interesting
fault setting associated with the ancient mine site of Semdah,
located at the eastern edge of the Bowling Alley, which was
considered a regional graben structure. From east to west
the following rock units are recognised at Semdah:
Geotimes volcanics followed by Lasail pillow lavas and Alley
volcanics. THe Semdah gossans appear to be located along
or in the vicinity of the Lasail Alley contact zone.
To the north of Semdah a major north- south trending, near
vertical fault has been located, Lasail pillow lavas and an
umber horizon are in faulted contact with volcanics of the
Alley unit. Attitude of the beds and pillows suggest that
the western block of Alley volcanics has been down-thrown
but the amount of displacement is unknown.
If the sulphide mineralization, worked by the ancient miners,
is located in the Geotimes- Lasail sequence, then a western
ore extension could have been truncated by the major fault
and the western portion would be down faulted and buried
by the Alley volcanics.
2.4.2 AIM OF EXPLORATION
After the geological outcrop mapping of the Semdah area
(scale 1 : 5000) has shown the geological setting of Semdah,
detailed mapping of the pit and surrounding areas is aimed
at:
— determining the stratigraphic position of the
mined out mineralization within the volcanic
units - Geotimes and Lasail,
— investigating the faulted contact between Geotimes
- Lasail - pit area and the westerly Alley
volcanics •
— tracing the major fault through the mine area
from its north exposure.
If geological and structural evidence support this concept
a geophysical investigation will evaluate the flat area to
the west of the ancient pit. Gravity appears to be most
suited for such an investigation, supported by a ground
U
i^'

.»
magnetic survey and possibly by a suitable E.M. method. , .
Anomalous indications within the area investigated will be
tested with diamond drilling.
2.5 KHABIYAT PROSPECT NO. 33
2.5.1 GEOLOGICAL SETTING - EXPLORATION RESULTS
The Khabiyat Prospect No. 33 was explored in 1975 and 1981
and four boreholes from 125.00 metres to 282.84 metres
were drilled early in 1981.
Khabiyat is located in Alley volcanics. To the west Geotimes
volcanics are conformably overlain by Alley volcanics
and a well developed umber horizon rharks the contact.
The umber dips at 30* to 35° to the east indicating a
basinal structure underlying the small Khabiyat gossan. Geo- ,1'j'
•y V
logical mapping confimed this setting and a HLEM survey 1^6' ;-
indcated several narrow,steeply dipping conductor axes.
Four boreholes were drilled to test the conductors and
possibly investigate the contact zone of Geotimes - Alley
volcanics, considered a favourable location for the deposition
of sulphides.
All three drill holes failed to reach the target contact of
the rock units but the boreholes intersected weak dissemination
of sulphides within the Alley volcanics'. DDH 33^17
showed pyrite dissemination and sparse chalcopyrite over a
drill length of 62.18 metres of 0.07% Cu and 0.37 % Zn
with peak values of 0.32 X Cu and 0.92 % Zn between 85 and
88 nrtetres (dis^semination from drill collar 64 metres to
126.18 metres).
DDH 33-18 gave the following assay results over a
length of 77.72 metres (35.96 to 113.68 metres): 0.06 % Cu
and 0.22 % Zn ( high values of 0.08X Cu and 0.56, Zn between
83.51 and 92.35 metres).
2.5.2 AIM OF EXPLORATION
Previous exploratory drilling has indicated very weak sulphide
dissemination in lower Alley volcanics and since the deepest
borehole failed to reach the Geotimes - Alley contact,
further investigations will be restricted to a broader and ^'
,0°;

• »
and more deuiled geophysical survey.
A gravity survey will investigate the ground to pinpoint any
anomalous area which could indicate the existence of masses
of higher density at depth. Percussion drilling will be used
to determine the nature of turiace near high density masses.
Diamond drilling exploring deeper seated high density bodies
must be accompanied by down the hole geophysical surveying.
2.6 fi.^.ARJl6.9.,P'^QSPECT NO. 160 - N.E. GHARRAQ
2.6.1 GEOLOGICAL SETTING - EXPLORATION RESULTS
A P.E.M. Survey indicated two good conductors with
multiple channel response at Gharraq No. 160.
Diamond drilling ( 3 boreholes) failed to intersect a plausible
source for these well defined conductors. Gharraq No. 160
and N.E. Gharraq being a large umber occurrence are situated
in Alley volcanics which are presumably underlain by Geotimes
lavas.
2.6.2 AIM OF EXPLORATION
Mapping on aerial photographs will establish the geological
setting of these two prospects and a grid will be the basis
for detailed geological outcrop mapping.
Geochemical chip sampling and geophysics (Magnetics ) will
evaluate the prospects for the existence of near surface
concealed mineralization and produce possible drilling targets.
2.7 ASSAY AB PROSPECT NO. 5
2.7.1 GEOLOGICAL SETTING - EXPLORATION RESULTS
The prospect is within cumulate and pegmatized gabbros,
which are invaded by diabase dykes. Mineralization appears
to be associated with a roughly north-south trending shear.
A HLEM survey indicated a conductor axis coinciding with
secondary gossanous material containing accummulated brochantite
layers. Diamond drilling ( 3 boreholes ), testing
the conductor failed to intersect any mineralization.
A VLF survey ( Very Low Frequency), subsequently carried
out, placed the conductor zone to the west of the HLEM

conductor axis. Survey results were interpreted to indicate
a semi - vertical conductor of 10 to 60 metres width and
with a depth range from 40 metres to 130 metres. Volume
was estimated at 236,375 m' with a relatively high conductivity,
making this a very promising target for diamond drilling.
2.7.2. FOLLOW-UP EXPLORATION
One diamond drill hole of 60 metres length and angled at
45° to the west is required to test the conductive zone.
In case a sulphide intersection is made two additional boreholes
of 100 metres length are budgeted and a follow-up
geological survey including gridding of 3 months duration is
programmed. If negative results are obtained in the initial
borehole the prospect will be written off.
2.8 LASAIL - AARJA - BAYDA - GHAYTH AREA
2.8.1 GEOLOGICAL REVIEW
The large mining area has been explorefd since 1973 without
mudh success in discovering new econbuic sulphide mineralization.
Economic mineralization has been proven at Bayda,
Aarja, Lasail, Lasail west and Ghayth.
Underground geological studies at Lasail and Bayda have
given new information on the mode of sulphide occurrence
resulting in a refined ore formation setting. The fact that
geophysical investigations prior to 1978 failed to indicate
cortcealed sulphide occurrences, at Bayda and south of the
Aarja orebody, warrants a renewed close investigation of
areas adjoining the known ore deposits in a concentrated
effort at evaluating this ground.

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INTRODUCTION
Are porphyry copper and Kuroko-type massive
sulfide deposits incompatible?
Richard H, Sillitoe
Department of Mining Geology, Royal School of Mines, Imperial College of Science and Technology
Prince Consort Road, London SW7 2BP, England
ABSTRACT
Porphyry copper-molybdenum-gold
' deposits and polymetallic, Kuroko-type
yoinassive sulfide deposits are both generated
in dominantly calc-alkaiic voicano-plutonic
arcs at convergent plate boundaries (for
example, Sawkins, 1972; Sillitoe, 1972).
Kuroko-type deposits are generated only
in submarine magmatic arcs, whereas
porphyry copper deposits are emplaced in
both submarine (for example, Highland
Valley, British Columbia—Osatenko and
Jones, 1976; Recsk, Hungary—Baksa and
others, 1974) and subaerial arcs. Moreover,
in island arcs, proximity of subaerial and
submarine environments is commonplace.
Consequently, the presence of only one of
the two ore-deposit types in any one district
poses an enigma, which has perplexed
many workers, particularly in Japan (for
example, Ishihara, 1974), In the few cases
where a fairly clo.se spatial relationship
between porphyry and Kuroko-type deposils
exists, as in Baluchistan, Pakistan
(Sillitoe, 1978), and in central Queensland
(Moonmera porphyry copper and Mt.
Morgan massive sulfide), it appears to be
fortuitous because an appreciable gap
separates their times of emplacement. This
report suggests that the apparent incompatibility
may in fact be real and that it
may be due to fundamental differences
in the voicano-plutonic settings of the
two ore-deposit types,
MASSIVE SULFIDES AND CALDERAS
Cauldron subsidence was a widespread
phenomenon across appreciable segments
of calc-alkalic magmatic arcs during specific
time intervals. During such intervals,
volcanic fields dominated by andesiticdacitic
stratovolcanoes gave way to overlapping
caldera complexes and areally ex­
.GEOLOGY, V. 8, p. 11-14. JANUARY 1980
It is suggested that porphyry copper deposits and Kuroko-type nias,sive
sulfide deposits are incompatible because the former are generated beneatli
andesitic-dacitic stratovolcanoes, whereas the latter are precipitated during
or after rhyolitic to rhyodacitic volcanism within resurgent calderas.
Episodes of lithospheric tension in subduction-related arcs may favor
cauldron subsidence at the expense of stratovolcano development.
tensive fields of silicic ignimbrite (Smith
and Bailey, 1968; Elston and others, 1976a;
Steven and Lipman, 1976). Ignimbrite is
erupted from highly differentiated, nearsurface
magma chambers along ring fracture
zones, thereby resulting in subsidence
of crustal blocks as much as 40 km in
diameter. Ignimbrites, or, in a submarine
environment, silicic tuffs, partially fill the
collapse calderas and accumulate, also,
as thinner outflow sheets for considerable
distances beyond the ring fracture zones
(Fig. IB), Many calderas undergo postcollapse
resurgence, which commonly
entails doming of the subsided block as a
result of emplacement of silicic flow-dome
complexes and underlying stocks and
plutons, both centrally and localized
by ring fracture zones.
A subordinate role for metallization in
the caldera cycle was proposed by McKee
(1976) on the basis of studies in Nevada,
and it is clear that caldera collapse is a
mechanism whereby volatiles and contained
metals are dissipated as components
of ignimbrite (Elston, 1978a), as opposed
to their concentration and eventual release
during cooling of subvolcanic magma
chambers. Nevertheless, resurgent magmatism
has been claimed as a potential oreforming
event in the subaerial mid-Tertiary
cauldron subsidence province of the southern
Rocky Mountains (Elston and others,
1976b), although only a structural control
by ring and radial fractures rather than a
true genetic connection of most of the
base- and precious-metal veins and skarn
deposits also has been proposed (Lipman
and others, 1976).
Recently, however, submarine resurgent
calderas have been proposed as the principal
sites for generation of Kuroko-type
massive sulfide deposits (Hodgson and
Lydon, 1977; Fig. IB). The enhanced permeability
resulting from collapse-induced
WOK L O . KJ.
ring and radial fracturing permits establishment
of convective hydrothermal systems
(for example, Taylor, 1974), at the outlets
of which Kuroko deposits are precipitated
(for example, Ohmoto and Rye, 1974).
Nevertheless, several lines of evidence also
support a crucial magmatic contribution
to the sea-water-dominated ore fluids
(Sato, 1977; Ishihara and Sasaki, 1978;
F. J. Sawkins and J. Kowalik, 1979, personal
commun.). If Kuroko deposit generation
is related to resurgence of submarine
calderas, then an explanation is at
hand for (1) the ubiquitous occurrence of
the deposits in silicic pyroclastic sequences,
commonly near their tops, and, furtherm'ore;
for the close association of many
Kuroko deposits with felsic lava domes
and accompanying breccias; and (2) their
restriction to a small percentage of submarine
volcanic provinces and, within
individual districts, their generation in
clusters at a specific stratigraphic horizon.
In northeastern Japan, some 70 mid-
Miocene Kuroko deposits were emplaced
above a thick silicic tuff sequence—now
interpreted as a product of caldera collapse—and
are commonly located on the
flanks of rhyolitic to dacitic lava domes,
the positions of which now are thought to
be controlled by ring fracture zones rather
than by the margins of sedimentary basins
(Ohmoto, 1978). In the pre-eminent Hokuroku
district, five resurgent cauldrons,
each having Kuroko deposits (Kouda and
Koide, 1978), are nested within the 20-kmwide
basin first recognized as a subsidence
structure by Tanimura (1973).
In the Eastern Pontid province of northeastern
Turkey, 19 Kuroko deposits of
Jurassic-Neocomian age and 54 of Late
Cretaceous age occur at the tops of thick
rhyodacitic pyroclastic. units, which themselves
overlie basaltic and andesitic sequences.
Pejatovic (1977) documented
11

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^SRMtt»tVW9a

1971) and still retains vestiges of its original
form (Sillitoe, 1973). At Safford, Arizona,
radiometric dating has shown that
andesitic volcanism, stock and dike intrusion,
and development of four porphyry
copper deposits spanned only 5 m.y.
(Dunn, 1978), In the Baguio district of
Ihe Philippines, andesitic-dacitic volcanic
rocks of middle to late Miocene age are
in part coeval with prophyry copperbearing
stocks at Santo Tomas II and
Black Mountain (Balce and others, 1979).
Similariy, in the Highland Valley district
of British Columbia, the coinposite
Guichon Creek batholith, host to nine
porphyry copper deposits, is considered
to be comagmatic with enclosing andesitic
volcanic rock (McMillan, 1976). More
commonly, however, the age of premineralization
andesitic-dacitic volcanic
rock relative to that of the porphyry deposits
is poorly known, although in parts
of several provinces, including southwest
United States-northwestern Mexico, the
Philippines, Papua New Guinea, the Carpathian-Balkan
belt, and the central
Andes, a comagmatic relationship is suspected.
Moreover, where immediately
premineralization volcanic rocks are
present, silicic representatives, particularly
ignimbrites, are conspicuous by their scarcity,
as for example in the southwestern
United States (Titley, 1972). The apparently
subordinate role played by ignimbrites
and silicic tuffs in volcanic sequences
closely related to porphyry copper deposits
suggests that their emplacement is not
favored by cauldron subsidence settings,
a conclusion supported by the notable
paucity of annular features, such as ring
fractures and dikes, in the vicinity of
porphyry copper deposits.
Furthermore, cauldron subsidence
provinces generally lack known major
porphyry copper deposits and seem to
have only a few incipient developments.
In the southern Rocky Mountains of
Colorado and New Mexico, a mid-Tertiary
subaerial cauldron subsidence province
lacks contemporaneous porphyry copper
deposits, in strong contrast to the preceding
Laramide interval, although minor,
pyritic disseminated sulfides have been
reported (Elston and others, 1976b;
Lipman and others, 1976), and porphyry
copper deposits may occur in depth beneath
prominent zones of advanced argillic
alteration and silicification, as at Summityille.
Colorado (Sillitoe, 1977), The extensive,
silicic volcanic province of Late
Cretaceous-early Tertiary age on the inner
side of southwest Japan and adjoining
southern Korea is interpreted as having
developed by cauldron subsidence and has
only minor porphyry-type mineralization
(Sillitoe, 1980a), Similarly, the minor
porphyry-type occurrences recently described
from northeast Queensland,
Australia, by Horton (1978) occur in a
Permian-Carboniferous subaerial cauldron
subsidence province dominated by rhyodacitic
ignimbrites (Branch, 1966).
The submarine cauldron subsidence
provinces mentioned above as the locales
for Kuroko-type mineralization also are
devoid of porphyry-type mineralization.
In both northeastern Japan and the Eastern
Pontid belt, for example, tonalitic and
granodioritic stocks were emplaced immediately
after massive sulfide deposition,
probably during resurgence, but they have
no porphyry deposits (Ishihara, 1974;
Pejalovid, 1977), although in northeastern
Japan they are associated with epithermal
base- and precious-metal veins (Yamaoka,
1976).
The subordinate role of porphyry
copper-type mineralization during resurgent
plutonism may be tentatively explained
(Sillitoe, 1980b) by a combination
of (1) depletion of magma chambers in
magmatic-hydrothermal fluids and energy
during ignimbrite eruption, thereby allowing
an insufficient build-up of fluids to
cause retrograde boiling, their explosive
release, and consequent porphyry copper
formation; (2) progressive rather than explosive
loss of magmatic-hydrothermal
fiuids (to give massive sulfide, vein, and/or
skarn deposits) because of the "leaky"
structural setting induced by ring and
radial fracturing; and (3) the lesser time
interval for evolution of magma chambers
in comparison to that available beneath
stratovolcano fields.
STRATOVOLCANOES VERSUS
CALDERAS
A fundamental problem is posed by
the relatively abrupt initiation of cauldron
subsidence across appreciable segments
of subduction-related stratovolcanic arcs.
It is suggested here that the regional
imposition of an extensional tectonic
regime, possibly due to a slowing or cessation
of subduction or a change in direction
or angle of subduction, would favor
cauldron subsidence. Under regional
lithospheric'tension, near-surface emplacement
of large magma chambers and failure
of their roofs would be facilitated, thereby
assisting ignimbrite eruption and caldera
collapse. Although interarc extension
occurs, regional tension might be more
likely to develop as back-arc.settings are
approached, a suggestion supported by
transitions from late Cenozoic calderaignimbrite
provinces on continental crust
to marginal ocean basins: the Taupo zone
of New Zealand to the Lau basin, and .
Sumatra to the Andaman basin.
Elston (1978b) attributed the onset of
mid-Tertiary cauldron subsidence in the
southern Rocky Mountains to the development
of a back-arc tensional regime, consequent
upon a relaxation of compressive
stresses across the continental margin as
subduction slowed. The same explanation
also was offered by Lambert (1974) for the
inception of Eocene subaerial cauldron
subsidence in the Sloko province of British
Columbia and the Yukon. In northeastern
Japan, extensional conditions giving rise
to regional graben development parallel
to the trench prevailed during Kuroko
emplacement (for example, Ishihara, 1974)
and, as in the Eastern Pontid belt during
at least the Late Cretaceous Kurokoforming
event (Pejatovid, 1977), the magmatic
arc was constructed on the trench
side of an actively opening marginal ocean
basin. Regional extension is further supported
by the occurrence in these cauldron
subsidence provinces of subordinate volumes
of basalt in close association with
the calc-alkalic volcanic rocks. Furthermore,
Scheibner and Markham (1976)
considered that the Kuroko-type deposits
at Woodlawn, Captains Flat, and elsewhere
in New South Wales, Australia,
were localized by interarc rift zones along
a Silurian island-arc system.
CONCLUSIONS
An incompatibility of Kuroko-type
and porphyry copper-type deposits results
from the predominance of the former
in resurgent calderas and the latter beneath
stratovolcanoes. This explanation also
accounts for the prevalence of rhyolitic
to rhyodacitic pyroclastic rocks as hosts
for Kuroko deposits, in contrast to the
largely andesitic to dacitic composition
of volcanic rocks associated with porphyry
copper provinces. An example is the absence
of porphyry copper deposits from
Japan, where the principal episodes of
calc-alkaline magmatism, during Late
Cretaceous-early Tertiary and mid-Tertiary
time, were dominated by cauldron subsidence,
in strong contrast to the Philippines,
where Cenozoic magmatism is
largely andesitic-dacitic in composition
and porphyry copper deposits are
vyidespread.
Although it is widely appreciated that
search for Kuroko-type deposits is best
concentrated in submarine, silicic volcanic
sequences, it may also be concluded that
porphyry copper exploration is best conducted
in volcanic provinces dominated
by andesites and not rhyolites. If cauldron
subsidence provinces are to be explored
for porphyry copper deposits, then stocks
related to remnants of precollapse stratovolcano
fields could offer the most
promising targets.
Finally, the incompatibility favored
here casts serious doubts on models
(Branch, 1976; Colley, 1976) that consider
porphyry copper and massive sulfide
deposits of Kuroko type to have been
generated in the same hydrothermal system,
albeit at deep and surficial levels,
respectively.
GEOLOGY 13

d
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ACKNOWLEDGMENTS
Reviewed by \V, E. l-'lslon, S. Ishihara, and
I-. J. Sawkins. Visits to Kuroko deposils in
northeastern Japan, organized by Ihc Society
of Mining Geologists of Japan, and discussions
with H, 1-, Bonham, Jr,, C, W. Burnham, and
l^lstun were valuable.
MANUSCRIPT R1-CI:IV1:D APRIL 19, 1979
MANUSCRIPT ACCEPTl-D OCT. 26, 1979
14 fHlNTEP IN U.:J.A. JANUARY 1980
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JOURNAL OF Cli-OPHYSICAI. UtSl.-.ARCH, VOL. Ki,, NO. ii-1.. l',.\Cil- ..M'Kii iO, !9H|
Tectonic S-^ilmg for Ophiolite Obduction in Oman
ROBtiRT G, Coi.lM,.SN
L'..S. (ieuloyjcal Survey, Menlo Park, C.'ulij.iinid 94025
The Samail ophioli'.c- i:i part of an elongate bell in the Middle liasi ihal forms an integral part of ihe
..\lpiiie mouniain chains ihal n-.kc up ihe northern boundary of tht: Arabian-African plalc. The Samail
ophioliie rcprcscr.i.., .i portion u\ Ihc Tethyan ocean crust li-c.-.l ,a a spieading.center of M:.Jdle Ctelaceou.s
age vt.'ei;v-.niani.in). l.')uririB ihc Crelaceous sprcadinj; of itic Telhyan Sea, Gondwa'i;: Land ainlinucd
ii.s di.->pcisai, ami ihe Arubian-Aliican plale drilled northward aboul 10°. These cvcrii.s combined
with ihe opposite lolanyn >)f Eurasia and Africa inilialcd ihe closinj; of the Telhyan during ihc L,iie Cielaceoii.s.
Al ihc -;rly stages of closure, downwarping of ihc Arabian conlinenlal margin combine..) wiih
•.he con^pres.sio.ial forces of closure from the Burasian plate iniliated obduciion of ilic Tethyan ;:i;eanic
cf'.i.';! along piecxi.siing Iransforni faulLs, and still ho; .ceunic crust was deniched.along oh!'.;.,..,; iH-iriiica-t
dipping ihru.sl faults Amphiboliles developed al Ihc ba.se of ihe delacbcd hot peridolile ;i:., ; wa;; Ihru.sl
.si'ijihward over oceanic volcanic and sedimentary rocks. Plate configuralions combined with palin.spa.stic
teconsiructions show thai subduction and atlendanl large-scale island arc volcani.sm did not c;oin.ir)cii'.;r.
until after the Telhyan sea b ;.;;ui to close and after the Samail ophiolite was emplaced southward aci
the Arabian conlinental inaigm. The Samail ophiolite nappe now rests upon a melange consisling maiii..
of pelagic sediments volcanics, ,i' 'I detached fragments of the ba,-.;;: amphiboliles which in turn rest on
autochthonous shell carbonates oi iic .Arabian platform. Laterius a-.:^ conglomerates with reworked laterites
on the eroded upper surface of the ophiolite indicate a period of emergence prior to the deposition
of shallow waier .Maestrichtlan carbonates. Following emplacement (Focene) of the Samail ophioliie, the
lelhyan oceanic crust began northward subduction, and active arc volcanism started just north of Ihe
P'cscnt Jaz Murian depression in Iran.
iNTROI.iUCilC-,--:
t3|->hioiik-s of the Middle La.-;; occur in elongate belLs that
iijiikc up :ii: integral pan ol'ihe .Mpine mountain chains forming,
tr,..: iiorih boundary ot the .'"..'abiiin pliiit (Figure I). These
.iphioiiics extend eastward an.l soulhv^-ard from Cyprus into
HLit;iy ./id Syria, thence along ihc Turkey-Iran border told
bi;li southeasiw-ard through Kernunsliah and Neyriz in Iran,
and linaily across the Persian Oiilf inlo Oman [Ricou. 19711.
Currciit deUiilcd siudies of the ophii.'lites of ihe Middle East
dc'nionstr;i!c thai the igneous pioccs.scs from which they delive
require iheir formation as .ccnnic crust at some type of
^rl!cadini; center [Ca.u. Iy;)3; Gass and Smi'win^, 1973; Parrot,
I'JT^: Juteau et al.. 1977; Moore.^ am: > ,rie, 1971; Grecnbaum,
iv7.'; Pcurce, 1975). Such spreading. ridgt;s as the present-day
Mici .'\tlantic Ridge may J .rnV in deep ticeans [Bryan and
Moure, 1977], vviihiii marjiinal or-back arc basin.s [Karig,
'y'i], or in small ocean basi.o.s.:.. .-ti a.-; the Red Sea [Coleman
i-l (/'. 1977), The purp;.>se of iltr- [ .^cr is lo reconstruct the
;i-.-i:.iogic and tectonic ,scuin,;i of ihc Oman region during and
iii-ir ;iie emplacement of.(he S,in\...i; i.phiolite and to suggest
'vypothe.ses as to its pclroiecKMiK ii.;^ i->, This paper provides a
.--L-ttional setting lor othe- p;if:K:i,s (hut K liO'A- in this special volume
on the Samail ophiolite, On;,i!.,,
The existence of a 'Iciiv/rti; S.: during Late Triassic
'.'ir.iugh Cretaceous time ihn.uf!;oui thi:; legion has been sugfic>;ted
by the presence of opiu-liMi :.:.-iert .sequences |^/i.'ciu.
jv.'i; Glennie ei al., 197.3, 1974; .Ti.x.«.'';>) I977j. These ophioliU-chert
sequences are consi.ji-r., i 1 .•'i;scnt fragments of
.:;i'.ieni oceanic cru.st empFiccj ,.. •M •- ... ,;.cntal margins dur-
.ng a compressional phase in;ii in k,{v':d ;he disappearance of
;h',; Telhyan Sea [Smith and HV/
.Miirhell, 1977). The presjiH-.- , !'
r..!sned ophioUte fragiiieni-, " .-;
.rhis paper is not subject to l.i.bi.
th;r ,'\nii-ric;an Geophysical Linior,.
Mf(-::.-. 197(>; Welland and
'--„i;iii;^i; Ci.insisting of dis-
;-,i,queni.:.-':, ;.;id limestone
...py:;ghi. PL-hiriKed in 1981 by
number 80BOX()-i 2497
blocks in a iinciir array from CypnJs to Oman that separates
the crusi:il eiemenis of Gondwana and l-urasia is now rc(o.-icd
10 as the suulh f'cihys suture [Stoneley, 1974, I975|. it seems
geneially agit.'cd ihal the Tethys suiiiVe represents the rcntnants
of- ;'ow vanished ocean, although the acttiai '.ectuniL
situaiion tharailowed fiagmenis from ihc lltKit v\ he,?.,y occ
anic cnist to be incorporated into the conv.:';:e;i; continetiiai
margins of Arabia and liurasia remains .;.....r-rov;.-.sial. .S;.'
neley [1975] provided a regiunal synthes;, • i "he sotiiyicrn
Telhyan ophioliies and suggested that they rcpre.-.ciii ILncar
intrusioas/exiru.'-ion.'; i>i • .aiiDc. material along tht; inactive
Arabian margin under c- ,n;...ons of tension, l.-piili,.: accDmpanying
intrusions initi;-,;,'. Miutliward gravity sli-iing v^l the
ophiolites onto the passive coniinciitai margin. Glenme. et ai
(1973, 1974] after an ir;'Ciisiv-j ~M\^^ ni'ihe Oman MnunLains
concluded that the ophiolites repr' .eir. iVagments oi'Tethyan

.-1
;1
. ,1
?•
2448
. 20*
20«
Pd. ^Xid.
-^••y •:•:-:>:.yy'^.^,L
A.F-R,.;l,;G;;A;yi;),
COLEMAN: OMAN OpmoLtrE TiicrONns
-It
(Tx^CB^:^
^ pppd^y
cmd^:.yP^''^d '/ -
# ^ . - ' - ; • ' -
' < ^ ^
Fig.; l.,J':peneraU2cd_:tectohic rnap showing distribution of ophiolites along Tethys suture and modified after Ga/iii-er
.'-, •'y.:.d'::i:ipd'i^ 11,966); Black areasincludeboth ophiolite and colored melange jwnes. ; ,,
The mobility of these;idifterent segments from the time of
Gondwana accretion to the preserit plate-tectonic copfigura-
.-tion is stiJJl.controyersiaL--'.,'J7;.=^'-i:-:;'fj.':,.- :d.,] .-••;.. i * ''•dyp'':-,
.-••V y^vV-aARABlAN-Pll^TFORM'. pi 'v ''^p.-'d- P
The Arabian peninsula, earlier, attached to Africa, is char-.
acterized in the west by ah extensive uplifted area of Pre--
Cambrian rocks that correlate with the Mozambique-East African
belt (Figiire 1). The; Precambrian of Saudi Arabia has ho!
Archean cores, and current workers have shovvn that develop-,
ment of the shield occurred dtiring the late Precambrian with,
the formation of successively yoiinger island arcs eastward as
the west dipping subduction zones shifted eastward [Schmidt,
et at., 1978]. This .phase was followed by a major continental
collision on the east side, of the Arabian Shield about 600 m.y.
ago that may have accompanied the accretion of India to East
Africa to form Phanerozoic Gondwana. The northwest trending
left-lateral Najd faults (600 m.y.) may have formed as a
result of the Indian accretion [Schmidt etal., 1978].';'
Najd faults are transgressed by quartz sandstone and lime-'
stone containing Late Cambrian trilobites of the stable platform
facies [Schmidt et ai, 1978]. Thus the Precambrian basement
has been remarkably stable since this transgression and
Najd faulting, and only-gentle'epeirogenic movement has occurred
up to the present time. A total of nearly 5500 m of shelf
sediment from.Cambrian to Pliocene was deposited upon the
Arabian peninsula. J3/;0H'n[ 1972] showed on his tectonic map
of the Arabian Peninsula that the structural contours on Precambrian
basement extend down to 6Q00 m and form a major
trough within the Rub Al Khali desert region. The lower Pa­
leozoic rocks are generally unfossiliferous and consLsl mostly
of terrestrial clastic deposits. Transgressive across these deposits
is a thick section of marine sedimentary carbonate rocks of
Late Permian and Triassic age [Powers etal., 1966], Above the
y4':.y
.Sni'ai
, SS".-.
Neyriz.. i >i{; ;. IRAN
%.
, , • • d^-
-. is I j ^^Bahain -y-'^'i fj,'}hn.
20".-l—.
I, Odiat s . 1 Dubai/
.60''
^ V>.sch„ ,°^o.v^^
(IMAM
Fig. 2. Index map of Arabia-Iran area showing the principal geo-
- graphic locations.

c
o
: CoLF.MAN: OMAN. OFHIOLITI-; TECIPNICS ' 2499
M.Y. ARABIA OMAN TETHYAN OCEAN ZAGROS MAKRAN >BA2MAN
sedlinents
[~~| Flysch deposits
IIIII} Platfonn deposits.
.)-'

''i^'.'Q
n
-•3
J:^ri
••JT.-»|
m
li

C
c
C-
These sedinientary rocks all occupy a foredeep on the continental
margin [Brown, 1972), and their stratigraphic relations
suggest that the Samail ophiolite was emplaced sometime during
the Late Cretaceous (Coniacian to.Maestrichtlan) [Glennie
etal.. 1974). - ^;, • '' .. --^ . :
Evidence that Oman marks the edge of the Arabian continental
margin during the period of shelf carbonate deposition
is provided by the parautochthonous Sumeini Group exposed
in the northern sector of the Oman Mountains [Glennie el ai,
, 1974). Sedimentary rocks from the Sumeini Group appear to
be intermediate between shallow marine and deep water turbidites
and may represent continental slope deposits [Glennie
etal.,i974\. :y' i' d'l-:. ''dyd'-P ';'"-•'
Tectonically overlying the Hajar Supergroup and sedimentary
rocks of the Sumeini Group is a sequence of thin, imbricated
nappes containing sedimentary rocks that range from
radiolarian chert, through limestone turbidites, to some shallow
water marine carbonate rocks; the sequence was called
the Hawasina allochthonous unit by Glennie et ai [1974]. The
Hawasina sedimentary rocks have indiyidual age ranges that
overlap the Permian to Senonian range of the Hajar Supergroup.
Carefiil stratigraphic and paleontologic studies by
Glennie el a/, (1974) have allowed palinspastic reconstruction
of the site of deposition ofthe Hawasina sediments: a deep
ocean whose south boundary was the Arabian continental
margin and which extended northeastward to a spreading
ridge in the Tethyan Sea (Figure 3). Thiis the present configuration
ofthe Hawiasinanappes is due to southward transport
across the subsiding Arabian niargin into a foredeep [Brotvn,
1972] where the more distal nappies, occupy higher structural
.levels in thcpile.-',; .,;^'y;.4 ;•-';'-;;;•:;•'.:,•.-• ,''.•;'.:
Accompanying these pelagic Hawasina nappes as the highest
tectonic member is the Sainail nappe, a gigantic mass of
ancient oceanic crust (ophiojite) formed in the Tethyan Sea
during Cretaceous spreading [/{e(n/Mir

:-i 2MI2 COLKMAN: OMAN OI'HIOI.ITI; TLC-IONKS
. ^ -
•C'.
Ill ^1
i.>«
••-1
- "A
d
. - 1
r -J
:^^ I
"•1
shelf sedimentary-rocks. Within this large area dominated by
flysch deposits are no platform sedimentary rocks equivalent
to those found on the Arabian platform and no contempoeraneous
volcanic rocks [Ahmed, 1969) (Figure 3).
The Cretaceous and Paleocene pelagic sedimentary rocks,
distal turbidite, and volcanic sequences of the Makran arc assumed
to have been deposited on oceanic crust formed as part
of the Tethyaii Sea; Evidence for this deposition is found
along the north, boundary of the;Makran, where a narrow
zone of ophiolites consisting.of peridolile, gabbro, calc-alkaline
sheeted dikes and pillow lavas, and pelagic sedimentary
depo.sits forms the boundary between the Lut block and a narrow
continuation of the Sanandaj-Sirjaii zone represented by
the Bajgan complex of metamorphic rocks and the Dur-kan
complex of shelf limestone,(A/cCa//, 1978] (Figure 4), In some
areas, interbedded pelagic rocks within pillow lavas yield mi-crofossils
that indicate a range from Early Cretaceous to early
Paleocene in the Dar Anar complex; from Late Cretaceous to
early Paleocene in the Mokhtarabad complex; and from Campanian
to Maestrichtian in the Ganj complex. The pillow
lavas and associated sedimentary rocks are unconformably.
overlain by Eocene shallow Vater deposits. These ophiolitesare
faulted southward against the Diir-kan Ridge, a structural
unit that separates them from the Makran flysch [Houshmand-
Zadeh. 1977). The Dur-kan Ridge is a narrow (20 km) band
extending 200 km eastward, where it wedges out between the
ophiolites and the Makran Cenozoic flysch, although it niay
extend farther eastward to the northeast of Iranshahr and in
K.uh-e Birk [McCall, 1978). The ridge, which is intensely deformed
contains Carboniferpiis, Perniian, Early and Late Cretaceous,
and PaleoiDene sedimentary deposits [McCall, \919a,
b, c]. The Late Cretaceou.s and iPaleocene rocks are shallow
water limestone and .clastic.rocks interlayered with basaltic
and andesitic lavas, breccia, and tu IT. To the south, the Durkan
Ridge is thrust over ophiolitic melange along north dipping
reverse faults, :mainly steeply inclined (//oMj/iffJo/i^-Za-
deh, 1911; AytrCaW,T979flj..,Thcse melanges and flysch fonri,;
only narrow elongate;zonesthat-trend east and separate the ,
Dur-kan Ridge.from the,Eocene and younger flysch (Figure
4), The Eocene flysch south ofthe melange Ls.also deformed',
along north dipping thrtists. The occurrence of exotic blocks
of ophiolites and older rocks tectonically introduced by the
north dipping fauhs suggests that .the Eocene flysch was de-.
posited,on an accretipnary prism of ophiolitic melange
(A/cCa//, 1979Z>],or perhaps-was derived from tectonically dis-';
lurbed Tethyan oceanic crust. South ofthe Eocene flysch, the -
Makran zone is.bccupied predominately by lower and middle
Miocene flysch deposits::;Nprth dipping faults bring Eocene
flysch over these yoiinger turbidites, which become younger
southward and are-in turn, succeeded by Miocene and Phocene
shelf deppsits to the south, where themaximum thickness
is estimated to be 10,000 m (G. J, H, McCall, written communication,
1979). This regujar southward ydunging combined
..with north dipping faults has been interpreted as accretion
and migration of convergent conlinental margin in this direction
[/ar/iOMii/aw

G
' .COLEMAN: OMAN OPHIOLITE TECTONICS
OMAN IRAN
iaz' Muridii -
Depression
Fig. 5. Stylized cross section frona Oman to Iran. Ocean crust (ophiolites) wiihin the Gulf of Oraan.are. considered lo
be part of the Tethyan iKean crust Configuration of the flysch deposiu taken from IVhiie and Xoa [1979] C L marks the
coast hne of the Makran area in Iran
[Smith, 1971) Its former presence has been established mamly
by the occurrence of ophiolite-chert sequences along the pres-.
ent-day Tethys suture. The amount ;pf,oceanic crust formed
within the Telhyan Sea has not yet,been.established. However,
most estimates indicate that the Telhyan Sea thai occupied
the Arabian continental margin was probably a narrow
seaway [Sm/r/i, 1971 ;;5/t>cifc/*n. 1974; Son«en/eW, 1978], PaUn^-;,
2503
imately 2400 to 3000 km of oceanic crust could have been
: consui^ied. There is no evidence that there existed that much
yTethyan bceanic .crust or that subduction continued at these
', same: rates for the last; 60 iri.y. The geologic data on the Samail
points to obduction of only a very snaall amount ofthe
youngest Telhyan Sea in this area and that if large tracts of
,'older >Tethyan pceaniccrust; were formed, they have either
pastic reconstructioDis using least squares, continental fits, and ; been subducted to the north,under the Eurasian plate or may
paleomagnetic data usually, show a large Tethyan Sea.ex- • iform at^least part of the pceanic crust in the Gulf of Oman.
panding eastward beyond the African and Eurasian plates.: : V The iithblogic. record, cpmbined with paleontologic evi­
[Smith and Briden, 1977, Owen, 1976),.Evidence derived from;, dence, has allowed a palinspastic reconstruction that shows
the Samail ophioUte will provide some answers relative to the the Tethyan Sea in this area, to have consisted of a medial
puzzle ofthe grpwib and disappearance ofthe Tethyan Sea. , '.spreading ridge covered on its flanks by pelagic chert grading
However, it is unlikely-that the information in the Oman sec­ into a thickening wedge of turbidites towards the,conlinenlal
tor can be directly, applied to the 'Greater Telhyan Sea!' ,: -rise ofthe Arabian continental .margin [Glennie el ai, 1974),
Reconstruction of;discontinuous exposures of sheeted dikes > Oman exotic blocks of Permian and Triassic age, consisting of
in the Oman Mountains reveals a paleo-spreading ridge ori­ shallow,water coralline limestone deposited on pillow lavas,
ented at approximately NI5°-^20°W and a maximum,spread-, represent high-standing reefal facies that probably represent
ing width of 275 km [Pallister, 1981]. Isotopic U-Pb ages of islands or marginal upfaulted blocks within the Telhyan Sea
zircons from plagiogranites within the Samail ophiolite [Glennie, et al., 1974) (Figure 3). Reefal facies resting on vol­
thought to represent igneous activity related.to ocean crust canic rocks along the margin of the present Red S^a provide
formation average about 95 m.y! [Tiilon et ai, 1981). Biosira- an actualistic model for these Permian exotics in Oman [Cole^
tigraphic ages of radiolarians contained in umbers and cherts man el,ai,.1911]. Anplher plausible explanation is that these
interbedded within, pillow lavas of the.Samail ophiolite are exotics represent reefal facies along thet early Tethyan.rifi that
Cenomanian to,Turonian;('~86-100 m.y.). Thus the radio­ separated Africa and Eurasia,..;
metric and fossil :ages are concordant and show that the Sa-' The Samail ophiolite, now forming the highest nappe of the
mail ophiolite was formed during the Middle Cretaceous. allochthonous sequence in Oman, is considered to represent
Even though pelagic sediments,wiihin the Hawasina nappes pan of the middle Cretaceous Telhyan oceanic crust and up­
contain TriassicrJurassic fossils and occasionally some interper mantle. Reconstruction of its stratigraphic sequence shows
bedded volcanics, there:is no evidence of Triassic-Jurassic a basal metamorphic peridotite approximately 9-12 km thick
pceanic crust within the Oman mountains.
that, represents a depleted mantle [fiout/ier and Coleman,
The present Gulf of Oman, approximately 380 km wide, is 1981], Overlying the peridotite is approximately 5 km of
probably underlain!by Telhyan oceanic crust generated dur­ cumulate gabbro consisting of alternating layere that reveal a
ing the Jurassic.and Cretaceous, Northward subduction along history of batch crystallization in a coniiiiuously forming
the Makran coasiinay have started, during the Eocene, as in­ magma chamber [Hopson and Pallister, 1978] Sheeted dikes
dicated by the age of the. calc-alkaline volcanic arc north of form a l.S-km layer above the gabbro and pillow lava on top
the Jaz Murian depression (Jung el oA, 1976], Jacob and Quitl- of the sheeted dikes cap this remarkable assemblage of igmeyer
[1979] showed present-day northward slip vectors of 4 neous rocks. Comparison of the actual thickness, igneous his­
and 5 cm/yr along the Zagros and Makran, respectively, if tory, and seismic velocities with present-day oceanic crust
these slip rales are related tp northward subduction that has leads to the nearly undisputable conclusion that these rocks
.been going on since before the Eocene, (60 m.y), then approx­ formed at some ancient Telhyan spreading ridge.,
vSL

2504 COLEMAN: OMAN OPHIOLITE TECTONICS
Coniacian ~B5 my
TETHYS
Begin Detacttment metamoiphism
90 my
QMAM IRAN
Fig 6 Schematic diagrams depicting detachment and initial emplacement of the Samail ophioUte (a) Begmmng of
detathmeoi in Cenomaman ume where crust is thin and upper mantle is sttU hot neat active spreading along a Tethyan -
ridge crest, Detachment is initialed by closure of Telhyan ocean as Africa (Arabia) moves nor^waid. (fc) continued closure
of the Tethyan ocean exposes oceanic crust to extensive erosion above sot level. CoDlineaial margin along Oman is de- ,
! pres3cd,'and some oceanic and.continentai.material is utidenhrust. Some gravity ididing of the pelagic sedimeats accompanies
the emplacement of the'Samail ophiolite naippe.' Pinal coafiguration of UieSamait ophiolite in rcUtion^p;to the '
Xjulf of Om&n and ptesentfday iiorihwatd;subducuoa.ondier the Makran ooudtne is «hown in.Figure;S..Patterns used, in'
''the diagranis'are the Mme,.as thoM.explauwd--in\l:i^«r«8..3'and,5.{':,;f:-'^^ .•^^•"^''•'yyd-''':
', /.' Aloiig ihe.baseof .the teclooized peridotite is a narrow ;K>ne: : meol and erosion, and before the final transgression of Late
of meiamorphic rocks, grading from garnet amphiboUlb (usu- ; Cretaceous shallow water UmtKione. "!
.. ally thinner than 1 on) atlhe contact downward into amphibol .: The amount of melange underlying the .Samail ophioUte
. lite, then into greenschist, and hnallyvinto unmetainorphosed appears to inaekse from south ld;i»orth across strike, and the
Hawasina sedimentary an,d volcanic rocks over a ditstance of Hawasina sedimentary rocks rftowonly inxbrication soulhless
than I km.. As shown belpw; this upsidesiowa meumpr-, , .ward and appear to be increasingly broken tip northward un-
phic aureole resulted,from the priginai detachment of the Sa-' tilinelangepredoramates under the ophiolhe: ; :<
mail ophiolite frpmtheTethyan Sea crust before it was cm;,, i vTo tbe north of Oman at Neyriz, Iran, a nearly: identical se-.
placed onto the contineatal margin of Oman. The *At/*'Ar; quence is present (Figure 2). Here, resting on Cenomanian
. age dates on amphibole from tbes« metamorphic rocks gives and Turonian limestone of the Arabian platfonn are a series
an age of apprpximalely 90 m.y. .[^Uei^uw ,

G
C
evidence of extensive island arc volcanism. Thus the Tethyan .,
Sea in this region al this time tnay have been a narrovy ocean
trough connected tp.the .shallow epicontinental seas of. the
Arabian platform.;,; \ .,:; ; ' -'
U-Pb ages on the plagiogranites within the massive gabbros
of the Samail ophioUte suggest that seafloorspreading was occurring
at least by Middle Cretaceous but may have begun by
the Early Cretacepus according to Nd isotopic age studies
[McCulloch, 1979); Assuming that spreading continued until
the end of the Turonian, as indicated by interiayered sedimentary
rocks within the pillow lava.s, approximately 44 m.y.
of seafloor spreading is estimated, only about 15% which is :
represented in the Samail ophiolite nappes [/"a/toer, 1981). :
The Tethyan seaway along the,Arabian plate may have been
a graben-horst tectonic feature that included only minor;
amounts or new crust fprmed before ,;the. Early Cretaceous.
. Available radiometric ages on other ignepus members of
Tethyan ophiolites are usually Middle Jurassic or Middle C:retaceous
and indicate that continuous spreading from Triassic
to Cretaceous has not been established by radiometric dating
: of.Tethyan ophiolites. Thus the Saniail ophiolite may, represent
only a relatively young part of the Tethyan crust and may
. not be part of ampre extensive Tethyan Sea that developed
during the Triassic'^and. Jurassic. Or' conversely, there may
never have existed a huge TelhyanSea required by palinspas-;'
tic reconstructions based on an earth .of,constant volume.
Al the same time that spreading look jplace in the Tethys,
Gondwana continued,to disperse; however, during the Cretaceous,
northward, drift ;of, Africa ;(+Arabia) by about 10",
combined with,opposite rptatipn;of Eurasia and Africa' closed
the Tethys [S/Mi(A, |971): Indirect evidence that may relate to
this closure.can be seen in the stratigraphic record as the.widcspread
unconformity between the Wasia and Aruma formations
on the Arabian platform [Powers et ai, 1966] (Figure 3).'
On the continental edge along the north coast of Oman a forc;
deep containing.clasticsedimeritary deposits indicates warp- -
ing along the margin of Oman. These deposits, which, consist
mainly of reworked pelagic sedirnent from the Hawasina ba­
sin to the north, indicate.an upwarping of the Tethyan Sea;:,
floor to the north [Glennie et «/„ 1974).Tt is particulariy diffi-;;
cult to tie these events direi:tly-tp the now-vanLshed Tethyan
Sea, although the cessation of spreading during the Con- ;
iacian, combined' with the closure of Africa against Eurasia, ;
produced the regionallectonic events that preceded emplace- '
ment of the Samail ophiolite. During the, early, stages of closure,
downwarping of the Arabian I'continental margin, combined
with compressional; forces,,'.;from: Eurasia, initialed
, obdiiction,of the Tethyan oceanic crust along the preexisting
Owen-Murray fracture zone to Iheeasl.and the Oman line to
the west, and still-hot oceanic crust near a spreading center
was detached along oblique northeast dipping thrust faults,
(Figure 6). A, detachment thrust within the Tethyan Sea
would more Ukely have been formed in the zone of active
necking at a spreading, center,-where the strength of the.un-.
derlying peridotite would still'be Tow because temperatures •
would continue tp remain high. Tapponnier and Francheteau
[197i8) calculated Ihal at adistauce pf 15 to 20 km from a
spreading ridge,Memperatures; of 900°C would occur at a
depth of approximately 10 km, and the depleted harzburgite
would have a stress difference of less, than 10 bars. An estimate
of the stress in detachment-metamorphic rocks at the
base of the pendolite is about 1500 bars [Boudier. and Coleman,
1981] It is uncerlam how long these conditions of high
COLIMAN OMAN OPHIOIITL TICIONICS 2505
' temperature and low strength would prevail, but if continental
collision between Arabia and Eurasia took place shortly after
spreading ceased, the area near the ridge would be the weak-
, est zpne either within the newTethyan oceanic crust or within
the.older conlinental plates thus could provide a weak plastic
• zone for detachment and metamorphism. .
;As Eurasia continued its closure,against the Arabian plate,
the overlying Hawasina sedimentary deposits may have become
detached and moved into the foredeep along the Ara-
' 'bian margin, perhaps as that edge moved under the oceanic
'crust. As the detached hot oceanic crust was thrust ,southward
oyer cooler oceanic crust, its bottom temperatures were further
sustained by frictional heating. Finally, it came to rest on
'top of the Hawasina Grpup, and its metamorphic aureole was
vvelded toThe bottom of the peridolile [ Woodcock and Robertson.
1911-, Ghent and Stout, 1981], Turonian (90 m.y.) K-Ar
.ages on the amphiboUte formed during detachment indicate
that detachment coincided with initial formation of the foredeep.
The ophioUte nappe inovement following detachment
could have been continuous or sporadic. However, no evidence
exists of the lime required to emplace a nappe of such
proportions, either by gravity sliding or by tectonically drawing
the Hawasina Group along with the Arabian continental
margin beneath the ophiolite.by plate convergence. The ex­
tensive laterite on the Samail ophiolite apparently formed after
detachment and either before or after final emplacement
of the pphiolite, (Figure 6). Because laterites can form only
subaerlally,; the d

c
2.SU0 C0LIM\N OMANOPHIOIIH rLCIONl'CS
mail nappe, serpentinite melanges are found directly under
the Samail peridotite, and often these overlie;a volcanic melange
made up of agglomerate, pillow lavas, gabbro, and pe­
plate along the Makran coastline. Formation of a flysch accretiunal
wedge beginning in the Eocene continues today within
the active subduction zone marked by the Makran continental
slope and by the remnants of Tethyan pceanic crust under-
ridotite in a tulfaceous tnatrix.'None of these melanges ap- =
pears to be the direct-product of deep-seated plastic , lying the Gulf of Oman (Figure 6). The active arc volcanism is
deformation in a tectonic .situation, such as an active sub-, •some 450 km north ofthe subduction zone trace in the Gulf of
duction zone. In fact,.the Hawasiha.happes show progressive Oman [Jung et ai, 1976]. The moderate present-day seismicity
northward disruption that may ;.be-a product of plale con­ marks a shallow-dipping thrust zone [Jacob and Quillmeyer,
vergence combined with gravity,: sliding. Furthermore, the, - 1979], Late Cretaceous ophiolites with calc-alkaline lavas and
complete ab.sence of conteniporaneous calc-alkaline ypl-! dikes,, which occupy the inner margin ofthe Makran flysch, ;
canism on the Arabian-plate rules out soijthward subduction.. appear to have marginal basin or island arc alfiiiiiies. In those
The small volume of calc-alkaUne volcanic rocks in the Hawa-; places the association of the ophiolites with blueschist derived
sina sedimentary deposits does not reqtiire a southward subr./ from Late Cretaceous sedimentary deposits as well as the
duction, and those volcanic rocks that, extend back to,the Tri- , presence of volcanic rocks demand a metamorphic and ig­
assic may be the prpducts of graben-hprst-related volcanism ' neous history, distinct from the Samail ophioUte. Further incharacteristic
of early opening of the Tethyan Sea [Glennie et .' ..vestigalions are required to fit;the Makran ophiolites into the
ai, 1914]. '••'P^Ppfpt''y''•^[p'd•''•^••d•:•: • • '< •'•'-^•tectonic
history of the region: • .
The geologic evidence;,points to a possible two-stage em--. •
;Y •',
placement of the Saniail ophiolite; early detachment of a hot::
DISCUSSION OF E.MPLACEMENTMODEI-S
.slab along weak zones of a still-codling spreading center, com- o; "Anyone knowledgeable of Oman.geology wiU realize that
bined with formation of a metamorphic aureole at the base of'• - any summary of the regionallectonic setting is dependent on
the ophiolite. Continued plate convergence and upwarping of .the data of numerous geologists. Several of the more recent
the Tethyan oceanic floor along an Arabian margin as well as reports concerning the emplacement ofthe Samail ophiolite
oaset of erosion and later fprmation of laterite on the ex-',; , and their, relation lo our present state of knowledge are com­
humed and eroded pphiplilefmark the early stages of emplace-^ , mented on below. . : :-, "
ment. Finally, a'combination pf gravity sliding (as suggested {.Smith and Woodcock [1976].proposed that serpentinization
by the Hawasina melange) southward into the foredeep.along;; /ofthe mantle under a strip of the:Tethyan Sea marginal to the
the Arabian margin and progressive convergence of the now-lj; contineint would induce uplifl by expansion. With this elevat­
sinking continental edge under the oceanic crust has.moved' ing mechanism, slabs of oceanic crust and associated sedimen­
the Samail ophioUte to its.final resting place (Figure 6). No di- , tary deposils could then gravity slide onto continental mar­
reel evidence exists on the distance of the total convergence, gins; Sm^th and Woodcock, [1976) argued that enough
but Glennie et ai [1974] estimated hundreds of kilometers, and serpentinization would result from, dehydration pf a suiking
a minimum of at least 165 km is indicated by the maximiam slab being subducted along the same margin. No quantitative
exposure width'olithe Samail ophiolite.-
figures were given for the amount of vertical uplift required to
Evidence for; subduction along the Eurasian plate during initiate gravity sliding, bill in the case of Oman it was esti­
the initial closing of the Tethyan Sea, beginning in the Turomated that at least 3 km of uplift would have been required to;
nian and extending through early Eocene, is missing. This ap­ elevate the oceanic crust from abyssal depths (3 km). The apparent
lack of subduction induced deformation, uplifl, de-'. parent absence of southward subduction along the Arabian
tachment, and convergence within the Tethyan oceanic crusi. plate during the Late Cretaceous certainly precludes serpenli-
The formation of fpredeeps along the Arabian continental nization/expansion as an alternative hypothesis for emplace­
margin suggests several possible mechanisms for emplacement.' ment of the Samail ophioUte: y >;':,; ;';•,;
of the Samail ophiolite. Thei low freeboard of the continental . Welland and Milchell [1977] suggested another model for
margin, combined,with the elevation of the ophioUte during emplacement of the Samail ophiolite: southward thrusting of
detachment'at the spreading.ridge, could initiate southward pceanic criisi over the Arabian plate during consumption of
gravity sliding of the detached.ophioiite and overlying pelagic crust in a; nonh dipping subdiictipn-zone.. Their model re­
sediments. Also, the submergence of the north margin ofthe quires that' northward, subduction be established before em­
Arabian plate, could be related to underthrusting or underplacement and that tectonic stacking take place within the acdrawing
of the ,«iontinent below the pceanic,crust by plate .concretionary wedge of this subduction zone. Tectonic
vergence. •:••'•• ••• ; '• . ': -y-y'v'- .4'-;.' •'•''..':• -•'-'•', emplacement of oceanic lithosphere within the accretionary
Appearance of continentail margin volcanism in Iran during, prism is visualized as the shearing ofl" of large fragments of
the Eocene demonstrates that northward subduction of tbe oceanic crust by high-angle north dipping reverse faults or by
Tethyan oceanic crust did not reach mantle depths until,.that underthrusts in the accretionary wedge, so that oceanic crust
time [Forster et dii 1912; Jung et ai; 1976]. Therefore during ' intrudes sedimentary deposits of the accretionary wedge. This
the Late Cretai;eous and Paleocene deformatipn, detachment,
model does not account for the formation of laterite on top of
gravity'sliding, -and convergence of Tethyan oceanic crust
the Samail ophiolite nor does il explain the meiamorphic au­
were the dominant,forces.- The nearly synchronous emplacereoles.
However,' the younger'ophioUtes interior to the Makment
of Tethyan oceanic crust in many; areas (Cyprus, Gizil
ran accretionary wedge could easily represent the tectonic sit- •
nation iUustrated in the Welland and Mitchell model.
Dagh, Neyriz) on the passive margin of the Afro-Arabian
plate can be accounted,for by the apparent absence of north­ Brookfietd [1977] in a review of the emplacement mechaward
subduction during that time. ;.
nisms for aU Mesozoic and Cenozoic ophioUte nappes sug­
Alter emplacement of the Samad ophioUte the Telhyaii gested that a subduction zpne was formed within the Tethyan
oceanic crust began northward subduction under the Eurasian Sea. that had a large component of transcurrent fault move-

c
C:
ment oblique lo the Arabian plate. Small amounts ofcaJc-alkaline
volcanic rocks in the Hawasina Group.provide the only
evidence for this possible subduction complex in the Tethyan
Sea during the Late Cretaceous. According tp Brookfield, continued
subduction .and transcurrent movement, brought the
Arabian plate into this oblique subduction zone, where it was
downwarped. Continued' underthrusting created south di-
- COLEMAN: OMAN OPHIOLITE TECTONICS 2507
margin, along wilhtectonic convergence and underthrusting
of the continental margin. The other reports in this volume
• present detailed facts that tend to support this picture ofthe
:, general, petrotectonic evolution ofthe Samail ophiolite.
;;. Acknowledgments. Jl is difficull lo produce a getieral paper in an
: area where the geology is complex and not yec fully understood. I
have had considerable help and encouragement in this task from nu-
recled nappes of Hawasina. sedimentary deposils and em-, ' • merous colleagues. In particular, I thank ClilTord Hopson and John
placed the Samail ophiolite: onto the Arabian continental !,; Pallister ofthe University of California, Santa Barbara, Robert Gregmargin.
A transform fault could have been present then, as ,' 'ory ofthe California Institute of Technology, and Edgar Bailey ofthe
pointed out by SmUli [197 l]i butiittle evidence exists for sub­ y 'U.S. Geological Survey, Menlo Park, California—all of whom partic;.^
. ipaied in a joini NSF-USGS projecl wiih me in Oman, both in the
duction or island arc; activity within the Tethyan Sea at; that
.; (ieJd and later in stimulating discussions. Glen Brown of the U.S.
lime. . 4;^y.,:...d'-'\p^'''y,j./dP'-dl^-' -'-;-„;;•;>'•,."•-';-, .' Geological Survey, Reston, Virginia, provided insights towards my
Gealey (1977] in iiis'variation dfj8/-o^e/

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1
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y
I
251)8 COLLMAN OMAN OPHIOLITE TKCTONICS
Oman Mountains and adjacent areas, Geol Soc Amer Hull, Hd,
1183-1191, 1977. ' • * - . ' ••'
Ghent, E, D., and M. Z. Stout, Metamorphism at the base ofthe Sa- :
. mail ophiolite, southeastern Oman mountains, J. Geophys. Res., 86,
this issue, 1981. /::••,. ,'-: >,....'' ,V'--'-. :• .- -. • .;
Glennie, K W., M.G, A, Boeuf, M:'w. Hughes-Clark, M. Moody-
Stuart, W. F. H. Pilaar, and B. M. Reinhardt,,Late Cretaceous nap-,.
;: pes. ill the Oman, Mountains arid-.their.geologic evolution, Amer. ..
, As.s. Petrol Geoi Bull,,57,.5-21, I913r ' ' . : : «:
Glennie, K.;W,;,M:G, A.,Boeuf, M.,W; Hughes-Clarke, M. Moody-
Stuart, W; F; H. Pilaar, and B; M. Reinhardt, Geology of the Oman
Mountains, Part One:rrext),,Part Two (Tables and Illustrations),
. :. Part Three {Enclosures)^ i(on:Ned..,Geol,Miinhouki4ndiaGenoot.
•" ' yern., .?y; 423,vl974,:--.:'-;%3t>'-i':''; :-• •'•':/••'•:('•': .. -.'•' .'.;:v.^'-'•/>•-
Greenba'um, D!,; Magmaticiprbcesses at'ocean ridges and evidence:
from ,the;Tr(x)dOs:raa,ssif, Cyprus,.lAfatuz-e ,/'A>'i. Sci,, 2iS, 18-21,' :
llopson,.C:.'A., and J.,S: Pallister,'Gabbro sections in Samail ophiol-'-'
lie, southeastern Oman - Mountains,; Geol Soc. Amer.: Abstr: .Pro-'
gram-10,424; m8':.,]..f;-dyy.:i':.,f.':'' ..:••;•.. ;-^'."'-. ,-;-:.'. .':,'
Houshmand-Zadeh,".A.\. Ophiolite's of south; Iran and their genetic
prtiblems, preliminary'refKirty-.Geo.L'Siirv, Iran, Tehran,; 1977, .
Jacob, K. H.v and.R.Li.QuiUraeyer,.The Makran region of Pakistan ;
and.Iran: Treiich-arc system,with active plale subduction, in Geody-
nurj(«o/faAK»a/i,editcdby A.Earahand K.-A. De Jong, pp. 305-.:,
317, GeologicafSiirvey';of Pakistan,'Que.Ha, 1979, ' '.:•.. ,:;/,.
sique-ullrabasiquc du Kizil Dag (Hatay, Turquie), Sci Terre, 18,
143-172, 1973.
Pearcc, J. A., Ba.salt geochemistry used to investigate past tectonic environments
on Cyprus, rec/onop^^'rici, 25, 41-67, 1975.
Powers, R. W., L. F, Ramirez, .C. D. Redmond, and E. L. Elberg, Ge-..
ology of the Arabian Peninsula—Sedimentary geology of Saudi
Arabia, U.S. Geol.Surv. Prof. Pap, 560rA D1-DI47, 1966.
Reinhardt, B, M., Oii the genesis and emplacemerit of ophiolites in-
',f the Oman Mountains geosyncliiie, Schweii,.Mineral Pelrogr.,Miti.,
: 49, 1-30,1969. •'•'.' ]•:':'••• .'rdy^^^--'-^ ^-y\; • ••' •
Ricou, L.-E.,,Le croissant-ophiolitique.peri-arabe;"une ceinture de
- nappes mises in place au Cretace superieur, Rev.- Geogr. Phys. Geol
•' Dyn.; 8,.321-'i49, 197}.y ''d •:'; "'•'' \;':'';'' -'"• ''.''•''
Ricou, L. E., Evolution structurale des zagidesde la region clef de
. Neyriz (Zagros Iranien),'>Afem. Soc. Geol. Fr,'125. 140, 1916.
Ricou, L. E., J. Brand, and 1. H. Brunn, Le Za.gfo$,'Mem. Hors. Ser.
• SocGeol fr.. 8, 33-52, 1977.* ; ,:.-.;^;:, •' ' • . .:. '^- .. ; '
Schmidt, D. L., D, G.'Hadley, and D. B. Stoe.ser, Late Prolerozoic
crustal. history of the Arabian shield, southern Najd province,
, 'Kingdom of Saudi Arabia, Saudi Arabian Prof Rep. 251, p. 44, U.S.
'GeoL Surv;; Reston, Va., 1978..;. ;:'•; .;':>. .J .. J.
Smith, A. G., Alpine deformation of the'oceanic areas ofthe Tethys,
Mediterranean, and Mlanlic, Geol Soc. Amer. Bull; 82, 2039-2070;
• ',1971, , '•;; y,y .y , : ".;^:, •
Smith; A. 'G., and J. C. Briden, Mesozoic and Cenozoic paleoconii-
,, nental maps, 63 pp., Caiinbridge University Press, New York,, 1977,
Jung, D., M; O; C.'Kursten.anii M: rTarkin;Post:Mes6zoic volcanism ''• Smith',; A. G., and N! H. Woodcock,'-Emplacement model,for some -
in Iran and its relation to the subduction ofthe Afro-Arabian underv : ',;:'Tctbyan'ophiolites, ';;/;:
the.Eurasian plate^.in'/f/ar Between Continental'and Oceanic Rifting, '• Sonnenfeld,,?., Eurasian ophiolites and.ihe Phanerozoic Tethys Sea,
, vol,.2;,edited'by A,;Piigetrrand^'ran,M979c. .-.:. dSoc: Amer. Bull. S8;mi-10»&, 1911. '--''"'
McCulloch, M. -T.;. A' Nd-lisotoptc study of the Samail ophiolite, Eos :.:> :Whiie, R. S;,' Deformation of the Makran continental margin, in
Trans. AG.U..6g, 963, 1979.^^.,:::':.'!; 'yd'.-:'} .y,, -':.• '\y .'.'. J'y'dp .•'Geodynamics of Pakistan, edited by A. Farah and A. DeJong, pp.
Moody.'y: ,p:, Late Cretaceoiis happesiii Ornan^Mounlains and their'' 295-303; Geological Survey of Pakislan, Quetta, 1979.
geologic evolulibn; Discussion;'X»ier.''>

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 86, NO. B4, PAGliS 'ly-l ^.V; j. .Al'KlL I'), 19X1
Metamorphism at the Base of the Samail Ophiolite,
Southeastern Oman Mountains ,
EDWARD D. GHENT AND MAVIS Z. STOUT
Department of Geology and Geophysics, University of Calgary, Calgary, Alberta, Canada T2N 1N4
Metamorphic rocks, showing an inverted meiamorphic zonation from upper amphibolite facies to
greenschi-st facies, occur beneath the Samail ophiolite. The metamorphic protolith was a section of marine
basalts, Mn^rich cherts, and argillitcs. Garnet-clinopyroxene amphiboliles occur within 2 m of the
contucL hornblende-clinopyroxenc as.scniblages occur within 80 m ofthe contact, and lower amphibolite
facies rocks persist to 130 m from the contact. The higher-grade rocks show polyphase deformation, cataclaslic
fabrics, and partial retrogression lo greenschist facies assemblages; however, lower-grade phylliles
show evidence of only one episode of metainorphic crystallization. Unmetamorphosed sediments in contact
with the basal meiamorphic sheet do not show evidence of polyphase deformation. The distribution
coelficicnt K,) = FeO/MgO gar/FeO/MgO cpx ranges from 4.4 lo 5.3, suggesting a 7" range of 755°-
»65"C at 200 MPa, Low jadeite conlenl in clinopyroxene and low glaucophane content of Ca amphiboles
arc consistent with moderate pressures of crysiallization. The meiamorphic sheet is inferred to be of composite
origin. The highest-grade rocks were tectonically transported ihe greatest distance, and the lowergrade
rocks were successively incorporated into the sheet as the peridotite was thrust over progressively
cooler rocks. Residual heat from the ophiolite is the dominant heal source for the metamorphism, and
this could have been augmented by a limited amount of frictional heat generated during thrusting. These
thermal constraints suggest that the metamorphism occurred eariy in ihe tectonic transport history of the
Samail ophiolite.
INTRODUCTION
The ba.sal contacts of many allocthonous ophiolite complexes
are characterized by the presence of thin subjacent
sheets of relatively high metamorphic grade [Williams and
Smyth, 1973; Coleman, 1911; Woodcock and Robertson, 1977).
The meiamorphic rocks always lie in a similar structural position
along, or near to, the contact ofthe ophiolites with underlying
sedimentary and volcanic rocks. The metamorphic rocks
are directly overlain by ultramafic rocks or ,scrpeniinized ultramafic
rocks, never by higher levels in the ophiolite .sequence.
The maximum metamorphic grade reaches upper amphil>oliie
to hornblende granuUte facies, and the grade rapidly
decreases structurally downward. Although these metamorphic
rocks have been reported from a number of weU-known
ophiolite complexes, few detailed data on mineral chemistry
and interpretation of/*-7'conditions attending metamorphism
have ben published [Coleman, 1977,-pp. 114-117].
Sheets of metamorphic rocks are well exposed in a number
of localities along the basal contact ofthe Samail ophioUte in.
the Oman Mountains (Figure I), providing a particularly
good area to study metamorphic rocks a.ssociated with ophiolite
complexes. The purpose of this paper is lo present a detailed
geologic map of a part of the basal contact of the Samail
ophiolite; to discuss the structural relationships between
the Samail ophiolite, the basal metamorphic rocks, and the
adjacent unmetamorphosed strata; to document the mineralogy
and petrology of the metamorphic rocks; and to interpret
the conditions of pressure, temperature, and fluid composition
(P-T-X) accompanying the metamoiphism Finally, we briefly
consider the implications of the melainorphism in the light of
ophiolite emplacement and plate tectonics.
Previous Work on BasaiMetamorphic Rocks
Below the Samad Ophiolite
Glennie et al [1974, pp. 239-241] described sheets of metamorphic
rocks, up to several hundred meters thick, inter-
Copyright © 1981 by the American Geophysical Union
Paper number 80B0486.
OI48-0227/81/080B-0486$OI.OO
calated between the Samail nappe and underlying sediments.
They pointed out that these metamorphic sheets are discontinuous
and are not everywhere found between the Samail
nappe and the underlying sediments. They divided the metamorphic
rocks into two .series; (I) a monometamorphic, greenschist
facies series consisting of melamorpho.sed cherts, siliceous
shales, and basalts similar to those of the Hawasina
Group and (2) a polymelamorphic series consisting of amphiboUtes,
quartzites, and calc-sUicates. The earUer, highergrade
metamorphism of the polymelamorphic rocks was said
to be hornblende granuUte facies, and the later metamorphism
was greenschist facies. The higher-grade rocks occur near
the base ofthe ophiolite, and Glennie et al [1974] stale that
these metamorphic rocks are in thrust fault cpntact with the
lower-grade monometamorphic rocks. ,
Alleman and Peters [1972, pp. 679-681] also describe two series
of metamorphic rocks in the northern Oman Mountains
and briefly discuss earlier interpretations of this metamorphism.
Their description of these rocks is quite similar to that of
Glennie et al [1974], and they report K-Ar ages on the lowergrade
metamorphism of near 83 ± 5 m.y. They also state that
the contacts between the Samail ophiolite and the metamorphic
rocks and between the metamorphic rocks and the
Hawasina sediments are tectonic contacts.
Scope of Present Study
Preliminary field investigations of the basal contact of the
Samail ophioUte were made by Bailey and Coleman in 1975.
During the 1977 field season, several parts ofthe basal contact
were studied, and R. Coleman and R. Gregory made a tape
and compass map of the 'Green Pool' area in Wadi Tayin
near.Mahlah (Figure 2). Ghent used this latter map as the
basis for his field work in January 1978. In addition to the
Green Pool area, Ghent visited the basal contact of the Samail
ophiolite in several other areas in Wadi Tayin as weU as
near Ibra (Figure 1) [Bailey. 1981] and outside of the present
map area. Although the section at the Green Pool is con-
2557

• i f '
i-'^
i (JtiiiNr AND Siour: MI-IAMOKFHISM AI- BASI; ot- SAMAU. Oi'iiioi.iri;
• • • p \
\st,^ Mizbar ^ ^ ^ , Jl\\ V
f~^ METAMORPHIC SLAB
1 1 PERIDOTITE
0 5
L.—A.—1.,, i * ,1
1 KILOMETRES
GENERALIZED GEOLOGIC MAP OF PART
OF BASAL CONTACT OF SAMAIL OPHIOLITE
^"^A,,^ A]i^ Hammam\j>
X
T / ^
WAD
y
i
1 TAYIN
GREEN POOL AREA
/
/ 58''36 E
— — 23°05 N ,
Fig, 1. GeneraUzed geological map of part ofthe basal conuct ofthe Samail ophiolite showing the distribution of metamorphic
slabs and localities referred to in texL The geology is simplified after jSai/e^-(1981).
sidered to show The most complete section of metamorphic
rocks, we have used samples and, observations from these
other areas.
FIELD RELATIONS AND AGE OF METAMORPHISM
Stratigraphy and Structure
The contact between Ihe Samail ophioUte and the basal
metamorphic rocks is well exposed at the Green Pool area in
Wadi Tayin (Figures 1 and 2). The contact between the metamorphic
rocks and the basal peridotite is sharp, and the foUalion
and/or bedding in the meiamorphic rocks generaUy dip
toward the contact (Figure 2).
The section at the Green Pool area, Wadi Tayin, jjroceeding
structurally downward from the contact between the
metamorphic sheet and the peridotite, is as foUows: (1) amphibolite,
foliated to gneissic with compositional layering,
dominated by cataclastic fabrics, garnet present within 2 m of
contact, map unit approximately 30-40 m thick; (2) interbedded
metachen-phylUte, interlayered with amphibolite (1-2
cm (-H) thick) at top of section, contains muscovite-piemontite
± Mn garnet, map unit approximately 20-25 m thick; (3) finegrained
amphibolite with interlayers of metachert, map unit
approximately 60 m thick, grades downward into unit 4; (4)
greenschist and Ught green phylUte to slate, contains lenses of
ironstone (1 cm thick) and chert, thickness not known; and (5)
Hawasinai Grotip maroon to green argilUtes and chert. The
contact between units 4 and 5 appears to be gradational, but
in other localities in Wadi Tayin the contact is sharp and appears
to be tectonic (C. A. Hopson, personal communication,
1979). Veins of piemontite occur within Hawasina Group
chert, over I km from the peridotite contact in nonschistose,
apparently little metamorphosed samples. The sequence of
metamorphosed basalts, Mn-rich cherts, ironstones, and argil­
Utes is interpreted as having been deposited under marine
conditions.
Foliation in the amphibolites adjacent to the peridotite contact
is approximately paraUel to the contact, but locally, the
foliation is truncated by the contact, indicating movement
along the contact after the formation of the foUation. In the
Hammam area (Figure 1) Uthologic layering is truncated at
the contact. In addition, different metamorphic liihologies
other than high-grade amphibolites occur in contact with (seridotite,
that is, green phylUtes, near Hammam. UUramafic
tectonites (mylonitic peridotites), now partly to completely
serpentinized, are always in contact with the metamorphic
sheets; higher parts of the ophioUte complex are not observed
in contact with the metamorphic rocks. Metamorphic sheets
are missing along much of the length of the basal external
contact of the Samail ophiolite (Figure T), and the basal peridotite
is in contact with Hawasina Group melange.
At the metamorphic sheet-peridotite contact near the
Green Pool, pods of rodingite are elongated parallel to the
contact, and veins of xonotlite cut the adjacent amphibolite.
Epidote and calcite veins are abundant, and the typical occurrence
of these minerals is as coatings on joint surfaces normal
to the foliation. In thin section, xonotlite veins are observed to
cut both epidote veins and metamorphic clinopyroxene.
In the Green Pool area, compositional layering in the amphibolites
is isocUnally folded. Axial planes of the folds are
approximately parallel to the metamorphic sheet-peridotite
contact and are approximately parallel to bedding in the adjacent
chert-shale unit.
According to Boudier and Coleman [1981] the fabric in the
basal mylonitic harzburgites is the same as that in the underlying
metamorphic sheet. Quartzites (metacherts) are foliated,
and quartz c axis fabric diagrams show a strong stretching lineation.
Boudier and Coleman [1981] interpret this fabric in the

c:
f-'
r -
:GHENT ANO STOUT; MHTAMORPIIISM AT BASE or SAMAIL OwiiOLiri-- 2559
The basal meiamorphic sheets and several kilometers of the
peridolile section are cut by diabase dikes [Hopson el ai, 1981).
According to J. E. PaUisler (personal communication, 1979)
i these dikes are high in TiOj and faU on the midocean ridge
Jbasalt (MORB) trend of ^wn and Nesbitl[l91S] with respect to
CaO/TiOj and AljOj/TiOz plots and are transitional between
the MORB and oceanic island'fields on TiOi/PjOj plots.
These dikes are fresh in relation to the sheeted dikes and are,
not deformed. These relationships suggest that the mela-
,morphism'occurred at a time.at which basaltic magma was,
still available beneath the ophioUte sheet and that the meta-.
,inori>hismtc)ok place when these rpcks were sliU in an oceanic:
.'ienyircnuaenCy''''d/ddyy^dydy -"d r •:,'•:• 'd'- _
!; \ln tectonic melanges hear Rustaxi and theHawasba window;,
slabs of metamorphic rocks, occur as part of; the Hawa-
; sina mdahgC; This fact indicates that inetamorphism at the
basal contact of the Samail ophioUte occurted prior to the
vproduction.of the melange [Hopson et al...19%\\. Glennie et al.-
, [1974, p: 239) also repori the occurrence of'slices of the meta-
V moiphic sheet'in the'OmaJi Mdlange." •
:The Samail ophioUte is unconformably oyerlain by Maestrichtian-Tertiary
shallow-water limestones, providing a mini-
; mum age for the emplacement of the ophioUte. Amaximum
age of emplacement is given by Campanian .sediments which .
underlie the ophiolite [Glennie el ai, 1974). •;
'Tilton el ai [1981] have measured uranium-lead agds ranging
from 95 ± I to 98 ± I Ma dn.zircon from eight samples of
; plagiogranite from the Samajil ophioUte, suggesimg igneous
; crystallization of the ophioUte in late Albian time. . -'.
. K-Ar age» on the basal Tnetamorphic sheets have been reported
by Allernann and Peters\\9i2]. Biotites from the,poly- .
metamorphic series and from the monometamorphic series
;•;;-•• r~l.{''»«f Mna^niryy^l] ::y.y^yMn:::.y ••;]:., '•;r
yield K-Ar ages of 85 l: 5 and 87 ,±5 Ma, respectively [Laniphere.Vm].
':'.'' '-r.^d y.'pp,P'-:: y" • P\
• ,'•• ^';o,««i«;«»ipi,Hi~>S';^:#f'^r^'r^ >':»«ir»r«. ;''•' ..;;:;;':; Hornblendes ifrom withiii 5 in, of the peridotite contact and
-rri MatdclMrt^ ;V'' J'!'V':''.,'»..!;£r
'-' r--n -^ '.-,.;•'-'-''.-;'-'-'---.,.-'- ",.,^^2lJ Trfnd,ond piling* of lin»al«n ' .*' .: ' 1981). The highest-grade rocks hiaye ages which are only
[••JJi ,Piriiioii»'.-;_;-,.j,,;.,.,-.'.-;;i-., ,i|.;,:;;;,.,..r,,. . •- . • ,,-•-• ...,- , ,-. --.•-,-
--.»-»- , .^ ;,-,'-•' -.'; ?.,''V;.-.'.\', A,n 'Sompfo Mcotion and lOfitpIo nuntbdrt ffforrad *
-.-:'H3 "*tan«. ,.;,..,;.;;;„ ..;..-v,.. ,;,•«>,„ in ,^,;.. .;. • ;i/-, •. ^- -..-:-,' .. sUghlly younger than the crystallization ages of the Samail
: ::'•:•- ..•' -'.-; .,• ;':; :v-:.'..;.',:lv-'frTn-- ' "• "-' .-'"•;-.-"- ••' • •- ? ophiolite, suggesting thai detachment of. the ophiolite oc-.
:.•;•'., .«;.,i,-, J,-.t ;;;.'-;-:-j;.,.,;;v-'v.'^-.•,*°*^- '.'•..: ;: ''•.-, ' ' '' - .
-, Fig.:2.'.-; Gisologic map,and;cross section bf the. Green Poof area,.
Wadi Tayin (geology by Coleman and Gregory in 1977; additional
geology by Ghent in 1978), Samples with numbers less than 100 have
the prefix .78-G (e.g., 78-G-7),:and samples with numbers greater than
100 have the prefix.C (e.g,,:;Crl34?l)...These prefixes are omitted for-
'daniy.[^\p'p:p:Cp:yppppp:, ••'•;':',,:,^,'.'. ..'. [ -. ':.''•' •'.
harzburgitek as being dueVto'a low-iemperalure/high-stress
deformatioii associated with suboceanic deiachmeiit of peridotites
over oceanic crusL;,^*?^''-•-•,;;;,•- .'".' ^ -•-- —•,.:••''..''"':.'••
Superimposed upon the structures produced durug pene­
trative isoclinal folding are structures associated with more
brittle deformation. Steep faults offset amphiboUie-metachert
contacts (Figure 2), and kink folds (up to 0.5-m amplitude)
are particularly well developed in phylliles. Quartz veins are
thickened (from about 0.5 to nearly 2 cm thick) in the hinges
of some of these folds. Fold axes generaUy plunge gently to
•the south and east (15°-20° (Figure 2)), and axial planes have
•variable orientations but are generally steeply dipping. Some
: kink folds are asymmetric and show southward vergence. The
adjacent Hawasina Group cherts and argiUites do not show
evidence of the polyphase defprniatiorL, .:
, Age of Metamorphism ••^--:;-; ';;'

256U
lOiinNTAND STOUT: MtTAMOKiniisM AT BASI-or SAMAIL OI'IUOLITI-.
-TABLE 1 Mineral Assemblages in Amphiboliles and Greenschists From Basal Meiamorphic Rocks,
Samdil Ophiolite, Oman
Sample
0^3
G-7
G-13
G-20
G-21
G-22
G-24
G-25
G-26
G-27
G-32 ••
G-53
G-6JB
OM-2 lie
OM-217
C-139.1
C-153-1
hb
X~
X
X
X
X
X
X
-X
X
X
X
X
X
X
X
X
ga
"x~
X
X
X
X
X
X
cpx
x~
X
X
X
X
X
X
X
pi
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
cp
X
X
X
X
X
X
x»
X
X
X
X
X
X
X
act
X
M
M
M
M
M
M
X
X
X
ch\
X
X
X
X
X
' X
X
X
X
Oii-
X
X*
bi
M
il
X
X
: X
r ; ' "
'' 'X;
V
; '. .
• .'X-:-
' ''X-'.'
- x'
:'^.:X'
X.
sph
X
y-.:X ,
•'' X:
':P\
^-x-;'
-'\.X'^
X
;~'X"
;-'Xl'
••KXV
('-.' -v; . • -^"(
VX--
• / . '. .• •
rui
.'*• '
-.,7/^-
'•d^\.
-.'.' • ,^-" -,
. ••--. V
t: ' '•••':
•''.;•* ' ' ' '
;-.;^ X -,
f'X-,; P^ '.•
''d''
pyr
-.
•:,x
;,,;':.
' ' " : - . - •
';•'."•;. .
.;.:"' :
• ' . , . : ; , - :
•:-'' .'-
The dbtevidtions used ate as toUows hb, hornblende, ga, garnet, cpx, cUnopytoxeac; pi, plagioclase;
cp, cpidoie, act, actinolite, chl, chlonie, qz, quartz, bi, biutite, il, ilmciiite, sph, .sphene; rut,, rutile; and
pyr, pyriie X means present, and M means minor « •,•;;. :tv.! : .;.
' 'Veins - ' '. Ji'.-t;.M'V";.>.'y'-:-'V"-
plagioclase-nch layers on the scale of 10-15 cm Amphibole
crystals lend to be stubby and he m the foliation plane, but
megascopic mineral Imeation is only rarely observed No relict
Igneous icxtures have been observed, ihe amphiboUies are
thoroughly recrysullued meiamoiT)hit tectonites In ihin section
the effects of po&lcrysiaUine deformation are obvious
Amphiboles have streamlined ('fish') shapes and arc elongated
in ihe plane of fotiatton Larger amphibole crystals often
have smooihconlatas with adjacent grams but locally ate
cut by bands of finer-grained, strained amphibole of different
optic orienuiion.,Maiiy,amphibole crystals are cut by microscopic
veins of epidote and calcile.. Most amphibole crystals
show shadowy extinction, and some crystals exhibit polygonal,
Most of the amphibolites show patliaT retrogression to
greenschist facies In some samples (7 8-G-32) the retrogression
IS not associated.with extreme caiaclasis: Coarsegrained
medium green hornblende is in ooniaci with coarsegrained
blue-green aainoUte (Table 4). Epidote is abundant,
and smaU amounu of lepidoblasiic Mg-rich chlorite are present,
Plagioclase ts partly aiiered to sericite, but where il is
fresh, oUgoclase (Aiiji) istiramed by albite (Anjs). Albite also
,;Occiusabdiscrele.grains.v ';;• ; : ,: : ^. .
f : A gradational contact between .coarser-grained schistose lo
: gneissic amphibolites and' finer-grained amphibole schists
(called greenschists on the map) has been mapped (Figure 2).
Some oflhe rocks mapped as greenschists (78-G-63B) contain
structure.-LocaUy extreme defprmaiion has produced giains
: "hornblende (Table 4>-pla^pclase (An^)-epidote with smaller
orequahi.sirained, amphibole (up lo 3 mm in size) set in a
amounts of bluc-grcen actinoUte wid albite. The wide range in
groundmass of finergra^iiied amphibole, feldspar, and chlorite:;
- grain size pf strained amphibole,; epidote, and. plagioclase over
Amphibole grairis commonly;show.color,zoning, and the typidistances
of a few/milUmcters;suggcsis the possibiUly that
; cal sequences from thie ijuier parts of crystals lo the marg,in& of. • these rocks have suffcred.arieduciion in grain size through
crystals arc brown i*;,greca-r* blue-green, .; • ;: , ,;; 4'cataclasis.-.-,,. . •• P\'y\.;;' '''••..•-:'"-'\r:-'d'' • '" '
Meiabasite garnets, with,a maximum grain size of, 10 mm, ' Fine-grained green amphibole scluits and phylUtes (78-G-
have not been observedJmore.than 2 m from ihe' peridotite j 13) contain chloriie-green hornblende; (actinoUle)-epidote-
contact. These garnets; usually do not show crystal faces and quartz-albiie-calcite,;; Discontiaudus. plagioclase-quartz cal-
contain inclusions of^;cU»ppyroxene, brown hornblende, ilme-, clte-rich layers and pods alternate with araphibole-epidolenite,
sphene,, rutile^; pyrite, cpidptc, and chlorite. No internal , chlprilc-rich layers. The schistosily. is cut by calcite veins, but
schistosily defincdby inclusion trailshasbeenobserved: Garr some veins are also parallel, to, the schistosily. Biotite grains
net crystals arettypicaliy^ fractured and partly aUe;redlo,chlo- - are rare and are almost completely aUered.to chlorite. -
••riic'., '}.'-.p^'''Ppi'--:;/''-.yp-:. ;• •'•." ^-d :.-yP-.' ••]•:'.
CVmopyroxene; usually occurs as colorless to Ught green
equant crystals up.to I mm in.maximum dimetision. The py-
Chemistry of Metabasites of Baskiy
. roxcne:crysials;usually show strain shadows and sometimes
< Metamorphic Sheets ' ;• '-y y '
. , :
occur in aggregates of smaller crystals (e.g., sample 78-G-20) Chemical analyses of six arophiboUles and greenschists are
derived by caiaclasis of larger, crystals.. Clinopyroxene-hom- presenied in Table 2, "The mineralogy and the FcjOj, H^O
blende assemblages occur throughout the amphiboUte to dis-. (+), and COj contents of these rocks indicate thai they have
lances 80 m below the ophioUte cpntact (sample 78-G-27). been subjected to lowrtemperalure alteration. The problem of
Plagioclase?is commonly altered to a fine-grained turbid modification of original igneous chemistry has been discussed
mixture of sericite, >pidote, calcite, and opaques. It occurs by a number of authors [e.g., Beswick ctnd Soucie, 1978; Floyd
both in pla^Oclase-amphibple-cUnopyroxene mosaics as well and Winchester, 1975\. Some success in the characterization of
as in plagioclase-nch layers which paraUel the schistosily de­ tectonic environineiils has been achieved by the use of elefined
by amphibole,prefertcd orientation, Where it is fresh, ments, such as P, Ti,;Zr, Y, Nb, and rare earth elements, that
plagioclase commonly shows strain sht^dows, but lameUar are considered to be immobile during alteration.
twmnmg IS not often observed: . .. /' ;. ;;. ;, According to Floyd arui Witichester [19751 the majority ol

c
SiOz
TiOj
AI2O3
FejO,
FeO
MnO
MgO
CaO
NdzO
KjO
P2O5 '
H2O*
H2O-
CO2
Sum
Ba
Ni
Rb
Sr
V
Zn
Zr
Y
B
Co
Cu
Cr
Yb
GllINI AND SlOin MITAMORPIIISM AT BASI Ol- SAM ML Ol'IIIOLIIC 25;(ahalysts li: Ania and ^H
' '^U =5',^;'-,-A ::';,p';;; Survey Laboratories by C. Heropoulos arid B. King..' .,''•;•: •:- -. ; - " .'•''W.-;;--;-::•-4';-:.'' ";•.:•;•(„"•.;
• '• ?•;•': :;;r-5:',;,:;-*Analysts\reip«rl loss on ignition less ep^^^^ *V;-'''.;" , -,.,.:..:: ' ' '',
continental and oceanic .tholeiites have less than about 1.8 wt chlorile-muscovite-quartz in the Green Pool area, are consis-
% TiOj with,a nearly constantrTiQi/Zr ratio (TiOj X iO*/Zr. tent with lower greenschist facies ihetaniorphism [Turner.
~ |50).,Excepl for one sample (OM-222), aU of the other . 1968, pp. 271-274).
Oman basal metamorphic rocks have these chemical charac- ; -Fine-grained schists, phylUtes, and slates from the Green
teristics. •_. d\;'\-''-''.', ddp;i: \lp'' ;^;

,rt- iUAi
S1O2
T1O2
AI,0,
FeO'
MnO
MgO
CaO
Sum
Si
TI
Al
Fe
Mn
Mg
Ca
Sumt
Almandine
Spessamne
Pyrope
Grossular
t.'
TABLE 3 Electron Microprobe Analyses of Garnets From the Basal Metamorphic Sheet, Samail Ophiolite, Oman
G-3 G-22 G-51A G-53 OM-2UC1 OM-2nC2 OM-217 OM-314 OM-607 C-139-1 C-145 C-153-la C-l53-lb
39 0
02
20 7
23 4
15
48
114
1010
3 02
001
189
151
0 10
OSS
094
8 02
48 80
3 10
17 70
30 40
All analyses are in weight percent
•Total Fe expressed as FeO
fSum of all cations
38 7
01
212
25 1
09
64
78
100 2
300
001
194
163
006
0 74
0 65
8 03
5290
190
24 10
2120
37 8
01
20 0
17 2
14 6
41
43
98 1
3 05
000
191
1 16
100
0 49
0 37
7 98
38 30
3310
16 20
12 30
38 8
01
20 8
24 5
10
«2
88
1002
3 01
001
190
159
007
072
0 73
8 03
51 10
2 10
23 20'
23 60
>
39 0
^ 01
213
23 7
01
77
70
998
Number
3 01
001
194
153
007
0 89
0 57
8 02
Weight Percent
39 1
01
213
234
09
81
69
998
38 8
01
20 8
24 5
01
62
88
100 2
"«'
38 1
00
21 1
25 8
80
56
15
1001
of Ions on the Basis of 12 Oxygens
3 01 3 01 3 01
001 0 01 000
193 190 196
151 159 170
006 007 054
093 072 066
0 57 0 73 0 13
8 02 8 03 800
End Member Molecular Proportions
50 10 49 20 5110
2 20 190 2 10
29 00 3040 23 20
18 80 18 50 23 60
56 20
17 70
2190
4 20
38 4
01
21 I
27 4
52
54
30
100 6
3 02
000
195
180
0 35
064
0 25
8 01
59 20
1150
2100
8 30
38 3
01
21 1
27 6
09
58
66
100 4
2 99
001
194
180
006
0 67
0 55
8 02
58 40
190
2180
17 90
•,
37 4
01
19 8
17 0
156
48
26
97 3
3 05
001
190
1 16
107
0 58
0 23
800
38 20
3S40
1900
7 50
•11
38 9
0 1
212
24 4
9
54
96
100 5
301
OOI
193
158
006
062
0 79
800
5170
200
20 40
26 00
•1«fc-
39 2
02
210
24 1
12
44
10 8
100 9
304
001
191
156
0 08
051
090
801
SI 30
2 50
16 60
29 so
^ ^ *1 ..-t, t>*MI_
rr
z
-t
>
z
c
>
2
>

SiO
TiO
AI.O,
FeO*
MnO
MgO
CaO
Na^O
K^O
Sum
Si
Al'^
Al^'
Tl
Fe
Mn
Mg
Ca
Na
K
G-3
42 0
20
125
14 9
02
113
lis
20
05
96 9
r^ n
631
169
0 52
0 23
187
002
254
185
0 58
0 10
G7
400
09
14 3
20 3
03
80
120
19
1 1
98 8
6 08
192
0 65
Oil
2 58
004
182
195
0 56
021
-
G-13
46 1
04
90
16 4
03
12 0
IIS
19
03
97 9
6 84
1 16
043
004
2 03
004
266
183
0 55
0 05
All analyses arc in weight percent
•Total Fe expressed as FeO
TABLE 4 Electron Microprobe Analvses of Calcic Amphiboles From the Basal Metamorphic Sheet, Samail Ophiohte Oman O
G-20
41 1
10
13 6
18 2
03
95
122
19
10
98 8
6 19
181
060
Oil
2 30
004
2 12
196
0 55
0 19
G21
41 1
14
127
17 0
02
•02
119
19
OS
969
6 25
175
0 53
0 16
2 16
003
2 32
193
0 55
0 10
G22
43 6
10
MS
16 2
03
112
12 0
18
03
97 9
6 50
130
0 52
0 12
2 02
003
250
191
051
005
G 24
410
13
13 2
17 3
02
100
120
18
10
97 8
G-2S
43 2
09
12 2
15 S
02
IIS
12 3
IS
09
98 2
G-26 G27
AS 6
09
109
IS 1
02
120
119
15
03
98 4
Weight Percent
42 9
06
119
16 7
02
106
12 1
IS
09
97 4
G
32 1
448
06
12 1
157
03
119
12 0
17
08
999
G
32-2
53 2
01
35
96
03
17 8
13 0
04
01
98 0
G-53
42 0
20
13 0
15 7
01
114
113
22
04
97 7
Ntanber of Cations on the Basis of--46
Anionic Charge
6 20 642 668 645 651 7 55 6 24
180 158 132 J 55 ' 149 045 " 176
0 55 0 57 0 57 056 0 59 0 13 0 52
0 14 010 0 10 0 07 007 001 022
2 19 193 185 2 10 191 1 15 196
0 03 003 003 003 003 0 03 002
2 27 254 2 63 2 38 iS9 3 77 2 52
194 195 187 195 187 198 180
054 044 042 044 049 0 12 0 63
019 1 16 ' 005 0 17 014 0 02 0 07
G-63B
45 4
04
10 3
125
02
14 0
12 2
12
03
V65
671
129
051
005
154
003
3 08
194
0 34
006
OM
211C1
^44 1
18
119
13 2
01
134
110
18
01
97 4
648
152
0 53
0 20
162
OOI
294
173
051
002
OM-
211C2
440
19
118
- 13 1
01
13 2
110
19
01
97 1
648
152
0 52
021
162
002
290
174
0 53
002
OM
217
42 2
1 9
129
15 3
01
114
113
22
04
97 7
6 29
171
0 56
0 21
190
0 02
2 53
180
064
0 07
C-
154-1
54 5
00
28
17
03
23 6
13 2
06
02
96 9
7 57
0 41
0 03
000
0 20
0 03
4 88
197
0 15
004
G-13A
506
02
44
15 1
03
136
12 2
I I
04
97 9
7 42
0 58
0 18
0 02
185
004
2 97
192
031
0 07
--:'-> -
' 'Z
y'-'^
%• o
:'\P:
' ' ' 2
• >
2
•-
s
5
-OB
>
'£
- 'o
XA
>
- ' r'
;'•• -O
. i

2564 GHKNT AND Srour: MLTAMOKPHISM AT BASE OF SAMAIL OI'HIOLII'H
S1O2
T1O2
Al.Oj
leO
MnO
MgO
tdO
Na20
Sum
Si
Al
Sum
Al
Tl
Fe
Mn
Mg
Ca
Na
Sum*
TABLE 5: Electron Microprobe Analyses of Clinopyroxenes From Basal Meiamorphic SheeL Samail Ophioliie, Oman
" OM- OM-
G3 G-20 G-22 G-25 G-27 G-53 2I1C(I) 2IIC(2) OM 217 C-139-1 C-153-1 C-154-1,
49 4
08
51
110
02
112
218
09
1004
186
0 14
200
0 09
0 02
0 35
0 01
0 63
0 88
006
404
50 3
03
44
II I
04
10 9
22 9
08
101 I
188
0 12
' 200
oos"
OOI
>^ 0 35
OOI
061
0 92
006
404
516
04
35
10 0
04
12 3
219
07
100 8
192
0 08
200
007
OOI
031
OOI
0 68
0 87
005
400
52 4
02
21
96
03
12 3
22 8
06
.1002
196
004
200
0 05
000
0 30
001
0 68
091
004
399
Weight Percent
49 4 49 8
01 05
26 47
109 ,10 5
03 02
lis lis
22 4 215
07 09
97 9 996
50 5
01
33
82
04
13 6
213
03
97 7
50 3
05
43
84
01
132
213
07
98 8
Number of Jons on the Basis of Six Oxygens
192
008
200
i
004
000
0 35
OOI
0 67
093
005
4 05
All analyses are in weight percent Total Fe is expressed as FeO
, * Sum of all cations
lower Mg/Fe ratio [cf Malpas, 1979) Garnet grams from the
Samail amphiboUtes show little intemdl compositional variation
Garnets from metacherts are generaUy fmer gramed (up to
0 5 mni) and have better developed crystal faces The spessar-
188
0 12
200
009
OOI
0 33
001
0 65
0 87
006
4 02
, tinecontehtsjof ,th«>e'garnets are rela^ high (up to 35.4'
mpl % (Tahle 3)).jStr6ng compdsilionar zoning istypical, with ;.
• crystal margiiw typicallyrricher,in,Mn and lower injMg and,Fe};;::
;..;"lban '.cr^siai^.fxiTe&S'Si^p-iy'y^ ;V:f ''^"P'dP-'PypJ:
••[Calcic^mphiboledyp'-i'}Pyy§y% '•••yjiip. •Py.ft:'py'.yd
jCalciciamphiboles are present in aU metabasite samples, ':
•and thex
variation for the Y vibration direction has been,related to the::
:c,hemistry.of,,th.e;calcic amphibole [cf. -A'/j/>j,'1965],'and brown:',
hornblende,is fo^nd; at higher:metamorphic grades.; Brown :',
hornblende is^npt,found riiorett^ m .below the peridotite'
•contact. "'•^''';^'t,;-;-';':;'.'-'':^:-:, :''-.•: :--;-;:
In our interpretation:of P-F conditions attending meta-J: G-13
8.3 -'•.' ;..--0,4 . -. 2.2-12,4 - ,
morphism.we have lised recalculations of slnictural formulae *' ,GT23 '..yX-:3A'. ;:- • l.l. ; - : :.-. • . 1.0-5.0 •. •
with aU iron.as ferrOusand minimum ferric iron consistent'"
:G-24 ;';... :-4.9 . ..-; • 0.6: . - ,-- 2.0-7.0
G-2S . '. . 39.9 = : : 1:4 ' 36.0-42.0
- with'stoichiometry;;j^

c S102
c
GHLNT AND SIOUT MLrAMORI'HIhtH At BASI Oh SAMAII OPIIIOLirF 2565
TABLL 7 Electron Microprobe Analyses of Fpidoie Group Minerals From Basal Metamorphic Sheet,
Samail Ophiolite, Oman
T102
A1203
FejO,*
MnOt
MgO
CaO
Sum
Si
Al '
Sum
Al
Tl
Fe
Mn
Mg
Ca
G-24
37 8
25 1 ,
" lis
V
23 4
97 8
•Toul Fe expressed as Fe20)
tTotal Mn expressed as Mn20
f
G25
39 0
26 8
95
23 7
990
1*
Number oJ Ions on Basis of • -25 Anionic Charge
- 2 99 , ,
'•> 0 01
3 02
3 03
2 95
0 05
300
3 02 - 3 03 300
/
2 33
* 068"
198
3
245 ,
0 55
196
'
G-32
Weight Percent
38 8
J
24 8
12 0
23 3
98 9
2 28
' ' 070
gressive albite (An, 3) In some of the higher-metamorphicgrade
samples (78-G-23,24) only albite was observed, and it is
inferred that this albite formed durug a retrogressive greenschLSt
facies metamorphism
Coexistmg albite and K-feldspar (sample C-154-1) m a
metasedimentary rock approximately 60 m from the contact
(Figure 1) are near-pure end-member compositions
Eptdote ''
Electron microprobe analyses of six epidotes from the basal
metamorphic rocks are presented m Table 7 Five samples
from metabasites have very low contents of Ti, Mn, and Mg,
and pistacite content ranges from 18 to 23 mol % One sample
from a metachert contains 5 mol.% piemontite end-member
and exhibits piemontite;. absprptiph: colprs and pleochroic;'
195
i
G-63B
37 4
02
25 3
118
01
01
23 4
98 3
2 30
001
0 70
0 01
001
198
C 142 2
38 2
^25 5
112
23 5
98 4
300
300
2 36
'
066
197
C-154-1
36 3
01
22 6
12 8
23
01
23 0
97 1
2 92
0 08
300
2 08
0005
078
0 16
OOI
199
sistent with upper amphibolite to hornblende granuUte facies
hornblendes In general, the Ti content is lowest in hornblendes
farthest from the ophioUte contact (Table 4, Figure 2)
Fleet and Bamelt (1978) have chosen the boundary between
low- and high-pressure hornblendes as AI'^/AI^' = 2 0, which
is essentutUy equivalent to the 5-kbar Une of Raase (1974) Samail
hornblendes have an Al'^/Al*" range of 2 32-3 47, which
plots m the field of low pressure (Al'^/Al*' > 20) The low
content of Na (M(4)) with low Al^' is also consistent with
lower metamorphic pressure [Doolan et al, 191 i]
Distribution ofMg and Fe Between Coexisting
Hornblende and Clinopyroxene
Kretzand Jen [1978] have suggested that the Mg-Fe distnbution,coefficient
for.::coexisting hornblende ;and cUnopyrox-
• scheme;;.;{-•;)-,•.;:,,,;:'p-dy '•)'. ' P.-'••.: Ip.-'• '

2566
GHI-NT,ANO STOUT: MI=.TAMORI'IIISM AT BASI; OI' SAMAIL OPHIOLITE
.^.•TABL.E'9:' Estiroalipn of, Meiamorphic Temperaiurcs for Sanwil Amphiboliles Based Upon Oamei--
'.,& ; ': ; .!.... CUnopyroxcne Equilibria ; -,
: Sample lnK„ Xc^
XM„; KWood[19771,and.oiher8. The topic was recently reviewed by
granuUte facies .ijCretz and Jen, :1978, p. 5341. .The lowestyal-:.; ^;Ga«gMly [1979], Saxena li9791,';and Elto and Green [19791.
ues of Ko occur in samples immediately adjaceiit to the oph--.. yiRd/ieim and Green [19741 and £iiK;andCreen [19791 have
iolite contact but:there;is; no significant trend in J^j, for sam-; X, presented; experimental datatodcindhstrale that the distribu-
: pies more ^lan; 10 m;from'thc contact; that "is, the values of Ka";^'. ;,tion qf Mg and,F? between coexistinggamet afnd clinopyrox­
suggest np;sighificant;vartation in metamorphic grade.!;; ;

c:
c
GHENI AND SlOUT Ml-TAMORPlllSM AT BASI- OF SAMAIL OPHIOLITE 2567
•X ''•• are considered lo be small enough to be neglected. Temperature
estimates aUP «=! 200 MPa, using Ganguly's equaUon,
range from 865° to;920°C (Table,9). An uncertainty of ±100
MPa in the estimate of pressure leads to.an uncertainty; of
±3°C in the estiinate of temperature., :
Saxena [1919], using an expression from Ganguly (1979) to
correct for nonideality,in garnet solution and deriving a complex
expression for nonideality of clinopyoxene solid solutions
presented the lollowmg equation
8288+ 0O276P-FTt0(mofTempierciiwe'tmdFluidyp.d':p
Cotnposilioitfpr Calcareous Melacherts py'p-
One sample wiihin the metachert-metashale part of the sec- •
'lion (Figure 2) contains the asseniblage quartZTpiemontitediopsidc-iremolite-calcite-sphene-plagipclase-K-feldsparhematite.
P-T-X conditions,can be estimated from the foUowing
equdibria:. ;, -,,:'; •., '^:yP4'ddp'-'i'\ '..' --i '

2568
GHENT AND STOUT METAIVIORPHISM AT BASE OE SAMAIL OPHIOLITE
and alkali feldspar ,(Or»„Abj,Ano.3). These compositions plot geobaromcler can be made for upper amphiboUte facies me­
on the limbs of the K-Na feldspar solviis and do not provide a tabasites from Three Valley Gap, British Columbia [Ghent el
precise estimate of temperature. Inspection of the curves prcr ;; ai. 1977). These rocks contain quartz, and the jadeite contents
sented by Stormer [I9'75) suggests a. temperature of eqiiilibra- ' ;'of six clinopyroxenes are near 3-4 mol %, with albite contents
tion of less than 400°C.;'-':'. :'-^ -'i^^.v:; •.;;;;;- -;• • ;' ."? .,; of plagioclase ranging from 37 to 68 mol %. Using a temper-
.j; ature estimate of 630°C, based upon the Riheim-Green gar-
Comparison of Metabasite Mineral Assemblages- ''•';' '• Jd : net-cUnopyroxene caUbration, the estimated pressure ranges
.tVith Experimental Phase Eguilibria\.> •/',;: '': 1 ; frpm 310 to 580 MPa. Associated peUtic.rocks contain gamet-
; plagioclase-sillimanite-quartz, and using anorthite-grossular-
, Clinopyroxene-hornblende asseinblages: persist to 80 m
.: 'quartz-Al2Si05 equilibria [Ghent, 1916; Ghent et ai, 1977) at
from the peridotite contact, suggesting P„jO-7'conditions to
t;; 630°C, the pressure estimate is near 590 MPa. Thus estimates
the right of curve 3 and the left of curve 4 (for PH^O = Ps (Fig­
; :of pressure using jadeite-albite-silica yield pressures cpmure
3)). Hornblende-oUgoclase without stable chlorite persists
:j; parable to those estimated from other equiUbria.
to at least 130 m from. the:cohtapt,,suggesting Pu^-T fx>ndi-:
With these uncertainties it is obvious that.the estimate of
lions to the right of curi;c2XforPH,'o ^ f^ (Figure 3)). Abun-;
pressure attending metamorphism at the base of the Samail
danl chlorite appears at:greater distances from the peridotite
contact (saniple78r;G^13:(Figure 3)), suggesting lower temper-';
; .ophiplite cannot be accurately esUmated, except lo say that it;
, atures of crystaUiJation;';A|bite occurs; at distancesof less than;
;: was of the order of SOCH^OO MPa and .is within the limits of
;;! maximumldad pressure .based dn;straligraphic-structiiial iir-:
TOO m from the peridotite.contaci;;l>;utTVi?.ii'^c'y this al-; p:gamevM/pyp pdpp'py'^'::;d p'.-..'/p \^'.- -'•' •. ;^..;.;
; bitew^ prcKlucedvby retrpgrcK^
Estimate i^'Afe^nw/pifc^^^
J|:t;jjpwpii5iyOFjTH AND. SOURCE
" ' If .the rocks ofthe basal metamorphic^ sheet were metamor-.^ 'dydMi:d-.'of-^HEAppc>^ .
phosed beneath the Samail pphiolite; an estimate of the thick-'
ness of the Samail ophiolite would prpyjde an.estimate of the;, ;/:•:£; Polyphase deformation seen ihthe higher.7grade amphiboload
pressure attending.meUmorphuro.,The; ultramafic 8e(>;
^TUtes is not present in the underlying;lower-grade greenschists
tion varies from.8;to 12'km,;thick frbni wesl-to east(^r^
i;;;;(tC^/eman.;1977;,this study]. Ill addition; thehighey-gr amand
Coleman, 1981], and the gabbro and basaltic dike sectipa
;'phiboiites- suffered a second greenschist ;faci^, metamorphic .
is approximately 7'krii thick [Pa//«/fr,flm/ //o/>5on, ,1981]; If
;tf event; whereas the Tower-grade rocks, show evidence of only
;:he episode of metamorphic crystallization. K-Ar dates on the
the niaximum thickness of the;Samail ophioUte were present'
V higher-grade metamorphic rocks suggest^ that they cooled beat
ihe.time pf metamorphiccrysiaUization, the maximum load,
'':[ low argon blocking temperatures neariy: 10 Ma before these
pressure would have been ofthe order of 600 MPa (Figure 3).,:
< temperatures were reached in the lower-grade rpcks/
An estimate of pressure attendmg metamorphism cAn| be
' ;:The metamorphic gradient outward from the ophiolite con-,
made from the foUowmg equdibnum ' ,;:;.!.;
';.tact;;shows apparent reversals in grade.;Because of the per-
NaAlSi308
^ albile
NaAlSijOo -F S1O2
jaUeite quartz
' Vasiye;character:bf the retrogressive;metamorphism throughtout
the basal metamorphic sheet, it is difficult to demonstrate
:^?.that;some, of the lower-grade rocks;are, not simply derived
vifrom the^higher-grade,rocks by retrogressive metamprphism.
Using the expenmental data of Newton and Smith (1967); the,; .;> :Lower greenschist facies asseinblage;s in metacherts and. meta-..
equiUbnum constant equation IS y:yy: ,.y ';;morphosed argillaceous rocks, for example, sample C-154-1,
HGr" = 0 = •mn^.^^r-^^^''-'^
T T
; are succeeded at greater distances from the ophiolite contact
,; by,lower amphiboUte facies assemblages, for exaihple, sample
;78-Gr32 (Figure 2). Crysitallinities of;T.O-A micas in the lower -
;:;^'greenschist facies metasedimentary; rocks'show an apparent
+ log aNaAisijO."' + log as.o, - log On^oiP^
:^|regiilar decrease in grade away from the ophioUte contact, but
where AG/ is Ihe free energy change at P and 7", a is acliyiiy,.: .^albiterepidote-amphiboUte facies asseinblages are present in:
px IS pyroxene, and pi is plagioclase There are a number of;, ...fine-grained, mafic phyUites at greater distances from the condifficulties
encountered m usmg this equdibnum Estimation '-tact (sample 78TO-I3 (Figure 2)). .Discontinuities in metamprof
the jadeite. content; of.'the Samail clinopyroxenes.;is not 'phic grade have been proposed within basal metamorphic
unambiguous: ;Ai:ibw!cpncenlratipns of jadeite soUd solution; : rocks beneath Newfoundland ophioUtes [Jamieson, 1979).
in clinopyroxene thi;. activity of jadeite is,difficult to estimale.y ' We propose the foUowing model: the metamorphic sheet is
accurately. Quartz is hot present in the metabasite mineiral as­ ;bf composite origin. The higher-grade part ofthe sheet nearsemblages,
so that the silica activity wiU be less than I. Using est the ophioUte contact represents the earUest tectonic sUce \
an ideal solution model,;ih this case with activities set equal to welded on the base;of the ophioUte and the;metamorphic
mole fractions ("Tables Sand 6), we have an^isi,oJ" °! 0.05 (all rocks which'have been transported the greatest distance. As
Na assigned to,;jadeite), aKr,Aisi,o,''';=? 0.70, and aSiOj == I at the ophiolite was transported, successively lower-grade inelar
800° ±50° C, and the calculated pressure is near 660 ;± 40
MPa, For an activity of silica less than I and aU other conditions
constant the estimated pressure will be lower. If the activity
coefficient of jadeite, ill clinopyroxene is greater than I,
aU other conditions being equal, the estimated pressure wUl be
higher Some estimate of the accuracy of this equdibnum as a
morphic sUces were picked up, and the higher-grade rocks
were subjected to later deformation and retrogressive inetamorphism.
Because of the occurrence of. fine-scale interlayering
of metachert and metabasalt and the occurrence of .
metachert-metashale sequences the tectonic sUces could have
been of the order of tens of meters thick Since there are ap-

C;
Gill NT AND STOb'T MLTAMOKPHISM AT BASI Of SAMAII OPIIIOLITE 2569
parent discontinuities in metamorphic grade outward from frtctianal Heating
(he ophiolite contact and since there are apparently both gra- To explain inverted metamorphic zonation beneath a thrust
daiionai and sharp contactsbetween low'jnetarnorphic grade "sheet iii southern California, CraAa»ia/ii/£'//^/a« might be applied to the rnetamorphism beneath the Newfoundland
ophioUtes. A/a//i lions, is an e;iothermicrea0ton, The; temperature reached in; ;;j,eai[ing. V .;,',./, ' .'}
' the basal metarnorphic.aiireole, of the order of 800°C, is out- >;';: Quantitative estimates of the teraperature increase at the
,, side the upper, temperature-sta bill ty limit of serpentine miner- r

^T-V
• ^ 'ii!
*%V ;;, Wadi Tayin '• '.' ';?:.%
- OM-217;. •' -S "garnetaraphibolite:;'-/at
peridotite contact, Wadi- ;t;:, •;'.'885;''i979, •• ';•"'•.•;,::.;.;;:.•'-'?'-; ... .'• .;; -.
.;. • :,'.'^yi-^ ';;'';^----^v'-'.'-^:-^: r;;^:;:'-^'-^";^-,:'
Aiwa, Wadi Tayin. :•;'.';-;;;. Glennie, K.'W,',M.G, A. Boef„M; W. Hughes-Clarke, M. Hoody-
15 m below amphibolite^.Wadi'. ;.' Stuart, W. F. H: Pilaar, and 8. M. Reinhardt, Geology of the Oman
, OM-SUj' •>;':;'';gariiet.iiuart!aie-;s3:t:'
!;•'Tayin;; , •..'' •.^''•••i'ly'j-:,-' ; Mounuins, 1, Verh. K. Ned Geoi Mijnbouwkd. Genoot.. 31, 239-
, .OM-607,;..y;,yganiet amphibolite.::';: ;:Wadi Nujum,,Ud haybah ;' ':? i'.'241, 1974. ./;', " :i ..;..v.;.' .:-.:'' i .-'. • V • >: ' ' .- ' -:
^iGrabam, C; M!,,Metabasite'amphiboleis ofthe Scottish' Dalradian,
/ Coiitrii}. Mineral Petrol, 47, I65rl85, 1974. •
'.;:Grabam, CM., and P. C. England; Themuirreginies and regional .
v';4cll:noH'/e ,':We thank-J; Oi'Xiou, C. Hopspii, J: Pallister,.:
- ;' metamorphism in the vicinity of; overthrusl faults: An example of
-'R. G. Colemari,,and;p.;Moore for;constructive reviews of tbe.manu-';
.-shear healing and inverted metamorphic zonation from southern
'script. £. p,,Gbcnt:acknowledges the cooperation and assistance of
; California, £ar/A P/ane/.Sc/. X««.,i/, 142-152, 1976.
. M; Kassin, .Director of the Department of Mineral Resources, Pirec-;.
' Hewitt, P.,.Stability of tbe assemblage muscovite-calcitc-quartz. Am.
torate General or;Petrolcum and Mioerab, Sultanate of Oman, and -
Mineral. Sa,l%S-19l, 1913.'. ' : : ' : v
.other'scientists in the;deparimenL Field assistance foir E. D..Ghent
Hopson, C. A., R, G. Coleman, R. T; Gregory, J. S. Pallister, and E.
:was provided by a National Science,Foundation grant to,C::A. Hop-
H. Bailey, Geologic section through the Samail,pphiolite and assoson.
Laboratory work was supported by National Science and, Engir.>'
.••.•• dated rocks along a Muscat-Ibra transect, southeastern Oman
neering Reswrch;C^uncii;pf Canada grant A-4379 to Ghent;.. •
'Mountains,'/ G«op/i>'i-Rei', 5d, this issue, 1981. •••...• -, '. -
: Jamieson, R. A., The origin of the dynamothcnnal aureole beneath
'REFERENCES
•j.the White Hills peridotite.and.'its bearing on ophiolite emplace-
Albee, A, L.; and!,: Ray, Correction factors for electron probe micro-, ;,,. ment, Geo/./iMoc. Can.ytftilr., 4, 60, 1979. : ;
.analysis of,,silicates, oxides, carbonates, phosphates and sulfates,•; ;'• Kreu, R., arid L-. S. Jen,, EOecl of temperature on the distribution of-
: . Mg and Fe^* between calcic pyroxene and. hornblende. Can. Min-
.'^":;^na/.;ai«n;;«,;i408.-i4i4.-i970;';',!-;;.:; ,^--, .--.v:' r';-'':.-^'-:''• j;i-';«r4,76, 533-537, l,978.(•.^ :;',.'--;:': :''; :;-- , ' •
,-Ailemann, ;F;, and X ;Peters, The ophioUte-radiolarite belt; of the;
,'Kiibler, B.,-La crisiallinite dc I'itliteet les zones lout i fait supirieures
i-sNoith-itJniaa M

•It-
- j;- ;
-;\-
. :-*.:'• •'.: •'• -•••::: ,.,io,s.-.'^-°""°'-" : ::' „^„..»».«=«
•;/ : . '..cy^^'^'^''^. >d,^.^^
it>^ "^'t 5C^ ^^^ 'UeniaV study of '^^ ,„ pfe«. ^..UiV ^^ ^'^' and cUnopV » ^^^ ^ HJ ^ ^cthV*"
t";;S ^'^.!ribrla,/i-Jj,ornbVcndeJ^,«Ob ^,__ V^oodcocWJ^,,p,ic tocks
,.«.t.«io«°«'4',',S,
's-«"''''"°*

«9 ,«^' .cO
^v>^>^^-^ V.xO

A«ihJk:a^fe8awfl^^
c '
-/( bt.1 Qjin.i
SW
t\^usdndam
penimula
• —
\ 1
:

.^'•Kvfe,T,-ffi«i,>. ..,.t:';i.i.-a:^-:,:,.-•-.^..--tiifai^
-i^;;';
iiiDi phic >in.-el or the base of the Semail
,ji|]i(iliic .scqui nte However in the norlh-
—ir.]) li^iwa.sina window ihe Jebel Abidd
l-.xoiic is parti) i)\erl,iin bv a sequence of
pilldw l;iv;is (Scirlc and others, 1980)
Ihcsc bas:ilts arc extremely depleted in the ^
•inuiKibilc" trace elements and light rarei.;;iiih
clcniciiis (.ompaied to those underly:;
ing till.- liincsuines and do not appear to be
rcliili-d 1(1 the II IVbi \olcan1c-Om4n
l;\•• r ''-'•; ." : ^•'
•;•'•-,'.' '•..'•.. V '•
y y " ' '••'.
P---:'' p *v " ' • --^
." ' . ' ; • ' ' , • • / . • •':•
' , - • • '•' '.
.; " , • ' ' ~\ • \ ''
-p'.dr ••_.;•;';"' - V
•,;ii.,- V • yy_xd ..'• ••
-'-•%••• ' - " ^ ' J ' " . '• • • ' • ' '
.-'!•'•- •' 'd.- • '.'' • ,
^dpy--p''
•..;. c
'.;. .f-'o
:'"'.c.^'-
.;. ,,0 Y
•„, 0 J.
;,' ra- -"u
. : a thick sequence of Iran
sitional tholeiitic pillow basalts and tuffs
Geochemistry of these IdVds shows that the
alkali basalts art highlj enriched in the
"incompatible' elements (li Zr, Hf, P, Ce,
1
/
r„
"o
and Nb) and the hght rare-eartn elements
compared tu even the most alkdlie mid
ocean ridge basahs The Haybi transttional
(dlkdlic-thnleiitic) lavas are also eniiched in
these elements, but to a lesser exien' than
the ankdramites The two volcanic types
form one continuous stratigraphic unit
within thrust slices
Volcanic rocks beneath Permian L\oiit
0

.Ajisvi^ijKc.- .Hi,.«.tafwm.TiittMitmmaHiiH«»h.i

lift'iusuuics have not been studied geoclKm-
;.;iUy bui were recorded by Glennie and
hers (I^J74).as being pcirogrdphieally sim-
__;.r tsi ibu>trotnatopoToids,'and sk'eleial fragments
.scluding brachiopods, .gastropods, and
cchinoderrti plates,-Rvigosc corals locally
make up about' 40% of theirock which is
inierpretcd as aiypical reef association
(compare James;. l97,H).S.cvi?£g.:^|;r:>^ V; matrix: Clasts of Jurassic and Cretaceous
Hawastna.iediments aisQ:occur in the oiistostromes;;
Radiolaria from the matrix
have been dated as middle to Law Cretaceous
(E.;Pas8agnb;T979, personal
comrouh,).,,The oUstoslrbmes are interpreted
as synlectipnic sedimentary slide
deposits that accumulated in a rapidly
deepening trough duringemplacement of
the thrust sheets.Thcy include all liihologies
of the Hawasina Complex, bui Exoiic
limestone clasls are most charactensiic and
abundant. ^acics: \.;
The Jebel Qamar.Ex.btic limestones aind . ;§•,
dolomites in the U tided Arab ;Emirates arc
ihe only two Ex;oticsiknbwn ihat show a '
Mammonia Complex of Cyprus (Robertson
and Woodcock, 1979), and the Zagros. V
Mountains oflran (Ricou; 1971; Stocklin,
1974). In all these areas they are commonly
associated with volcanic rocks and iransr
ported pelagic sediments and ophiolites /
(for example, Lapierre atid Rocci, 1976;
Searle and others. 1980): '; : "
Three paleoenvironmenis of shallowmarine
carbonate sedimentaiion have been
recognized in the Oman Mountains. From
mid-Permian to Cenomanian time (Fig.
3), a span of about 120 m.y., conditions on
the continental margin were continuously
stable, with steady deposition of shallow-
47

—/"'""•"•" d »~ ~^ I— I—75——"7^''"r"'''''"'"*"?^'^'"-'*~''*^''''°"i"*"'**'"'''*^^
li'^Tja "^lY"—r-^- • >-*'-'-^-^-^-"«'*i -.^ - i.^* -hi.., .-na —ywiWufflj&^fi^tj^.,^^^*!!
c
:c
I'liie liineiiones No igneous roeks occur
1 th e(|u;;nec C drboiidtes of Ihe
1,1 11. I ] (;r )up art interpreted as a shelli
I^t s^ijLu net and are considered to be
(> ir nitoehih JROUS (Oleniiit and others
I ^""l) I inally the Oman Fxotic limestones
lurtneiJ is»i lied seamounts or guyots in the
tdilj Mdw-iirid bjsin
Pilmspasiie reconstruction of the Oman
I Mitmeiitul mdrj-in and early Tethyan
< eeun basin e ui be attempted using this
d Ita (jlennic dnd others (1973) presented
two aiterii itive hypotheses for the origin of
tlie I Kotic Iniestonc!. One model (Glennie
and others I9"'1 Fig 9, p 23) shows the
1 \uiie limestones depowitd on horsts of
pre Permt in bdicmcni over which pillow
I ivdb were rxtruded to form a bubstrate
i his model does not however, explain the
U THIASSIC
Continental
Shelf
edge
Slope
margin Sumetni Hamrat Duru
9P 9P
SW
U TRIASSIC
Pre-Permian basement
Mdhii tm r I I r 'T.
b Saiq (m
Sumetni
9P
fact that the 1 xoties are in .itijbly tec- .
tonicdily superposed over llduasinu thrust
sheets rathi r tha i under them ds one
would expect Fhe carbonates dione pro­
vide no clue dbout the ndiure of the base- *
ment, but the local volcanie substrate
suggests that a trdnsiiional (tontinent-;"..: ..
ocedn) crust is more likely with the one '.;.
exception of Jebel Qamai which shows a
probably Ordovician basement
A second model more favored by Glen-, .„
me and others (1973, Fig 8, p 19) shows
the Exotic limestones forming as seamounts'.
on the flanks of an actively spreading .«' ; ..;'
oceanic ridge (Fig Sa) fhere is no reason ,.
why carbonate reelal build-ups should not ,
accumulate on the flanks of oceanic ridges;:'
although they have not been reported from;.
modern-day examples If Iceland, for' '
gj U. j-ll- '„-
Abyssal plain
Ai Ayn
tm
Haifa
fm
Drowned Al Aridh Tnassie
l*ermidn megebreccis Exotic
seamount
example, were siiuaied in the tropics, this
could easily be the.case. However, the
-Haybi volcanic substrate rocks do not
compare with any known mid-ocean ridge
; basalts. Ankaramites and transitional
alkalic-tholeiitic basulis are commonly
known from ocean islands on the margins
of rifted continents, and a,comparison with
.: the present-day East-African cpasl-lndian
Ocean area is considered more likely.
Our alternative model for the origin of
the Oman Exotic limestones is shown in
Figure 5b. Permian Exotics accumulated
either.on basement horsts or on volcanic
seamounts thafwere subsequently >
:"drowned""during marine transgression.
Triassic Exotics formed reef-associated
•/carbonate build-ups on early oceanic vol- ,
canic seamounts or islands The Al Aridh
-•^••^fn: d\r
Spreading
ridge
Al Aridh Exotic
megabreccia limestone
SW NE
Oceanic crust
MID CRETACEOUS
Autochthon
Sumeini
gp Oiistostromes Exotics Semail Ophiolite
SW
Figure S Reconstruction of Oman conlinental margin at end of Tnassic time a After Glennie and others (1973), b model proposed in this
paper; see text lor discussion; c: Oman conlinental margin during middle-Late Cretaceous, when olistostrome deposits accumulated in
rapidly deepening trough, before and during emplacement of all allochthonous units.'
NE
GEOLOGY; JANUARY !,9H;>

^^^^^^^^^^Mfii^^^»^4^?'^'plp...^'.: ;':^(Vti;gfi.'i;:'yi?ik:;::!,aS^';v-:i;i:^^
m:g:ibrcccias were derived fromthese sea-t, ;:;:REFEKENCKS-CITED "•"• •"r-^---:: :'::•
^iisoiints and accunriulated in:,surrounding; .;^: .;'Abbale, r.:.,,Bortololti, V., ami I'asserini; I*;;'; .;
ilee-pe-r water environments. The nature of J:; .v; ' • .;i970. Introduction to ihc geology of the''';
the- "uansitional crust" from continent to-.:'.;; . • ;•; Northern Apennines: Scdimcmary Geology,
,:;;V; v. 4, p..207-250, 521-558.
utean nimains speculative, asit doeSjai.V^^^
':ft,Bax,ter; A. M., 1976, Geochemistry and peiibmost
passive,continental.m,argins';(fpri^;...| , genesis of primitive alkali basalt from Mauexamplc
Fasi African coast) and beneath;>;f >,!='• riiius, Indian Ocean; Geological Society of
carbotiate build-ups on suchWgins(fbr^5;»^':;^meric^ Bulletin, v. 87„p. 1028-1034,, ;.
, • , , ,,., .u A„,,„ cv„.;,>«-' ^*^°^*'''"'--^-'^"d Rossi; D., 1974, Triassic carexample,
.Bahamas).ln Jhe Oman:Exotlcs, y.-sts and Mineralogists Special'Pul>lica-.Tj/
volcanic seamounts on ritted;conrinenulor.t:;'Vi;;''''°"''^^ P;;3?v3^^' - \ '.-"'P '': '••
early oceanic crust. Present-day:^na|ogues^^.;^;^,„f^^r^,„jf^.VB„
may be islands such as the'Cpnipresv'a;;jJ;;:,:,fv;y:? j^versity of tl^ 1962,=:
(Strong, :| 972).-Maurilius..(Baxter,jl.976),;%:;;;?'>^ ' -••'-.; '"'; -dy^:::' ••
and Reunion (Upton and WadSWOrtb,;"'v'.''^^^^ Evidence of slump phenomena ;
1972), off.he coast of Madagascat;^hicr>S;:i;^;^'":^7
. , .; . • . ~;--V'j.,.,.c ;:-::;;-i-.i-explorationin Sicily; World Petroleum*
have similar volcaniCTocks,and:reef:;^0:i/:.|j;ftiv;*r.:'. *;5,,thetr geologic evolution; American'A«tM>cia-\.
1 riassic Exotics, subsidence llnally^ut-,S;=s«p:^i;;^
^ paced Exotic:.sedimentajtioiV'The:.l^te[T;rt-Cjl^ ;':;- '''d ,' '-dydfyi'dd.
assic is marked oh the auto

'.. ";:::;.r~; •:—-...—.-.---T——--;,-.-—i---—;...••, . ^ '. ,d --''.y-; -^ :-. ,;. ;lriicti.irc's in nruissivo p'v'i iii;, ir;id;,qiiaiiiiii(;5 of s|-jli;ili.-rii':;, .-in-
. "Tin; intcrn^tioiuil p|>liioliV'; Syni,o.osii-i'o,.* 'h'i'lcl jii,Ni;co5iri, .; . -"utKlci l',/;ng f|i.iarr;;'- cSIr,,; iii;--sul|if-ii(|o;sii.-K:kwr)i k .-md .--(Ji.-.iOJni
-^ Cyprus, from 1 to 0 April, 1979, v^fao qttiatii/ud by the ' ;^ fi;rrotTiaiicj.'itioati sudimcnis (unibors)': Tiiu Kiilavo;:so'„
Goolofjical Survtjy Df.'partinerit of Cyprus.'This report was -, ;; ;orrjl)p(lics usually occur as tectonic zones with a hutjii
f>re(jnru(l by Dr. PVSione.t. ':• 'p'.y^..:,.:..-:^ •p;'r^:\d • .- j';:'ci;inlh :,yvi(lt,hvratip, Thoy are froquently hounried on one
C
, ' ' ::.-•'" ''. : y'dd'•:'^'P •d'.'^P^dy.- ;',;.;.5;:sidc by'faults,;y/hich'vveru also the Ipcali/ihy struct^
ho (lomlriont thcinc of The meeting vyas the'devolof)meni';;'trt',;,:On ihe othersidc by. prq-miner.alization'lavaV'with cither a
and stru"cturn of Tcthyano'phiolites? In nrlahyjbcalities;''-' .i;':*:';;ttronsitional or a faulted'contact: Gold and silver-are locally
field evide'nce as to their environment of'originis eqtjiwocai;; 4;^^^^ with'the sulphidebodics and have tieen'
To overcome this problem ,a variety of geochemical;« hpp-d-''. comincrcially recovered fi;om'someigossans.
techniques have been applied to distinguish, for^example/; '::'^ In Oman tlie largest ore deposit, Lasail, exhibits most of
between ocean-floorfjasalts, calc-al|e floors of small ocean,basinsrather,than,segmeritspf{'-;;: ^;M^^ deposits by
jceanic crust that were generated at majoroceanic; .j;;!;;*^^^^^^^^ from large volumes of magnna. Differential
spieading centres. ;" .%f; : '.y .;; ;;:: ^''n;^;:};;-^:;?,;:^::';;;;'^^ and-infdiiding are both'possible mechanisms, but a
The iiniformitarianinterprctation of ophiolites is^'^i'^.^:'".' 'multistage origin is likely and would;have involved deepcomplicated
by recent studies:that show that largo areas of} , 'seated partial njelting of peridotite; slow upwelling and
the present Atlantic floonare'characterized by basalts'withi,.:.V^cooling of the melt in a zone of grayifational instability and
trace-element compositions that are significantly different;;...'; fowfpidihg and fracturing followed by.limited solid-state
from the'average'mid-ocean ridge basalt..Basaltsfrom.^;;-:' fjpw; . :--%;f.,\ ' -• -
different ridge segments also have different trace-element; ;;>.;: The unusual aspects of ultramafic-related mineralization
ratios; these may be consistent jn basalts that were ; ; i;:.;:'" ,that yyere described were the Cu^Ni-Co.sulphides and.
produced at the same ridge segment over'tens;pf millions ;-' ^-"arsenides within the tectonized and serpentinized
of years. Investigations of niodein back-arc:basins, such as';;?;>; Peridotites and dunites of the Limassol Forest P,lutonic ,;
the Lau basin in the western Pacific and.ElransficId Strait in .:^^;:. Complex, Qyp^^^^^ the occurrence of platinum.group ) ;
the Scotia Sea area; suggest that thebasalts that are .^;; ':;•;;,?" rminerals in the Kokkinorptsps chromite body/Cyprus, '••',.
generated may be very diverse in composition. There is''';:',.:;;';'':,'•"'^apppferitly magnetite that contained ,
some evidence,that.fluids.deriyed.fronri.the subduction slab,,--v;.appreciable Ni,,C,o.and;C the Naga.Hills, northeast .
rfiay contaminate the source area;ofback-arc basalts and ..•;.:..:;^\Jpdia,Tlje magnetite body is overlain by a group of ,
produce, lavas withconipositipns that are transitional fo the; ;.''P . • .
is,Ui(id-nrc typo. . ; '^{i.'-; = ''•;•;'•'< : ' ' :. :"•:' :./t;'-;'' Studies of piocessesat active oceanic ridges shovy that
One important sectioopfthe symposium was concerned ;;;;; the hot springs on the Galapagos spreading ridge are
with the metallogenesis associated with ophiolites. ;, ;;I, ';'"?;enriched in K, Li; Co. Ba, Mn and Si; but depleted in Cu,
Examples from Norway and the United States of America,;j:;,.'.:.Ni and Cd„;Extrapplatip!i of the observed data suggests that,
vveru discussed, as well as many from the Tethyan.belt, -..p.-p,^^'', sulphide-fprming minerals to ieai;h the sui-facc, water-
Descriptions of thepyrite-chalcopyritc bodiesiii the .;;;:,.'';;;.; X temperatures nuistbe >: 75"C.' Observed conditions were,
Kalavasscs aies of Cyprus illustratedthe characteristics of.::.:; ,,-t:closo:^ pf pure MnOj crusts of ,
'typical' Cypiustvpi;iniiitiializatioii.;Tho niinoralized zones ;'the typo reported at. sevcial ridge crests. These obseived-.
are coiitciinf;tl withiii the pillow-lava st;quence and are ''.•.:.',: and experimental data i.uivo a good idea of the conditions of
c
!;?uci:>leii with faults.thni probably.harder a palaoo inodiaii. :';; dcpositioti of the massivo sulphide deposits (sphalerite- .
it v.-illcy. Thi.-y ate chiiracterizod miniJ.Mlogicaliy by ; .. ''...•;; .chalcopyritD-pyrite-marcasite) that were recently
cOlloiorrii textures that are surrpund'jd by.eiittcdial grains iti ;.disGovered on the East Pacific f^isc. The sulphides are
till) n ,-issivi; pyi it«, ahiindanl; it on at id ti,tariium,oxide ; •: X''.,,,.- associated with ochre and amorphous iron oxides and
'-..•':' , ' ' : : - ;; ';•.;:;.'; liydroxidos; Those East Pacific Rise sulphide deposits
•i icc:dirii-;-i (.il il-,e iv'"l>"siiirn will 1)0 pulilisliud in U)Qll;t)v the , .i ii , ,. . ,t „ , , i -r
„ , ,, , ,„, • ; \,- •;; . • - . piou.dj|y repiiisont Iho (iiodorn aiuloiiuo of ciiprilerous
i;r,.:,t,.,lc;„c,.l ficiencus..fidi.b;w.,l.. This t.piirtUv publish..! "'''''V"^ ^^''P'"^^' ''''"^^"^ "^^^ ^"^ assOC.Ued with ophtolllc
..-i;h th. .>.rn,i..ion ot il,. Oiicctor/lnatit^it. oi;.Ceolouicjii,t;clo,u;es '^oiiiplexos and pit.vide vulii:i!)ie .n;,.ght into the mode of
I :-.•.: iu'- frm;ilioii of the'CvpiUitype'dftpositS;,

Ophiolite: A group of mafic and ultramafic igneous oigiii rocks ranging from a
spilite and basalt to gabbro and peridotite, including rocks rich in serpentine,
chlorite, epidote, and albite derived from them by later metamor- ,/*
phism, whose origin is associated with an early phase of the development
of a geosyncline.
Ophiolitic stiite: The association of ultramafic rocks with coarse-grained
gabbro, coarse-grained diabase, volcanic rock, and red radiolarian chert
in the Tethyan mountain system.

-'X
'Oman Exotics''-^
eclated with the early stages of continental rifting
yd^r'P'-'y'-' ' M.P.SearlB./ •' '''^
, -;;:' Gcniogy..iVleiri.orlal Univetsity ol fvle'wfoundland; St,,..)ohf)'s, Nirwfoundland. Canud,-i A1B CiXf.
G M Graham"
C/Oi U'.uersi*y, MiittcvKfiyrie,,. L(»g' D. Gnt:NT ANO MAVISiZv;STOUT , ;:;;^
Piciureol'the Sheeted Dike Complex ofthe Samail Ophiolite Near ibra, Onian
•••,./ '':-.y'dP:'X.y •••.'::],^.-''P •''':: .'iOUt-t S. P/\U.iSTlitCiv • • ,-, -••].'.y.p'd --; ••^iPP
THE GEOLOGY OF QMAN"
• ' . . ,;.;.-,.: ;-• -;' '• . • •^ B Y .-'•'•;•;''•';;•;';' - ' :
V ; ^ vD. M. MORTON*, V

\
t._
d n
K^n
B
I
th
¥'-
1^
*
•°°°^
Figure 6.
Hemer et al: Middle East
2147
0^ /?u
W.JMHltMUgflWlTO '.ujHiiw^Bi»a!;i^v.^Mmnni.iiijnjiipimHiBiBniin

C
Figure 5.
Company Field
Duma
Fateh
Total
SW Fateh
Total
Falah
Rashid
Total Dubai
Reservoir
Ham
Mishrif
Thamama
Mishrif
Thamama
' Mishrif
Thamama
.,..~«^-«.^m«i.iBmai«w»^^
Hidmer et al: Middle East
Table 9. Dubai Production, 1980
1980
Oil Production, bbl
—
—
54,551,166
69,038,848
3,353,839
890,535
127,834,388
2146
Cumulative
—
—
587,178,877
423,054,317
6,918,887
1,491,175
1,018,643,256
dAf^
dc^
BuJ
/"fTJ
Wells
—
—
40
32
7
3
82

. /
..,.^«..^i.. Uplift of
;)a.-;.siv,- niargin of the African conriiienr'and an island, arc. Field re-' .the dphiolire .slab rcsu Irs from compressional .shorrcning in rhti.lnre-arc Innb rocks dur-
•irc limb of an island-arc edifice at cunsidtVable depth. Uplift of the; J; ing cplhsion and after subdu^^ Subsequently, the fore-arc
iiplin.;:!c il.ib resulted frojn both compressional shortening"and' limb opbii/liteSj raised to sea level arui'above, arc maintained there
;M;.staric iiifcraction of the contipentai crust with the mantle rock it:.- isostarically by'their underpinning of ;ajminental crust,
uiidenhrust.'"Oiis model may apply to inany other itiajorophioliteifr:'':,.••''.' .; .J ' . '
:tfcas oi the world, specifically^NVwfoiindktid,;rCuba, northern ;';AREA1;CE6U)G ; •.•.,; -•.,,
Venc.itieb,;Cypnis,;th;,:;,Urals, eastenisCelcbes,;^New,,Guinea, andr''^^ '''• y'. ' ' • • •
New Caiedunia. • ; .• ••:'''•'-p.P'd'i'd'^^ '":'" '-' " ' ,,:. '"';.;'FiguiX';l;illiistrate.«i the arcal-gtoiogic relationship-; in and .i!v rifling.bui,did not :reach:fhi';it'present position until .Upper Cretaceous Ccnomaman shelf carbonate rocks (the H3J;!r
.-irly f;c'r;i;ir titt c Jii tn norti along with IndiaT \ sea floor Super-Group of Glennie), Upper Cretaccou.s foreland ,basin dr-
, i;)i-c;idi/i),! of iiu 1^ iM 's 0 til. .vid later. .: p::«.v I.;',.•..'Ucric.i8»llvtin,,.-,.'H»,:.p. 111*3-1131, 4 fij;^., A-u^(iM 11^77, Doc ; . ' ' .
•• - ' / • " • ^•-.^-> '!-:•-• ;•; • - ' . • • ' ' 1 1 8 3 ;• .-..:'' ',

c
' d"
P.
<
F4^^dtfeH¥la^£nfil'^^^
i>;.»
vc, K, GI:ALI:Y.
1. .,iMn^as-;ic'aKe:-Th.:'ru;bidk.i'c

-lAOD
M^
;,'ORHisiu'>n, r.ro'.cnur.c'evaiid present disiributiofi to she \v;ih!-';ih
h(irii-.:a':i.;i!
tonri:itions'th:-iV h;vv-c been assij;ned to this '(if';-iip v.:iry in :.'i^v ftoivi
Permian to iviiddU:.(.reiaieous, but they havi., in cuisiinon a dcposi.
tiimal environment of a suhmanuc.scree slope, cil.>•^c ti) •.\ c:irhun;ite
shelf edge. 1 believe tli;u the Sumeini.Group rcpics.-ms the iastformed
nappe scqui-ncc, incorporating rocks iir,iiii:diyii ly a.liuciiii
to,the Arabian caibimate platfo.nn, and thai it d.--.;'. not diik-r
rnaterially from the liawasina Group in its tectonic si'^,mli;::incc.
lies, differs markedly ttoni the test of the'Hawasina tormuiions.. , , 4. T"hc adiaceiii Gulf of Oman is here interpreted i^s ;i irr.u};ir.:ii
Tiic I,)!!!;!!! \-.xotii-„s arc isolated.hmestorie blocks, some «cr\' hii'i^v, basin developed to ihc nonhc-ast of an advancing arc diuii^.j^ l.;»ti;
v;u-/in^; irom li;hifK'd limestone to brecciated marble veined with Cretaceous time, although data to prove this ave meager, h is
r(;d sihcct)us mud, frequently on a foundation of sheared mafic piUjJ known that a substantial thickness of Palcogenu and Keo.j,cne ^cd-
, 'low layas, h'aunas from less dUerc'd parts are of Permian and 'rri;tsiments is present off the On-ian coastj thai a refraction protiit in riKsic
av;c and shaUdw-marine, mostly recfoid,'environment. Age AWA .west-central Ciulf of Oman is interpreted to indicate 3.7 km ot sed­
^i:\\er.\\ envii'onmnu ate.entirely consistent with "derivation from'iments on oceanic crust. (CWws and others, 1969), and that along
the- autochthonous Akhdar Gtoupof the Arabian,platc_. The Trias-;;., the Makran coast, ophiolites oiLatf Cretaceous and P.-ileocen.- ;rf;e
sic rectal element in the Oman txotics,,however, when compared havebeen incorporated in a subduction complex in which 1-,OCLIK'
',vith the restricted. sh:iUow-iniinne,;to possibly continental cnvi-;. and ;Miocene tlysch are important .tonstiiucnts (Eai>.t-brpader regi9nal;i^ of the Arabian
m;iil iiappe-were etyiplaixd on tht underlying Hawasina units. The j,, plate aipd those pieces of Irain with which it interacted prior lu and
thesis presented here; is that the, Oman Exotics were teaonically ; during emplaccn-jent ,cii the: Oman ophiolites. Comput aticm ot rel a •
traiisferted from the .Vrahian plai^ to tbe aUocbthoncjUs Semail slab,^" tivemption between .Africa and Eurasia, based on Atlantic opening,
-at considerable depth, which- accounti for the 4ute>rdntial .btittle;; indicates ab

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!;i;;.i-,i,I fri);ii PerDiian to. Late Cretaceous lime,T'ajeomagnvticdara of the severe internal, deformati()ii they undervvcnl during the
•il.;,-: tlv.- i,,/hulfaLOi;thc.nedded
Karakoruin, and, Indiamoycdncifthwarti together in Late CrctaT"; red' radiolarian; chert and -silictfied Uniestotie ,(Hali,w Formadoii)
ceous time in response tooceanrtloor spreading l>eginning at about 'and cc'iiritmetre- to, decimerre-beiided.,''»ed::'ahd. green radiolarian
anoiTialy 28 time (Maestrichtian;;.McKenzic and Sclater, 1971).; ,;,cheits .separated,by thin siUaousisluleJ^^^ Both
However, central Irandid not reach its priesent position relative to . lithpkigics . are believed .toVindicate^abyssal environment. The
tlu- Rczaiyeh^Esfandagheh block imtiljrmdved westward by right-.ibathynketiric outer swell, about I30,km.td the southwest oi tbe
inieral slip, along a,fault,zone,at or rieiir the:present Great Kaviri-vtrench shown in diagram'A'oFFigure 4, was.later,the site of a sig- .,,
i;-.iilt in Paleogcne time as India collided with continental elements ,; nificant uncpnfonnity when, the condnentar.platc crossed it. Sush
in .\fghanistan. .Vlore recent motion in the general Greiit Kavif.i;,;an;uriconformity is characteiisdc of foreland basinsi according 10
taiilt areii has been .left-lateral, apparently in response ti).nonheast,;;: observations O. Salveson (1975, personal commun.).
to nonh-northeast conipression(Nowroozi, 1972; Mohajer-Ashjai .:;;,: Diagram B in Figure 4 depicts the approach of the Arabian conand
others, 1975).' I believe that this is'a result of compression de-.;^',tinental; margin,' with itscoyer^pf predominaritly shallovy-water
veloped by Neogene to Holoccneconvi;rgence of Arabia and Iran ; carbonates of Middle Permian; tp Cenomanian age>(Hajar Supci
contemporaneous with the Red Sea-Gulf of Aden opening. ;:.Group.;of Glciinic). These were; deposited on conrinental crust
: ,'\lihougl! the vvidth ofthe Tethys cannot be determined cm avail-, ficompose^ Precambriaii crystalline rocks overlain by Lite
able data, Glennie concluded .that palinspastic reconstructitm of the;' Proterozoic-eariy Paleozoic clastic, carbonate, and volcanic rocks,
Oman nappes shows the Hawasinasca to have been at very least: rifted in (probably) early Permian or late Carboniferous time,
•100 krn wide and probably more than 1,200 km wide. Figure 3 has; Structure imputed to the older clastic rocks and crystalline basebeen
constructed with the assiimpiiori that the south branch of the ment is entirely conjectural. At the time depicted in this diagram,
Ttthys wasat least 1,200 kmwide and that most of the northwest; the continent had reached the axis ofthe outer swell, resulting in a
aiul \vesf motion-of Africa rclative.to Eurasia from 80 m,y. to 53 . regional unconformity during Turonian time which separates the
rn,y. ago took place along the Zagros cnish:zone. Positions of the', Hajar.Supcr-Group from the overlying deeper-water pelagic shales •
.•nain continental masses in Figure 3 are based on paleogeographic. and turbidites of the Muti Formation. The continental slope, rise,
reconstructions tnade by E.-S.-Parker (1975, personal commun.).: and abyssal plain between the Arabian platform and the trench
Sizes and sh.ipes of tbe smaller plates are only approximate because, were the depositional site in which tjic Hamrat Duru, Wasbrah, ,\\

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Axi'5 OUT[:R

mtmMki, >r-iifi. IIIIII I i--,^.^^.^-.,.,,^^^^,^,^,^^,^^^^^^^ ^^^^
-, -X'--/ P:'--d.p-'~ppmi0ippiV:ii?id:ri6^ •.- •:• • "^ , ,,,(;,;,,
,^ylydrixiphcrdForilid[tmsyyuri^uln^^ ^1^^..,..,,;,,,,;,;,,,, f;,r,,„,,^ atui
middle C:i^raceouri^meVBytbis.nipei^h^;niore;distal;P,arts-o(;f^^^ tvibhrfK, and b.is;iltv are
{onn:itsim :mj the; abyssal. Halfa:Aai)d;'Elaliw; Fdrniations' Were.;; mcfanidqihosed'W'7IH' j^rcenschist :fac!cs ;Al!eni:inn and IViers,
-b-iiif; ifivorporated ni tht;;suMuctipn.,complexidrfning in front pf;;:^972), Tiiis;sui;grtts (onnaiion at di-prh and elcvaird teoiperatiire
(iu- en.vruaching arc.'Crti-Stal striieture;and bathyiiictry,of thi; .foie-vV'produa-d.bv friction;iI heating m tlie viciiiiiy of the niasfer fault,
•ifc ,^egiu/i :smodeied:on!thecentralAletitians.((;;row, I97:?).,'rhe'^-^^^^ liird mid others /I97,vet;ly- ovet:ly
, du: lindc,! thrusting of. fhe,carbonatf,pl.Ttforfn,-yyitH a natural eleva-;- ing Semail Opiiiolite nappe. The ')e amphiboliles kmphfboliics show subsequent subseq-uent in
iK^n soiiic 5 km.atx)ve.iid;acentf>cos^ to:laie-zCphyilirizatidn persists upward for stVme.distance in soft, interlayers
-J,, ,(,ampanian:Fiqa Formation,'w.hich began as'a,;5hallow-water C3rr'-';';pf the'Upper.Peiimtan stfatii;- Mprtoii.'s'observation suggests that
;; bonate,but graded;rapidly upwa'r;d to d^^^^^
: ' Diagram;£ ifl Figurt:{4 depittsia'tnorc advanced stage in theob7;V'nt|nestton; it is believed that untif more infonnatit)/! becomes
v; ,duction prcicess, Topograph, and bathyinerry'arc in:part basedori;;;.Javailabic,the possibilityIthat thi's;event correlates with.the rime of
,';, Timor,;where gravity data indicate a.stage in which underthrusting.fgreensc/iiist-facies itietamorphism aecpmpanying ophiolite.pbducco.'itinental
crust reaches astfar:as its hortheirn:ctiast(Chamalaun;-.:;;tion in nonhem Oman should riot be ruled out. 'There are too many
', and orhers, 19-76/. Atahis;suge;:in ©man,.:the;contincmt metamorphic facies to permit an
/;'• tcracring with the derise pceanic,,cr'ustal part of the fore-arc liinb..>\sj-. ;acciirate estimate of the depth;at which'the' Oman metamorphic
.f,hecpni:inent.'il plate'uriderthrusr the denser hanging wall,;isosratiCj''; rocks developed. However.'a depth between J.P and 25 km seems
:"'- ,ad;«sriiient began. Th'c.;«;nsuing gepincrry developed by,the,intcrac-;';;:rea.son3bly consistent with;rhe;data at hand.
rripn between the'com()ressiye,;imderthrusdngand is that the mantle rock of the fore-arc limb ,va>
IS believed that this;intcraction would have developed a flacicnihg ";al.so strongly deformed by interaction with'the;subducring conii-
::,".:' in rhe shallow part,isftKeBenipff zoneand'a:s;tecpeningbek)W,;with ; nental.slab. If water were available from sediment on rhe dov^'lll;oi;•
, a resulting 'tendency\Tpr''the*:underthrusiing;cpntiiiema 'ing plate, if seems probiible that such deformatipn would pronifHc
, -^s.; override and;detac,h:frpm.the,cieepervpartbr;the^zpne; • ^•J ^ by r!c•
••^^• .Arihis;stagc^.the;maiJi,-#^^^^ the pbducting vcloping a zone of low shear strength in the vicinity of the nuisti/
•:;-, fore-arciinib TfomthfXrafcian plate^shif^^^^^ ver)-widesprc;id zoneni
• .:;.tnielange-piletobi;cf>rneest^^^^^^ peridotite at-the;,base of"the Semail sheet. Avias
•;; vdccn melarige'and;forelarc limb. If'seems reasonable'to;suppipse:-/y(19()7), pbscrved an analogous.situatioir in New Caledonia. Hal!
., : that'the';pre:ex;is'ting;/,eastrdipRii]g.-iinbricate;«rucm^^ ;fhiar serpentinizaiion;played aii imporraiu Rile i
,;;:,,;mclange greatly lacilitatedJbreaktHrpugb of the new-master fault.,; pp TaHr"* suture zone in .sautlua
; ;Tlvis,maj6r.ch3iigcpfthet}tfustplanc.from the;fe >: . ;;; ,;'
. ro its' topaccoiiiits,for theirelatJdnships observed in the field: among ;' At the stage shown in diagrafnE of Figure 4, although ohdiicric icrini)-'
;;',(he rncl.-inge^'-,theExotK:limestpne;block.s, an begun there was no marked effect evident yet in the forehitiJ
;••;The.depth at which fragments^'pf the platform- carbonates .were;;/ basin.'The Muti Formation,derived from the eastern iionvulcanic
;.. ,rransferred fo the hanjgingwall,m,ust have been cprisiderabletP ex-,;* outer arc, continued to be deposited at.the base of the mcl.ingc
, plain the brecciation;'and-nwrm'orization;of the Oman Exotics, ' ;,' slope, but with transfer of rhe master fault to the top of the- nu lunj^c
' ., OfhercMdcnce that the obduction pn>cess takes place at consid- pile, presumably it was no longer being subducted easfwaid. l-i.j,i
ti;able depth is seen in the northern Oman Mountains, where sili- -pelagic deposiupn continued.farther west m the foreland basin.
'jlltc
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uxjuj JM, •^»wii*W.u^**Ja*i'\»4.!Ufe..fc> L^tiW't^tt*jjSMfe 2, p. 9~1S ^ ,
f iilrman, R, C, 1967, GUueophane i«.hists from Cahfbmia and New
( altdooM Ttcfonophys/c*., v 4, p 4'^^- 4'//i
1971, I'liie tfcronic cnpfattment of upptr mantle pendotifc along
,.onrjii«.niJi t-dKe> /our Ceuph>$ Research,* 76, p. M\l-\1X1
Divif s, H L, »nd *>ni(t{i. / f . IVl, Geology of eastern Papua ffwwl, ^v
Amtma Kuli, V 82, p 3>''9-3?J2. J ", j
Diwc), J E , and Bird, J M , iV70, Mountain belts and the new'global
levronius Jour Ceophvs^ Rest arch, ii 7"'a^ fne ophiolite mcJaiij^t, a *orl»*ideproblem on Tethyan
ix,impirs fi/ogje Ctoi Hflvnidt v 67, p 47!*-iU7
IJI.iifii', (^ W , Boeuf M G A , Clark, M *' H , Mwdy-Stuart, M . Pilaar.
VI 1 H riii Kti'ifiijrdt, B \f IV), J.jȣ C rtraitous nappes in
('in ir MouniJiii, j/id ihtir j^eoiog/cal evuliuion Am A^Kll I'ctro
Uuin Gioli >,iMs 1^'iil , V S7, o 5-27
--JV7-1 Gcoioi,v of thi Oman Vlouiitain* Koninkt \cdcrlJnd^ Geol.
Mi|/i/iouwkiifidjg Genoot Vt/h , v 31, p I-^'liJ
Ciou J \, jy7i, Cru'.tal aod upptr maiulc stmctun of rhi central
Aiiutiaji Art Cc-ol Sot Amcni.d Bull, V, W, p 2l6!^-,;i!>2
ffdi, K , lv''6, Ophiolite cmplatt ment and the evolution of rht rjuru«>iitiifi.
zone louthcaitern Turltey Gto' Soc Amtrita Bull v 87,
p i'rs ji'ds
Kiii^ I., I9~'i, AJI improved retonstrurtion of GonJvkanaland, i«lading.
0 H , and Ruriiorn S K , eds, Iniplicanonsot (.oiitinttir.ii drit; to tiit
Earth scit-iitts 1 ondon, Atadeniit l're^^ p 6,>J-S6i
Krtippcr, A L, ind Sotolov, S D, (9''4, IVc-uppcr Siiuiiun ti ,OIIK
•.hutts 111 fht /eiM.rt lucaj.'ii Gtottcronits, no 6, p jS''-J61
K'-um'.itk, V K, IVo /ur Bcvvtgung Jer Jranis«l>-Af|,'nn/n.h(ii Phiit
Geo! KuikKchaii, V 6), p 909-92^
lees G V(, IViS, Ihi gtolog> d/id tccioni,.4 i( Cirmn and oi pirts if
south tjsttrn Arabia Geo! Sot London Qunt Jiiir, v *i-(,
p SSS A-'O
Miresth, Vi V |V''4, J'Jjie ttitoniti ongin of the Caohdi in in m i an
system of northini South Amenta Discu-^ioii and proposal Gtoi
Soc Amtriid Bull, t SS, p t>69-682.
McKen/ie, D, and StIjter, / G, J9'''l, TTicevolurion of dtclndian Otijn
smce the L-itt ( rctateou* Royal Astron Sot. Geophyn Jnur, v 24,
P 437-J2S
Mitchell, AH G , 1974, Flysch-ophiolitc successions pv>lanty inditators in
art and coili-jion type orogtns: Namre, v, 248, p. 747-749
Mitthell, \. H, and Reading, H C., 1971, Lvolution of island 3n.s Jour
Geology,» 79, p 253-284.
Mohajer-Ash/ai, A , Behzadf, H, sndBerbenan, M., J975, Retietuons on
the ngidiry of the I ut block aod recent trustal dclonnanon in eastern
Iran, Tectonophywd, v 2J, p 281-301,
Mprfon,0 M, 19 ?9, The geology pf Oman World Petroleum C nrig, 5tii,
New york J959. Ptpc„ laic i, paf»er 14; p 277-294
f^OvurcHiii, A. A., 1972, Focal medwwiim of eanlwjuake* m Persia, Tiirkc»,
Weil Pakistan, and Afghanistan and plate tecroojcs of the Middle
Last iei^niol, Sot Affjtnca BulL, * 62, p W3- in
thr Oman Mountains geosjmclme: Schuctzcr Mineralog, u Pt irog
Mm,. V 4V. p i -30.
-Rt^rc, D., and Mahafei, S., 1972, A finst comnborwn ofthe MOcT RAP
agrecflKnts tv the kiiowle(%e pf Iranian geology. Pans, Ldmons
lechnip, p. I -JS ^
khraber, A, Wnpperr, D„ Wittekindt, H., ami Wolfan. R . 1972, Geol-
' - pgy and perrotruin potennais of crnttaJ and south Atghamsran Am
' ' As*oc Petroleum Ceok^sts Boll-, v 56, p ) 494 -1 > 19
Soffel, H.. Forster, R, and Becker, H,, J975. Preliminary polar i*ander
path e( central Iran, Joor Cwphysics, v, 41, p 541-543
Stocklin, J,j 1974, Possible ancient connnenial raargms ii Iran, tn flufk,
C A., and Drake, C L, eds , The geology of konnnental niarguis
Mew Vork-Heidelbctg-Beriin, Spnngcr-Verlag. p H'^S-Hd'^
Sfockfin, f,, and N'abavi, M. H, 1973, Tectonic map of Iran, Gtol Survcv
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671
MANUSCRIPT Rtd-fvto B\ THE SoaiTv AUGUST D, 19''6
RkVISED MANPSCKIPT RitrivED Drt£MBEK i", 1976
MAMPSCHIPT Acrri'tED FtBSOAay 5, 1977
rVi led 111 U S A

i« r, - " I,
1. V •
• \ , ' • • '.." '" •- v,!."' •• .,," r" '•,.'.."' • .. I .. . y^.). i" -•'.'V
' ' I
I."
The American Associstion of Petioleum Geologists Rulletli) |
V 53 No 3 (Mtrcti 1969) P 6^6 671, 30 figs !
Late Cretaceous Eugeosynclinal Sedimentation, Gravity Tectonics; and
Ophiolite Emplacement in Oman Mountains, Southeast Arabia'
Abstract The Oman Mountains border Ihe Cult of
Oman from Ihe Arabian Sea lb the- mouth of Ihe Persian,:
Gulf ' .-• :p' /•'•d "''-.;'" "'". -.' :
Tha Jebel Akhdar anticline forms the central, core of
the mountains ond exposes a section of massive.lime-;
stones which range in age from Permian (transgressive
on a Precambrian nucleus)* lo late Tertiaryi Ihe latter
fringe the uplift. Intercalated in this sequence, between ;
well dated latest Crelocebus sediments, is a thick, con^
loried assemblage of rocks.composed, from base to lop,;
of turbidile limestone ond rodiqlorian chert .(Hawosino.
Group), massive exotic blocks of. Permo-Trlpssic Hmesione,
and a thick sheet of serpentinic 'igneous rock
(Semail igneous series). This association of cocks, which
IS comparable to that known from many complex .Lpra-^
mide orogenic belts, con be'studied with'odvanlage.in.
Oman wheie Ihe sequence hoi .been lillle dislurlwd.
since lis emplocemenf during, the ..lotesl .Crefqceoyt
(Campanion Maestrichtian). :;.,.:, ;, : :>'
The absence of recognizable latest:Cretaceous fossils.;
in the Howasino, the ;common 'occurrence of well-prer
served Permion lo middle Cretaceous species, and the.;
contorted features of Ihe strata hove led some geologists
to poslulole that these, sediments were deposited but-:
side of thuir present location during a prolonged pre-'
late Cretaceous interval and then teclonicolly emploced
during the latest Cretaceous; However,' it is. concluded.;
from field data presented herein that the'Hawasina was
deposited m its present,location during latest Cretaceous
t i m e ':''•- ' '' -. . ' . .'
Regional stratigraphic -correlations show that northeast
Oman wai situated for'out on the Arobion - platform
where quiel corbonole .sedimentation persisted from ;
Permian lo middle Cretaceous time during prolonged;
regionol tectonic - quiescence. Sedimentary ond; fedonic
quiescence ended.,during^ latest .Cretaceous-time: when
' Manuscript received, December 26, 1967; accepted,
M

i^^
»ii*rtrtlfMHi >itfct>iHj|rf>HtiiiUlsr 1 ^•^•'tuiy../ -*'
ricun Association ol Pelroteuni Geologists Bulletin'
53. No. 3
Melbourne; Austrolto"
TIO pelagic shale, origlnaHng . from 'a
e, was deposited ocron northeastern,',
ont with major normol faulting. ' -r
ies, north of the Aruma province, give .
form of basal boulder beds, turbidites,
minat gravity slides of sharp contempor-;
n. Lower Hawasina deep-water turbidite .
yielded an inverted faunol sequence of-
Fossils, whereas the overlying cherty^
only pelagic Radioloria. Thus the'whote.'
t be older than the reworked youngest
us fossils present in, the basal beds.
gradtrtg, and constitution of the car'
lateriat in the Hawasina, and the align-,
limestone blocks indicate that the sedi-v
3 was a northwest-southeasl-trending upto
middle Cretaceous corbonate rocks,
jn MoiiT^-ins. The absence of terrigenousand
i 3I submarine volcanism sug- '
urce i*v_. was a submerged seamount.'
high is believed to hove been by means!^
ints activated by repetitive and at times^',
f movement, ' •.••fi
ments compare with present deep'Watet'''
e Puerto Rico Trench where faunolly :'
oozes of abyssal facies are interbeddedf'
turbidites rich in reworked older and,
shallow-water fauna. The absence of.^
(lotesr Cretaceous) shejf fauna in'the'
7Uted to the seamount source area being ^
ic, whereas the absence of contemporon-.
coreous fauna was the result' of . dis- v;
descent to abyssal depths.-Ttie latest
a Shale is compared' with Holocene
nal sediment occurring above 4,500*m .*
jh which received Hawasina sediments
been bounded by a steep block-faulted
whereas the southwestern limb became
lly through the neritic Aruma belt lo
tonate plotform. At the close of the
deposition, volcanism ond catastrophic.'
ling dislodged the remnants of Permo-'
sedimentary rocks from the seomouni,.
ded into Ihe trough ai huge gravity
Kawr, 250 sq mi), leaving the seomouni,'
isement uplift. Regionol tension relief •
finally by crustal separation and flood
if ultrobosic magma which blanketed/;
cope and cooled slowly, under grebt"
e, along the axis of the trough.. '
is interpretation, the sedimentation of .
:onsidered to hove been contcmporonesition
ot the latest Cretaceous Arumo
block-fault tectonism in the orogenic
with Ir^tjrswn latest Cretoceous tension
outh^f lasin slope. Compressionol.
DVrfOsiV^^^ ^,,e attributed to conlempor-„
umping of the beds on the steep
the trough, combined with-the subse-:
/ »
y-.i 1' si ; J/
Late Cretaceous Eugeosynclinal Sedimentation/S.E. Arabia 627
^'cquent "bulldozing"'effect which massive, slides of exotic duced the hypothesis of massive Upper Creta­
.'"..blocks ond _the thick Sempil eruptives hod on theiin-
;-'compelenl sediments-;. ,;;
;;>; Oil prospects;in the Howosino belt ore difficult lo
-,;^ej,plore and ossess for several reasons, not Ihe least of:
-which is the mosking effect which contorted chert has'.
ceous thrust tectonics to explain the complex
field relations of the. radiolarite . (which he
dated as Jurassic)," exotic blocks, and - serpen-,
tine. • . : '; 'i--- ' ' •
Von seismic ond gravity exploration for more simple
V'Structures in the compeleni sub-Hawosino limestone, iuc-';
•'cession, which;, is hydrocarbon-bearing below Arumo v
i Shole Ql,,Fahud,-'Notih,,and Vibol oil fields. . ; {-' '•"
. The same problem .was aiialyzed by Morton
,(1959), who dated the radiolarite series and ultramafic
rocks as Late.Cretaceous and attributed
their chaotic state. to contemporaneous
gravity-slide tectonics. More recently Tschopp
>JSTKOpVCTt(Mpdy: ';.:>• ; ' ' ••"; ^- ; ;';., .,;-;' •'''; ;(1967a) has coiifirmedMortph's: interpretation.
The Oman- Mountains form a spectacular,- ;;The complex combination of structural and
'barrier>tretching for nearly. 400 mi along the » stratigraphic problems which typify most
- northeast coast of Muscat and Oman. On the/; ophiolite/radiolarite eugeosynclinal fills,around
;northeast the mountains are bounded .by.; the ;; the world is magnificently displayed in Oman,
; deep waters of the Gulf of Oman .whereas on;,' ;where weak Tertiary tectonism has done little
•the southwest featureless grayel; plains stretch-f to complicate an already confused geologic sit­
;,;:into the wide expanse of the Rub-al-Khali sand;; uation. An attempt,is made here to analyze the
.^;>ea'(Fig;^i)..''y...;-;;•!,.'-../:;•..'- •, -• .,}.y,,py field data again and to try,to identify and iso­
;:• -The topography;of the mountains is rugged,;!;;' late fundamental and unequivocal evidence on
iwith bare limestone pealcs rising to 10,000 ft.',; •which to base an interpretation of the evolution
Deep wadi gorges with walls rising sheer to the,;:' of eyents within the Late Cretaceous ,e,ugeosyn-,
;f skyline cutvintb the limestone massifs. Vegeta-i;/. ;clirie!of,Omari^|;;\',vv;,;;;-:;{>'";;,;V5,;•'!;;".;;;.,.., -, '.i •--;
;;i.tion is.rcstrictcd to stunted thorn bushes except;.;-' 'RECIONAIL E>fVlRONMEip;V.';V.-|v.;';;'i,;, ,-, ^
t/at the wadi moiiths;;where villages, built;rouhd ^
^,; a 1 central fort,- are;;" enveloped by date palm i; ;'; ^Before considering the Upper Cretaceous ge-.
.'sgroves. On; the;;iiprlhern slopes of the moun-i/ ology of the complex Oraan Mountain area, it
?tains the town; of; Muscat nestles in a rockyj is necessary to describe the regional geologic
,, bowl with serpentine; arms forming a fine natu^v framework. N.ot only is it;important to piece to­
.^I'-ral'harbor..--.•;'.V;i is;';*';''.;^^! •••' ' '•'''''•'.! ^.-.p; gether the , contemporantJous sedimentary and
y. Geologically, the Oman .Mountains are dom-, •-structural
framework, but also when, as in this
•;inated.by three limestone massifs: the Ruus al - case, there is controversy regarding the time of
;; Jibid which forms the Musandam Peninsula; inception of the orogene (/>., Jurassic of Lees
;.;and guards the entrance to the Persian Gulf;';', ,i>ersu.f Late Cretaceous of Morton), it is neces­
;;the,-J,ebel-Akhdar'anticline with a deeply in-V;' sary to reconstruct earlier environments to ascer­
cised core exposing Precambrian rocks; and thei;- tain if po.stulated events and sedimentary condi-
Sayh:;Hatat; uplift,'a structurally coxnplex ,;v .tions;can logically have been associated with
; domed.feature which also has an incised core-,';' them. Strong events within an; orogene are
exposing Precairibrian metamorphic rocks.,; '• ;; ' echoed by weaker pulses in the more stable sur­
•'-, The'massive limestone carapaces of Jebel;, roundings, and slight changes in stratigraphy
Akhdar and Sayh Hatat, which range in n^p. and structure can aid; in the proper interpreta-
,from Permian lo middle Cretaceous (Cenomav;H 'tion of the set^uence. of events within the oro­
;}; nian), are girdled by a chaotic mixture of rar% genic.area,itself.-,,;.'|;-;...--,;.'-,\'•--,;.'
diolarian chert'and limestone and detached bx-'",; •: V. , ' Regional Sbratigraphy
•; otic blocks of limestone—all of, them, blanketed ;:j
by a vast.sheet of serpentinic rocks, ' :/'i .\:p^ 'iTo give a foundation ia time to the stratif"t,.
The mountain structure is framed by onlapry ;'graphic environment of the Oman Mountain
r-ping Upper.Cretaceous and Tertiary limestone.|:;'; orogeny, the; sedimentary "regimes, that gov-
Imbeds that form a fringe of lower hills aroundv; ;erned the area from the time of the Permian
jlj^the area. •-'/V; ;•'•';';-':' ;. '. ..''d^-dp.i^ •transgression over older Paleozoic/Precambrian
'ijf The first comprehensive attempt to analyze;?' ,"basement" until deposition in Cenomanian
-the geology of the Oman Mountains was made;.;-; time are discussed briefly, prior to the more
; # by Lees (1928). Lees' attention was focused on;;*; crucial analysis of Upper Cretaceous (Santo-
:;;•;• Uhe fascinating problems of structure and stra-, nian-Maestrichtian) facies environments.
'vtigraphy presented by the chaotic mixture o£> Perino-Triaisic /ac/e.v.—Autochthonous con-
^ radiolarite and ophiolitic rocks, arid he intro-;;, ,trol points for reconstruction of Permo-Triassic
s >^ ' ^ % : ^ . ^
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•%'••••'••.' ,"--• "'•'• ' • ? : • • ' V ' .* ' '•-,'...
628 H. H. Wilson
facies provinces are widely;spaced, from Kuh- ' basal Jurassic Elphinstone beds and Albian
e Gakhum in Iran (James and VVynd, 1965) Nahr Umr Shale, The Elphinstone beds, which
through Jebel Akhdar and Sayh Jlatat in the include green shale and sandy limestone, were
Oman;''Mountains V and ,;.southward through described frpm Jebel Hagab (Hudson et' ai,
Fahud j)hlo.;i.,; well. (Hudson and Sudbtiry, . 1954b)-r-an allochthonous limestone mass in ,
1959) • itcjj^the/lbutcrop ;area • cif Huqf .in the •4 'J northernmost Oman. The beds probably corre­
southeast,;>-,..:';^i;'f- .;-';"'•-•' -i,-,' •;;>•-;•' •..•^•-•'i-'''Xy late .with .the \Marrat Formation of Saudi Ara­
These control points indicate a steady southbia. The beds are not well represented in autochward
decrease in thickness and increase in terf.. thonous sections in Oman and it must be as­
rigerious.clastic content of the Permian strata,.- sumed that the source,for the.se fine clastic sed­
In Kuh-e-Gakhum and the Oman Mountain iments must have been far distant from the
sections.the.PermpTTriassic is entirely carbon­ : area now occupied by the Oman Mountains.
ate ;8helfliinestone,and dolomite. Likewise; air The Nahr Umr Shale (Albian) is wide­
lochthonousPermorTriassic blocks and re-, spread over Arabia, and the origin of the clas­
worked material in' Upper Cretaceous seditic material also is from the south and west. In
ments, of ;;the. Oman Mountain orogenic belt are the Fahud area the Nahr Umr is about 400 ft
exclusively of carbpnatecomppsition. The ex­ thick, but northward in Jebel Akhdar (Wadi
otic blocks (which are .considered torhave slid Mi'aidin), the clastic/eletnent has been greatly
trom the;,GuIf of Oman ;area) show a, greater reduced and marly OrZ»//o///ja limestone-pre­
thickness pf-Triassic carbonate; than, do the audominates, indicating a more seaward position;
tochthonous sections. . , >. . ;-' ••', Most;of the. Rhaetic-Cenomanian sediments
These data, coupled) 'with information on
Saudi Arabian ptitcrops (Powers e/ al.,^966),
indicate that Pefmo-Triassic seas lapped\ onto
the Arabo-Nubian continent on the south and
west, and that on the north, there was quiet carr,
bonafe,-shelf sediirientation across a wide area
indicate shallow-water, carbonate-shelf deposi- -
tion. A gradual thinning takes place northward
from Central Oman toward the Oman Mountains
and, in Sayh Hatat, much of the succession
seems to be missing, although absence of
recognizable fossils through dolomitization and
with.a carbonate depocenter ;lying somewhere .recrystallization prevents proper correlation.
northof the Oman Mountains. Throughout this However, the great quantity of reworked clasts
period the present site of the Oman Mountains (almost exclusively .carbonates) and fossils
was .characterized by quiet ^^carbonate-shelf, oi^iginating fix)m this interval which appear in i
shallow-water sedimentation far from any land- the overlying Hawasina sediments leaves little
mass - '-..y." ';t'-- ^.;;-'v' - doubt that a substantial thickness of car­
Jurassic-rntddle Cretaceotis fades.—-The
stratigraphic control points for this time span
are more numerous than those for the Permo-
Tnassic, particularly by addition of such reference
points as Qeslim in Iran (James and
Wynd, 1965), Rig as,-Zakum'(Elder and
bonate-shelf; sedimeiits of Rhaetic-Cenomanian
age were deposited, iiorth of the Oman
Mountains, /,e..' at least as far north as the area
from which the reworked material was being
derived (which is thought to have been the
Gulf pf Oman); :. ' . '
Grieves, 1965), and Murban (Hajash, 1967) From, this reconstruction it appears that
in 'Vbu Ohabi and'several well sections in quiet carbonate-shelf deposition predominated
Oman, in addition to' autochthonous field sec­ throughout. Rhaetic-Cenomanian time across
tions such as Wadi' Mi'aidin in the , Oman the area of the Oman Mountains and north of
Mountains The lithologic types across the en­ them. The end of the Cenomanian is marked
tire region are largely carbonate-shelf limestone by a regional hiatus at which the Coniacian-Tii-
with terrigenous clastic elements appearing on roniaa interval is missing. This widespread hia­
the south and west
tus can be' traced from southwestern Iran :
Two notable facies changes which occur in across a large part of southern Arabia, includ­
the monotonous carbonate sequence are the ing the whoje of Oman.
FIG 1 —GeneraJized geologic map and location map of Oman and surroundings containing all Arabian
localities mentioned in text excepting some in Jebel Akhdar area which are given on Figure 16 (see inset). Section
along hne D-D'IS shown on Figure 27. . '. ; - -;;;..',*.'
t T
•» ,»
m->
I

., - ,.. • , • •'!••.•• ••^'^^y.\'..'''y.P ^P -.y y d •
•. * - ' f . • -» I ^ ^'^: 4 1 -, „ ' ' •
• ' . I' ^ , ., . ^' V V -s, • ^ ' 1' ,. . ' "
' -, > ' , s
c Elphinstone - beds and;, Albian
lale. The Elphinstone beds, which
shale and sandy limestone, were
in Jebel Hagab (Hudson ef ai,
allochthonous limestone mass in;
Oman. The beds probably corrcT
Marrat Formation of Saudi AraT
arc not well represented in autoch-j
>ns in Oman and it must bcase
source ior these fine clastic sedr
have been far distant frpni;4he;
ipied by the Oman Mountains.;:.;;';
Umr Shale (Albian) is;wilier^
.labia, and the origin of the,clasr.
so is from the south and west ,In
r . i l , - * -• , - • » _ ' -
:a the Nahr Umr, is'about;40Q ft
^•f'^^
rthward in Jtjbel Akhdar.(Wadi -i,.;, • -jfJHitt.Jaiam
clastic element has been greatly
marly Or/j/VoZ/na limestone, prcTi
licating a more seaward position.5
; Rhaetic-Cenomanian sediments''
iw-water, carbonate-shelf. deposi-,il
thinning takes place northward;
OmP ward the Qtnan,Moiin-
baBWii*-. ;;'".,'(--';•;••..-J."-- -•^;;;-,i--'>-;-\
Jayh^^ itait, much of thcsucces-
".v:;,.-.v-v-V.,r%.'" -. (../,. !\',v''i
'• n • . ; i, .-,.',•..- ^ - . . . . ^'
be missing, although .absericevpf;
jssils through dolomitization and. '"f-yy.py •:•"-•"- '-Hi •: y d '"'>.:'V-.I%;T P^m,
VJ';':'-;-'';Ax," VA.'.'jv.'^v ...J.';.-" .-.'1';..';, ••:--':-i:. •• ,?'5fe^-^B
n prevents proper -, correlation, i'S'itefT'iy.st,;^';'*! '•^•-•/•''•Mn.'uaitiimiyr--:'*'-i^^^ii^^
^reat quantity of reworked, clasts -fc.-l:/.:../-;-/'*.^'?*-''';-^ ,-':••',-.' -.... .;i .^/(. ;/•*"'';,-.' .w*»i.«sf/:
M + y:^3ppppy.'i^^
sively carbonates) • and fos.sils" ^Py^:Py•€:'!=''*i *^vy i ;:.-•-•-•^-""H;;^':••;•^i;•;f;-•,^v',.ft^!|f j^^J^J tX:,d§0did:.'- P \d
^^ppf!>***

^•'\
•tj
» -
JlOS^
*-\
s' "n
U*
f
*« -f
' ' I*.
H. H. Wilson . .
^ I?
' '
'nlitii n'fti* I
In the Jebel Akhdar the Cenomanian, Wasia This tectolacies wedge is formed by the
Limestone at the top of the Musandam group i' radiolarite/ophiolite melange of the Hawasina
ot limestones is capped by 3'm of ferruginous and Seinail Formations of the Oman Mounoohtic
limestone (fig 15). The same ferrugi­ -:tains; ; :;.f.- ';;' •-'.'.•''" .
nous layer appears also at the top of the Wasia The Aruma neritic 'shale facies can be traced
in Jebel Qusaibah, 75 km southwest (Fig. 2). northward below the Hawasina complex, from
and a comparable tcrruginous interval occurs the Fahiid area, where il is more than 4,000 ft
in rubbly limestone at the top, of the Savak :thick, to, the^south flank of Jebel Akhdar where
Formation in Khusestan, Iran (James and it crops .out as the Muti Fprmation in .Wadi
Wynd, 1965) The shallow-water carbonate Mi'aidin in a comparable'neritic shale facies
ferruginous deposits ;pf. the Cenomanian-; about 670 ft thick, but,with intercalated con-
brought to a close a long period of carbonate-" glomerate! The Aruma Shale is rich in pelagic
shelf deposition, the original extent of .which Foraminifera, and Radiolaria,; indicating an
can be traced across a wide area of southeastr;:";;, open-sea environinent. •
ern Arabia and southwestern: Iran. Facies,con-j:;. ITie .regional depositional environment
trol extends northward .as far as surface jsec- v/hich can be interprettjd from the facies distritions
allow in the Oman Mountains. Since dis-,( bution is that of a broad carbonate shelf stradtnbution
and grading of the re worked. Juras-'-dling the greater part of. Arabia,. and grading
sic-middle Cretaceous material in Upper Creta-•^r northeastward into more open-sea and deeper
ceous beds of Jebel Akhdar indicate.a sediment "•; water conditions; The distribution and. lateral
source north of the present Oman Mountain,;-?.grading of clastic material in this model necesarea,
Jurassic-Cenomanian carbonate shelf fa-I; sitate a sediment source north of the present
cies presumably extended into the Gulf ofl 'site of the Oman Mountains.
Oman The reworked material certainly giyes ;' ..posl-Creiaceous fades.—Maestrichtian shal­
no evidence of any facies change or change-of low-water carbonate deposits which lie unconsedimentary
environment in the, area from : formably on contorted radiolarites in the Oman
which It originated >'} Mountains are. overlain, by Paleocene-middle
Late Santonian Maeitrichtian fades.—"ihc. ; Eocene clear-water Alve.olina limestone., which
Turonian Santonian hiatus is followed by the' • was laid down across a wide area. Good outfirst
major facics change in northeastern Oman;;,; crops of these limestones can be seen at Ibri on
alter the long period of carbonate depo.sitioh the south side of the Oman Mountains and also
From control points in Iran and southeastern' west of Muscat';on .the north side of the moun­
Arabia the original facies provinces of this tains. The scarcity of terrigenous material, par­
Upper Cretaceous interval can be shown, to ticularly in the middle Eocene beds, leaves little
have a distinct pattern (Fig. 2)., Thus, the' doubt tiiat the present mountain area was comdominantly
carbonate province, of the Aruma'. ;pletely,submerged during this period. Later
Formation in the southwest interfingers north­ Tertiary deposits occur in varied facies reflecteastward
with neritic marl and shale of the.-^. ; ing the onset of-the Zagros orogeny:
Gurpi Formation in Iran and the Aruma shale,.'
of northern Oman This rather .broad correla­
- ,; Regional Tectonics
tion becomes more complex in Oman, because - ': Pre-Campanian.—From the nature of the re­
the apparently contormable sequence pf the; gional stratigraphy, it can be seen that the car­
carbonate province (which ranges in age from' bonate, facies ranging from Permian to Ceno-
Santonian to Maestrichtian) becomes split to-;, ; manian time gives evidence for gentle epeiroge-
ward the Oman Mountains into a greatly exr' netic .movements. The stable Arabian area is
panded Aruma Shale of late Santonian-earliest ;
notable.for its tectonic quiescence, which was.
Maestrichtian igc which is separated ^ by a
ruffled only-by the "growth". structures that
major wedge of eugeosynclinal rocks J from ;
formedV traps for major oil accumulations.
overlying shallow water Maestrichtian beds.
Growth of these structures has been shown lo
Fio 2 —Reconstruction of facies provinces during Campanian lime, southeastern Arabia and neighboring
Iran Clasuc sediments arc interpreted as originating from the northeast probably by erosion of submarine ridges
by turbidity currents trig^trcd by seismic activity. Section along line D-D', is shown on Figure 27.
St»-
'\:i

•;" I I
^ »
i
« s
V. *i -1 * 1,'^, *' -• V *
a^ -_.AiM.Jfaa...•'. mi.fcMA>^. *.^w.. yi> iftAf-
> wedge is formed bv the
)litc nictuiigc ol the Hawasina
malions ol Ihe Oman Moun-
:ritic shale facics can be trated
' the Hawasina complex, Irom
where it is more than 4,000 ft
h flank of Jebel Akhdar where
the Muti Formation in Wadi
jtnparable neritic shale facies
ck, but with intercalated eon-
^ruma Shale is rich in pelagic
id Radiolaria, inditatiiig an
ment.
depositional environment
.'rpreted from the taeies distiia
broad carbonatt shelf str idpart
of Arabia, and grading
to more open-sea and deeper
The distribution and lateral
material in this model necessource
north of the present
Slountains.
s fay —Maeslnehtian shal
ate (^ /sits which lie uneonarted^i~adiolarites
in the Oman
verlain by. Paleoeenc-middle
;r Alveolina limestone whith
:ross a wide area Good outestones
can be seen at Ibii on
he Oman Mountains and .ilso
1 the north side ot the moun-
; of terrigenous m Uerial, parddle
Eocene beds leaves little
sent mountain are i was com-
I during this period Liter
)ccur in varied facies rellect-
; Zagros orogeny
bnal Tectonics
—From the nature of the reit
can be seen that the caring
from Permian to Cenoividence
for gentle epeirogerhe
stable Arabian area is
snic quiescence, which «as
; "growth" structures that
major oil accumulations
uctures has been shown to
»)r->-
jsij>'^'"'^-Vrabia and neighboring
byl; .an of'subinarinc ridges
Vll^r-fig igure 27.
K
Y' -1 1 I. j " '
Late Cretaceous Eugeosynclinal Sedimentation, S.E. Arabia 631
.^^n^rd.-nm^'i^'^^'mf^^^^^
-e"
' t

\ >
' *.V
. i
', , * . ' - IS 1 , ." .'«"*;.'. ' s , ,' , tf I
1. ( * • ~' .*- , . - • /^ •I'^'-'Z'd'i «'. r. 'v' •'-•:

'•j£u«A,
.m.£lrnk»t'^
r t '
I *
• /•* I, *'. -^
Late Crefaceous Eugeos/nclinai Sedimentation, S.E. Arabia 633
11.111 Mountains piescnts a ophiolite on the Jebel Akhdar anticline was cannot be produced to refute old hypotheses or
jumbled locks be-low the breached in post-Miocene time
build new ones.
enc uncontorniity.
Moie important in the reconstruetion of Eo­ In the Oman Mountains the Late Creta-
-7-Post-Crctaccpus tectumc cene paleogeography is the conclusion that,' if ..' ceous orogenic belt has been little disturbed by
an Mountains was miieh the effect of the Oligocene and post-Miocene j subsequent Tertiary tectonism and, in addition,
I tbe neighboring Zagros movements in the Oman,;Mountains,, is dis­ ;the striicture of this belt is'well ex|X).sed be-
•f Iran. Nonetheless, the counted, folding and uplift of the Jebel Akhdar '-cause of deep'dissection and a lack of vegeta-
)Ost-,Crctaceous movements and Jebel Nakhl anticlines would be-nearly; if. •; tion. •Re.solulion of the problems can be con-
I so that their total eliect not completely, eliminated.;: This conclusion is .3'iiiseci by the profu.sion of observable, data, but
lefore analyzing Late Cre- supported also by the scarcity-of erosional de-: ' an;;attempt is made; herein to resolve the style
themselves.
tritus ot flanking Paleocene-Eocene rocks. The. ,;';and sequence of events within the eugeosyninces
south and west of the distribution of clastic materiai:, in these rocks ;: cline as a whole, by reference to ciertain. key ob-
narked tectonic activity is suggests a source area nofthtjf Jebel Akhdar.. * v;fservations;where .field, relations are clear-cut,
ir;unconformity at the base
, ;.-",•'" ;-'-;'^j''v;-;'.'^,>'."-.;.-.;. ,.".;-. ?,;0f, these criteria the stratigraphic succession
nd post-Miocene-Holocene STHAIICBAPHIC succt.ssipN'tN;-;;;^;'-'i';;;v;' •?':;;'•; .displayed in Wadi Mi'aidin, on tbe south flank
ft, and. regional tilting
OMAN MOUNTAINS Evcis,ostiNCi.iNK-''X:'-.'::''X- ;; of'JebeL Akhdar;and the situation of the; Jebel'
veraents are , evident from •' Tbe chaotic mixture of sedimentary and ig-; ;=; Ka\w exotic bllockarefundameiitaL ;}'-,>;>>.
isgression of Miocene car- neous rocks which tilled the Ornan Mountains:
rocks. At Fahud, Burdigal- eugeosyncline ((Lees, 1928;;Morton, ;i959).is' .;;;j.;-*;V'f::.V';;Wadi.'-Mi'aid/n Sticcession-- •''::'X"
I angular unconformity on comparable with that found in similar sei.smi- ;:;:;.:';.VVadi" Mi'aidin is a .deeply incLsed dry river.
)Iy limestone. The difference > cally active troughs described, frorn, Syria and . ..valley which dis,sects the southeast flank of the
le greater part of the present Turkey (Dubertref, 1965; Rigp di iRighi .and, j;;^Jebel!Akhdar, anticline (Fig. 3); In this gorge,
hud( .formed before the Cortesini, 1964) and the East Celebes (Kiindig,: ^r there is a: continuous and nearly unbroken se-;
iph. J4»n.fie Omaii Mountains 1956b), to mention only ;twd of the many ex­ •i^tjiience^bf J exposures ' in' a'southward-dipping
ments were stronger, and ID amples studied All the typical/criteria such as v;tsuccession ranging from Permian dolomite
i Eocene rocks clip steeply , turbidity current deposits,;'contemporaneous: 'lying;unconformably on Precambrian rocks to
the Miocene is folded only slumping, "dumped" sediments/massive gravity «;.;Upper,. Cretaceous rocks, of. the Hawasina
ikhdar anticline was formed slides, contemporaneous erosion of submarine- fGroiip (Figs.; 4. 5); jThe.'section is especially
pre-Miocene Alpine folding, topography, tectonic erosioti,.ahd emplacement ^important to this study,, because it shows the
iank of fhe mountains, near of massive bodies of ultrabasic ;igneous rock' ;;;sedimentaty transition from Campanian neritic
imestone transgresses folded are well exemplified in the; Oman Moiintains,^ f'shale (ArumarMuli) into tHe, overlying abyssal
ies directly on Upper Creta- As a result of this complex admixture of rocks ;;tf;sediriients of the Hawasina^ Group and thus
iiinile and Hawasina-chert. it is extremely difficult to identify thS; original .{Clarifies the origin of the eugeosyncline. In a
rabian Peninsula, post-Mio- stratigraphic succession or clisposition of sedir; ;,• similar geologic setting in southeast Turkey this
pnerally are well displaced mentary provinces, without which a proper; ; ;;trans>tional sequence was obliterated by the exg
and folding iri southcast- analysis of tectonic events is impo.ssible. ;; :j ;;;rreme mobility of the back slope of the eugeoin,
1964) and by northeasticninsula
which resulted in Some of the more actite problems which, ; syncline.In fact, this is generally ;the case inre
sedimentary; cover from ^ beset the investigator in this inobile; belt are: .;;Cthe Oman Mountains also, v
'est of Riyadh,
(1) the distinction between allochthonous and . • . Upper Musandam {Wasia .Limestone).-^
intains, Miocene sediments
autochthonous rocks and the original location iJ The Wasia Limestone in Wadi Mi-aidin;is,deowe
ver, at least as impor-
of the former, (2) the extent to which horizon­ .veloped in; normal carbonate-shelf facies and
of the present mountain
tal planes of dislocation indicate considerable .'.the. uppermost part of this .sequence is comhoruontal
displacement or mere local slump­ ';.;; posed of a 3-m-thick bed of ferruginous oolite
cene vertical uplift Eroing,
(3) the controlling forces for the tensional "•packed with shell debris; This deposit is wideai-sed
to more than 1,000
and compressional structiirar features presl^nt;; '. spread and appears also at Jebel Qusaiba 75
udson et al., 1954b, Lees,
(4) the separation of contemporaneous, pens'-, r.;km.southwest; it is at the base of a major sediof
the most recent move-
contemporaneous, and • subsequent tectonic; !;me;ntary hiatus above which Turonian-Conialocks
at Jebel,al Abyadh
movements; and (5) the recognition of re-; ;;ciah sediments are absent. The depositional enow
stand at 5,000 ft; The worked,, commonly inbnogeneiic, fauna in a , vironment appears to have .been one of pro­
f alluvial detritus, which jumbled,^ sedimentary sequence in; which the; longed and widespread very shallow-wafer con-
h and south flanksof;;the sedirnents jthemselves. are barren of datable ditions, without variation over the site of the
;ry juvenile drainage pat- contemporaneous fauna.
subsequent Oman eugeosyncline, .. '
mselves confirm these
In such a complex association of rocks evi­ , ?; Basal shale, of Hdwa.'iina Group • {Muti'For-
>. On the basis of these dence can be produced to support many differi motion).—The Muti Formation (Tschopp,
0 suppose that the origi- ent hypotheses, and in many instances the situ­ 1967a) is named for a locality 10 km northeast
1 radiolarite and Semail ation IS so confused that unequivocal evidence of Wadi Mi'aidtn (Fig 4) In Wadi Mi'aidin -
^^^'^'tl.^fJ^I^M^.'WWglWi'f^ •rt^PlgpgSFPHiEB^WfP

,?j?^
1 »
Fic, .^.—Oblique air photograph of lower Wadi Mi'aidin outcrop area, on south flank of Jebel Akhdar, Oman,
southeast Arabia, illu.straling norma] contact,of Campanian .shale conglomerate of Muli Formation willi underlying
limeslonc of upper Musandam (Wasia Formation), Above the Mull Formation resistant beds of Wjdi Mi'aidin
Limestone conglomerate grade upward inlo thin-bedded radiolarian limestone and chert at Birkat al Maws
(bottom). See also Figure 13. For location see Figs. I, 4, 16.
o
1 ^
X
X
5
o
3
""te
R!-"; •"'
t ,
^,
f -
L*. %
K" ''•i"'*
Ksa /^"
» I. '
1- -.^ - -
I

Tl
rt
O
5*
8 E"
— c
o 5
8
.= E
I?
o O
a 3
^•P
E
c
•",5.
>
FIG 3 —Oblique air pholopiaph of lower Wadi Mi aidin outcrop area, on south flank ot Jebe! Akhdar, Oman,
soulheist Arabia illu'=lralinu normil contact of Campinian sh-iU crnploneratc of Muti Formation with underlying
limestone of upper Musindim (\\dsn Forn-ntion) Abo\e the Muli Formauon rcsistinl beds of \\idi Mi aidin
Limestone conglomerate grade upward into thin bedded ndiohrnn limestone and chert at Birk it al Maws
(bottom) See also Figure 13 For location see Figs 1 4 16
r
J-* '•-A

,^ belt of jumbled Hawasina t
beds At Jebel Qusaibah the Muti Formation
reappears as the basal shale of the Aruma, con- ,'
taining the same pelagic microfauna and lying j
on the same ferruginous oolite at the top oi |

out 670 ft thick and is com- ,
e which weathers olive green,
ition as an incompetent for- -
kvo massive competent lime-;
shale is intricately fractured'
il "pencil" shale. The base of .,
sharp lithologic break above ;
idam ferruginous oolite. The ,
shale is very glauconitic and ;i
tion there are several sandy;
c layers. The conglomerate •;
predominantly of cobbles.off;
1 (Wasia) limestone, com-^;
Praealveolina cretacea, but';;
ridam elements are also; pres-'fe'
calcareous sandstone. is' presT' -
of the formation, which is-;
ssivi;, resistant, conglomeratic ;•;;
the Wadi Mi'aidin. . - • vV
e contains a pelagic microabundant
Radiolaria and the "
fer/^'" 'ohotruncana carinatap
ori Jn as latest Santonian^ V
:uts the outcrop (Fig.'3) but
sly obscure the succession.;nee
to suggest that the forma-;,;
)ved from its original deposi-.;
can be designated conftdetitly;.;
nation in Wadi Mi'aidin is in;;.
y with the type locality on the -.'f
of Jebel Nakhl and can be • '
irth along the flank to include.'
lescribed in Morton's (1959).;;.
ion, where there is evidently a'
;rate content. Westward from;
le outcrop can be traced with-.
for 10 km lo a point where it ,•
' by the Jebel al Hawrah exotic
ff is considered to be due to.;-;
by the exotic block in late,^'
ne. • '. . , •:•.'•'.'. '^;S•
the mountain area the;, Muti;;"
ably can be correlated with''
s' (1928) section at Jebel Rais •;
th, with Fukhairi beds in the',
ea (Hudson etal., 1954b),>'.
a pelagic Campanian fauna isi;
I beds containing Musandam '•-.
;ments. Southward from Wadi;
,i F~'mation is believed to un-
1 ( ; of jumbled Hawasina ;
Jusaibah the Muti Formation';
basal shale of the Aruma, con-';'
pelagic microfauna, and lying '
ruginous oolite at the:top of;-
J'mi^iLMm,%^l.m.mj:JMmfi^9VWiS^.f/;mmi^.i!,!.
Late Cretaceous Eugeosynclinal Sedimentation, S.E. Arabia
the Wasia Limestone. Farther south ^toward
i Fahud, where, the Aruma is very ,vyell developed,
the: Muti Formation, correlates. paleontologically
with the lowerC. caW/K/ra zone pf the
SjAruma Shale,(Tschopp, 1967b)., The pelagic
• fauna of the lowerAriiina Shale and Mali For-
'':(\&tiqa' {Glqbigerina, Globotruncana, and Ra-
'diolaria) indicates an open-sea: environment
:;. with nioderately deep water. iThe, regional grajdalioii;froiii
coarse clastic cipntenl in.the Oman
^Mountains to'pure shale at Fahud and carbpn-
*atie; farther soijthwest;siiggests a. sedimentary
^tsource-area; northeast" of ;the;;/preseht; Oman
y'Moiintains;; :The cpriibinationfbf pelagic shale
JCand .conglomerate .in.the Muti-Formation sugigesls,
that;the congiomerate/was;.deposited in
Kfairly.deep water ..The presence of .Wasia Liiiiei;st6he
cpbbles'in the Muli Formation indicates
initial-,;uplift, 6f;'the sediment-source area and
Serosipi^-pfifuppernibst beds of the .Musandam
;Jlimestone;i;;group .(Fig, 15), ."The nioderate
;;;rouncliiig;.bf ;'spme'of iheVcobbles suggests that
|lhe^erGsipii,may,vhave been fluviatilc, i.e.i the
•'source area'was;emergent. Ill view of the con^.
i,siderable;:-volume of coarse and fine clastic
;fmaterial 'deposited (lower; Aruma!; iShale and ;
-*; Muti .Formation), it'is probable.-that, by the
i end.of this .sedimentary phase, a large proper-'
Sjlioniipf the Wasia (Upper Miisandam): had^;
gbeenstripped from the source area' and.the-
:• older .limestones 'exposed. The; presents; of
;^nearly';,complete ,Musandam /sections- in:'the '
v.'JebeL-Akhdar.'area (keeping in. mind the'pri- .
f.mary.northward,depositional thinning, Fig..27)
; shows that no significant erosion took place in
this region, but that it constituted a' deposi-;
Iional area. The cutout of Upper Musandam :
• section in Sayh Hatat, at; Jebel Rais (Lees,
;;i928),;'and Jebel" Hagab (Hudson et al.,'
M 954b) may have been due to later erosion of:
i.the back slope of.the eugeosyncline during the
'time of Hawa.sina deposition, but the very c6m-'j
,; plex fiicld relations in these areas do npt,allpvvr3;
firm conclusions.; •!•"'••.••
y, Wadi Mi'aidin Liiue.Uone.-yThc Muti, shale
(•and conglomerate are oyerlain by a topographjic-feature-forming
series of limestone and limer
;;-;,stone-conglpmerate.about-1,540 ft.thick. .The"•
; top.of the series is selected at the point where
;/radiolarian chert becomes the dominant lithol-
•'..pgy. Most of the -formauon is composed of
oolitic limestone,, usually with some clastic
;; material Included, and generally is thick bedded.
•Thin partings of carbonate mudstone. occur
;Vwithin .tins section.; Toward the top of the for--
';;'matibn;.limestone-becorhes thin bedded and ;
:; plalyi|>with;:^cherty? layers increasing upward^;;;
Ftc. 6.—Matisive angubr clast of limestone contained
iiix'conglonieratic beds of'Wadi Mi'aidtn Limestone.
Block is believed to, have bee;ii; transported to abyssal
;dcpths by powerful turbidity'currenis. Locality: Wadi
'Mi'aidin.;' -,'; '• '.y.' '^^-Xp' ;-;,'-o''••.','••
Sedimentary structures include; current Janiinations,
cross-bedding, and washouts. In the
thin-bedded upper beds there; are examples of
contemporaneous slump' structures (Fig. 10),
as well as loadcasts, "fucoids," large ripple
marks, and turbidity-current features. "
;;. The clastic elements range from, sand-size
paiticles to blocks 4 ft across (Fig. 6). Except
at the base of the formation, where quartz sand
grains are common, the clastic elements are almost
exclusively carbonates, representing a
wide, variety of limestone and dolomite (Figs.
;7„8). These elements are very poorly sorted
-and range in shape from angular to subrounded.
Commonly the margins are serrated.
vv The Wadi Mi'aidin Limestone contains a variety
of derived faunas both as fossils within
; conglomeratic elements and as reworked microfaunas
which have been washed from their
;6riginal host rock and redeposited, commonly
in an almost undamaged condition.. . ;
• The lowest beds of the formation contain
numerous Orfc»7o//'/ia. sp. (Fig. .9), considered
to be a monogenetic derived fauna. At the time
of writing no specific determination of the
large Foraminifera had been made and they
may belong either to the O. concdva group,
which occurs abundantly in the Upper Musandam
(Wasia and Nahr Umr Formations), or to
the O. discoidea group which, in the Musan-
wmm.'" j:irK,f:^z\^j*.y:'^T;s^W*f?'l^'W-J^^-^^d^. •.-.il

•»!..> 1
'I •-
.. I
.'•f* ' ' .'
* ' ' • -.
i'
-%
J
V. ,,i !^
1 '•'. \ --"'•'.• v'^ •;••-••• > - > V-, ; ' - •:.,.- ;.
. • : •^'••' •• • • ' .••••:'.. '4 , • - . • : . ' - -;.-'•:'.-/-" , -'• '•' ''• \ •
• •••• •.'' f p p p ••;?•••'•.?•>-.-:-:;;.=*;• •;;. •,.-.'!^y^ •••; -:
.?
' • ' .i
i

U'^
' ' . k •
i
/ I
I « w 0"
vv '"i .'-. '. *r*
:" ' • • ' ^•' ''^ '* ... •'?•"• . ''•••"•-• • ••'"' • '^- '' '. - • .
tijy^ll 1 >JMI IIIIII^-'-MA MIT • 1 I III. Ill I iiiih ^••TTiiTlftll'lliMtnnWIMlpPWWIWMllWiifflWW'^i^T^^TTlnTT^
fera occurring in the overlj ing
!iequencc the followingsmicro- 1
ollct ted. - • -.
llll
r.wr
irni)
/|,V
UXI
lU-il
Agc'range
Jur;i.ssic ''
Jurassic ,'
Jurassic , "'
Jiii:issic
rri;issic-Ceiu)maiii;in j
Jurassic-l-arlv Crct ILHUIS 1
gloriierute elements in many
gal debris and a large ptoporncnis
weie probably derived
c. One Middle Permian fusu
i;erina sp,) has been identified
ble contained larger Foramtnitentatively
idenlificd asiVrit-af
, The thin carbonatermudstone
sequence, as well as the upper
Is, cr^^'in abundant Radiolaria
valci ^.ina.
rom the field relation vyith the
i shale, the age of the Wadi
tone must clearly be younger
st of the derived fauna which it
the presence of Orb'tiqlina at
sequence and the probable oc
aea/i't'ci/i/ia-bearing cobbles es
this age can certainly not be
an and more probably is younmanian.
This proves .that not
Jurassic-Lower Cretaceous mt
Wadi Mi'aidin Limestone a debut
also that the radiolarian
sequence which follows nor
te limestone conglomerate and
tains derived fauna, is similariy
:ous age. The nature of the basal
le Muti, Formation leaves little
from hand specimen shown on Figure
r and rounded carbonate liihoclasis
cn dislodged from submarine canyon
ably been abraded and broken down
raiisport. Top left plate shows large
and "Oligostegiim" fauna. This lilho
habiy" ••:! right plate shows lithoelasis
of / - angular lithoclast of vugJ5y
iwo\~.6clasls of bryozoan limestone
op left, well-rounded pebble of loosely
represent last stage ot breakdown of
•!ii

- -l 5=.
t s ••
1 ' J'
T

't-n
i ^ g ^
Late Cretaceous Eugeosynclinal Sedimentation, ;S.E. Arabia 641
were deposited. Abyssal depths exceeding gin for the reworked oolites it is noteworthy
25,000 ft, such as those now found in .the' that oolitic limestones are not well represented
Puerto Rico Trench probably were dominant in?; in the.Musandam limestone of Wadi Mi'aidin
the Oman Mountains area at that time with the., or its equivalents on the south. .However,
• result that the delicate calcareous tests of pe­ 'oolites are an important constituent in the Jiirlagic
Foraminifera; would have, been dissolved" :;;assic jlimestones of northern Oman (Hudson
during;their'Iong;descent to the sea bed. At • and Chatton, 1959) and in the Neocomian
;r pill... of Wadi Mi aidin Limestone
rial in center ut held u> r idioUnan
the same time the tests' of Radiolaria survived { 'Fahliyan Formation in southern Iran (James ,
the jourtiey ;because of the relative insolubility ,• and Wynd, 1965).,; These . formations may
'•,of silica at extreine depths.. Under these condi-;,? jtherefore have been the supply source .for
ttons deposition, of' the Wadi Mi'aidin ,Lime-' graded oolites in the Wadi Mi'aidin Limestone,
stone iriust, have",beet) through the agency; of; '^a supposition which is supported by the presturbidity
currents; as described by Ericson^ eljl ';,ence of well-rounded, .oolitic limestone eleal
(1952); ifor,.the preseni Piierto Rico Trench;; >?inenti5.in the formation (Fig. 8), The coarser
and Nares; basin.'One might expect conteinporr- •;:;and more angular rock fragments; occurring
"aneous pelagic;or shallow-waler fauna lb have) ;; within, the Wadi Mi'aidin oolites may have
been;;swept, in from the;basin,;shelf, together: •originated from lateral slumps along submarine
with;;;the /eworked faunas jfrom older rocks.; vcanybn courses. The,serrated margins of many
However, apart from the "rare Globotruncanaf ifof the limestone'conglomeratic clasts may be
sp".;;repprled/by Mprlon (1959) from the de-f; due tp preferential re-solution of tbe calcium
trital limestone of. the Wadi Semail section,, .;;carbonate during transport to abyssal depths or
there is.;no.evidence of washed-in, datable, con-;^ ;;verful ero-
[itly normal relation with the;;' >abrasion only in the turbid medium provided :;fsional force on the backslope of the ;trough
Formation, the inverted se-;,^' by density currents. The poor sorting of clastic;;' 'down which they flowed.
on products from the domi-,- 'elements (Fig. 7) is also typical of turbidity
;ments in the Muti shale, into, ^ ."current, deposits described from, many, parts of :,i Some evidence regarding the gradient and
liddle Cretaceous-Jurassic ele- :, Iheworid. The oolite which forms the matrix "'direction of sca-rfloor slope at Wadi Mi'aidin is
di Mi'aidin Limestone, displays ., j of most Wadi Mi^aidin Limestone strata (Figs.- .;provided by the slump structures in the upper­
lal erosional-depositional 'pro-'-'; 7, 8) poses an interesting environmental probr. most beds of the,formation (Figs. 10, 11),
ii'lem; i.e., the incorporation of angular limestone:. .where slump fold axes strike WNW-ESE and
lal environment of the':Wadi' ;. 'clasts (Fig. 8) and borings filled with radiola-' ;:thereby indicate a SSW slump or gravity creep.
5nc can be extrapolated from, >; • rian niud (Fig. 9) eliminates the possibility: - 'The Wadi Mi'aidin Limestone crops out
criteria. It is remarkable that»,:; that'the oolites are i>i situ, shallow-water de­ 'above the Muti Formation along the southeast
luna consists almost entirely of;; posits. On the other hand, if the oolites were ' flank of the Jebel Nakhl anticline but is cut off,
eas the older Muti Formation ,,,re worked: from a contemporaneous shelf envir with the Muti Formation, west of Wadi
Aruma Formation (which iS'-;" *'' rohment they should contain traces of a'con­ - Mi'aidin. The cprreilation of this formation
e contemporaneous with the - temporaneous Late Cretaceous shelf fauna, but across. the Oman Mountains generally is not
sediments) are rich in pelagic ' ;(;tbis has not been found. Available evidence clear because of the extremely confused field
minifera as well as Radiolaria.';';>; ;v,.suggests that the Wadi Mi'aidin oolites are sec- relations. However, the basal oolitic, microcon-
1 of the depositional areas can;!-' i^ond cycle oolites reworked from older oolitic , glomeratic limestone with reworked Orhitolina
ived such a radical change inj'v : limestones; the freeing of oolites from the par- that crops out along the southern fringe of the
iditions as to prevent the pe-;.!, erit rock was accomplished by turbidity current Hamrat Duru and which is in tectonic contact
calcareous tests from hving,, v V, washing action during long distance transport with the underlying Aruma Shale near Jebel
th/ liolaria lo thrive. The-; - into deep water in, the same way that contained Qusaibah is almost certainly the lateral
rtaiiir^'is related lo the depth', Foramimfera were released. In seeking an ori­ equivalent of the Wadi Mi'aidin Limestone.
1 the Wadi Mi'aidin sediments
It is probable that the formation was im-
aiBWasiBasjMiasssBBBSfflrarannmssnjii

'J. i
^^' - ^ ;- -^
r
"-,5,. ! " ' **' .*
r
•
»1. , •
!• 1.
•f
•e »
t »
Ik r
,-* , ' -'r '^
> bit
.4
• ^ ^
I ' l l
A '''' ' '
IT**.'
'"pyP
- -^ '
I
If.
'7
Y It
>• - I '
f
I
1
K
?
)i
1
FIO. 10.-—Beds of oolitic (turbidite) limestone alter- ,
iiating with cherty radiolarian limestone showing (pre- |
lithification) contemporaneous slump structures. •
[•• Sf'.d- ' ""V'' ir • ^•«t^'''-\'^-V«rf~ '" •^^'^Pl
J y^fti «''.•.7'iSiyTTvf.'•< *.;~!r-ft.'*i*'''?l#l
vr^lSl^^^!iSSKmk'li^siS(!^Sf^S^SS^ff^^^!S^4^>l^i
Slumped sequence is folded (right hand 'side of phoio) .'
-^y later (posUithification) movements, probably con- \
temporaneous with terminar terminal Hawasina exoiic block ! j
slides, Beds belong to transitional .zone between Wadi i
Mi'aidin Limestone and "radiolarite: complex" and are i
exposed at entrance, to Wadi Mi'aidin. Location on .f
Figure 13. ;;;";i ;,,,._ ',--". ..,..-- '\
. . . - - . - ' ' ' , . ' • - , ; . - . . - - *
-- y f f j . f . - . . • , ; ' • . - • , . . , -
5 v«w; . , , , • . . . . .
evenly deposited in the form of deep-sea fan- \
glomerate, with lenticular masses being depos- j
ited in front, of the principal turbidity-current ,
channels; Toward the south (Hamrat Duru) f
and away from the source area the clastic ele- \
ments become sniaUer in size and reduced in i
quantity., V; (.
The conglomeratic content of the formation |
indicates that the submarine ridge which constituted
the sediment-source area had been
FIG 11 —Contemporaneous deformation of cherty limestone and oolitic limestone. Diagram is. taken from -
Figuie 10 with vertical dip removed. Underthrusting toward SSW probably due to gravitational creep of uncon- i.
solidated sediments down northeast slope of Hawasina trough. ,'
W5Mf«t«rrtiM>-JLJfegMV'Bfflg5i!!SrsWB'

f OOIIUL (turbidite) limestone alicr-
' radiolarian limestone showing (preiiteniporaneous
slump slructuies.
is folded (right hand side of photo),
licalion) niovcmcals, probably con.;
h tcrniinul Hawasina exoiic block
K to transitional zone between Wadi
e and "radiolarite complex" and are
ICC to Wadi Mi'aidin, Location oh-
1 in the form of deep-sea fan-;
lenticular masses being, deposthe
principal turbidity-current;
rd the south (Hamrat Duru).j
the source area the clastic ele--;
imaller in size and reduced in;;
;ratic content of the formation
e submarine ridge which consti-<
,ment-source area ,ha,d been'
lit ,ie. Diagram is taken from
le Kf-gi:avitational creep ot uncon-
',
i ,< *
- V. ' 1 - ' I •
t...,Llti.•AJfaJa^i.;•,„^:JLvAfe^Allria^.:Ai;LA'..?A^a^rJ^j.i^
^i
- ' i: -•. ' dant Campanian fauna. However, it is not ceri;S;;Mbst'
of fthe Hawasina Group, which; crbps; ; tain whether, this represents an interdigitation
Oiout across .a,wide area (Fig. 12)-, is considered; .of Arijma or whelher.iit is the noain bpdy of the
• ;uiider5;theiterin ;;"radiolarite complexii'VvThese ; .(Muti) Aruma. -• ,
:sediments,:which have been described in some;- ''/Although there is no unequivocal evidence
/detailjby .Lees ,(1928), are characteristicallyy .for dating the "radiolarite complex",by its conthin;bedded
to flaggy, and the dominant lithp-'- ' taihed fauna, its lower age limit can be fixed by
logicvtypes are: radiolarian chert and porcelaf.-, reference to its normal contact with the transi­
, neous to,dense limestone with numerous thin tional radiolarian. sequence, at the top of the
intercalations of fissile shale. Colors are. typi-,;; jiVVadi Mi'aidin Limestone. This relation is por-
cally red,; green, and gray. Toward .the top of;; j trayed in the composite stratigraphic column
i; the series; spilitic. volcanic rocks. are interca- f \(Fig; 15) and in the Wadi Mi'aidin structural
:;iated: along the.northern and central parts of-, ;, cross section (Figs. 4, 5). , i; •
the outcrop area. This sequence of rocks is ex-: , , The depositional environment that, governed
tremely .incbmpetent; and, quite apart from the ' Hhe sedimentation of the"radiolarite complex"
structural complexities resulting from contenK,' is believed to have been dominated by the abysporanebus
movements, their response lo the se- -, ;sal water depth which had been established
vere;;terminal orogenic deformation has, been;', .during the;preceding Wadi Mi'aidin Limestone
suchi'asilpi,obscure their original relations with;, ;-phase. However, as can be noted from the exis­
the older sediments. As a result of these structence of the transition zone into thin-bedded
tural; complexities; it has been impossible to; limestone and chert at Wadi Mi'aidin," the rate
measure a;true stratigraphic thickness for the.( .;pf clastic (particularly coarse clastic), deposi-
' radiolarite; complex" arid even the gross thick­ , tion was greatly reduced during the deposition
ness is characterized by great variations. Lees'; of the main radiolarite sequence, "
(1928),Jebel Rais section measured more than ' .;' Depositional conditions can be compared
5,000 ft;l?ut; considerably greater thicknesses; with lho.se of the Nares basin and Puerto Rico
certainly!-,accumulated along the axis of the \ ; Trench (Ericson et ai, 1952), where red silitrougH.:;'
;'

i»
*'"
.^'
s t *. '
t.<
c**'.
t i
>»
*. *
) I t ^'
i
1 I
Ra* Madhrano—
•
, - :',:•
, '•
• P-'
/ • *
' / *
T"
N
'•. 1—^ ^
...-. . ......
^—fl
.
•
-y t
y /
, /
^ ~(/fas al Kobth) >
MASIRA .^.
^
• J -I» . ^Y'^ =T*? "'T^ 'r^FT^-^'W; -.,s P'-l
-N

.;!>?'
R A N
I. , ' . ' '••-
IL F OF OM AN
"O/-/
> • *•-??- '-r ^
y.', ,.^ '^/.-,-v^''"' """^.^ic^
Fit, 13—View west'across Wadi Mi'aidin mouth at Birkat al Mawz illustrating thick-b«:dded Wadi Mi'aidin
Limestone conglomerates, pn right, paitsing upward into thin-bedded radiolarite series.. Morphology of radiolarite
slope has smoothed aspect possibly due to tectonjclieveliag in late Campanian time by massive gravity slides such
> as Jebel al Hawrah.in left background..Contemporaneous slump^ structures shown.on Figure 10 are located in
thm bedded series in middle distance above geologist's head. '' ;; ./ - ,,, ; ' '.''•''
fauna is restricted to Radiolaria. However, a;
-.notable point of difference in this analogy is
;.the nature Vof, the respective reworked fauna
.since the ;Hplpcene abyssal ^sediments sampled
/.by. Ericson W;a/. (1952) in the Puerto Rico
Trench contain an aibundant contemporaneous ;
fauna swept off the continental shelf and island .,«-.
margins, together with reworked faiinas from'
older sediments, whereas the Hawasina carbon- ; k
ate turbidites are dominated by faunas re-, .j'
worked from older rocks to the exclusioij of.; ,|,
contemporaneous forms. •' • ; - f
As was- postulated for the Wadi Mi'aidin t
Limestone,/, it seems that, the'source area of |;
Hawasina turbidites was not. a shallow-water ;'
continental margin nor an island archipelago,
but rather' a submerged seamount, situated '*
below neritic depth and starved of shallow-water
fauna, .and rising from abyssal depths as a
block-faulted mass of Permian to Cenomanian
carbonate rocks. Evidence to support a seamount,
interpretation i,S; the dominance of re­ FIG. 14.—Turbidite flow structures in granular,
worked, carbonate rock particles in the Hawa- limestone with thin cherty layers from Hawasina
sina tip,the cx.clusion of" terrigenous material -"radiolarite complex." Locality Jebel Yankul. Location
;. .-.,.. ,?;" .;:"' ' . . ' ; -on Figure 1 nortli of Ibri.
•i-m « I.
Fio IZ-rrMap-of OmarilMountains area illustrating location of Hawasina radiolarite facies outcrops with an
•;-. ;';'• :. .''-, ••''. • extrapolation of original area of deposition.! , . '

1^^ ,
m^^ '
I •
* -' r . n" *
A I * » ->
k «a r •!. -. ,
WADI MIAIDlN MEASURED SECTION WITH
SUCCEEDING SEQUENCE ESTIMATED BY
CONSTRUCTION ALONG SECTION LINE-BIRKAT AL
MOWZ- JEBEL AL FAY - BAHLAH
-1 -.^ ^ -;-
W* P-uy S^Sfr'^^-iW-"^*"* ^V".*^Mt^J^^,(,.^*yi».,jF^
r c
Coorse texturt ultramafics of Bohloh synclin* Mainly Mrpent ni>td
ond bonded pendolili Full thickness not shown
Lst (of Jcbtl ol Foy) eiotic blocli cmplocod by gravity sliding
&.9I mass «n snaiifroo Probgbiy ^rmo-Triassic ogi iNoi sampled in f leid }
Tectonic contact- tlidt plan*
Schematic inlerpretolion of sequence of Rodloloritc. Cht, red, bm and gn, tnbd with
Inlercotatcd floggy and ploty Lst, barren ef contemporaneous founa (eseept rodieloria)
."fucoids'l lorge current ripple marks, lood costs,etc Whole series much contorted —
;praventlag true thickness estimate
TOP OF MEASURED SECTION IN WADI MI'AIDIN
Tronsition sequence lo "typical" Rodiolorian Ght series Lynand Len of rodiolorian CM olternoting
with platy Lst with "fucoids"etc. and ool lime Ornst. Contemporoneous slump structures.
Lst, m bd od,often gritty and cgl.Lst with ong and poorly rnd elements of older Lsl-
Neor base Lstscontain increasing quontilles of Oz Grn, Reworked Orbitolino
1.
1 n 1
Key h) abbt^viahons I
Is^
mass
k^A
C/t/ir/t
g/7
/>7A/
Len
OO/
6ms/
m6d
.eg/
a/7y
A/7

TOP OF MEASURED SECTION IN WAOI MI'AIOIN
Tronsitioit sequence to"typicol' Rodiolarion Cht series Lynond Len of radiolarian Cht alternating
with ploty Lst with "fucoids etc and ool lime 6r!\sl Contemporaneous slun-p structures
Lst.iti bd od,often gritty and cgl Lst with ong oni poorly rnd elements of older Lst
Neor base Lstseontoin increasing quontities of Oz Grn Reworked Orbitoting
common neor bose.? Pragalvoltno og. pr#««nlInCql «lem«nt» Reworlted Jur0«sic
Prb«olvBolincr croocQO tntoy^Sfr^j^^gin^yf^p "li''J*? XnVfcT'^^^^^'**-' * *' -"
3m fe ool Let tProbobty represents Turonian-Conioclan time gop-Regtonal disconformlty)
Lsl,(y, bioelasllc with prqeol»eoIina cretoygp
Lst ai«d Sh. obd Orbitetino concovo
fe Lst ol contoct
Lst, dhgy-blk bioclastic
Abd Orbitolino discolded
Del, gy with FusuHelds
Do) dkgy-blk
Trilobites (Phltipsldee) Productids. Corols. ete
r
Afa's/
//
rvx
/4?C
Be
Ba
//
Afua's/c/?e
J,fA/
r

^.f
. "
X-v
? 1 t
V
I
^ji.*^'
M-r,
,»8f I
'A.
s
' 'i
tf
if T
I HI--
-11 ' -
y» "sr
' l . l
t
" • . . '
"^ ••'-'•"-' •* '*'"M-rf^'iiitidfcM.ii''t' lihii -iiWYtirli
j ' A,*'""'''''' •* sA i I
t iiAiirflmitiinfarirh/i'rf I irssilnViii'>.^te*iAj^
f
648 H. H. Wilson
I
[
and plant; debris. Furthermore, the terminal smaller exotics of the pre-Permian "basement" t
volcanism was almost exclusively submarine. have been recognized. ,- ,- " • ,'
Thus; the Hawasina sediments may represent The post-radiolarile exotics occur.northeast, i'
tvpes that , were completely independent of of a fairly well-defined line which trends I
terrestrial erosion and that VesuUed entirely WNW-ESE in continuation of the Jebel Bu- fj
from submarine seismic activity which triggered waydah ^ axis .- (Fig. i= 16). - This limiting line prob-
powerful'turbidity currents. Such sediments ably coincides with the axis of the abyssal f
could be expected in the abyssal depressions trough toward which the exotic blocks gravi- |
bordering present-day seamounts, such as the .lated.. . . -j
Saya de Malha Bank in the Indian Ocean east • Individual examples, and particularly Jebel j
of Madagascar (Heezen and,Tharpi,; 1965) and;; Kawr, provide basic informatibn on which to %
may only now be coming ;wilhin reach,of the develop hypotheses regarding the origin of the |'
oceanogfaphers' exploratbry equipment.;: . exotics. Jebel Kawr is a massive limestone ex- J
Iri the; ceiJtral and northern part of the "ra­ otic which forms a mountain rising sheer for f
diolarite; complex"-—for exainple; in the Jebel neariy 6,000 ft frpm low-lying hummocky to- ;
Rais.area (Lees, 1928) and near the village of pography carved out of the surrounding radi- (;
Amlali-^vyest of Jebel Kawr)—there ;are good ., olariles (Fig. 17). The outcropping part of the /
outcrpps'pf .spilitic pillowlavainterniixed with'exotic: exceeds, 600 ;sq kin in area, but to this j'
radiolarian, chert, "These submarine volcanics, must be added an unknown eastern extension j
which appear in the uppermost part of the se- ; which plungesbelow the Semaii; Structurally, |
quence, did not extend into the southern part ' Jebal Kawr is a huge raft of probable Triassic i
of the radiolarite trough and there'is no evi-;; limestone, more than'3,000 ft thick, which is |
dence of them in the Hamrat Duru area.'The; folded inlo distinct anticlinal and synclinal ele- !'
lavas; probably were extruded through tension merits. Folding is thought to be late Tertiary |
fractures; which developed along the"^northern (contemporaneous with the.Jebel Akhdar fold), |
margin of the trough, presiumably just north of and the raft was, probably emplaced as a sub- f:
today's Batinah coast, from which lavas flowed horizontal sheet;; •;;?•:
southwestward down Ihc subsea slope to abys­ . Jebel Kawr is underlain by contorted Hawasal
depths. The late occurrence of volcanic acsina radiolarite, with a slide-plane contact that
tivity in the, radiolarite sequence prompts the is visible iti the eroded core of the anticline and
deduction that;any, silica enrichment of sea­ along the northern margin of the block. The
water ;provided:by ;such' volcanism could not limestone exoiic is-overlain by ultramafic ig­
have contributed to the siliceous content of the; neous rock, an outlier of which is preserved in
radiolarites as a'whole. •
theSint syncline (Fig. 18),'vvhereas the main
Although Lees (1928). reported tuffacepus mass of Semail,ophiolite is preserved in the |
rocks in the Jebel Rais area, there is little or no steep plunge of this syncline at Al Ala (Fig. i
other evidence for subaerial volcanism and
there is no doubt that eruption was mainly sub-',;
marine.:;;;'-',,;'.--;;' .;.'•'' -;•.' ' ;,---'','_ r;;.-'''.';
;-,::}:-';"-';.--'-, .Exotic Blocks-'-'•-;•
Exotic blocks, principally of liniestone, are a
,19). • ••' '•;•';.'. I
The Jebel Kawr limestone, measured along -
Wadi Nadan which dissects the southwest flank |
of the Kawr anticline and breaches the radi- ;'
olarite core! is d= 3,100 ft thick (Fig, 15) and i
consists mainly of light-gray, massive limestone [
spectacular feature of the geology of the Oman', beds with several zones of limestone breccia.
Mountains. Relatively small exotics occur in possibly .solution breccias indicating the origi:
the Wadi Mi'aidin Limestone (Fig. 6), but- nal presence of evaporites in the sectioii. The ,
they are insignificant compared with the moun- - basal beds of the seqiience are breccia conlaintam-sizeplistostromes
which followed the depo- ' ing elements of red chert atid volcanics ifrom '
siiion of the "radiolarite complex." The most the underlying Hawasina. ;
spectacular exotics in the post-radiolarile suite The fauna of the Jebel Kawr limestone is {
are composed of white, generally shattered, and largely nondiagnostic because of recrystalli- [
recrystaliized limestone which stands out in zation. The uppermost beds contain tintinnids ,'
contrast; to'the darker radiolarite and serpen- ,of probable Berriasian age, but at lower interr j,
time rpbks in which they tie. The limestone vals the most striking fossil is a very large lam- |.
blocks are mainly of Permo-Triassic age (Lees,- ellibranch which is found in abundance in sev- '-
1928), but iii a few places Jurassic to earliest eral beds and has tentatively been identified as -t
Cretaceous carbonates are represented. Other Mcgalodon sp. Specific identification is pre- ii

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late Cretaceous Eugeosynclinal Sedimentation, S.E. Arabia 649
I the prc-Permtan "basement" vented by complete recrystallization of the shell obliterated. In addition to the . large exotics
izcd
r, structure a,nd bticause the fossils are welded shown pn the geologic.map (Fig. 16) there are
larite exotics occur northeast •t'-'into the;matrix of the rock; !From,available evi4 nunierous; smaller ones. The chaotic picture of
ll-defined line which trends :;;dence,-"lhe;Jebel Kawr limestone could range in; ;; random blocks of limestone ."floating", prcca-
antinuation of the Jebel BU-.J /age frpm Permianto earliest Cretaceous. How-'; jjfiriously in a langled"sea" of radiolarites is typi­
;. 16). This lirniting line prob^; i/^ever^j^Jsince;;Permian limesfone, even in exotic/ cal of tht; whole of the central and northern
/ith the axis of the abyssal ;4iblocks; generally contains easily identifiable fu-; .parts of thie "radiolarite complex" (Fig. 21).
hich the exotic blocks gravi- "ilsuiinids; (Lees,; 1928) which do not appear in; ;' Although Permo-Triassic Umestone com-
;tthe:-Jebel, Kawr beds, most of this limestone ; prises most of the exotic blocks, there art; premples,
and particularly Jebel' I *may, belong to the Triassic, with perhaps some Permian blocks, specifically at Said bin Sahran
isic information on which to ';• jJurassiCrBerriasian at the, top. Cprrelation ;bf ;,(also known as Khadra) 35 km east^sputheast
;s regarding the origin of thei- ;pthe*iallpchlhoiious Wadi Nadan section with the;; ; of Wadi Mi'aidin. At tliat locality an anticlinal
NT is a massive limestone eXr;; ,%utbchthohous Wadi Mi'aiditi section (Fig. 15) structure formed of Hawasina beds.rises out of;;;
a mountain rising sheer-'for'' ^shpws,; that; the Kawr section; is the; thicker?' ;; ;the blanket of Semailserpentitie.fFigsi 29;.30).
rom low-lying hummocky„ 10^5; |,*eyen; if the;whole Mi'atduj Permiain seqiience isS |;0n the; southwest plunge of the Said bin Sahran
out of the surrounding fadi-'^ ^4included;--:';* •,•;','•;; ^•p¥''^:'PP'-.-'y.' ;•*• '-''..y'^'x'ii ;.featureis a raft, about 300 m long, of;chlorite
. The outcropping partof the-' IfV (;Much;;thicker Triassicssequences than those Ischist resting on jumbled Hawasina and over-
•0 sq km in area, but 'lb this-; present in Jebel Akhdar have beep measured in* :.lain by serpentine.. On the north, along: the ,
n unknown eastern extension^ Wadi_ Mijlas on; the north flank of Sayh; Hatat ••} flanks of the uplift, Semail ultramafic rocks lie
ilow the Semail. Structurally,-; v;(40 km southeastpf Muscat), .where carbonate; directly on radiolarite and limestone exotics; It
luge raft of probable Triassic; 1; rocks tentatively assigned to the Triassic-Lower; seems probable that the Ais epidote schist and/
than,,.1.000 fl thick, which, isi Cretacepus;'exceed 4,800 ft in thickness; in; >. quartzite described, by.; Hudson el ai (1954a)
:t a nal and synclinal ele-' .•jjebel Hagab (Hudson•«?;';«/,- 1954b), where ;,in the Jebel Qamar,area also constitute exotic
thfcwjint lo be late Tertiary,' ^ ?2-560 ft pf Triassic is present; and in southeast-, blocks derived from .basement.;The position of
> with the JebelAkhdai; fold);;; ^ern Iran at; Kuh-e-Gahkum( James and Wynd, the Ais metamorphics between the ultramafic
probably emplaced as; a;su^:'! 1965);; where.4,500 ft.has been measured; Ap ;'- rocks of the ;Silayah igneous series and the
; thoiigh these sections may,have been displaced Kharmil chert (which are synonymous with Se-,
inderlain by cpiilortedHawa-:^ tectbnicallyl from their; original locations, iij '•ifmail igneous rocks and Hawasina radiolarite)
ith a slide-plane contact that, . coraparisoriiwith Wadi jMi'aidin and other auto- is exactly the .same as that of the schist at Said
aded core of the anticline and- I ,;chlhonbiis-;sequences in JebeLAkhdar, they in- bin Sahran. Similarly,,; the imetamorphosed
n margin of thje block. The;. J; ;dicate a nbrthward .increase in original Triassic; amygdaloidal basalts of the Shamal beds de-:
is overlain by ultramaific ig-; y' depositional thickness. It is therefore concluded .scribed by Hudson f fa/; (1954b) in the Jebel'
tlier of which is preserved in • .;;that the Jebel ;Kawr limestone, slid from an /Hagab area are probably ''basement" exotics.:
(Fig. 18), whereas the main ;'original position far.north-of the present Oman Not only does the trachytic, amygdaloidal na-;
)phiolite is preserved in the jMpuntains—probably from a location now in "tiire of the rock closely resemble Hormuz vol­
[lis syncline at Al Ala, (Fig.;: ',i;;,the Giilf of' .Oman';;',In fact,' the derivation of' canics described from salt domes in- southwest-;
;these blocks frbm any other direction is pre- em Iran, but also the presence of terrestrial
r limestone, measured; along . ; jicluded by the presence of undisturbed autochr lava flows is incompatible with the abyssal en­
h dissects the .southwest flank; I'ithonous sections in Jebel Akhdar and the stable vironment in which the Hawasina sediments
:Iine and breaches; the; radi-" jVshelf, pri the southiiAs more information be-i ; were deposited. Furthermore, there is, no evi-,
3,100 ft thick (Fig. ;i5) and., Icbmes'/available, it;;may be possible to reconr; /dence of subaerial volcanisin - in the form of
light-gray, tiiassive limestone; it'struct Peirmo-Triassic isopach-facies maps with ; tuff of bentonite in the Upper Cretaceous sedi-;
zones of limestone breccia, , ; igreater. accuracy and, coupled with a rnore de- ments of the region. The metamorphism might
sreccias indicating the-Jprigi-,;' v^tailed, exahiination,of, the exotic;blocks Ihem- be attributed to thermal alteration by overlying
'aporites in the section'. The; J^jiselves, ;a ihore precise extrapdlatipn of thei;r ophiolitic rocks but this hypothesis is untenable,
equence are breccia contaiii- /-•briginal location may be made, ; i J . J if the basal Semail contact,is considered over
id chert and volcanics from";
the region as a whole since underlying sedi­
';ri J sPfhei^; large limestone exotic blocks which
ivasina. • ! ,; ^.,',-.>;;.
ments ai-e normally unmetamorphosed.
l;4fbrm prominent features in theregipn south of
he Jebel Kawr Hmestone is' JJebel Akhdar (see Fig., 16) are; from west to Field evidence suggests, therefore, that the
Stic because of recryslalh- ' a; ^st, Jebel Misht, Jebel Misfah (Fig. 20)i Jehel- depositional environment during this period of
;npst beds contain tintinnids.; Jykhamilah, Jebel al Hawrah, and Jebel al Fay. gravity sliding reriiained much the same as that
sian age, but at lower inter- ' (These massive limestone bodies,have a similar during the preceding period of radiolarite depo­
ng/ il is a very large.lam-' '/aspect to the Jebel Kawr exoiic, except that the sition; i.e., water depths were abyssal over the.
f(.\ ./in abundance in ,sevV' ^V degree of •;shattering and recrystaUizatipn in- 'Jebel Akhdar area and.ihe source of "sedi­
tentatively been identified as • ' creases greatly in the smaller exotics, iri many ment" was from the north The dislodgemenl
lecific identification is pre­ of which the bedding planes have been almost of the huge slabs of rock probably resulted;
'H'^'7'i^'^!bsi'^'ml1^iSiiJi^U4iti?vjtM*ti,-miwji':\'sr VMMt'tUWJKmi"^
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r^— SYNCLINAL AXIS
• SLIDE PLANE OF EXOTIC BUOCKS
IC isi Arabia For location -see Fieuri |-T«nts >" eugeosynclinal sequence are apparent on west side of map at Jebel Kawr. a massive raft of exotic
;ores Exposing Precambrian sedm^^^^ ^*^? limestone which overrides radiolarites and is overlain by Semail ophioUtes. Sections along lines AA'.
ks cs Hanked by Late LaTcretaceous Cretaceous ^geF^^^ euge'
Wadi Mi'aidin area. (see inset) is shown, on
iphiolite. Time and tectonic relation

652
SM.
.
Fio. 17.—Jebel Kawr exotic block viewed from southeast illustrating breached anticlinal core with allochthonous ,?>
Triassic limestone overriding contorted Hawasina On right, Semail ultrainahc rocks overlie Kawr limestone in . L •
Sint syncline Locaton of photograph on west side of Figiue 16
from violent seismic activity along the northern the descent of these slabs down the basin >
submerged uplift which, together with the lu- slope The sediment source area was first |
bncating effect of fissure eruptions, promoted stripped of the Mesozoic-Permian carbonate j^;
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inticlinal core with allochthonous
lock:, overlie Kawr limestone m
esi bs down the basin
nt^sourtc area was first
lesozoic Permian carbonate
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il - I -..V I.'.- • . i- _-,. -I . J* " '. . .»dV^ii . . -.-I ... - •• ' ^"i
Late Cretaceous Eugeosynclinal Sedimentahon, S E Arabia 653
Fia 18 —Jebel Kawr Perched syncline of Sint viewed from west and illustraung remanent outlier of Semail
ophiolite preserved m axis of fold In background, mam body of Semail ophiolite can be seen occupying Bahlah
syncline Locaitoo of photograph on west side of Figure 16
cover which remained after the previous erosional
phases, then blocks and/or slabs of the
pre-Permian basement iLself probably were
shaken loose and followed the limestone exotics
into the abyssal depths
Consideration ot the stratigraphic position of
exotic blocks in Oman g'v&s the impression tliat
they may have been emplaced at different times
during the deposition of the "radiolarite complex
" All exotics are tootless and, it the
smaller blocks are observed enveloped in jumbled
radiolarite beds, it is nearly impossible to
determine whether they arrived at this position
by sliding across the top of these beds at the
end ot the radiolarite depositional period, or
whether they belong lo a stratigraphic interval
within the crumpled beds on which they now
lie. The true picture is brought out by the
^ "transgression" of the basal slide plane ot the
large exotics over greatly varying thicknesses of
the underlying radiolarites, a situation well illustrated,
at Jebel Kawrand Jebel Misfah (Fig./
20), and. Jebel Misht; ' ,, .,"-; ;; ^V^ ; '-
The iipper stratigraphic limit of the main exotic,
suite is clearly defined by the ov.erlyirig Sc^
mail.,ophiohtes, /not, only in the Jebel Kawr
areiai'i-but/also in the Oman Mountains region
generally, where exotics either project through
the erosional fringe of the Semail or outcrop in
close proximity to it. (Figs, 16, 22,23). , • /
Semail Igneous Series ; , /
The name "Semail" was first introduced by
^Pilgrim (1908), who described the serpentinic
Igneous rocks which arc displayed in Wadi Semail,
southwest of Muscat, as the "Semail Intrusive
Series" and dated them as Late Cretaceous.
Lees (1928) .reassigned the series to
Upper Jurassic-Lower Cretacepus and renamed
It "Semail igneous Series," since he considered
that both intrusive; and extnisive ignepus^rdcks
were present. •/"'••-.,',;;•'; '..;•:/
Ultramafic rocks belonging to the SemaU igneous
series blanket an enormous area in
Oman, stretching the length of the mountain
belt froni Ras al Hadd to the, base of the Musandam
Peninsula (Fig. 24). The total outcrop
area, amounting to considerably more, than
5,000 sq mi, must; represent one of the most
sfiectacular-exppsures of serpentinic rocks in
the world.,-:;"-',.,• .;;;/•'.;-'•'',
The varied suite of ultramafic. rocks which
comprise the Semail igneous series has been described
by Lees (1928) and, although more detailed
study of the igneous rocks would add
greatly to the resolution of genetic problems, it
is beyond the scope of this work to describe the
petrography. Suffice it to say that most of the
/igneous rock is formed of mafic and serpentinic
ultramafics ranging in composition' from gabbroic
to fieridotitic, commonly, with very
coarsely crystalline texture.
In the Wadi Jizzi area, west-northwest of
•Jebel Akhdar, Lees (1928) observed 4,000 ft
of "iiitrtisive" ultramafic rocks which overlie,
with a sheared contact, unmetamorphosed Hawasina
radiolarite and interbe;dded keratophyre
lava flows Lees interpreted the overlying "in-

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Late Cretaceous Eugeosynclinal Sedimentahon, S.E. Arabia 655
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Late Cretaceous Eugeosynclinal Sedimentation, S.E. Arabia 659
FIG 25 —Dip slopes m Scniad scrpenunued pcridouie "Bedding" effect is due to selective erosion along
.:,-;-, zones of differential, crystal segregation. Dip and strike are concordant with underlying Mesozoic limestone on the
;;?'^southeast flank.of Jebel Nakhl anticline. Because Jebel Nakhl structure was formed in late Tertiary time writer
,".Y': deduces that the pseudobedding of Semail was horizontal when body was emplaced in Late Cretaceous time.
..'/fLocalitylOkmsouth-rSouthwcst of Semail village type locality..See Figure 16. . - ,
/;vpljirite,/aiid basic igneous rocks and their rede-. ;/ tation of the sedimentary sequence. Data from
i.t/position as detritus during the Maestrichtian. In .the Jebal Akhdar area serve as a key to the
.pth.& Trucial State of Sharjah a conglomeratic se- / whole area. ;. •..,;;../
,;;;(juence 7,000 ft thick wilh reworked Semail cle- \ ITie evidence gathered from autochthonous
;|.;merits is reported by,Standring (1961): This Xsections, exotic blocks, and elements from
.'/.'/serieS;is dated as Campanian-Maestrichtian but ' postrSantoniaii conglomeratic formations con­
, ,;;is,clearly: postrSemail and therefore may repre- cerning facies distribution in pre-Santonian sed­
;;'?sent erosion following strong terminal faulting iments indicates that no major tecionic activity
-.on the Rusal Jibal structural trend. There is took place during Permian to Santonian time
;Klittle .evidence,of pronounced Late Cretaceous • and that, throughout this long period, quiet car-
;.w •;, ;//erosion of Hawasina-Semail sediments in the ;; 1 bonate. deposition continued. IThe Ornan, Moun­
/;? Akhdar.area, and such features as Jebel Kawr tain area was wiihin a broad, stable carbonate
•/ shelf, whereas on the northeast a steeper basin
;: well as the Aruma and Wasia al Fahud and.Le- slope culminated in an emerging positive ele­
"/khwair on the outer basin slope, had been ment in the present Gulf of Oman. Initial uplift
/;:* achieved (Fig. 26) and shallow-water carbon-' along the northeastern margin of the basin
- ate deposition predominated across a wide area. caused erosion of Mesozoic carbonate forma­
• .'SEQUENCE OF TECTONIC EVENTS -
tions and deposition of detritus as coarse elastics
of the Muti Formation in the Jebel Akhdar area
L/; / . The sequence of tectoiiic events in the Oman and progressively finer elastics of the Aruma
^Ibuntains follows logically from the interpre- Shale toward the southwest.
'^' FIG. 24.—Map of Oman Mountains area and surroundings shows outcrop areas of Semail ultrabasic rocks
with extrapolation of original area covered by extrusion. Possible location of root zones of fissure eruption are
showri along intersectiiig NNE-SSW and NW-SE tension fracture belts.

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Flo. 26.—Paleoccne limestone lying unconformably.on
peneplaned. vertical, thin-bedded siliceous lime-'^
stone of • Hawasina "radiolarite complex." Locality -
Jifra anticline, S km west of.-Ibri. See Figure 1. . -t \
Phase 2: initial seismic phase.—Rapid and;
overall deepening of the basin area followed
during the-Campanian, with the formation of
an abyssal trough along the foot of the steep
northeastern basin slope by tensional block
faulting. Because of overall subsidence the upthrown
Oman Gulf block remained submerged.
Seismic activiiiy along the fracture zone caused
the rapid breakup of upper Paleozoic-Mesozoic
rocks along the positive seamount and the;
dumping of coarse elastics by turbidity currents
into the abyssal trough, lo form the Wadi/;
Ml aidin Limestone conglomerates, which grade/
laterally into finer clastic rocks toward the '
southwest (Hamrat Duru area), Contempora- '
neous, incipient tension fractures, parallel with, /
the abyssal trough, developed along the oiiler
margin'of the basin, as at Fahud and Nalih.
In the broader framework, the writer believes
that major tension fracture zones trending
NNE-SSW developed along the southeast
Indian Ocean coast of Oman and east of the
Straits of Hormuz. Those fracture systems intersected
the Oman Gulf fracture belt at either
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end and similar troughs developed along them.
The bathymelric pattern thus created would
have been comparable with that now seen in
the Solomon Sea; where abyssal trenches, bordering
the Solomon Islands and New Britain,
impinge at right angles. Bathymelric slopes on
the steep inner limb of the Oman trough could
have been of the order of 1:10 or more.
• Phase 3: inter-cirogenic subsidence.—The de- ;
position of/coarse'conglomerates of the Wadi
Mi'aidin Limestone was followed, during Campanian-early-Maestrichtian
time, by a period
of relative quiescence, during which a thick series
of radiolarian chert and limestone was deposited
chemically and/by weak turbidity currents.
Abyssal depths were maintained as the
fate of subsidence matched that of deposition.
Sporadic seismic. activity continued and prompted
slumping of semiconsolidated sediments
along the steep northeast limb of the basin,
whereas toward the shallower outer limb of the
trotigh abyssal radiolarian chert graded into pelagic
radiolarian shale of the Aruma Shale.
Continued subsidence steadily built up tension
alongthe limbs of the abyssal trough.
, Phase 4: initial volcanism.—The relief of
tension along the, steep back slope of the
trough was first evidenced by submarine eruption
of spilitic-keratophyre lava flows of Wadi
Jizzi from fissures along the back-slope hinge
line. This activity heralded the catastrophic tec-
-tonic phase. ;' ,
Phase 5: fundamental tension faulting and
gravity slidihg.-—^The sudden relief of tension
which, had built up during phase 3 was accomplished
by tension faulting along the entire submarine
ridge which formed the steep back
: slope of the trough, and also along the outer
basin slope "hinge; line" at Fahud and Natih.
Elsewhere along the outer basin slope, crustal
warping developed {e.g., at Lekhwair:
Tschoppi 1967a), probably al ppinls of inters
section of basement fracture trends.
. .Vertical movement of aboul 4,000 fI has
been measured at the Fahud fault, but this was
certainly insigiiificant in cpmparison with the
major cruslal adjustment along abyssal fractures
which shattered the inner orogenic zone.
Huge exotic blocks of Permo-Triassic limestone,
representing the remnant cover over
basement after the erosion of phase 1, broke
away and descended the steep back slope toward
tihe axis of the abyssal trough. In places,
the blocks were accompanied by fragments
from the underlying basement itself.
The exotic "suite'.' includes all sizes of ele-

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troughs developed along them.;-,
: pattern thus created, would/
larable with that now seen in i
I, where abyssal trenches, bor- il
non Islands and New Britain,/'/^
angles. Bathymetric slopes pn
mb of the Oman trough.couldr;
order of 1:10 or more, .
orogenic subsidence.—The de-'f
>e conglomerates of the Wadi:"^
ne was followed, during Cam-"
estrichtian time, by a period .
;ence, during which a thick se-,,;
n chert and limestone was de-/;
ly and by weak turbidity cur- ,
eplhs were maintained as the
:e matched that of deposition, ;
activity continued and pro->
of semiconsolidated sediments
northeast limb of the;basin,/
he shallower outer limb of the//
diolarian chert graded into pe-

hM
I I'
Wilson
ments ranging trom a tew cubic meters to spectacular
mounlain-sized blocks, such as Jcbcl
Kawr It IS probable that the exotics which
reached the axis of the abyssal trough had broken
dway from much larger raits which slid on
planes of decollement Irom the Oman Gull
positive, forming a gravity-slide "tront" higher
on the back slope of the tiough lliis situation
is suggested by probable repetition of large
sheets of sediments in the Sayh Hatat area,
south of Muscat.
Evidence suggests that the northwesl-southeasi-trending
limit line of exotic blocks which
can be traced south ol Jebel Akhdar represents
the base of the abyssal slope. If this is so then
- the Jebel Akhdar (old must entirely post-date
the gravity slides, because its paleotopographic
expression would otherwise have blocked their
path of descent
Although It IS fairiy clear (lom the disposition
of exoucs in the Akhdar area that sliding
was from northeast to soulhwest, it ts probable
that contemporaneous sliding from southeast to
northwest took place in the Jebel Hagab area
, - This possibility is supported not only by structural
lineaments but also by Hudson et n/'s
(1954b) observation that grooving below the
Hagab "thrust" is northwest and also by J V
Harrison's observation (in Hudson et al,
1954b) in southeast Iran along the Zendan
front, north-northeast of the Musandam Peninsula,
that the older rocks along this "Ihrust"
have experienced movement from east to west
- In recent work J E G W Greenwood (oral
commun ) has observed serpentinite resting on
metamorphic rocks, including chert, flysch sediments,
and volcanics, in the Tayiban-Masafi
area, 50 km south of Jebel Hagab Greenwood
considers that these rocks represent a metamorphic
"facics" ot the Hawasina, but it also
seems possible that they may belong to Precambrian
basement, since this contains flyschlike
sediments, chert, and volcanics {e g., Thaniya
Group in Aden, Beydoun, 1964) If the
Tayiban contact is with basement, then this
would be analogous to the writer's interpretation
of Semail-basement relations northeast of
Jebel Akhdar in the Gulf of Oman (Fig 27)
In their passage down the abyssal slope the
exotic blocks had both a gouging and abrasive
effect, and they appear to have swept or "bulldozed"
the sedimentary cover of the back slope
into the axial area of the trough Evidence for
this "tectonic erosion" is visible in the general
reduction of Hawasina thickness in a northeasteily
directly below the Semail and by the wedg­
ing ol crushed Hawasina beds below such etot- j
ics as Jebel Misfah (Fig 20) and lebd Misht \
An even more spectacular example of tectonic >
erosion is provided by the Jebel al Hawrah ex- l
out (Figs 28, 29, 30), which evidently has i
sliced away the Muti and Wadi Mi'aidtn For- «
mations and lies almost directly on uppet Mu- \
sandam (Wasia) limestone These units appear )
to have been removed along the entire southern \
flank ot lebel Akhdar by abrasive action of the «
Jebel Kawr exotic suite or by the succeeding !
onrush of Semail magma j
The possibility that such sliding and abrasion
took place in late Tertiary time afler the uplift (
of Jebel Akhdar is negated by the position of i
the blocks below the massive body of Semail, \
which occupies the Bahlah syncline It is illogical
to assume that the huge Semail body now
filling the Bahlah syncline slid down the south
flank of the young Akhdar anticline A further
manifestauon of gravily-shde abrasion is i
thought lo be the smoothed or "glaciated" ap- |
pearance of the beveled, updip end of ladiolar- 1
ties at the top of the Wadt Mi'aidtn section '
(Fig 13). I
Field relations in the "radiolarite complex" !
south of Jebel Akhdar indicate that near the j
base of the abyssal slope the exotics overrode, I
and finally came to rest on, the "bulldozed" j
pile of Hawasina sediments j
Crustal Separation and OphioUte Extrusion \
The faulting and breakaway of exotic blocks /
are believed to have been followed immediately t
by cruslal separation which developed along re- I
gional tension fractures (Fig 27) These abys- )
sal fractures were on such a scale that ultra- [
iiiahc magma could pour out in flood eruption
Exotic blocks were engulfed and perhaps car- j
ried farther down the abyssal slope hy the igneous
...ous flood.
flood I
the imposition of this huge body of high |
density material on the already disrupted mass. \
of incompetent radiolarite is believed to have ,
introduced compressional stresses on the rad - j
olariles. to which they responded by buckling |
and overihrusting along fold axes parallel with
the Igneous front The buckling extended up
the outer basin slope and disrupted the highh i
incompelent zone of inlerfingering Hawasina ',
radiolarite and pelagic Aruma Shale forma- ,
lions
The very coarsely crystalline texture which \
IS typical of many large bodies of ultramafn.
serpentinic rocks around the world, of which *
the Semail is another example, has led uuin)
Miri^

X •> - '
ij>|>wyf.iii./infS"-n x>lt.uu ^ij:. >''i^oi*^^'•I ^^*'1Bt^'•^^^•^A^^hlW.l^fiLla'lk.•^lWl•L•^iUlf«>4^fek»~
iina beds below such csot-
Fig, 20) and Jebel Misht
,icular example of tectonic
ly the Jebel al Hawrah ex-
30), which evidently; has
li and Wadi Mi'aidirn Fprnost
directly on upper Mulestone.
These units appear
id along the entire southern
ar by abrasive'actionof the
suite or by,,the. succeeding
Tiagma. / ; -;
\at such sliding and abrasion
lertiary time after the uplift
s negated by the posilioti of
the massive body of Semail,
i Bahlah syncline. It isjiUogit
the huge Semail body; now
syncline slid down the south
I Akhdar anticline. A further
gravity-slide abrasion./ is
sm--''" ed or "glaciated" ap-
•.vei.^ ..'P'iip eiid of radiplar-
I the"" Wadi Mi'aidin ;section
in the "radiolarite coihplex"
vhdar indicate that near .the
II slope the exotics overrode,
to rest on, the "bulldozed"
ediments. ''///.'
on and Ophiolite Extrusion
1 breakaway of exotic blocks
'e been followed immediateW
311 which developed albng retures
(Fig. 27). These'abyson
such a scale that ultrad
pour out in flood eruption.
2 engulfed and perhaps carthe
abyssal slope by the ig-
of this huge body of high
^ the already disrupted mass
diolarite is believed to have
;ssional stre-sses on the radithey
responded by buckling
along fold axes parallel with
The buckling extended up
pe and disrupted the highly
of inlerfingering Hawasina
.lagic Aruni'a Shale forma-
lyr .talline texture ;which
large bodies of ultramafic
iround the,world, of which
her example, has ,led;many
I- il'
Late Cretaceous Eugeosynclinal Sedimentation, S.E. Arabia
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666 H. H. Wilson
pled with the absence of contact metamorphism
and the lack of feeder dikes cutting the entire
pre-Semail Jebel Akhdar surface, makes tn situ
intrusion an untenable hypothesis Io support
an intrusive origin tor tht Semail it is necessary
to introduce the ultramafic mass in the manner
postulated by lees, as an allochthonous body
which was intruded outside the area and
reached Us preseni position by thrusting or
gravity sliding
The absence of mahc rock detritus in the
Wadi Mi'aidin conglomerale and of igneous
veins in Permo-Triassic exotic blocks rules
out the possibility of intrusion into the posl-
Cambrian sedimentary cover which lay along
the inner margin ot tht eugeosyncline There
remains only the possibility that intrusive Semail
was emplaced into Precambrian basement
of the positive block which defined this inner
margin If this happened, then the allochthonous
Semail mass would have been associated
intricately with the host basement, but there is
no evidence tor such an association, and the
Semail is remarkable for its homogeneity
throughout its extensive area of outcrop
The mechanism for emplacement of a hypothetical
allochthonous Semail body requires
consideration of the nature ot the exotic slides
which immediately preceded it These formed
typically broken and randomly scattered rafts
of massive limestone, in contrast, the enormous
Semail sheet is remarkably cohesive If the Se-
;;mad had been introduced in a solidified form
mlo the same abyssal environment as that
which received the exotic slides, then tt, too,
should have been broken up
A striking feature of the Semail is its "bedded"
appearance, a characteristic evidently
stemming from ditferential weathering along
planes of crystal segregation Because this
"bedding" dtp is concordant with late Tertiary
folded strata of Jebel Akhdar and Jebel Nakhl
(Fig. 25), the writer concludes that the "bedding"
was horizontal when the body was emplaced,
a situation hardly to be expected in so
massive a sheet had it been introduced tectonically
in a solid state from outside
It is nonetheless necessary to account for the
overall coarsely cr)slal texture of the Semail,
which requires a prolonged crystallization period,
eompar.ible with that of intrusive rocks.
The explanation may be related to the rate al
which extrusion took place during the catastrophic
climax of the orogeny. The writer sug­
-tl
gests that the Semail was extruded as a "flood"
eruption from huge, abyssal, tension fissures
that developed along the steep northeast flank
of the eugeosynclinal trough. Such a catastrophic
eruption, which may have occurred
during an "instant" of geologic time, prohibited
the formation of pillow lavas and gave no time
for the formation of sedimentary breaks. The
crystal mush evidently piled up at such a rate
that heat and liquidity vyere retained in the
body as a,whole as it accumulated at abyssal
depths of more lhan,30,000 ft, like those in the
Mariana Sea today. .The effect of the high containing
pressure on the Uquid magnaa may well
have been /an. important factor conlrolUng
chemical processes during crystallization.,
If siich aprocess/did take place, the uppermost
part of ttie extruded mass should have
lost heal at a faster rate than the body as a
whole, and in this way the presence of spilitic
rocks overlying coarser textured types, as described
from Hatay and northwestern Syria by
Dubertret (1955), could be explained. If more
than one eruption took place, there should be
evidence of fine-grained layers in the sequence,
such as that, described .by Grihdley (1958) .
from the Eglinton Valley in New Zealand. In
Oman the uppermost surface of the Semail was
subjected to erosion diiring the Maestrichtian,
and again following late Tertiary Zagros movements,
so that evidence tp support this hypothesis
/may have been lost. Similarly, the basal
layers should also be finer grained, and to verify
this point a detailed study of the Sint inlier
and its contact with the Jebel Kawir limestone
might be very rewarding.
According to this interpretation, the actual
root zone of Semail eruption was in the present
Gulf of Oman (Fig. 24) and thus is lost lo
view. However, Lees (1928) described dikes of
coarse-grained gabbro and granodiorite stocks
1,5()0 ft in diameter in the Wadi Jizzi and Wadi
Halla areas, which may niark the fringe of the
Jebel Akhdar root zone or of an intersecting
Jebel Hagab-area root zone, ll is reasonable to
postulate that the root; being the only truly intrusive
element, would have a different crystallization
history and might lack the serpentinization
of, the extrusive element for lack of contact
with seawater. The writer suggests that the
root zone for, the Gulf of Oman (Fig. 27), if
stripped of all extrusive and sedimentary cover,
might be comparable to ancient ultrabasic intrusive
bodies such as the BushveW complex.
.^

\"'''" vva. extru •
• ,iiMli«>iiiHf«l>ilitl
Lote Cretaceous Eugeosync/ina/ Sedimontafion S e Arabia
) metamorphism of an^ .
/•^ Piiiow lavaf aiS^'P^^^^bited ;4,^S'^f'?hic:/r^^^
'e^.t;„ ''.;""" of:Lafe^/Crpfr.r
T'«^°'P««ional
baS^SfT'^ ^^^^'^^'ief
'•most surface of th. c
•vidence fo sunni fP^^ '"ove
^ —..wo. ..-'-::",;^/;;. ;;.-•;,
^Pbito;;ienieErosion and Sfabil«a£dS^
.wnary leattire.-/;^' ..;••-• • -v;- -.
^o be finer sSed^' '^ ''^^
detailed stul; ^L^f '« ver-
*'ith the Jebel K '"'"^'"^ir^phtc
o;^^:^ff" ;, ^-^^nated - the bafa-1^ ; ;,;NW-SE trending normal faults with small
The SemaiJ extrusion terminated fhe,cata-;,NErSW cross-faults,at Fahud and Natih give
ophtc orogenic, phase and quiescence/fol-^'ciear evidence.pfcnistal tension over this limb
ved From thie thickness of the Semail, it, of the basin io Maestricbfian time,, and it is
seems impossible tfiat an abyssal trough about^ /not , logical, to postulate, contemporaneous
30,000 ft deep vvasiSIIed. One must »«""-- Vn—-- •• - liinb. In tf"'«;-•—
^'S- 24) and th ^^^ P^'^sent
=es(1928) i» •? '^ 'ost »o
/ fP^ that the as troiiph u became ../«---•' e^P^^^P^lK was be&"^°";"'"^ght be fexnS^
'"ay mark th f'''"'^ ^''d'
ootzonc h • '"'e^cting
««• bemg ^e o^r""''^ '^
^'W have r H,ff "*>' *'y m-
-'e-ent'f^^snf r
rhe Writer «,.„ ^ *^*'n-
"'^o/'ir„1S'-^5Mhe
-^^^dsedimeValy'ovef
^ancient ultrabasic ,„
w-«Mshveld complex
"On that fh^ •>.-r,.,y
_ .-..wiv ine cata- ' has be ^ _ .., lu ^jar-
. - w,,^j,fcnic phase in some localities/rThc-f alJel ti .._..o ana intersect fhe" Oman Gulf
tectonic cycle was completed with transgreisstpn;'i' belt in the vicinity of Dibba. The Masira-Ras
ofashallow-waterMaestricbdansea, : Jf/j;;";^^^^ which mc borders Masira-Ras the
TECTOMC MhCHANMM ;
., ...,.v..iiaKa ophiolite trend which borders the
• :;•••;*;%-vt-***'"^^^*^ ^^^^ ^^ Oman has the same NNE-
'/"'" •• ^' }. p.' p SSW trend and is also thought to belong to a
In the many interpretations of ophiolite belts; distinct fracture zone with its own extrusive
around fhe world the tectonic mechanism has f/zone parallel with the Hagab trend and interbeen
attributed variously to . compressional'lsecting the Oman Gulf belt north of Ras Jibsh
stresses with attendant thrusting, or tensional (Ra's al Khabbah), the problem of intcrpretstresses
with hascment block movements and ing the Masira-Ras Madhraka ophiolites is
gravity sliding, or a combination of the two. complicated by Jack of knowledge of fhe sub-

*
s
'J
V..*
I
.1;
Wilson
marine geology m the Arabian Sea Specifica\l;y,
- It lb sVill uncertain whether Masira Island is
bounded on the southeast by sialic crust which
foundered during Late Cretaceous or Tertiary
time or by oceanic crust
' The "dogleg" or "sawtooth" pattern of
ophioliie belts and tectonic hneamente in the
Oman-Iran region is interpreted to be a tension-relief
pattern resulting from regional meridional
tension which existed during latest
Cretaceous time It also can be seen, by reterence
lo the pre-Permun basement outcrops in
the core of Jebel Akhdar and on the Arabian
shield, that tbe fraelurc pattern was well established
m pre-Permian and probably Precambrian
times, and that a reactivaiion of the
ancient fracture system probably took place during
the Late Cretaceous orogeny Further reactivation
of the basement fracture pattern may
be reflected in the intersection of late Tertiary
Jebel Akhdar and Jebel Nakhl ttends, whteh
now dominate ihe Oman landscape (Ftgs 16,
29, 30)
The fracture pattern has been compared
with the disposition of abyssal troughs in the
Solomon Sea area, and further analogies can be
drawn from the present-day Indian Ocean fracture
pattern, troughs, and seamounts (Heezen
and "Tharp, 1965) Simdar cross-trends are apparent
m the relaUon between the Hatay-Amanos,
Idurus, and Cyprus ophiohte belts, and
perhaps also in the Guatemala-Cuba and Mexican
serpentine trends which may be associated
with latest Cielaceous orogeny
An interesting approach \.o the fundamental
causes of orogenesis has been made by
Kropotktn and Irapezmkov (1965), who gave
convincing evidence of the coincidence of
earthquakes with changes in speed of revolution
ot the earth, and the earth's orbit round
the sun These changes are related to possible
stresses exerted trom outside on the solar system
Considering this hypothesis in the context
of geological time, it seems very possible that
major orogenies may have been coincidental
with major disturbances originating outside the
planetary system which, by chain reaction,
' cause instability in the simatic substratum If
this IS so one must assume that a major extraterrestrial
disturbance took place during Campanian
time which triggered an upwelling of
ophiolitic materiai along zones of weakness on
» a worldwide scale Clearly, to bring this hypothesis
to life there must be a much closer
I liaison between astronomers and geologists
Also on astronomical grounds, Halm (1935)
IllbUii
-rgutd !o' Uie expansion o* the globe Ihiougl.
geologic lime, which resulted \n the sphl-up oJ
an originally complete sialic crust with the intervening
gaps being systematically hlled with
simatic materiai
Allhough crustal separation is invoked as a
mechanism for ophiohte extrusion in Oman,
there is no positive evidence which would support
a hypothesis for crustal separation on the
scale of continental drift If drill had occurred
away from the Oman Gulf fracture zone then
similar drift might be expected from contemporaneous
ophiohte-filled fracture systems
Thus, although the Gult of Oman ophiolite root
zone is blanketed from view by Tertiary sediments,
the Iranian, Turkish, and many other
I
.1*
ophiohte zones have been exposed by erosion
of their Tertiary cover and there is no evidence
for drift away from these fracture systems
In Carey's (1958) hypothesis on coniiuenul
drift he refers to the Red Sea and Persian Oulf
"rhombocha.sms" as evidence of crustal separation
and drift m the Arabian area By definition,
a rhombochasm impUes a gap in sialic
crust replaced by simatic crust In the Zagros-
Persian Gulf area there is no evidence for such
replacement either from outerops in the Zagros
or from deep drilling results and sali-plug evidence,
which together show that the crust, at
least down to the Precambnan, has not been
sundered
It beems, therefore, that the ophiolitic belts
which cut the Afro-Asian sialic crust are indicative
of a tensional stress situation during latest
Cretaceous lime, but that the relief of tension
was not marked by cruslal parting on a major
scale What is not clear is whether the conlmualion
of Ihc tension fracture system into the
contemporaneous oceanic areas resulted in a
much greater nfting and replacement of the
less resistant simatic crust Study of heat flow
and poleomagnetism in present-day oceanic
ridges suggests that this may well have been the
case and that overall global expansion may
i
I
I
.1
have resulted from growth (extension) of the
oceanic oeeanie ->»-j,».„ segments
CONCLUSIONS AND Tnt-iH BEABINC
ON OIL PROSPECTS
Geological evidence from the Oman Mountains
throws additional hght on the mechanism
and style of eugeosynclinal evolution and
ophiolite emplacement Convergence of re
gional and local stratigraphic and leCtonii
evidence leaves little doubt that the entire se
quence of events from eugeosynclinal incej
A

4, J
-A*Ak«Ji *'-»•-*- --j.il»-->- —>..J .»
expansion of the globe through
which resulted in the split-up of
omplete sialic tirust with the inbeing
systematically filled with
1. -, . ,. • ' • • ' : •
jslal separation is invoked as a
• ophiolite extrusion in Oman,
itive evidence which would supsis
for crustal separation on the
;ntal drift. If drift had.pccurred
Oman Gulf fracture zone then
ighl be expected froiii; contemlioUte-filled
'fracture systems
the Gulf of Oman ophibhle root
ed from view by /Tertiary sedilian,
Turkish, and. many other
have been exposed ,by erosion
y cover and there is no evidence
rom these fracture systems
958) hypothesis on continental
0 the Red Sea and Persian Gulf
;" as,,- ••dence of crustal separan
ll rabian area/ By definiichasm'implies
a gap:in sialic
)y simatic crust. In the Zagrosea
there is no evidence for such
ler from outcrops in the Zagros
rilling results and salt-plug eviigether
show that the crust, at
he Precambrian,. has;not been
refore, that the ophiolitic belts
fro-Asian sialic crust are indicnal
stress situation during latest
:, but that the relief of tension
by crustal parting on a major
ol clear is whether, the continnsion
fracture system ,into the
s oceanic areas resulted in a ,
fling and replacetnent of the
latic crust. Study of heat flow
:tism in present-day /oceanic
lat this may well have been the
jverafl global expansion may
am growth (extension); of the
o THEIR BEAHING , ;"'.,
TS- •'";..; -, .;;.,,/,,:;;
dence from the Oman Mountional
light on the mechanism
•ugeosynclinal evolution and
:enV''^ ; Convergence of re-
I ;^»s .graphic and tectonic
iltle doubt that the entire ses
from eugeosynclinal incep­
!gaBanMt!H.HWfeWJiti!!MMmi»!ii;-MMt"w,njni'mff'ife»mi.»f»i."j» ,
.Va,.A*hMiJteKAfe' AfciTHfemtAiwa^aaa*
h 1 J
.* : y ' i • '1 ' ' . ' ' '•
Lata Cretaceous Eugeosynclinal Sedimentation, S.E. Arabia 669
tion, through abyssal sedimentation and gravity geosynclinal sediments arc attributed to gravity
sliding, to the ;'culminaling.emplacement of sliding down the seismically active inner slope
ophiolites, tookplace during latest/Santonian-r/ of the trough and to the coinpressive'stresses/
early Maestrichtian time. •" - ; * '; /' exerted on the highly incompetent aby.ssal sedi-
The little-disturbed stratigraphic succession, ; ments by the abruptjemplacement, of huge ex-'
in Wadi Mi'aidin displays inverted faunal rela-' .jjbtic blocks and the subsequent;flood of efup;
tions which prove that contained Jurassic-midr / ,-,;t|ye ophiolites. ;••- ;',:;'•-;li ''•-:P^-':''''.y'' '. • '/,
die Cretaceous micrpfauiias /are reiyorked.Fur- ;;; ;TTie striking simibrity; of many bphiolite-ra- :
thermore, the (.normal ••transition ,pjf Wadi- wdiolarite associations around the, world necessi- ,
Mi'aidtn deep-water limestone seciiments into: -;'tates a common,mode of;origin, and the write'•;chert
belonging tc>;.the-"radiolarite complex"' • believes that the rock relations which are so well
warrants the additional conclusions that Juras-,. displayed in Oman may provide the key to reso-;
sic-Lower Cretaceous faunas iii the latter fa-* lulions in more complex regions. However, inore
cies are also rewbrked and that the whole;abys­ work is required in Oman to fill gaps in knowlsal
sedimentary sequence belongs to the Upper; edge. It will be particularly important to exam-:
Cretaceous These conclusions ,cast doubt on ine in detail the contacts of Semail igneous rocks'
some of the age assignments and tectonic in­ //with such exotic blocks as Jebel Kawr and Jebel
terpretations of radiolarite sequences in Turkey,, Misht and to gather more petrologic data on;
(Rigo de Right and/Cortesini, ,1964) and in ,, the. Semail; as a whole.,As a further check oh
many other localities (Gninau,V;1965). wheres age relations of the Aruma Shale and the Har
.dating has been; based,on-faunia contained in 1 wasina, it would be of value lo compare radioabyssal
luibidite-sediments.i/i '':'^pyp.:-' ''-j "•: /* ; Jarian assemblages from both formations.
An extnisive,mode/of emplacement for the -V. To; establish with ,.certainty 'that ophioiile
Semail ophiolites > in /Oman is supported •/eruption originates ifrom: intersecting tension
strongly by field evidence. The most plausible ; fracture belts requires corroboration frpm other
explanahon is that/flood ;eruption from gaping :;;;areas. The megastructural pattern visualized for
tension fissures took place.'at such speed that the Oman eugeosyncline would be analogous
the mass of accumulating magma was able to'. /with the crustal fragmentation hypothesis dis­
retain heat and liquidity. The pressure environcussed by Oppcnheim (1967), particularly in
ment was conditioned by the; water overburden ,' regard to the present structural pattern of the
in the abyssal trough'-which receiveii the ex-i submarine Lomonosov Range/in the Arctic
Iruded magma '';"- •'•,'.';.^..^•':>'•:•:' /.,';-•/''•-.;'••.' "Ocean. There geophysical and bathymetric sur-
TTie association of metamorphic ;rbcks with / veys indicate a pattern of vertical block fault- ,
ophiolites in Onian leads to the conclusions, ;,. ing, and magnetic profiles suggest sunken
that (1) ihermalcontact metamorphism from/ blocks of shield rocks, contradicting, the hyemplacement
of the Semail igneous series;was; ,'pothesis of westward continental drift.
minimal, and (2) where, ophiolites are in cbnr/ /•/Suitable source rocks for. the generation of
tact with metamorphic rocks, the latter inay be- ; pil have been proved in middle and Lower
either allochthonous exotic blocks of basement •Cretaceous carbonate rocks in fields of Yibal,
or autochthonous pre-Permian metamorphic'; •;Natih. and Fahud, which are south of the
basement on the back slope of the eugeosyn­ /Upper Cretaceous- eugeosyncline. These carcline,
which had,been swept clean of later sedi-,t;,bonate rocks also appear in similar facies in the
ments by the tectonic erosion of pre-Semail Jebel Akhdar and undoubtedly underlie the ingravityshdes
,;. , ',; .' • ', ;: , tervening subsurface area.
.Structural evidence and logical' extrapolation ;;- The abyssal radiolarite series which succeeds
from the established sequence of events,in the; :t;the middle Cretacepus carbonate rocks is.fau-
Oman Mountains lead to the conclusion that,a- ; nally starved and rnust be discounted as a
tensional structure environment governed the source; for hydrocarbons. The pelagic Aruma.
evolution of the Late Cretaceous orogeny. Con-, ; Shale, which was deposited iii a thick series on
sistent with this analysis, the writer suggests- ilhe outer slopes of the eugeosyncline, contains
that ophiohte extrusion look place from inter­ ' a rich Globigerina fauna and can be designated
secting northwest-southeast and NNE-SSW sets/ as a possible source formation, although there
of regional tension fractures which defined the / is no evidence to suppprt this.
boundaries of major cruslal blocks in the '/ Migration of oil put of the eugeosynclinal
Oman-Iran area.
foundations perhaps could have taken place
The intense folding and dislocation of eu­
when sufficient overburden was superimposed

ftv
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"',«• Wilson
SH^HSis^;^ •'• . Notes et M^m. Moyen-Orient, v. 6, p. .5-119. y
• ; i - H . • ••'•'• : •••• ' • • • ' : ; • -•'•'. '• • ' . ' • • . . •
Bricson, D. B.. M.: Ewing, and B. C. Heezen, 19.?:,
' Turbidity currents and; sediments in North Atlantic;
- Am. Assoc. Petroleum Geologists,Bull., v. 36, no. 3,-•
, • p. 489-511./ .-''-; "-.; '-/.; •-,•-•-.• '
GrindJey,. G. W;.; 1958, Tfid geology of. the Eglinton ;i
;, ;ValJey. Southland: New Zealand Geol.;,Survey Bull. ';
-Grunao.H, R,, 1965, Radiolarian cherts and asso-- .5
,. -. r- -wiwjjp,-'';;;: *;.;;-ciated rocks in space and time: Eclogae Geol,
formed - "^.v* -/ ,..1, by ZZeT'^''''' .-. iuuinwest a ^ tinielyftrap t'nii^S^^P'^ / ' Helveiiae, ;v.,58, no; 1. p. 157-208. ,
wasv/;
Vibai formed salt
Hajash. G. M./ 1967, The Abu Dhabi Sheikhdom—the
by contemporaneous growtlj ;:'of ./the * i':.;;onshore oilfield.?, hisiory.of exploration and develop^
*"" It pillow i""ow o""""f. ;•', j.-:>i;^ or ^/;?;?4;'/v! the ^ ':/- ment;/ 7th World Petroleum Cong. Proc., Mexico, v.
jossibje that both types r^f *-"-/ * ;5"2, p. 129-140,' ' j - '
•^•^-Clonic approach to continen-./
tal drift, ;« Sympowum on tontiiieiiial dri/l; Geol:
ogy Dept,/ Univcrsiiy of Jasmania, Hobart, p,
177-349 ,,,
/Chenevoy, M;;' 1959, Le substratum meianiorphique des
roches verles dans'leBaer et le.Bassit fSyrie sep-
-., temrionale)::^Notes'et Mim. Moyen-Orient, v. 7, .
• p. •1-17.-'.//;;;-:,-;;:,,: ' . ' ' - •
'Dubeitret, L:',' 1955,'" Geologie des roches verles dii
nord-ouest de ,1a Syrie ,et du; Halay (Turquie): ;,
• Elder, S., and K. F. C. Grieves, ,1965, Abu 0hab< ma-;'!
riiie areas geology; First Jnternat. Cong. Petroleum
; and the Sea, Monaco, May.J2-^20, sec. 1, tio. J27, p.
./Halm, J. Ki' B., 1935, -An;asirononuca! aspect of the -
; 4.evolution of the earth; Astron. Soc. South Africa,
.-,//; v; 4, no. J. p. .1-28. // • '.,,'. • --'
/Heezen, B; C., and M. .Tharp;.1965. Physiographic dia-/;
gram of the Indian'ocean, descriptive sheet: Geol. '
;• •, Soc. of America. ' ' '
Hudson, .R. G. S... R, W. Browne, and M. Chatton,
; , 1954a, The siructure and strap'graphy of the Jebel
i;. .Qamar area, Oman: Geol. Soc. London Circ, no.'
: 21, 3 May, p. 1-2. ; I
;———.and M; Chatton, 1959,The Musandam Lime
•;;j stone (Jurassic to, tower Cretaceous) of Oman,
tr- Arabia: Notes ,et Mem. Moyen-Orient, v, 7, p.
• ;69-93.-.;'' .--;•- ' . ; ' • • • . . .
:—— A./McGugan, and D. M. Morion, 1954b, The
,;f structure,of the Jebel Hagab area, Truciai Oman:
./Geol. .Soc, Lofldoi) Quart; Jour., v. JIO, p. 121-152,
.. ~—- and,M, Sudbury, 1959, Permian Brachiopoda
- /from southeast Arabia;,Notes et Mem. Moyen-Ori- .
ent, v; 7, p. 19-55. '
,,James, G..A, and J. G. Wynd, 1965. Stratigraphic no- „
1: mends lure of Iranian Oil Consortium agreement
area: Am. A.isoc. Pelroletim Geologists Bull. v. 49, ,
.„; lio. 12; p. 2182-2254.
Kaaden, L-. van der, 1963, The different concepts of
, the genesis of Aipinc-typc emplaced ultrabasic roct;s i
'and their implications on chromite prospection; Bull, '
Mineral Research Exploration Insi. of 'Tuflce/, no.
• =61, p. 41-56. • . -
Kcnt>; P. E„, 1966,'Discu-ssion -

4't*:";'.?
&jij^M.iS:2:^JJii^^iL
urn nn Lommciuil diift Geoliiy
ot I asm una, Hobait. p
; sub',11 Hum mt-t iinoiphique dts
c U;ii.r tl le 11 i^iit (Syne stpet
NKin Moyen Urii,nt. v 7,
Geoli>.;ie dc roche;, vertes du
yric. Ll lu llilay (Turquie)
>en-Orieiu, v. 6, p. 5-179,
. Grieve., lyi)*!, Abu Dhabi ma-
First IniLiiiii Cong PLirolcum
), Ma\ 12 20, sti. 1. no 127, p
wing, ind B C llcezen, 19"i2,
nd seilimcnts in North Atlantic
m G ologists Bull, v 36, no 3,
i, Thi, geology of the Eglinton
Sew /tal ind Geol Survey Bull
, Radiolciiij'i cherts and assoace
ind time Lclog.ie Geol
I, p. 157 208
The Abu Dhabi Sheikhdom—the
lory of exploration and dcveloplioleji''
Cong Proc. Mexico, v.
AnV . inomical aspect of the
rth: Astron. Soc. South Africa,
Tharp. 1965, Physiographic diapce;in,
descriptive sheet Geol
. W. Biowne, and M Chatton,
e and stratigraphy of the Jebel
: Geol Soc London Cue, no
on, 1959. The Musandam Lime
Lower Creuctous) of Oman,
M4m Moyen-Oricnt. v 7, p
and D M Morton, 1954b The
bel Hagab area Irutial Oman
Quart Jour v 110, p 121-152
ury, 19^9 Peimian Brachiopoda
bia: Notes el Mem Moyen Ori-
j. Wynd, 1965, StraUgraphic nolian
Oil Consoitium agreement
'cirokum Geologists Bull, v 49.
k
1963, The ditkrent concepts of
le-iypc empi iced ulir.ib,isic rocks
ns on chroinui: prospection Uull
ixploiautn Inst of Turkey, no
Disciiisioii //( M G Audle>gy
of I'ui uigiifsc Timor Geol
no. 1634 p 1949-1962
Yu. A Iiape/nikov. 1965. Varir
velocity of the earth's rotation,
he pole lud the rate of drift of
;ld and iheir possible association
;ocesiti Internal Geol Review.
he K..^ '" "1 "n^'= -in^ space of
relaiioii lo oiganic met miorph
lb, Jaarg 18, nu 4 ns p 1('6-
Late Cretaceous Eugeosynclinal Sedimentation, S.E. Arabia 671
1956b, Geology and ophiohte problems of
East-Celebes: Nederl Geol Mijnb Gen. Verh,
Geol Ser DI 16, p 210-233
Lees, G M , 1928, The geology and tectonics of Oman
and of parts of southeastern Arabia Geol Soc
London Quart Jour,v 84, no 336, p 585-670
Morton. D M . 1959, The geology of Oman 5th World
Petroleum Cong Proc . sec I. paper 14. p 1-14
Oppenheim. 'V, 1967. Critique of hypothesis of continental
drift. Am Assoc Petroleum Geologists Bull,
v 51, no 7, p 1354-1360
Pilgrim, G, 1908, Geology of the Persian Gulf and
adjoming poiuons ot Peisia and Arabia. Geol Inst
India Mem , v 34, p 4
Powers, R W, e/ a , 1966, Geology ot the Arabian
Peninsula, sedimentary geology ol Saudi Arabia
^ US GeoL Survey Prof Paper 560 D p 1>1-D147.
Rigo dc Right, M , and A Cortesini, 1964, Gravity tectonics
m foothills stmciure belt of southeast Turkey
Am Assoe Petroleum Geologists Bull. v. 48. no
12,p 1911-1937
Robiason. E., 1967, Submarine slides in White Limestone
Group. Jamaica Am Assoc Petroleum Geologists
Bull, V. 51, no 4, p 569-578
Standring. A J. 1961. An outline of tlie stratigraphy
of Qatar and the Trucial States Unpub paper read
at meeung of Arabian chapter. Am Inst Mining
Metall Engineers, Dhahraii
Sugden, N. 1962 Structural analysis and geological
predieUon for change of form with depths of some
Aiabian plains-type folds. Am Assoe Petroleum
Geologists Bull, v 46. p 2213-2228
Tschopp. R H, 1967a. The geneial geologv of Oman
7ih World Petroleum Congiess Proc. Mexico, v 2,
p 231-242
1967b. Development of the Fahud field: 7th
World Petroleum Congress Proc. Mexico, v 2, p
243-250
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1^

THE GEOLOGY OF OMAN
BY
D. M. MORTON*
Section I—Paper 14
ABSTRACT. Oniun is divisible into a northeast mountain -zone and a southwest desert foreland.
Flat-lying marine Oligo-Mioccne deposits cover most of the foreland, but older rocks crop out
along tlio gentle, block-faulted Hugf-Hauslii swell which runs northward from Ras Duqm for 100
miles. Here, (?) Lower Gimbrian dolomites and cIosUcs are overlapped unconformably by Ordovician,
Permian, Jurassic, Cretaceous, and Tcrtiaty marine sediments, the Paleozoic rocks being mainly
clastic, while tbe younger beds are mainly calcareous. These formations thicken northwestward into
the gentle foreland basin of Oman and Trucial Oman, where the only visible structures are salt domes
wiiicU probably rise from a Middle-Upper Cumbrian (Hormuz Series) source.
The Oman mouninin range has the overall structure of a complex geanticline, trending N-S in its
northern section and NW-SE in the south. Until die end of tbe Middle Cretaceous, the area was part
of the Oman foreland basin, with substantially the same sediments. But in Upper Cretaceous times,
while regional subsidence continued, large domal uplifts and block movements disrupted the present
axial zones, exposing die substrata to erosion and slumping, while vulcanism set the stage for radiolarite
deposition ("coloured melanges") under very disturbed conditions. This phase culminated in submarine
extrusion of ophiolite (serpentinite) "nappes" on an immense scale and probably in a viscous state.
Subsequently, Maestrichtian, Paleocene-Eocene, Oligocene and Miocene seas ebbed and flowed to
deposit littoral elastics and limestones along both flanks. In Neogene times local folding developed on
tbe west flank, and important tlirusting occurred in the extreme north with only minor repercussions
elsewhere. Regional emergence, with oscillations, followed the Miocene but tbe mountain range
continued to undergo differential uplift. \
RESUME. L'Oman se divise en une cone moniagneuse au Nord-Est et un avant-pays dcserii

c
^=:
t^
fK**?"****?***!
278
Introduction
Arabia (Fig. 1), south of its known productive oilfields,
has local traces of pctrolcuin in outcrops of the
Permian (Oman), the Jurassic (Hadhramaut), and
the Cretaceous (Oraan); and oil "shows," so far noncommercial,
have been found at several Paleozoic and
Mesozoic horizons in scattered wildcat wells in Oman.
These do not yet provide any coherent picture of oil
occurrence in the region, so that tlic present paper is
confined to a brief introductory account of their geological
background in Oman.
The prospective territory is mainly desert, exposing
flat-lying Tertiary to Recent deposits, where explora­
FIFTH WORLD PETROLEUM CONGRESS
Fig. 1—Regional Map of Soutb Arabia.
tion by aerial and geophysical surveys and drilling supplements
geological mapping. Deeper sections outcrou
in the mountains of Oman, and along the south coa.st
where geological reconnaissances and some detailed
local surveys have revealed the main features of the
tectonics and a considerable amount of stratigraphic
information. Intensive studies of microfacies have been
applied to supplement palcontological correlations.
Full hthological and palcontological details ana
nomenclatures of rock-stratigraphic units recognized in
the region, will appear in the Asia Volume of the
forthcoming International Lexicon of Stratigraphy.
Terms used here are already current in the literature.
• • Kwrio Murio 1$
•'^- MOUNTAINS
^ OIIFIELOS
ScoU in MiUi
too 200 300

y
THE CEOLOOY OF OMAN
fig. 2—Geological Map of Oman.
m'i'm0mii>l^'^mimm
279

y
c
280
Regional (Oology
The territory of Oman is divisible into a mountain
zone in the northeast and an almost featureless desert
foreland to the southwest (Fig, 2).
The foreland is topographically and geologically a
continuation of the gently-undulating shelf which extends
eastwards from the Precambrian Arabo-Nubian
mass of Hed jaz [16]. The mountain zone appears
along the east coast as a detached orogenic arc with
the overall structiire of a complex geanticline. It exposes
rocks, including serpentinites and radiolarites,
which have counterparts in the mountain ranges of
S.W. Iran (Zagros), and of landward Makran [3]—
"coloured melanges."
Lees [13] suggested that the serpentinites ("Semail"),
radiolarites ("Hawasina beds"), and underiying
limestones ("Musandam," etc.), had been thrust
individually on to the Arabian foreland by Pre-Gosau
nappe movements, from some geosynclinal zone to the
East; but evidence will be given to show that these
formations arc autochthonous [6, 8] and that their
chaotic structure is due to a region of "cfJusion tectonics"
[11] associated with Upper Cretaceous serpentinite
extrusions on a great scale. The milieu of
these extrusions can be studied to advantage in Oman
because subsequent compression has had relatively
slight and restricted effects, producing no well-defined
thrust-zone or folded foredeep comparable with those
of the Zagros range.
The regional relationships of Uie Oman orogen are
still open to speculation.
It may be a quasi-independent eruptive unit [8, p.
151]; but most authors assume that it has structural
links with Iran. Thus it has long been recognized that
the N-S strike of its northern sector is in approximate
alignment with an old structural trend through Central
Iran and beyond [2, 3]; yet there is no reappearance
of the Oman orogenic zone northwards in the Laristan
province of Iran across the Straits of Hormuz.
Lees [op. cit] regarded the range as a south-trending
branch of the Zagros "nappe zone," deflected southwestward
[cf. 8, Fig. 1] under the NNW-SSE late
Tertiary folds of the Biaban Coast (although these
show no effects of a discordant Upper Cretaceous substructure),
and continuing southward to include isolated
outcrops of serpentinite along the Batain Coast,
at Masira Island, and at Ras Madhraka.
FIFTH WORLD PETROLEUM CONGRESS
However, those outcrops have no extensions to the
north, where deep drilling (Fahud; Ghaba) and geophysical
maps reveal normal foreland conditions.
Lees mentioned the possibility that the Oman orogenic
zone might swing south-westwards off the Arabian
Coast; but the coastal geology and bathymetric
surveys off shore lend no support to this view, and the
serpentinites themselves are now known to be alien
elements in a foreland environment.
These observations are compatible with the results
of air and ground reconnaissance which indicate that
the Oman orogenic zone deflects wholly from a N-S
strike in the north, to a NW-SE strike in the southern
sector, where it is cut ofT rather abruptly by the Batain
Coast, trending NE-SW.
Previous authors have associated this NE-SW coastal
trend with large-scale normal faulting [5, opp, p. 20]
or wrench-faulting [15, Fig. 10; Henson in 4]. Both
may have occurred, and transcurrent shearing along
the "Masira fault zone" is invoked to account for the
anomalous coastal outcrops of serpentinite.
In the North the range ends suddenly at its intersection
with the Pirate Coast which also trends NE-
SW; and the coastal belt is characterized by parallel
normal and wrench-faulting and by stratigraphic variations.
Parallelism of the Batain and Pirate coasts, and the
conspicuous deflection of the Persian Gulf towards the
Straits of Hormuz, may be coincidental; on the other
hand it may be significant that their common trend is
that of the "aualitic lineament" [16] in the "rhcgmatic
shear pattern" (Sondcr) of Africa and Arabia
[6].
Wrench-faulting along the Batain coast may be associated
with the development or rejuvenation of NE-SW
shearing movements responsible for this pattern
(part); and the Pirate Coast trend may have a similar
explanation, though critical evidence is now concealed
by later deposits, particularly in the flat foreland.
Thus wrench-faulting on a very large scale could
account for detachment of the Oman orogenic zone
from former connections to the north and south.
This speculation [6] introduces considerations beyond
the scope of the present paper, but is noted here
as a possible alternative to other hypotheses concerning
the regional relationships of the Oman orogenic zone.
Space does not permit further discussion of these
problems in the present synopsis.
FL'
LA

FUKHAIRI SiiSS
tAKSHAIFA^*^ ?^
SHAMAL
MU&ANOAM
(LPHINSTONE
MIUHA
6AIL
HAGIL
BIH
I' 1 '\ DOLOMITE
hhrV) LIMESTONE
l"^*^! MARL
SHALE
SAND
ltrfiV\ CONGLOMERATE 8 BRECOA
'RADIOLARITES
y.Vi.VvM METAMORPHICS
E^S3 IGNEOUS
CHERTS.SECONDARY
THE OEOLOOY OF OMAN 281
fig. S—Stratigraphic Seetions of Oman.
FORMATION NAMES
SEE LEES, 1928;
HUDSON ETAL.ISS^(2)
' SEMAIL
, HAWASINA
: HATAT

'v/:^'
'C.
282
Oman Mountains
Excellent accounts of the physiography, rocks and
structures of the Oman mountaiiis have been given by
Lees [12, 13], so that attention may be confined here
to new information and modified interpretations resulting
from a considerable volume of later work
(Fig.2).
Stratigraphy
The oldest exposed formations appear in a scries of
axial uplifts, the largest of which are the Jebel Hagab
thrust, the Jabal Qamar block-fold, and the Jcbcl
Akhdar and Saih Hatat domes. These provide sections
down to the Paleozoic (Fig. 3).
The stratigraphy at Hagab and Qamar has been
described in publications [8, 9] to which the reader is
referred, and is summarized in Fig. 3, with suggested
revisions which are explained below. Descriptions
are given here of the most complete sections available,
which are exposed in the Akhdar and Saih Hatat areas
near Muscat.
PERMIAN
Results of rapid reconnaissances by Pilgrim and Lees
in the Saih Hatat dome, have been revised by R. Wetzel
and others (unpubl.).
The lowest exposed beds arc the Hatat phyllitcs and
schists [ 13], with basic minor intrusives, passing southwards
(in part) to quartzites. The original sediments
were elastics and pyroclastics, with a strong limestone
member which contains Permian fossils (Oldhamia
Waagen, etc.). They arc oyerlain by Upper Permian
fossiliferous limestones, concordantly in the north, but
with a 5° unconformity in the south. The dynamometamorphism
is of low-grade with sehistosity parallel
to the bedding, and it decreases upwards, so that fossil
molds at 90 m. below the Upper Permian limestone
coyer have survived its effects; but partial phyllitisa-
, tion persists upwards for some distance in soft interlayers
of this cover.
Marker beds above and below the top.of the Hatat
phyllitcs appear with little variation at several widelyseparated
points, so that slight horizontal shearing has
not greatly disturbed an essentially autochthonous and
depositional succes.sion [Wetzel et al.].
In Saih Hatat, Wetzel measured the following Permian
section above the Hatat phylUtes.
FIFTH WORLD PETROLEUM CONGRESS
Top. (c) Limestone, dark fetid, dolomitic with fossiliferous
zones [370 m.]; (b) PhyUites with intrusions
of green porphyry and andesitic lavas [100 m,]; (a)
Limestone, -pink to black with Bcllcrophon, brachiopods,
bryozoa and corals [340 m.].
In Jebel Akhdar the Upper Permian [525 m,] i.s
composed of dolomitised pcllcty or detrital limestones
with foraminifera and corals. This overlies a faulted
succession of limestones, dolomites and phyllitcs of
Permian age, containing fusulinas.
There is no evidence of unconformity at the top of
the Permian.
TRIASSIC
The Triassic has not been determined paleontologically
south of Qamar, but is believed to be represented
by dolomitised pellety or detrital limestone [652 m,] in
Akhdar, and by platey limestones and phyUites [100
m.] at Saih Hatat.
JURASSIC
In the Saih Hatat outcrops, the Jurassic is dolomitised
and without recognisable fossils.
At Jebel Akhdar, the earliest identifiable Jurassic
beds are Bathonian marly and dolomitic limestones,
[92 m,] without any visible unconformity at the base.
Fine sandstones and shales occur in the middle of this
sequence.
Upper Jurassic is represented by 41 m. of pellety
limestones with some dolomitic bands, containing
Pfenderina spp. nov., Nautiloctilina oolithica Mohlcr,
and Haurania sp. nov. In Oman, it appears that an
important unconformity without visible angular dis-
-«ordance, occurs at the top of the Jurassic, and that
the upper stages, including equivalents of the Riyadh
group of Saudi Arabia, are missing.
CRETACEOUS
The L. Cretaceous section of Akhdar [800 m.] exposes:
Top. (d) Aptian; marly, massive and pcllcty
limestones [150 m.], containing OrbUolina cf. tiiscoidea
Graz; (c) dolomitic limestones [240 m.]; (b)
radiolarian limestones [370 m,]; (a) crinoidal limestones
with CalpioneUa alpina Lorenz.
The Middle Cretaceous in Jebel Akhdar [304 m.]
reveals the following complete succession which is absent
in the north. Top. (c) Cenomanian-Turonian;
massive limestones [72 m.], with rudists (base) and
Uc

•jeolina cretacea (d'Archiac) ; (b) pcllcty limci',oT.ci
[109 m.] with OrbUolina cf. concava (Lamarck);
(a) mariy, silty limestone [122 m.] with O.
d. concava.
At Saih Hatat (Wadi Adi) the Lower and Middle
Cretaceous cannot be recognised owing to extreme
iilomidsadon of the limestones, which, however, grade
It the top into the overlying Hawasina beds (q.v.).
Along the Wadi Semail, between Akhdar and Saih
Iht.tt, the Upper Cretaceous sequence is as follows:
Jop. (c) serpentinites and gabbros [+ 1000 m.]; (d)
low grade metamorphics with basic igneous intrusions
[155 m.]; metamorphism is most intense at top; (c)
radiolarites [228 m.]; (b) finely detrital limestones,
lilicificd mudstones, and microconglomcrates with rare
Globotruncana sp., and reworked Orbitolina [76 m.];
(a) marls and sandy marls, grading into breccias and
rtin,';Iomcratcs [94 m.].
Unit (e) represents the 'Semail' of Lees [ 13], while
fd-a) corresponds to his 'Hawasina' beds.
Tlic contact between unit *a' and the Middle Cretjreous
is sharp but concordant, while that between
i}ie Hawasina beds and the Semail is also concordant,
tut slir;htly sheared to a degree which, in the author's
v'd :•• not indicate important thrusting.
.4^'/iilar succession is observed elsewhere in the
nngc so that it is probably normal and autochthorious;
irA iliis view is supported by the fact that the Hawalina
facics tongues westward into normal marine globirfinal
marls of the foreland [M. Chatton].
Further evidence in the same direction is provided
^-v geophysical surveys in 4he north foreland, which
mral an exceptionally high gravity-gradient rising
• iw^rds the mountains, suggesting that the Semail ex-
^n;'.ion5 arc dccp-rooted in situ.
Eroded surfaces of Hawasina and Semail are covered
. r. hoih flanks of the range by transgressive Macstricht-
1 -i.T conglomerates, marls and rudist reefs. The age
1 ir.gc of the Hawasina-Semail succession lies therefore
I^i-cwccn the Cenomanian or Turonian and the Maes-
'-•: 'htian, with scope for some diachronism. Since mag-
••-litc veins, probably the immediate after-effects of
•"i.Tnion [K. C. Dunham], have been found to cross
Hirjtrichtian—Semail conUcts, tbe Semail itself may
•; of Campanian-Maestrichtian age.
Tl-.tse conclusions differ from those of earlier pub-
:i">ioni which assumed a considex^le time interval,
THE OEOLOOY OF OMAN 283
mrr^mm'vmtmtmm
with orogenic movements, between the genesis of the
Semail-Hawasina complex, and deposition of the overlapping
Maestrichtian. Hawasina beds are typically
contorted under Semail cover, but this is attributed to
penecontemporaneous slumping, whatever their age
may be.
In the northern part of the range (Hagab; Qamar)
earlier dates (Triassic-Jurassic-Lower Cretaceous)
have been assigned to the Hawasina [8, 9] suggesting
repetition of the facies in Oman. However, evidence
for this interpretation is under review in these two
structurally-complex areas, because, at the Jabal Agah
dome between them, the stratigraphy approximates to
that at Wadi Semail. Thus the Qamar sequence [op.
cit.] of Ais schists (cf. Unit "d") and Kharmil cherts
(cf. Unit "c") is here underlain by detrital limestones
(cf. Units a & b; (?) and Makhsur beds—part) with a
basal conglomerate resting transgressively on eroded
Upper Musandam limestone of Lower Cretaceous age
(Fig. 3).
Correlation of displaced Hawasina beds is difficult
because the evidence of their radiolaria has been found
to be unreliable [G. F. Elliott] and they often contain
derived faunas, sometimes locally monogenetic, ranging
from Permian to Cretaceous; they also contain
numerous nia.-jsive slumped blocks of the sub-strata
(the klippen of Lees). The Semail itself has entrained
blocks of underlying, sediments. Sills of serpentinite
occasionally penetrate the Hawasina (e.g. near Jabal
Agah), and basic dykes of later date cut both formations
and their contacts. Pillow lavas appear locally in
the Upper Cretaceous (Wadi Jizzi, etc.) but their relationships
are imcertain.
, TERTIARY .
Cainozoic marine sediments overlap both flanks of
the mountain zone, marking separate transgressions of
Paleocene-Eocene, Oligocene, and Miocene age. Soirie
folding movements intervened between the Oligocene
and the Miocene.
Geological History
The detailed structure of the Oman Mountains (Fig.
4) is still imperfectly known but the main events in its
history are indicated by stratigraphic studies. These
show that the region was a stable part of the gentle
foreland basin of Trucial and Central Oman until the
end of Middle Cretaceous times. There is no evidence

t:
284 FIFTH WORLD PETROLEUM CONGRESS
W
J.Hofil
I 1 NEOCENE
S 3 OLIGOCENE • PALEOCENE
Ijljljl Normol Morino 1
pn] Howotino ftodi » UPPER CRETACEOUS
F^T.Aj Somoil . J
^ MIDDLE CRETACEOUS-JURASSIC
^ ^ TRIASSIC-PERMIAN
^ ^ UPPER PALAEOZOIC UndifF.
Ei lOWER PALAEOZOIC Undid.
ENE
(W)
Dibba
Tgg^j3^5^S^^3Sgc^is^5'
^ ^ ^ ^ ^ ^
ScoU In Mil«»
10
S>o Uvl
N«ag.n./ s,|,„
Olipo • Pol*DC«n«
NOTE 1, Abnomol opporoni ihicknoitoi of Howoiino b«da or* duo to contortion,
3, Soinail 'rooli' aro omillod bocouio thoir poiilioni oro unknown.
Fig. 4—Structural Cross^Sections of Oman Mountains.
to suggest that any Mesozoic geosynclinal zone devel-^; ,'at or towards the end of the Middle Cietaceous, when
oped to the cast, where the Gulf of Oman subsided at basal Hawasina breccias and conglomerates appeared
a much later.( (?)post-01igocene) date.
with derived faunas, indicating contemporaneous axial
The first movements recognisable in Oman arc indicated
by metamorphism and tectonic repetition of the
Hatat phyllitcs, which are not likely to have resulted
from, or followed, the broad folding of the Saih Hatat
and Akhdar dorncs in which they appear. Since these
dynamic eflects increase downwards in the deeper, incompetent
core of the structure, diminishing and disappearing
upwards in their competent cover, they may
have been caused by slight underthnisting of a pene­
emergence and erosion. In the overlying Hawasina
units, huge slumped masses of Permian—^Jurassic sediments
point to more violent local disruption and probably
block movements, accompanied by premonitory
vulcanicity (tufTs; basic extrusions). Associated silica
eiuichment of the sea water favoured the deposition
of radiolarites which are often chaotically slimiped and
contorted. The regime was evidently one of continued
planed basement [Henson].
regional subsidence with local uplift and archipelago
. • Local uplift due to this or some other case, began conditions in a scismically-activc orogenic zone.
S«al«y«l

C iis history culminated in the extrusion of ophiolite
.ppes" on an immense scale, and prpbably in a viscous
form and local low-grade dynamo-thermal metamorphism
of immediately underlying beds; and in
slight shearing of ophiolites already consolidated,
'i'hese generally rest on Hawasina beds, but at Jabal
Rann (near Qamar) they overlie a truncated, uplifted
dome or block of Rann (Ordovician) quartejtcs
and shales [9].
Semail extrusion, from "roots" so far undiscovered,
was probably accompanied by continued subsidence;
the upper part of the serpentinites is sometimes conglomeratic,
suggesting emplacement under isubmarine
conditions. However uplift and axial erosion followed
quickly, with deposition of flanking basal Maestrichtian
conglomerates, probably including the Ajma
boulder beds [9].
Apart from gentle oscillations which controlled subsequent
transgressions and regressions, there is little
evidence of further activity in the Oman range,until
post-Oligoccne, pre-Miocene folds appeared on the
west flank. It was probably at this time that axial uplifts
were accentuated, tilting their Semail-Hawasina
cover; and that thrusting occurred on a large scale in
thr -

286 FIFTH WORLD PETROLEUM CONGRESS
W
r"~l NEOCENE
B«S!>WSSrai»>!«^««?i!!W?!«»«!S!^^
^m OlICOCENE • PALEOCENE W
Normal it Marins 1
Howoti ino Bodi /^
^UPPEK CRETACEOUS
MIDDLE CRETACEOUS - JURASSIC
TRIASSIC-PERMIAN
^ ^ UPPER PALAEOZOIC Undiii.
^ 3 LOWER PALAEOZOIC UndiK.
Saciiont B,C & 6 Varlicol Seal* x 2
Thin N«og«fl« cov«r
Central Hugf
ScoU in MiUt
5 to IS
Fig. 5—Stmctural Cross-Sections of Oman Foreland.
tatolt
E
Duqm
ESE
(120')
S«a iovol
Soa Iovol
It is assumed that salt does not occur at depth in the geophysical evidence suggests that salt-doming occurs
outcrop area (or in the Oman range) because it mak^ at depth.
no appearances under conditions which should have These observations lend some support to the tentafavoured
extrusion. tive correlation suggested above.
ORDOVICIAN
Near Haushi, an ill-exposed sequence [550 m.] of
red sandstones and mottled shales with trilobites and
Cruziana (cf. Rann beds of Qamar), lies unconformably
on units (b) or (c) of the (?) Cambrian. At
Ghaba to the north-west. Lower Ordovician sandstones,
siltstones, shales and mudstones [2000 m. +]
containing Didymograptus bifidus (Hall) and Cruziana,
have been drilled without reaching the base; but
PERMIAN
At Haushi, the Ordovician is overlain by elastics
with boulder beds, the latter containing unsorted, subrounded
blocks of granite and porphyry, with occasional
Palaeozoic dolomites, ranging up to 2 m. diameter.
These boulder beds, composed exclusively of
Arabian rocks, are transgressive over a vnde area. An
aqua-glacial origin has been suggested [Chatton; Hudson
in 10], though other explanations are possible. The

I-
boulder beds contain interbedded sandstones with a
brachiopod fauna, and are overlain by 230 metres of
sandstones and red marls. The sandstones grade up
into an alternating sequence of marls and platy limestones
[36 m.] with a rich brachiopod, trilobitc and
goniatitc fauna of Sakmarian-Artinskian age.
IRIASSIC
Triassic rocks are not exposed in the Oman desert,
but 580 m. of dolomite with Lingula tenuissima Bronn,
and some anhydrite, arc assigned provisionally to the
Trias in a drilled section at Fahud.
JURASSIC , ,
The Lower Jurassic is not represented in the Hugf,
but at Nafun, 77 metres of Bathonian limestones with
Anabacia, restunconformabl) on (?) Lower Cambrian.
At Haushi, the Permian is followed by dolomites and
limestones [162 m.], ranging from Bathonian to low
Upper Jurassic age. A similar sequence was found
above the Trias in Fehud Well. There is everywhere,
at the base of the Jurassic, a thin clastic unit which
cannot be firmly dated.
OETACEOUS
At Haushi, the Lower Cretaceous [169 m.] lies unconformably
on the Jurassic and consists of dolomitic
and pcllcty limestones in the lower part, with chalky
limestones and porous dolomitic limestones above.
Orbitolina cf. disoidca occurs throughout.
The Lower/Middle Cretaceous contact is marked
by marls and sands [151 m.] with Orbitolina, etc.; and'
the overlying Middle Cretaceous is represented by
marly limestones [156 m.] with Orbitolina cf. concava.
These subdivisions can be followed with local variations
of thickness and lithology, throughout Oman.
The Upper Cretaceous with Globotruncana spp.
shows marked facies and thickness changes: Lower
Senonian marls in the Hugf change northwards into
wiulstoncs, hut become marly agi\in in the Fahud area.
Canipani.iii marly liiiicstonrs in the Hugf change to
iiiiirls northwards.
Serpentinites outcrop sporadically along the Batain
coast, and at Masira Island where they sur associated
with typical ( (?) Hawasina) radiolarites and covered
by Eocene. Shattered metamorphics (cf. Ais formation,
fide Dunham) and serpentinites appear at Ras Madluaka
under transgressive Oligocene. Basement serpen­
•^nMHW^M^M
THE OEOLOOY OF OMAN 287
tinites and amphibolites, striking NE-SW, occur in the
"metamorphic complex" at Murbat [ 1 ]; but pctrological
comparisons, and the presence of familiar radiolarites
at Masira, seem to demand correlation of the S.
Oman outcrops with the Scmail/Hawasina complex
of the Oman range. However, it is unlikely that they
are in their original positions because no traces of thcrn,
in situ or derived, or in transitional (radiolarian)
facies, arc to be found in adjacent comparative sections
of Hugf and Haushi.
They are, therefore, believed to have been displaced
from the Oman orogenic zone by post-Cretaceous, pre-
Oligocene wrench-faulting along the Batain Coastal
belt.
The Maestrichtian is transgressive and outcrops
over wide areas bordering the mountains and the Hugf-
Haushi swell. It is normally characterized by orbitoidal
limestones and rudist reefs with basal conglomerates,
sands and marls. At Fahud however, the Maestrichtian
is in a marl facies which reappean in a well at Juweiza,
overlying a thick Campanian section with flysch and
conglomerates, known only at this locality adjacent to
the Pirate Coast
; \ •
PALEOCENE-EOCENE
There is generally a break, without angular discordance,
between the Maestrichtian and the Paleoccne.
At Fahud, Maestrichtian marls are succeeded by Paleocene
[122 m.], consisting of yellow marls with abundant
Lockhartia haimei (Davies) below massive, nodular
and boulder-weathering limestones containing
species of Lockhartia, Kathina, Sakesaria, Daviesina
and Miscellanea (= Umm er Radhuma formation of
Saudi Arabia); Lower Eocene [124 m,], with chalky
marls and limestones, gypseous shales, dolomite and
dolomitic marls; Middle Eocene (top eroded), with
yellow marls and rubbly limestones containing abundant
Nummulites spp., Dictyoconcidcs cooki (Carter),
etc.
These deposits have a wide distribution in tlic
Oman-Dhofar foreland, but the Paleoccne occurs only
in one small outcrop in the Hugf area. The Middle
Eocene is most variable, appearing in a massive nummulitic
limestone facies at Buraimi, and in a globigcrinal
marl facies in the north coastal area. The Upper
Eocene is found only to the north of Ibri, typically at
Buraimi where it is represented by 250 m. of elastics

Q
288 FIFTH WORLD PETROLEUM CONGRESS
and limestones with Nummulites fabianii Prever, Pcllatispira
sp., etc.
The Eocene is believed to be well represented in a
thick Tertiary basin at Sur (Lees), and extends northwards
along the east coast.
OUCOCENE
The most complete Oligocene section is found at
Duqm. The Lower Oligocene [125 m.] is unconformable
on the Eocene and comprises echinoidal chalky
limestones overlying a marl, gypsum, and dolomitic
limestone sequence, with a basal reef containing derived
Eocene nummulites, etc. Above is a section [47
m.] of chalky limestones with peneroplidae and miliolidae
dated as Upper Oligocene, which extends far to
the west. At Ras Madhraka, chalky limestones with
Lepidocyclina overlie Hawasina-Semail rocks. Thin
Oligocene outcrops are also known on the Batinah
Coast, and at Jebel Hafit, all in reef facics; but at
Jabal Aii and Ras Sadr on the Pirate Coast, there is
a very thick Oligo-Mioccne section of marls and
evaporites similar to that of Qishm Island.
MIOCENE
The Miocene rests unconformably on the Oligocene.
At Fahud, the Miocene can be divided into a lower
unit of limestone, chalk and marl [33 m.] of Burdigalian
age, and an upper part [+90 m.] which is
largely detrital and evaporitic and has been correlated
with the Lower Pars of Qatar and the Trucial Coast.
Ostrea latimarginata Vrcdenburg, Clausinella persica
Cox, and C. amidii (Stcfani) are present with a reworked
fauna of Lower Eocenc-Macstrichtian ages.
The Burdigalian extends south and southwest towards
Dhofar. ,^
Late Tertiary deposits at Sur [13] have not been
studied in detail, but they differ soinewhat from those
of the Oman foreland. • •\
MIO-PLIOCENE
Extensive deposits of coarse gravel and conglomerates
occur above the definite marine Miocene at Fahud,
and they extend ^long mountain pediment.
Volcanics
Basalts, probably of Quaternary or Recent age, occur
at Ras Madhraka.
Structure
The desert region can be subdivided structurally
(Fig. 5) as follovirs:—
a) In the south coastal belt, the broad tabular Hugf-
Haushi swell can be seen trending NNE-SSW with a
core of Lower Palaeozoics running from Duqm to Latitude
21 **, and bounded on the west by a scarp exposing
Mesozoics and Tertiaries with low dip. Some of these
unconformable deposits reappear on the east flank in
the southern sector.
Stratigraphic observations show that differential
block movements of various ages from Paleozoic onwards
have affected this feature; it is cut by numerous
intersecting faults at diverse angles, the prevailing direction
being N-S. However, in its gross structure, the
core is roughly divided into major blocks with margins
striking ENE-WSW to NE-SW; and the latter trend
dominates geophysical survey patterns in a coastal belt
50-100 miles wide, reappearing in the geological mapping
of the Sur sector. It is considered that the prominence
of this trend is due to movements of the Masira
wrench-fault zone which may have had a long history
of recurrent activity.
There is no regular folding in the Hugf-Haushi area,
but there are several widely-spaced anticlines, averaging
7 miles (max. 20 miles) in length, and rising anomalously,
sometimes sharply, out of tabular surroundings
(e.g. Fig. 6). Two of these folds strike ENE-WSW, the
remainder having a N-S alignment, but most of them
are very irregular, with associated normal and wrenchfaulting.
The structures are attributed to the interplay
of vertical and horizontal block-movements in the
basement which probably lies at no great depth.
b) The area to the west and northwest of the Hugf
scarp is extremely flat and dips of the Tertiary strata
cannot be ascertained. However, geophysical surveys
reveal important subsurface faulting, and local salt
tectonics generally associated with faults at depth. At
several points salt plugs pierce the horizontal cover,
but only one of these reveals peripheral dips (3°) in
the Miocene overburden.
Acknowledgments
The author is indebted to the Management of Iraq
Petroleimn & Associated Companies for permission to
publish this sytiopsis; to K. C. Dunham for pctrological

^ y
TUB OEOLOOY OF OMAN 289
•T'""i*"'i.>-r'-w^«w< '^.'•'--'-y-'K^
Py^yP'P'''-''.'''-^"J./.
'.•^y:^ ••••V-;, :>^ " • -' •'. •• • • - - • •
y-:-y^y^:yxy-^yyy
.:;'v.-;: .;-/:^.-^j,,j^,^..,.,v. J..-;;;:::t- ,i;,>;•.,,
••'^'^,:/.;"-:^\-.\t0;;r:--'^: ••.•,.
; '•,. •..•.. . ':^-'r .'.•• yI}'•.••"• \ ' • -
'•yp-pd^^
pPdP'-^j:^''^pd-^\\:ip? y
ly^i'V'--'^'''
• ' . . ^ • . : ' . :
•y-;''
'•'d'! .^\.y\d^p-''.- d'.' \"
,-v .K:^:
•+\
^•;•'i::;>^•••
• d : ^'''^•••' d ^ ^
-> ixd.^d''^'':^p^yyK^,p.-:::y:'r:'
' '-yp-P':ypy'yr.yr '':-'-••
. •'•d^-'\dpf-.iPk-:y,y: y
• • ';"r ' -'^••i>-^;',l>«-^,h.;:... .-•;..;•'> •^:r
V,.:;'-'\V,."
\ll^ •
••i'^'^N.;
' • " ; > : - ; • ,•
...^ ,Sv
•-ddppdd.yPP
.•ymyyy^r\"-'^':s
"f-p;; >''Mv
^ ^ • \ - • : ; . ' • ; '
A> J
•V;.;;:i'}\;
Fig. 6—Air Photograph of Hatuhl Anticline, South Oman.
jiiuiiiiuui, iigi.ii
d'',d- ''•'
•-•• ?
T-^
.*.,. '..,/'
: • > ; ; - • ; ;
,1

^ ^
y
290 FIFTH WORLD PETROLEUM CONGRESS
services; to K. G. S. Hudson and M. Chatton for
paleontological-stratigraphical research; and to many
colleagues who have shared in the arduous work of exploration,
particularly T. F, Williamson and D. Glynn-
Jones [1936-7], L. S. Thompson and H. Hotchkiss
[1940], R. Wetzel [1949], and R. G. S. Hudson
[1951-2]. •
K. C. Dunham and F. R. S. Henson have kindly
reviewed the manuscript.
References
1. Fox, C. S., "The Geology and Mineral Resources
of Dhufar Province, Muscat and Oman," Muscat,
1947.
2. Furon, R., "La Geologie du Plateau Iranien,"
Rev. gcndrale des Sciences, Vol. XLVIII, No. 2,
pp. 36-43, 1937.
3. Gansser, A., "New Aspects of the Geology in Central
Iran," Proc. 4th World Petroleum Congress,
Sect. I/A/5, pp. 279-300; 1955.
4. Girdler, R. W., "The relationship of the Red Sea
to the East African Rift system," Quart. Joum.
Geol. Soc. London, Vol. CXIV, Part 1, pp. 79-
105; 1958.
5. Gregory, J, W., "The Rift Valleys and Geology of
East Africa," Seeky, Service & Co., Ltd., London;
1921.
6. Henson, F. R. S., "Observations on the Geology
and Petroleum Occurrences, of the Middle East,"
Proc. Third World Petr. Congr., Sect. I, pp. 118-
140; 1951.
7. Henson, F. R. S. and Elliott, G. F., Exhibition of
specimens of Collenia? from pre-Permian sedi­
ments in South Arabia, Proc. Geol. Soc. London, ^
No. 1561, 29th May; 1958.
8. Hudson, R. G. S., A. M. McGugan and D. M.
Morton, "The Structure of the Jebel Hagab Area,
Trucial Oman," Quart. Joum. Geol. Soc. London,
Vol. CX, pp. 121-152; 1954.
9. Hudson, R. G. S., R. V. Browne and M. Chatton,
"The Structure and Stratigraphy of the Jebel
Qamar area, Oman," Proc. Geol. Soc. London,
No. 1513; 15th June 1954.
10. King, L. C, "Basic paleogeography of Gondwanaland
during the late Paleozoic and Mesozoic eras,"
Quart. Journ. Geol. Soc. London, Vol. CXIV,
Part 1, pp. 47-77; 1958.
11. Kiindig, E., "The position in time and space of
the ophiolites with relation to orogenic metamorphism,"
Geol. en Mijnb. No. 4, New Series,
18th year, pp. 106-114; April 1956.
12. Lees, G. M., "The Physical Geography of South-
Eastem Arabia," Geograph. Joum., Vol. LXXI,
No. 5, pp. 441-470; 1928.
13. Lees, G. M., "The Geology and Tectonics of
, Oman and of Parts of South-Eastcrn Arabia,"
Quart. Joum. Geol. Soc London, Vol. LXXXIV,
No. 336, pp. 585-670; 1928;(with bibliography).
14. Schroeder, J. W., "Geologie de I'lle de Larak,"
Arch Sci. phys. et nat. 5th Per., Vol. 28, pp. 5-18;
Jan.-Feb. 1946.
15. Vening Meinesz, F. A., "Shear Pattems of the
Earth's Cmst," Trans. Amer. Geophys. Union,
Vol. 28, No. 1, pp. 1-61; 1947.
16. Von Wissmann, H., C. Rathjens, and F. Kossmat,
"Beitrage zur Tektonik Arabiens," Geol. Rundsch.
Vol. 33, pp. 221-353; 1942.
This paper was presented on June 3, 1959, by D.
M. MORTON.
Discussion
N. E. BAKER (Consulting Geologist, Upper Montclair,
N. /., U.S.A.). The factual geologic data presented
by the author represents a vast amount of
arduous field work by himself and many of his colleagues.
This is a major contribution to the geology
of Southern Arabia and the lower Arabian Gulf
area, ranking along with Lees' early work on the
geology of Oman. This present contribution embraces
knowledge gained from photogeology, surface exami-
' nations, geophysical surveys and subsurface studies of
the results of eight deep wells drilled in the area.
Hence it constitutes a solid foundation for future
regional studies.
The speculative portion of the paper is embraced
in the discussion of the "Regional Geology," conceming
the significance of the Oman Range with
respect to its relationship to the Zagros nappe zone
of Iran, As regards oil prospecting in the lower
Arabian Gulf with particular reference to the Trucial
Coast and Iran, this relationship is very important.
The author points to: 1) "elTusiori tectonics" as
responsible for this (Oman) "chaotic stmcture,"
rather than the results of thmst from the east as con

c ;ndcd by Lccs; 2) the lack of a "well-defined thrust
•^"ionc or folded fore-deep comparable with those of the
Zagros Range;" 3) the lack of any "reappearance of.
the Oman ijrogcnic zone northwards in the Laristan
Province of Iran across the Straits of Hormuz;" 4)
the absence of extensions to the north of the serpentinite
found along the Batain Coast, Masira Island
and at Ras Madhraka as shown by drilling in Fahud
and Ghaba; and 5) the parallelism of tdie Batain
and Pirate Coasts to the Oman trend, produced by
wrench-faulting. These are advanced to "account for
dctarhincnt of the Oman orogenic zone from former
connections to the north and south."
Lees {"The Geology and Tectonics of Oman,"
Q.J.G.S., LXXXIV, 1928] contends that the Cretaceous
folding of Iran bratKhes southwards from
the Zagros through Ras Musandam to Ras Madhraka
sou tit of the Hugf. Others contend that the Zagros
belt continues eastward into the Makran Coast of
southeastem Iran.
The configuration of the Arabian Gulf coast lines
of both Iran and the Trucial Coast, the parallel
structural trends in the Biaban and Batinah Coasts,
•^c intensity of structural coinpression in both the
gros and Oman belts of folding, and the presence
Zl large salt masses in the foreland areas of both
these regions are some of the conspicuous features
that make the direct relationship of structural and
stratigraphic factors on both sides of the Gulf appear
to be the result of uniform and contemporaneous
conditions.
The importance of determining the relationship
of the geologic factors of these areas for purpose of
oil finding is obvious. The stratigraphy of the forefront
of the Oman Range and that of the Batinah
coastal area as related to oil prospects, the stratigraphy
and structure of the Makran Coast and its
oil prospects, likewise the geological factors determining
the potentialities of Biaban coastal area, are
some of the important unknowns which may be related
to the effects of Oman orogeny.
If Lees' contention holds, nariiely that the Zagros
Cretaceous folding and subsequent deposition extends
southward into Oman, then oil prospects in
die forefront of the Oman Range, the Tmcial Coast
and the lower Arabian Gulf should be analogous to
those of southeastem Iran. Similarly, the Makran
^-'
THE CEOLOOY OF OMAN 291
.IJIII|WI|I.IIIIIHJ 1. !»i.«»l^»W
Coast and the cast flank of the Oman uplift both in
the Batinah and Biaban coastal areas should embrace
similar stmctural and stratigraphic conditions, having
equal or similar oil prospects. However, if the Oman
orogeny is independent and unrelated to the Zagros
as suggested by the present paper, the analogy cannot
be drawn.
Drilling in the forefront of the Oman Range has
not been productive of oil. Other clearly-defined
structures well out from the igneous belt remain untested.
Two successful wells, however, have been
completed off Das Island in the lower part of the
Arabian Gulf, well within the enclosed synclinal
basin.
A comprehensive regional study embracing the
geologic knowledge acquired both in Iran and in the
Tmcial Coast-Oman provinces would go far to
evaluate bil prospects of the region and would serve
to guide exploratory efforts. Though much useful
data is presented in the present paper, the author is
aware that: "The regional relationships of the Oman
orogen are still open to speculation."
This discussion poses the question rather than
attempts to solve it, in the hope that further useful
speculadon will result.
D. M. MORTON replies. I would like to thank Mr.
Baker for his discussion which brought into our discussion
today parts of the regional, story which I
omitted in our brief account. Firstly, to run over
some of the points Mr. Baker raised and probably repeadng
things I have said already in the paper, Dr.
Lees believed that the Semail, Hawasina and underlying
limestone succession had been thrust by predocile
movements from somewhere to the east and
into the territory of Oman.
As I already indicated in stratigraphic studies, we
believe that the Hawasina formation is a normal
body present in the mountains, and that the overlying
Semail unit is in situ.
Regarding the structural trends, some authors believe
that the Oman trend can be followed northward
into Central Iran, but in the Laristan Coast there
is no parallel structure to the Oman range.
Dr. Lees believed that the Oman orogen was a detached
arc from the 2^gros folding running through
Oman and swinging on along the Batain Coast where
the Masira Island ophiolites and those at. Ras
Madhraka crop out.>

^ :
292 FIFTH WORLD PETROLEUM CONGRESS
Essentially, the Oman range has a north-south
strike in its northern part and stops abmptly at the
Strait of Hormuz. In the southem part it swings into
a northwest-southeast strike and again stops abmptly
at the Batain Coast where, to the east, there is
another strike at right angles in this direction. The
Batain Coast is believed to be a fault coast, some
vertical movement, and also there is indication that
there has been wrench faulting along here.
Similarly, the parallelism of the Pirate Coast and
the studies in this area indicate that there may be
wrench faulting along this trend. In such case, the
Oman orogen, itself may have a continuation elsewhere,
from which it is now removed.
With regard to Mr. Baker's remarks that, if the
alternative theories are correct, there should be a
comparison between the Coastal Iran sediments and
those of Oman, to die best of my knowledge this is
not the case. We can follow our Oman foreland
deposits from the desert areas into the mountains
and the intertonguing of the radiolarites with the
marine globigerina marls of the Upper Cretaceous
seems to suggest that they are part of the same sedimentary
story.
I would like to echo Mr. Baker's remarks that perhaps
further discussion would be of great value to
all the people concerned with the geology in these
particular areas of Arabia and Iran.
Z. R. BEYDOUN (Iraq Petroleum Company, Ltd.,
London, England). I would like to add my thanks to
those of Mr. Baker and Mr. Morton for this very
interesting presentation on a previously relatively little
known area of Arabia.
His description of the (?) Cambrian of the Hugf
area is very interesting. In the Hadramaut, where a.
great deal of similar field work has been carried out,
we have found a group of old sediments which bear
very marked overall lithological similarities and unit
similarities to the Hugf beds. This suggests that the
Hadramaut beds may very likely be of similar (?)
Cambrian age. However, a big unconformity occurs
above these beds, and they arc generally overlain by
Upper Jurassic or Lower Cretaceous rocks, all of the
older part of the succession being absent.
With regard to the Tertiary, the Paleoccne. of
Southwest Arabia extends northeastward to the Oman
with much the same facies attd lithology as described
by Mr. Mortpii, and the break between the top of
the Cretaceous and the base of the Paleocene also
occurs in Southwest Arabia.
In view of the occurrence of salt domes in parts
of Southwest Arabia in which the age of the salt is
dated as Jurassic on the basis of fossils in the immediately
overiying shales, I would be grateful if
Mr. Morton could indicate how firm is the age dating
of the salt in the Oman. ,
D. M. MORTON replies. The age dating of the salt
in Oman is also tied in with the suggested correlation
with the salt domes of the Arabian Gulf. In
several of these domes, the salt brings out Cambrian
fossils and overlying red clastic beds, sometimes salt
pseudomorphs, and a general succes.sion has been
worked out for the Gulf area.
In Fahud, we know that the salt is certainly older
than Permian. In Ghaba, wc have drilled down
through 2000 meters of, Ordovician without encountering
any evaporites in the whole well section,
and there was originally an indication, on the basis
of geophysical results, of salt tectonics at depth in
this area.
At Haushi, to the east, more than 2000 meters of
Ordoviciari and possibly Upper Cambrian sediments
are exposed at the surface without any signs of
evaporites, but the underlying Lower Cambrian dolomites
themselves show an approach to evaporitic conditions.
It may well be that the salt is of upper Lower
Cambrian or lower Upper Cambrian age in Oman.
E, KUENDIG (Bataafse Internationale Petroleum
Maatschappij N.V., The Hague, The Netherlands).
I wish to congratulate Mr. Morton for his excellent
study of what we may call a classical orogen de-
-veloped from a eugeosynclinal habitat. It links up
very well with similar studies done in Kurdistan by
Washington-Gray, in Iran by Gansser and his colleagues,
and in Anatolia by Bailey.
Lees' original concept, that the Oman Mountains
should represent the proper nappe stmcture, has almost
disappeared and is being replaced by the acceptance
of eugeosynclinal gravity gliding, either of
the olistostrome type or of a sheet type. This is a
typical example of what I discuss in my paper (Paper
25, Section I) at this Congress.
I have only two specific questions to ask Mr.
Morton. When he refers to the metamorphism, as far
as I understand, there is a lower series, Permian (pos-

• . '
d
THE CEOLOOY OF OMAN
sibly Triassic), which has a low-grade regional metaniorjihism.
This is separated by a non-metamorphic
Mesozoic interval from a low-grade Upper Cretaceous
metamorphic scries. The latter is probably connected
with the Semail effusiva. Distribution, of this metamorphism
in the Oman mountains seems rather
strange, but it coiiicidcs with similar facts wc know
of other mountain systems, such as the Alpine ophiolite
belts, where a kind of selective metamorphism
takes place. . ,
So my question is: Are these metaiiiorphics of the
same origin or do they represent two periods of metamorphism
and consequently two periods of mountain
formation?
D. M. MORTON replies. I would like to thank Dr.
Kuendig for his remarks and answer his question regarding
the two metamorphisms in the Oman range.
The lowermost metamorphism in the Permian
(possibly Triassic—I would say Permian) beds increases
in degree from the top downward. But it has
been suggested that it results from or could result
from underthmsting of a peneplaned basement. I do
not and cannot enlarge on that theory which will be
stated elsewhere at a future date.
The uppermost metamorphism which occurs in the
Upper Cretaceous beds decreases in degree from the
top downwards, and it is believed to result perhaps
from the drag of a viscous Semail extrusion. It is
furthermore believed that the tvvo metamorphisms
occurred at different dates.
F. E. WELLINGS (Iraq Petroleum Company, Ltd.,
London, England). I would like to say a few words
about the oil prospects in this new country of Oman.
Until we went in there, it was entirely virgin territory
for non-Arabians including geologists. In fact, it is
the first desert country I have ever been in without
seeing somebody's previous car tracks. I would .like
to pay tribute to Mr. Morton, who first went there
with me, for the amount of geological work they have
done in this short period of just four years.
Fahud, the first well we drove in the middle of the
desert, was a beautiful antirlinc, an absolute natural,
which would have been drilled anytime before this
if one could have got to it. Unfortunately, it was a
dry hole except for some minor shows in the Jurassic,
Triassic and Permian. Because the stratigraphy was
unpromising, we did not drill the neighboring anticlines
and decided to drill something geophysical
293
elsewhere. Wc knew there were a number of exposed
piercement-type salt plugs which bring up rocks
which arc certainly early Paleozoic, if not Cambrian,
in age, though no fossils have been found. We drilled
on a seismic anticline, and that proved to be no
better.
In the neighboring Sheikdom of Dhofar, Richfield-
Citics Service did not have much better luck. They
found some oil in a sand about 2000 feet deep, but it
is so far non-commercial. They were also the first
non-Arabians to get into this country.
The third area which we are now exploring by
geophysics is the East Aden Protectorate, more commonly
known as the Hadramaut. There are no oil
indications there at the surface, but we have found
some gravity anomalies and we propose to put some
seismic crews there this autumn.
The nearest discovery in this great territory is
along the Trucial Coast and in the Arabian Gulf. We
have drilled five different seismic stmcturcs along
the Tmcial Coast without getting any oil. The Arab
zone, which is the producing horizon in Arabia and
in Qatar is not typically developed there, but more
recently BP and CFB drilled a seismic stmcture in
the sea bed near the Island of Das and they discovered
oil in the Lower Cretaceous limestone, a
formation which hitherto has not been productive
anywhere in the Persian Gulf area.
We are still testing gas and condensate in a well of
our own at Murban.
W. PHILLIPS (Economic Advisor to the Sultan of
Oman, New York, N. Y., U.S.A.), On behalf of
Sultan Said Ben Tymour, Sultan of Oman, I want to
add one or two remarks to the very distinguished
speakers who have spoken to us this morning, and
very adequately described the geology of the Sultanate
of Oman. I want to mention two or three points
which more or less fall into my own special province
as an archaeological explorer of Oman and economic
advisor. On behalf of the Directors of the American
Foundation for jhe Study of Man, we have conducted
extensive archaeological expeditions throughout this
entire area for many years before I introduced Cities
Service and Richfield into the Province of Dhofar on
behalf of the corporation of which I am president.
Cities Service and Richfield were not the first foreigners
in the Dhofar. Oman itself was extensively explored
by American missionaries beginning in 1890.

* • ' ' " ' ^ *
w
294 FIFTH WORLD PETROLEUM CONGRESS
Dhofar is not a sheikdom but one of many prov- fortunately have had to ihakie my living as a biblical
inces which arc ruled by the Sultan of Oman. I archaeologist. But I did want to straighten out a fewmight
also say that Oman has enjoyed treaty relations of these points with regard to the political and
with the United States dating from 1834, when our cultural anthropological aspect of the Sultanate of
own President Andrew Jackson helped to negotiate a Oman,
treaty with the great Said the Great. F. E. WELLINGS. My use of the word "sheikdom"
Please do not interpret these remaks as in any way for Dhofar was a slip pf the tongue. I know it is a
being critical. I was trained as a geologist, but un- province of Oman.
\ \
• >^IIIWI»I^II

f
SEVENTH WORLD PETROLEUM CONGRESS
Proceedings
VOLUME 2
ORIGIN OF OIL,
GEOLOGY AND GEOPHYSICS
V '•r\',
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WORLD PETROLEUM CONGRESS HIJXlKg®
ELSEVJER PUBLISHING CO. LTD
1967
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•974 . . • , . , , ; ; ';
Martin, 291
.Martin, R., 511
Martinez Rios, M., 634
McGulloh, T. H..'735,.777
McDonal, F. J., 585
Mclver, R.D., 25, 75
McNaughton, D. A., 289, 918
Mekhtiev, S. F., 543
Michon, D., 645
Miria,?,, 74, 871,923
Miriato, M., 447
Mirchink, M; F., 101
Montadert, L., 425, 457 ,
Moore, P. F., 457, 511, 634
Moore, P. G., 481
More, 289
Morrow, R. M., 141
Murray, R. C, 409 . •
Naficy, F., 287
Nalivkin, V. D., 109
Nickitenko, K. I., 697
Nomokonoff, V. P;, 778
Oleniri, V. B., 37
Oliver, F., 511
Gpina-Racines, 75
Oppenheim, 74
Osment.F.C, 141,288
Paran, V., 777, 871
Parra, J. J., 971
Pelet; R., 605, 634
Perrodon, A., 287
Polasek, T. C, 457
Polasek, T. L., 397
Author Index
Polshkov, M.K.,697,7.77
Pritula, Y. A,, 109
Qupn.D., 669
Radier, 288
Radier, H, G., 635
Razaghnia, M.T., 871, 922
Raid, 97.1
Renaud, 74
Reyes, A. G„ 653
Rjabinkin, L. A., 777
Robinson, R,, 74
Rovnin, L, L.lOl, 109
Rudd.E, A., 171
Rudkevich, M. Y., 109
Ruhl,W,-,457 ,' -
Salguiero, R., 779
Salvador, A., 73
Sandford, 292
Sanford,R. M., 181
.Sanz,R.,251,292
Sarkisyan, S. C;, 109
Sattlegger, J., 639, 922
Schmied, H.,371
Schott, 295
Schreiber, 513
Schreider, A., 633
Sengbush, R. L., 585
Shoikhet, P. A., 51.7
Shulze,76
Skelton, J. D., 633
Soilogub, y. B., 685
SolovoyoV, V.F., 863
Subbotin, S. 1., 685, 777
Tchirvinskaia, M. V., 777
Tempera, C.'„ 81
•Thachuk, A. R., 669
Tissot, B. P., 47, 75
Tokarev.V. P., 101
Tokarski, A., 457, 922
Trettin, H. P., 288 , ,
Tripp, K. R.. 653
Trofimuk, A. A., 109
- Tschopp, R. H., 231, 243, 288
Turchinenko, P. T., 685
Udink.H.G., 221
Uspenskaya, N. Y., 961
Vale, K.R., 291, 920, 927
van der Laan, G., 221
Vaneek, 289
van Hoeflaken, J. A., 294
Vanjan, L. L., 697, 777
Vassoevich, N. B., 37, 76
Verrien, J. T., 425,457
Visotski, I. v., 37
Vistelius, A. B., 561
Wallis.W. E.,783,917
Wdowiarz, S., 533
Weeder, 289
Wieseneder, H.,371, 457
Winnock, 294
Wood, G. v., 458, 487, 511
Woodward, 288
, Woodworth, 457
Zinszer, 971
Zuloaga, G., 73, 77 '

'nrilMiiiiiifflriiilrwri»^'wi'itiifflinii''iiiiiiiii-' III •HiiiiitaBilMiilciliiia •IriiiMliiiitiiliiinlilMiiiiiiiililMiiiitiiiil
Seventh World Petrpleum Congress. Proceedings, Vol, 2. I967,
Q^
Abstract
THE GENERAL GEOLOGY OF OMAN
During Cambrian elastics and carbonates were deposited
in two sedirnentary cycles in the Oman. Mountains
and Haushi-Huqf. At approximately the same
time a thick sequence of salt and other eyaporites was
formed in the desert plains.
Continental sedimentation occurred in the Cambro-
Ordovician near the Haushi-Huqf, passing westwards
and northwards to shallow rnarine depositions
(Ghaba). Thereafter erosion and non-deposition prevailed
until Permian transgression initiated an,almost
continuous period of carbonate sedimentation lasting
until end Cenomanian.
Lower and Middle Cretaceous carbonates of the
Thamama and Wasia Group provide the'oil in .Yibal,
Fahud and Natih.
INTRODUCTION
The paper presents a concise description of the
General Geology of Oman, Basic geological data were
obtained from exploration wells and from geological
and geophysical field work. The geological results and
conclusions are compiled from numerous P,D.(0)
reports. The extent of the area discussed is shown on
Fig, 1. The author's contribution is that of compiling
and elucidating results.
Since our geological knowledge of Oman is still
rather limited, only a' tentative geological history is presented.
During the next winter season (1966/67) additioiial
geological field work will be undertaken in the
Oman Mountains and as a result our present geological
concepts may have to be altered.
As early as 1924/25 geologists made, reconnaissance
trips aloiig the Batinah Coast and in the Jebel Akhdar
of Oman. In 1938/39 the coastal areas of Oman were
again visited.. During the years 1948/52 several geological
expeditions were carried out, but progress was
hampered because of difficult access and tribal conditions.
Only in 1954 was a detailed geological mapping
by R. H. TSCHOPP
Petroleum Development {Oman) Ltd,
16—11 •
There was a break of sedimentation from Turonian
to Lower Santonian. During Campanian a geosyncline
in the Oman Mountains was formed and flyschtype
sediments with exotic blocks were deposited.
Ultrabasic material (ophiolites) extruded, probably
along tension faults in the Gulf of Oman, and was
deposited in the geosyncline.
Consequent upon the infilling of the geosyncline a
compressional tectonic phase elevated the region ofthe
Oman Mountains. Thereafter a succession of Tertiary
marine transgression followed in Palaeocene, Oligocene
and Miocene.
Strong orogenetic movements occurred prior to Permian
transgression arid in Upper Cretaceous. Palaeozoic
evaporites caused salt tectonics. Severe Tertiary
movements took place also in late Oligocene-early
Miocene,
of surface structures in the desert west of the Oman
Mountains undertaken, .
Geological field observations, were mainly made in
the Oman Mountains and its foothills, and in the
Haushi-Huqf area. The geological mapping was
. facilitated by air photographs which cover almost the
entire country of Oman, Geological parties spent a
total of 65 party months in the field,
A large part of Oman has been covered with gravity
riieasureriients. Seismic investigations started in February.
1956 and since then roughly 13,500 km of lines
have been shot in the desert west ofthe Oman Mountains
and ofthe Haushi-Huqf,
The first well was spudded in 1956 in order to test
oil possibilities of Fahud, one of the mapped surface
structures. Since then some 27exploration/appraisal
wells have been drilled.
STRATIGRAPHY (Figs. 2, 3)
Basement
Basement in the sense of igneous rocks overlain unconformably
by sedimentary strata has not yet been
found in Oman, The nearest outcrops of crystalline
basement rocks are recorded from Murbat in Dhofar

••..•••iMU^itn iliimt II iiDllliliKIWriMWW iiin'ftiMiiriirifiiiifiTiiiiiriiniiMiii irnwiiiiii rii^iii
232
New Oil Producing Regions
Pig- I

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and from the Kuria Muria Islands oif the Dhofar
Coast.
PrcTPermian Formations
These formations outcrop in the Oman, Mountains
and in the HaushiTHuqf area. In both areas, but particularly
in Haushi-Huqf, two sedimentary cycles can
be recognized in the lower part of the pre-Permian
succession. The two cycles are represented by the
following formations:
Oman Moun-
Haiishi-Huqf tains
. Jebel Akhdar
Buah Fm.
Huqf. Shuram Fm.
Series
Second sedimentary
cycle
.y-New Oil Producing Regions 233
Kharus Fm.
Miaidin Fm.
Khufai Fm. First sedimentary Hajir Fm.
Abu Mahara Fm. cycle Mistal Fm.
The base of the first and oldest sedimentary cycle is
not visible but might overlie the crystalline Archean
basement at no great depth. The observed total thickness
for both cycles is more than 1,800 m in the Oman
Mountains and more than 1,200 m in the Haushi-Huqf.
The sediments of both cycles do not contain any
diagnostic fossils. An idea ofthe age can only be ob-
/'tained by indirect arguments.
The age possibly ranges from pre-Cambrian to
Middle Cambrian. This is based on a graptolite shale
of Lower Ordovician age which was encountered in the
Oman well Ghaba-1 and which overlies a monotonous
clastic sequence, whose upper part was dated as probably
Upper Cambrian (Lingulella cf. nicholsoni). This
clastic sequence correlates with sediments in the
Haushi-Huqf area which overiie unconformably the
second sedimentary cycle. An indication of pre-
Cambrian age may be the absence of any shelly fauna
in the sediments of these two sedimentary cycles.
First sedimentary cycle
In the Haushi-Huqf area the Abu Mahara and
Khufai Formations represent the first sedimentary
cycle. Fluviatile conditions existed at the base of the
cycle in the Abu Mahara, A marine transgression
bringing in tidal flat conditions persisted through most
ofthe Khufai. A terminal regression leading to supratidal
and evaporitic sedimentation took place in the
uppermost Khufai.
The Abu Mahara Formation is characterized by
sandstones and argillaceous siltstones to silty shales.
The Khufai Formation consists mainly of cherty dolomites.
In the Jebel Akhdar part of the Oman Mountains
the first sedimentary cycle is represcnlcd by the Mistal
conglomerate and the Hajir Formation. The Mistal
conglomerate at the base of the cycle is composed of
conglomeratic elastics cqnlciining basement rock types
and resembling tillites. The basal conglomerates are
followed by the Hajir Formation containing shallow
marine sandstones and thin tidal flat limestones and
sandstones.
Second sedimentary cycle
In the Haushi-Huqf area the second sedimentary
cycle is formed by the Shuram and Buah Formations.
The Shuram, mainly elastics, is slightly transgressive
with respect to the Khufai. Its base marks a very sudden
incoming of clastic material over a wide area, and
as such may correspond to an episode of uplift in the
source area of the sediments. The Buah Formation
• resembles the Khufai of the first cycle. It consists of
dolomitized tidal flat limestones.
The second sedimentary cycle of the Haushi-Huqf
corresponds with the Miaidin and Kharus Formations
of the Jebel Akhdar. The Miaidin Formation is a
monotonous succession of siltstones, sandstones and
subordinate limestone bands. The Kharus Formation
consists of mainly dolomites with silicified algal
stromatolites in the topmost part.
Evaporites
At approximately the same time as the sedimentation
of the two sedimentary cycles described above took
place, & thick sequence of salt and other evaporites was
deposited west of the Haushi-Huqf area, in a large
basin restricted by highs. These evaporites in Oman
occur over a wide area. They were found in the wells
Haima-1 and Fahud-1 and they outcrop in a series of
piercement salt domes in southern Oman, as well as
being supposed on geophysical grounds to underlie a
number of subsurface structures. The evaporite unit
is most probably identical with the Hormuz salt series
(pre-Middle Cambrian?) of Iran.
The exact relationship between the evaporites and
the Huqf Series is not clear. It may be that the evaporites
accumulated in restricted basins bounded by
positive elements on which the Huqf-type sediments
were deposited, in which case they would be lateral
equivalents.
A different interpretation is based on the fact that
wells in Dhofar have drilled through a salt horizon, and
reached cherty dolomites and crystalline limestones
which may be the equivalent of the Buah Formation
which belongs to the topmost part of the second
sedimentary cycle. On this view, the evaporites would
mark the continuation of the regression which commenced
al the top of the second sedimentary cycle.
The evaporites would thus be post-Buah.
Both these explanations ofthe prigin ofthe evapor- .
ites are tenable, although the presence of probably

'iX—-^
d
234
MiBiiiWrtmmmOTitv
New Oil Producing Region.s
Fig.2
^ ^ TERTIARY
IIIIIJI aEMAIL OPHIOLlTe lUCRET.l
[ I HAWASINA SROUP (U.CRETI
^:?^ UPPER CRETACEOUS
g '^ CENOMANIAN TO JURASSIC
Ras Maahroka
k'
PERMO-TRIASSIC
PALAEOZOIC 4, PRE CAMBRIAN
O WELL
•-'....') OIL FIELD
/fas Saih ol Moleh
MUSCAT
OMAN
GEOLOGICAL MAP
ILLUSTR, 2'
100
*'o-

t
(^^'
TERTIARY
JURASSIC
TRIASSIC
PERMIAN
CARBONIF
DEVONIAN
SILURIAN
CAMBRIAN
PRE-CAM!
lOCENC
.tOUNGER
M,1 tOC£N£
PALEOCENE
MAASTRICHTIAN
SANTONIAN
COHiaClAN.TUROW
U.CAMBRIAN
H .L.CAMBRIAN
PRE-CAMBRIAN
LEGEND
OR. CROUP
F. FORMATION
LSr LIMESTONE
DESERT PLAINS
•:;•.;>•:''-' L O W E R
'-ys,-
.Mil.
New Oil Producing Regions 235
HAUSHI-
HUQF
UMM f R RADI 'uMA f.y\ REMNANTS OF
LOWER TERTIARY
OMAN MOUNTAINS
JEBEL AKHOAR
DESERT PLAINS
rPWrn
ICABB0N4TCS).-
d p ?:-•'' '^'''^.C^ I CARBON A^ DEPOSITS'.EicOTICS-.j"^,3f?''-'A RUM A SHALE F. ?)V / ^ -"" VH AWASIN A-
./•,•> ARUMA 5NALE
>: ;tCLA3TlCSl.:;yV;>.:^-^t;-„._MAg.Sei.F^;
:7/.---'*.-.'.•.••..:
.-'(CLASTICS)-. ;.
»a • • BASE CONGLOMERATE
^ ^
HIATUS
DEPOSITION
•-^(CLflstics)^.-;d"„^HAmij^uMai^ F'-y-;;r;-:'tcLAsficsi'y;;^.
:.;'.^.^.r.-;^(cLA5T.cs).' dd\d/^^d%
^777/.y.v.-y.'.'-^'.-'.
HIYAM DOLOMITE
(SALT ANO OTHER EVAPORITES).'••.'V • KriUFAl f
HATAT METAMOfiPH
ASA MAHARA F
thick salt deposits is perhaps best explained by a basinal
origin.
Mahaita Humaid Formation and Fara Formation
Uplift and erosion of the whole Haushi-Huqf area,
with possibly some tectonic disturbances, including
tilting and/or faulting, followed the deposition of the
Huqf Series. Subsequent to it the Mahatta Humaid
Formation was laid down in the Haushi-Huqf area.
The formation reaches a thickness of about 550 m.
The environment is continental, partly fluviatile. The
sediments pass probably westwards and northwards
to shallow marine deposition.
The Mahatta Humaid Formation contains sandstones
with coloured chert grains and argillaceous siltstones.
The lower part, characterized by poor sorting,
coarse grain, much cross-bedding, variegated colours
and absence of fossils, is probably continental, perhaps
formed in sand dunes and/or in large alluvial fans
along Ihc western edge of an uplifted Huqf massif.
The correlation with the Jebel Akhdar part of the
Oman Mountains is not very clear, but the Mahatta
Fig.i
FTIcLATncsT^

,y-
236
;j,..,:a.,...j«.'M..jMa»j«»..» rmiiilitWitHiirffii
Ne-w Oil Producing Regions
The upper contact of the Hatat Metamorphics is a
distinct lithological break \yith the Hiyam Dolomite.
The latter unit consists of light coloiired dolomites.
The Amdeh (puartzite has a sharp, conformable con-.
tact with the underlying Hiyam Dolomite. The Amdeh
unit is a thick, monotonous, uniform sequence of more
or less silicified sandstones with thin,' epimetamorphosed
shale partings. The degree of metamorphism is
lower than that of the Hatat Metamorphics.
Post-Ordovician to pre-Permian rocks
In the Haushi-Huqf area a time gap from the Ordovician
(perhaps even the Cambrian) to the Permian
marks the most important sedimentary break. During
this time, there were tectonic rhovements which may
correspond to a major phase of movement in the
Oman Mountains and Sayh Hatat.
Rocks of post-Ordovician to pre-Permian age have
only been recognized in the well Haima-1. Palynological
work has proved the existence of Upper
Devonian to Lower Carboniferous sediments overlain
ijnconformably by Permian deposits.
Permo-Triassic Formations
After a period of erosion and peneplanation of aid
Palaeozoic rocks, the sea transgressed over Oman in
Permian time. This was the commencement of a more
or less continuous period pf carbonate sedimentation
which lasted until the end ofthe Cenomanian.
Permian sedimentation seems to have been in rather
shallow water throughoiit the basin. There is a diff"erentiation
into three types of depositional area:
areas of reduced sedimentation with strong terrigen-.
Otis influence (e.g. Haushi-Huqf)
areas of thicker sedimentation with strong terrigenous
influence (e.g. Haima-Ghaba area) ,
areas of thicker Sedimentation with little or no'terrigenous
elastics (e.g. Fahiid-Oman Mountains).
The pre-Permian unconformity is fofthe mostpart
very poorly exposed in the Haushi-Huqf area. The
Permian begins throughout this area, with a very coarse
basal conglomerate with igneous boulders, which
breaks down to a residual gravel.
The pre-Permian unconformity is also recognized in
the deep wells of Oman (Fahud-1, Ghaba-1, A,l Ghubar-1),
as well as in the Oman Mountains, as a sharp
break between the Permian and Lower Palaeozoic.
Rocks of Permo-Triassic age outcrop in the Haushi-
Huqf area and in the Oman Mountains. The following
formations can be distinguished from top to bottom:
Oman mountains
Haushi-Huqf Jebel Akhdar Sayh Haiat
Lusaba Limestone Fm. Akhdar Dolomile Mijlas Dolomije
Haushi Fm.
Haushi Foriimtion and Lusaba Limestone Formation
The Haushi Formation is characterized by conglomerates
at the base, resembling tillites, red sandstones,
sandy limestones and argillaceous siltstones. It is.pverlain
by the Lusaba Limestone Formation, with sharp
but conformable contact. The Lusaba consists mainly
of dense brownish-grey bioclaslic limestone. It is disconformably
overlain by the Jurassic.
Both the above described formations are of Permian
age throughout. The total thickness is more than 350 m.
The above rock stratigraphic subdivision can be closely
followed in the wells Ghaba-1, Al Ghubar-1 and
Haima-1, although the thicknesses are somewhat
greater.
The sedimentary environment ofthe Haushi-Lusaba
sequence may have been as follows: The basal conglomerateis
perhaps best explained as tillite, comparable
with the Permo-Carboniferous tillites of Central
Africa. No direct evidence for a terrestrial or marine
depositional environment was found, but its close association
with the Haushi marine beds makes the latter
more attractive. Rafting by icebergs would explain the
size of the boulders.
The conglomerate rapidly giyes way to marine sandstones
and limestones with abundant fauna. These are
believed to be beach deposits and the interbedded azoic
red beds may be lagoonal.
The Lusaba limestoftes are clearly fully marine, with
an abundant fauna, including larger forams. The
whole may represent a quiet neritic environment, with
shelly banks surrounded by areas of mud deposition.
Akhdar Dolomite and Mijlas Dolomite
These are primarily rock unit subdivisions established
in the field and traceable photogeologicaily.
Both units are further subdivided into two time/rock
units—Permian and Triassic—on the basis of field
observations and supported, partly, by palaeontological
results.
The Akhdar and Mijlas Dolomite is typically composed
of dark coloured dolomites, with a basal conglomerate
in places. Fusulinids are typical ofthe lower
part of the sequence.
The thickness ofthe Permian succession varies from
about 200-700 m. The Triassic dolomites reach thicknesses
of 1,600 m in Sayh Hatat.
Jurassic to Cenomanian sequence
This is a monotonous sequence of carbonates which
are difficult to subdivide into .sedimentary rock units,
particularly in the Oman MounUiins.
The exact age of the Jurassic transgression is not
known. In the Haushi-Huqf area no angular discordance
at the base of the Mesozoic sequence can be

if A'eii' Oil Producing Regions 237
tr
seen. In the Oman Mountains there is a break ranging
in character from angular unconformity lo disconformity.
The pre-Jurassic unconformity, with erosion
or absence of the upper part of the Permian and the
Triassic can also be recognized in the Ghaba, Al
Ghubar and Haima wells. It is not present in Fahud-1
where the section from Permian through Triassic
appears continuous.
The sediments ranging in age from Jurassic to Cenomanian
can be subdivided into the following rock
stratigraphic or time stratigraphic units:
Desert foreland
Wasia Lst. Fm.
Wasia Group:
Nahr Umr Fm. Musandam
Thamama Group
Jurassic carbonates
Oman
Mountains Haushi-Huqf
- Limestone -
- GroUp
Middle Cretaceous(Albiancenomanian
carbonates)
Lower Cretaceous
carbonates
Jurassic carbonates
Apart from the Wasia Group, the above units have
not been subdivided further. These are very monotonous
carbonate sequences, a lithological subdivision of
which may only be obtained by detailed studies of rock
samples on a regional basis. The correlations between
the wells is done at present with the help of log markers
and/or palynological.palaeontological biostratigraphic
zones.
The thickest Lower Cretaceous and Jurassic carbonate
sequence may be.in the region of Lekhwair or
just west of it (± 2,500 m). Here the base ofthe Jurassic
has not yet been reached by the drill.
Thamama Group
The top ofthe Thamama Group provides the known
oil reservoirs in Yibal. The age of this Group extends
from Valanginian to Aptian.
The base of the Thamama Group in the Oman
Mountains is identified wilh a light-grey, porcellanitic
limestone with chert nodules. The base contact with
the Jurassic is sharp and is marked by a few metres of
thinly bedded, crystalline, red-stained limestones.
The base of the Thamama Group in the wells ofthe
desert foreland is not' sharp. Around the Jurassic/
Cretaceous boundary determined on palynologica|
evidence, compact to dense, si|ty and argillaceous limestones
with pyrite-stained pellet debris and pseudooolitic
debris can be recognized sometimes. The
characteristic fauna for this facies is Trocholina palastiniensis
and Nautiloculina oolithica.
Wasia Croup
The lower part ofthe Wasia Group is the Nahr Umr
Shale Formation and the upper part is the Wasia
Limestone Formation.
The Nahr Umr Shale Formation has its thickest development
in the area of Lekhwair where about 200 m
of this Shale sequence were drilled. It ranges in age
from Albian to early Cenomanian.
This unit consists in general of brown non-calcareous
shales interbedded with thin layers of argillaceous
limestones.
The Wasia Limestone Formation provides the known
oil reservoirs in Fahud and Natih. The formation is
thickest developed in the region west of Lekhwair-
Yibal, The formation reaches here thicknesses of 700
to 800 m. The age of deposition is Albian to Cenomanian,
The Wasia Limestone Formation can be subdivided
into seven members,' viz, a, b, c, d, e, f, and g. The
lower part of the members is often characterized by
shaly beds and the upper part is sometimes chalky. The
b-member is bituminous. Some rudist fragments occur
in the limestones. /
The conditions of deposition for the Wasia Group
may have been as follows: after the deposition of the
Nahr Umr Shale, limestones were deposited in shallow
water. The bituminous intervals indicate probably a
slightly deeper, quiet environment in which only a few
bottom dwellers have been living. The limestones were
deposited jn shallower water where rudists could live.
Haushi-Huqf area
' This area continued to act as a positive element
through the Mesozoic with the result that sedimentary
thicknesses are greatly reduced compared with those
ofthe subsurface to the west and north.
The Jurassic and lowermost Cretaceous consists
predominantly of carbonate rocks which were deposited
under shallow water, probably in a coastal
complex of environments. The Lower Cretaceous unit
maintains a vei-y constant lithology and thickness. It
consists of chalky limestones containing a variety of
lamellibranch, rudist, foraminiferal and other bioclastic
debris, together with lithoclasts and pelletoids.
This is a shallow marine limestone with an alternation
of quiet and higher energy sedimentation, perhaps due
to occasional shoal development. The Middle Cretaceous
consists predominantly of soft rocks such as
marls and argillaceous sandy limestones. This unit is.
comparable with the mari-limestone sequence of the
subsurface Wasia Group, but the thickness is much less,
than in the wells to the west and must reflect a combination
of Middle Cretaceous activity of the Huqf, and
Upper Cretaceous erosion, perhaps predominantly the
latter, since the Middle Cretaceous lithofacies does not
show much sign of shallowing relative to areas to the
west.

I 238,
d'
-New Oil Producing Regions
Campanian to Maastrichtlan sequence
Basement block movements followed the deposition
of the Wasia Group. This broiight to a standstill the
almost continuous quiet carbonate sedimentation
which lasted from Jurassic to Cenomanian. Moreover,
these movements resulted in a break of sedimentation
for the interval Turonian to Lower Santonian. Middle
Cretaceous and older strata were eroded, folded aiid
faulted. Thrusting occurred in Sayh Hatat. A geosyncline
along the length of the Oman Mountains chain
was formed and flysch-type sediments with exotic
blocks reaching mountain sizes were deposited. Ultrabasic
material (ophiolites) extruded, probably along
tension faults in-the Gulf of O.man. northeast of the.
geosyncline. These ophiolites were deposited in the
geosynchne.of the Oman Mountains.
As a consequence of this lively geological history, a
series of time eqitivaJent but different lithological units
were deposited.
The Aruma Group
It ranges in age from uppermost Santonian to Maastrichtian.
It can be subdivided from top to bottom into'
the Aruma Limestone Formation and the Aruma Shale
Formation. Thicknesses of around 1,500 m have been
measured.
The Aruma Shale Formation consists of Upper Santonian
to Campanian globigcrinal shales which were
deposited across the desert area bf Oman. The lowest
part of these shales have been traced as far eastwards
as the south flank of Jebel Akhdar, where they form
the Muti Formation.
The Aruma Limestone Formation in the western part
of Oman is mainly an ailternation of marls and limestones
of Campanian to Maastrichtian age. In the
Oman Mountains, uplift and erosion preceded an
Aruma Limestone transgression of Maastrichtian age
which overlapped some northern and southern parts of
the range. ; - ; •
The Hawasina Groitp ' .
While deposition of the globigcrinal shales of the
Aruma Group continued uninterruptedly in the desert
foreland, geosynclinal sedirnents were deposited in the
area of the present Oman Mountains (Hawasina geosyncline).
Along the south side of Jebel Akhdar the top of the
Wasia Group is overlain by an iron-rich oolite which
may represent a concentrate from the weathering and
reworking of pre-existing carbonate sediments. This
iron oolite is regarded as at least partly time-equivalent
to the sedimentary break separating the Wasia and
Aruma Groups in the desert foreland.
In Jebel Akhdar this ferruginous deposit is overlain
by the Hawasina Group which commences at the base
with a conglomerate, followed by calcareous shales
(Muti Formation).and a succession of limestone conglomerates,
cherty limestones and shales, and radiolarites.
The total thickness iri Jebel Akhdar may be more
than 400 m. However, northwest of Jebel Akhdar one
thousand metres Or more of flysch-type sediments
(slightly metamorphosed) can be observed. These deposits
belong also to the Hawasina Group.
Exoiic blocks
Two belts of exotic limestone blocks are recognized.
These comprise a series entrained within the Hawasina
Group and a series overlying it. These blocks are,
generally, characteristically white limestones (bleached
in appearance), often somewhat brecciated and recrystaliized.
Sizes vary from some tens to many thousands
of cubic metres. Original bedding is seen in places.
Because of recrystallization it is often difficiilt or
impossible to identify the fauna of the exotic blocks.
Notwithstanding that, Permian to Cretaceous fauna
can be recognized. These blocks show no apparent
resemblance to the lithofacies of the PermianrMiddle
Cretaceous bf Oman and are therefore presumed to
have come from outside this area, probably from the
N.E.
Semail Ophiolites
These are ultrabasic extrusions which cover a vast
area of Oman, forming the largest almost continuous
outcrop of ophiolites in the Middle East. Little is
known of the subsurface form and thickness of the
various bodies of ophiolites as. contacts with other
rocks are seldom seen. Feeder pipes or fissures have
not so far been observed. The thickness is not known
but may be over 2,000 m in places.
Because there is not much evidence of igneous
activity, pillow lavas and ultrabasic erosion products,
within the greater part ofthe Hawasina Group in the
Oman Mountains, and because the Hawasina appears
to dip below the Semail, it is concluded that the Semail
Ophiolites are largely younger, marking the closing
stages of geosynclinal infilling (Upper Campanian-
Maastrichtian).
Seqiience of events in jhe Hawasina geosyncline
The geological history of this mixed series of basinal
radiolarites wilh turbidites and slump beds, the cherty
layers, exotic blocks and ophiolites is not yet clear.
Much more work is required. Al present the following
working hypothesis is put forward.

During Triassic to Middle Crctiiceous sedimentation
of carbonates took place in somc.area to the N or
NE ofthe Oman Mountains, probably in the Gulf
of Oman. •
Uplift in the Gulf of Oman area during Campanian
caused erosion of Middle and partly Lower Cretaceous
and Jurassic limestones and their deposition
as clastic limestones in the narrow elongated
Hawasina geosyncline centred just to the NE of
the present Oman Mountain axis. In addition,
sheets of rocks (exotics) coinprising late Palaeozoic
to Lower Cretaceous deposits, were gliding
into the geosyncline. These exotics can now be
found throughout the Hawasina Group.
Submarine volcanic activity occurred from foci in
the Gulf of Oman and contemporaneously cherty
limestones, shales and silica enriched radiolarites
were deposited along the northern slope of the
Hawasina geosyncline. These sedirnents were then
thrust more than a hundred kilometres towards
the S across the Jebel Akhdar and exotic masses
were carried passively on top of the thrust sheets.
Jebel Akhdar as well as probably Sayh Hatat may
have been geanticlines in Campanian, i.e. reg- .
ions of reduced sedimentation within the geosyncline.
This is suggested by the onlap of Muti
Formation along the S flank of Jebel Akhdar, by
Musandam pebbles to boulders in Hawasina
conglomerates and by, locally very reduced thicknesses.
The emplacemeiit of the igneous material known as
the Semail Ophiolites marks the closing stages of
the geosynclinal infilling during Upper Campanian-Maastrichtian.
Huge gliding sheets were probably
extruded along tension faults in the Gulf of
Oman,.again stimulated by uplifts. These ophiolite
sheets slid over the Hawasina and engulfed
everything, including the exotic blocks. Thrusting
may also have occurred.
After a period of non-deposition a quiet Maastrichtian
sea transgressed towards the Oman Mountains
and rudist reef hmestones, were deposited.
This transgression apparetitly only reached the N
and S extremities of the uplifted area.
• Tertiary sequence ,
Consequent upon the infilling of the Upper Cretaceous
Hawasina geosyncline, a coinpressional tectonic
phase elevated the region of the present Oman Mountains.
A widespread Paleocene marine transgression took
place, resting disconfornfiably on the Maastrichtian in
places and with evidence, of overlap onto older rocks.
A'fii' Oil Producing Regions 239
Continuous carbonate sedimentation lasted through
the Lower and Middle Eocene and in the Suneinah
area also through the Upper Eocene. .
. The centre of the Paleocene-Eocene basin is assumed
iri the area of Suneinah where a complete sequence of
about. 1,700 m was penetrated by the drill. Along the
edges of this basin the Upper Eocene sedirnents are
consistently missing in Oman (probably eroded).
In' the Eocene, evaporites were deposited in the
desert foreland but not in the Oman Mountains and
just SW of the foothills. '. '
The Paleocene-Eocene sequence can be subdivided
from top,to bottom into the following formations:
Dammam Formation
, Rus Formation (Evaporites)
Umm er Radhuma Formation
Oligocene carbonates were found in Suneinah and in
Lekhwair. Whilst in Suneinah no disconformlty can be
observed, the Oligocene carbonates in Lekhwair rest
disconformably on Lower Eocene rocks.
Thin Oligocene limestones are preserved in places
along the Batinah Coast, resting with mild angular discordance
on the older Palaeocene. The Oligocene also
rests with angular unconformity on the Middle Eocene
in S,Oman.
, The centre of the Oligocene basin is probably in
western. Dubai. From there it extends in southeastern
direction towards the Suneinah area. It is a rather
narrow elongated basin, its axis parallel to that of the
Oman Mountains. There is little indication of the
extent of the Oligocene sea! throughout the western
desert of Oman but much sediment may have been
removed by pre-Miocene erosion. :
A major folding phase in the Oman Mountains
followed the deposition of Oligocene sediments. The
visible fold elements of the Oman Mountains probably
adopted their final form at this time.
The last marine incursion occurred in the early Miocene.
This is evidenced almost throughout Oman where
gently folded Miocene limestones rest with angular unconformity
upon older formations.
,. TECTONICS (Fig. 4).. ^
Pre-Permian elements
Oman shows evidence of a major Palaeozoic orogeny.
The old Palaeozoic rocks,of Jebel Akhdar are
strongly folded with axial trends swinging from NE-
SW to ENE-WSW in the central region and oriented
nearly E-W in the S£, These alignments suggest a

'L 240 New Oil Producing Regions
. / ' • '

y
IfapfM
NW-SE to N-S direction of pressure. The variation in
axial trends might be due partly tp later folding movements.
In the Haushi-Huqf area there is evidence for post-
Huqf Series/pre-Mahatta Humaid movements. The
majority of the faults and folds alfect only the Huqf
Series and the Mahatta Humaid, so their age can only
be specified as post-Carnbrp-Ordovician,
Permian and later elements
Oman can be located in a regionaf setting of crustal
fauhs, resulting in the parallelism of the Pirate and
Batain Coasts. The S coast of Arabia is controlled by a
major fault zone and the Masira Fault is a feature of
this. It is evidenced by the occurrence of Semail Ophiolites
on the Masira Island and at Ras Madhraka.
Whether there is a horizontal component along the
Masira Fault is not yet proven. The forthcoming
planned gravity survey in the Wahiba Sands may
answer this question.
The Dibba Fault has a surface expression, bringing
Permo-Triassic and Musandam to the N into contact
with the Upper Cretaceous to the. S. Westwardly
directed overfolds and thrusts are characteristic ofthe
• northern block.
Apart from the above-mentioned faults which have
a NE-SW directipn, there is another important regional
tectonic line which has a NW-SE tp N-S trend. In the
Haushi-Huqf area it is the Khufai-Nafun fault zone.
The displacement across it is rather sm.all, mostly
downthrown to the east. The fault zone is made of a
number of fractures arranged en echelon and may well
be a basement fracture rejuvenated during Upper
Cretaceous time.
The Khufai-Nafun fault is probably the extension of
the Haushi fault, which in turn seems to prolong the
Maradi fault zone of the Natih area. In Maradi the
western block is downthroyvn arid the displacement
amounts to 100-150 m.
Fauhs which have a length of about 50 km, a WNW-
ESE trend and vertical displacements of around 1,000
m are observed in Natih and Fahud. They originated
probably towards the end of the deposition of the
Wasia Group and were fully developed during Upper
Cretaceous. These faults have trapped the oil accumulations
found in Natih and Fahud.
Important orogenetic movements occurred in the
Oman^ Mountains. Upper Cretaceous geosynclinal
sediments were thrust southwards more than a hundred
kilometres during late Campanian. Strong uplifts
happened in Tertiary towards the end of Eocene and
subsequent lo the deposition of Oligocene rock.s. There
are also indications of Quaternary uplifts..
New Oil Producing Regions 24)
Salt tectonics
Il is thought that during the Palaeozoic sufficient
overburden was deposited on the Cambrian mother,
salt to initiate migration, which probably was triggered
by embryonic basement movements, causing in general
the uplift ofthe Palaeozoic deposits. In migrating toward
the basin margin the evaporites accumulated into
pillows, which most probably reached their final pillow
stage at the end of the Permian.
With the end ofthe Permian, the pillow stage seemed
to have been achieved. Al Ghubar is an example for
this. Here the pillow stage came to an end in the late
Permian and most probably stayed stationary during
the Triassic-Liassic, during which times no or only
scattered deposition took place. The Al Ghubar pillow
was then reactivated in growth during the Mesozoic
main deposition and came to rest in the late Tertiary
(post-Miocene).
After the depositional break during the Triassic
(partly) and the Liassic considerable deposition into the
basin, continued during the Mesozoic and partly Tertiary
times. The overburden weight in the basin increased
to such an extent to initiate new migration in
forcing the pillow salt into piercement, thus initiating
the diapir stage, .resulting in surface and subsurface
domes. •'• •
4.
REFERENCES
DUNHAM, R. J., Classification of carbonate rocks, 1962,
AAPG Mem; 1, pp. 108-121.
DUBERTRET, L., Lexique Stratigraphique International,
Vol. Ill, ASIE, Fase. loa, Iraq;
HUDSON, R. G. S., Permian and Trias of Oman Peninsula,
Arabia, 1959, Geol. Mag. Vol. XCVII, No. 4.
LEES, G. M., The Geology and Tectonics of Oman, 1928,
Quart. Journ. Geoi. Soc. Vol. LXXXIV, part 4.
MORTON, D. M., The Geology of Oman, 1959, Fifth
World Petroleum Congress,
ABSTRACTO
La Geologia general de Oman
Durante el Canibrico, se depositaron en las montaiias
de Ornan y Haushi-Hugf clasticos y carbonatos en dos
ciclos sedimentarios; Aproximadamente al mismo
tiempo, se formo en los llanps del desierto una gruesa
secuencia de sal y otras evaporitas.
Durante elCambro-Ordovicico cerca de Haushi/
Hugf hubo sedimenlacion continental, pasando hacia
el oeste y el none a dcpositos marines de poca profundidad
(ghaba). Poslcriormenle preva|eci6 la erosion
y.falla de sedimenlacion hasta que la transgresion

t
242
del Perniicp inicio un periodo casi conlinuo de sedimenlacion
calcarea, que duro hasta el final del Ce-.
nomaniano.
Los carbonatos del Creiacico inferior y medio del
grupo Thamama y Wasia proporcionan el pelr6Iep en
Yibal, Fahud y Natih. ' .
Hubo una interrupcion en la sedimenlacion desde
el Turoniano hasta el Santoniano inferior. Durante el
Campaniano se formo un geosinclinal en las montaiias
de Oman y se depositaron sedimentos tipo "flysch" con
bloques exoticos. Hubo extrusiones de material ultrabasico
(ofiolitas) probablernente a lo largo de fallas de
New Oil Producing Regions
tensidn en el Golfo de Oman, que se deposilo en el
geosinclinal.
Consecuentemcnte al relleno del geosinclinal, una
fase tectonica compresiva cicvo la region dc las montaiias
de Oman. Despues siguio iina sucesion de transgresiones
marinas Terciarias en el Paleoceno, Oligoceno
y Mioceno.
Anteriores a la transgresion del Permico y durante el
Cretacico superior ocurrierpn fuerles movimientos
orogenicos. Las evaporitas del Paleozoico ocasionaron
tectonica salina. Durante el Oligoceno superior y
Mioceno inferior hubo fuerles movimientos terciarios.

;Seventh World Petroleum Congress. Proceedings, Vol. 2. I967.
c (^
^
r.
DEVELOPMENT OF THE FAHUD FIELD
Abstract
The Fahud culmination is expressed as an almost undisturbed
WNW-ESE trending anticline in outcropping
Eocene rocks. In the subsurface at Cretaceous level
the south flank is disturbed by a fault zone parallel to
the structural axis. The aggregated throw is about 4,000
ft. The upthrown northern block has a closed acreage of
about 27 km by 4 km. The vertical closure is roughly
3,200 ft.
There are indications that the Fahud structure
existed already as an uplift during Middle Cretaceous.
The principal vertical movements along the fault occurred
during Upper Cretaceous. Folding and uphft
but only minor faulting took place during Tertiary.,
Fahud was first tested on surface indication in 1957
but only the second well in 1964 based on seismic discovered
oil in commercial quantities in Middle Cretaceous
Wasia limestones. Chalky reservoirs separated
by shaly intercalations are capped by Campanian shales.
The gross oil column amounts to about 1,500 ft. The
gas cap is 360 ft high. Pressure data indicate that the
reservoirs probably have a common free water level. It
is assumed that communicatipn between reservoirs
exists. API gravity ofthe oil is 33-6° and sulphur content
about 1-15%. Regular oil prpduction is,expected to
start during the last quarter of 1967. '
INTRODUCTION
This paper presents the exploration history of the
Fahud oilfield and gives a detailed description ofthe
stratigraphy and tectonics observed in Fahud. The oil
accumulation conditions are also discussed. This papeishould
actually be seen as a continuation.of the paper
"The General Geology of Oman" in which a concise
description ofthe geological history of Qman is presented.
,
Fahud lies roughly half-way between the Gulf
coast of Sharjah and Abu Dhabi and the Arabian
Sea coast of SE Arabia. To the NE lies the main Oman
Mouiitain range, while to the SW is, the Umm as
by R. H- TSCHOPP
Petroleum Development {Oman), Ltd., P.D.\0)
Resume • . . •
La culmination de la structure de Fahud apparait
dans des affleurements de roches eocenes sous la forme
d'un anticlinal a orientation ONO/ESE pratiquement
non-accidentee. Dans le sous-sol, au niveau du Cretace,
le flanc SSO se disloque par une faille parallele a I'axe
de la structure et d'un rejet de 4,000 pieds environ. La
structure, longue de 27 km avec une largeur maximum
de 4 km, possede une fermeture contre faille qui s'eleve^
3.200 pieds. '
Un premier forage d'exploration, base sur des levees
de terrain, avail ete eff"ectue a Fahud en 1957, mais ce
n'est que le deuxieme puits, fore en 1964, et implante sur
renseignements sismiques, qui mit a jour des quantites
rentables de pelrole dans les calcaires de Wasia, d'age
Cretace moyen. Des reservoirs calcaires crayeux,
separes par des intercalations argileuses, sont recouverls
par des argiles du Campanien. Tons les reservoirs
possedent le meme plan d'eau. La hauteur globale de la
colonne d'huile est de 1,500 pieds.
Le gisement de Fahud se trouve maintenant en voie
de developpement et Ton prevoit que la production
pourra debuteren 1967. ,
Samim, an area of treacherous quicksands bordering
on to the Rub al Khali, or Empty Quarter (Fig. 1),
Fahud is in the Duru tribal area, this tribe occupying,
most ofthe desert region of Central Oman west ofthe
mountains. Ibri, approximately 100 km north of Fahud,
is the nearest and also the major town ofthe area, .
Fahud is located at about 50-60 km southwest ofthe
foothills ofthe Oman Mountains, in a vast plain where
the wadis flow from the foothills towards the Rub al
Khali. Rising 180 m above the surrounding plain the
morphology ofthe Fahud structure is controlled by the
feature forming Paleocene limestones. The western end
of Fahud is very rugged, being much dissected by sleep
gorges, but the eastern half is more deeply eroded,
forming a wide flat cirque which stretches almost across
. Ihe structure and exposes Upper Cretaceous chalky
marls belonging lo the Aruma Shale Formation.

£
t
w"
244
New Oil Producing Regions
Fig. I
AREA DISCUSSEO
OUTCROP AREA

Other than by air there are several ways of access to
Fahud:
(a) From Sharjah or Abu Dhabi on the' Trucial
Coast, via Buraymi. a distance of approximately
400 km. ,
(b) By sea to Ras Ducjm on the south coast, south of
: Al Huqf, and frpm there by land tp Fahud, a distance
of just over 320 km.
(c) By sea to Muscat or Ras Saih al Maleh on the
Batinah Coast and from there by road through the
mountains (Semail Gap), a distance of approximately
290 km.
At preseni the Saih al Maleh route is the most used
access over land. In fact the pipe line also follows this
route.
EXPLORATION HISTORY
The Fahud structure was first recognized from the air
in 1948 but was not visited by field geplogisls until
November 1954. A rapid structural survey took place
and the excellence ofthe anticline as a promising site
for a wildcat well was confirmed.
Fahud-1 was the first well to'be drilled in Oman. The
-. site was chosen asa result of a geological structural
survey made during the 1954-55 field season.
^ Fahud-1 was spudded in on 18th January, 1956, and
abandoned at 12,235 ft in Palaeozoic salt, wilh indications
of producible oil in a reduced Wasia Limestone
of Cenomanian age (Middle Cretaceous).
In 1960 gas was encountered in the Wasia of Yibal
and oil in commercial quantities in the same formation
at Natih. As a consequence of these discoveries more
attention was given to the Fahud structure, where a
Wasia accumulation of the same size as Natih was
expected. Based on seismic data a structural reappraisal
of the Fahud siructure was made and a new location,
Fahud-2, was spudded in on 24th December, 1963.
The location Fahud-2 had two principal objectives,
firstly to test the oil-bearing zones of the Wasia Limestone
Formation which, according to-the seismic section,
was likely to be much better developed than in
Fahud-1 and secondly, to test the possible oiUbearing
Thamama Group (Lower Cretaceous). .
Fahud-2 discovered oi| in comrnercial quantities in
the Wasia Limestone Formation. A reinterpretaiion of
the subsurface structure of Fahud was now carried out
in the lighl ofthe results from Fahud-1 and 2.
The sudden reduction in thickness of the Wasia
Limestones from about 1,400 ft in Fahud-2 to about
90 ft in Fahud-1 within 1^ km was noticed as a striking
fact. Three possibilities were considered in order to
explain the thin Wasia section iri Fahud-2: reduced de-
,, position; strong erosion; fault cul-ouL -
New Oil Producing Regions 245
The first possibility was not rated high. The second
one was considered more likely because top Wasia is an
erosion surface. However, afler a few additional appraisal
wells had been drilled it became evident that the
fault cut-out theory was the correct one.
STRATIGRAPHY
The sedimentary sequence drilled in Fahud comprises
predominantly shales and carbonate rocks. The
description ofthe carbonates is based on the "Dunham"
nomenclature,^
Tertiary
The Tertiary in Fahud consists only of the Lower
Eocene-Paleocene Umm er Radhuma Formation. It is
outcropping and forms dip slopes, which rise several
hundred feet above the desert plain. The upper part of
the formation consists of dolomitic, bioclaslic lime
packstones and of argillaceous wackestones developing
into mudstones with abundant cherts near the top. The
lower part comprises very porous limestone "boulder"
beds. The exposed and drilled thicknesses of this formar
tion vary between 0 and 900 ft.
Campanian to Albian
These deposits are divided into three formations:
Aruma Shale Formation, Wasia Limestone Formation
and Nahr Umr Formation.
Aruma shale formation (Upper Cretaceous: Campanian-
Santonian) . ' ;
This formation consists of dark-grey calcareous
shales which become more calcareous towards the top.
Some traces of slightly argillaceous dolomite have been
found in the lower 400 ft and above it the shales are
slightly silty with traces of black flakes, possibly mica.
Because the top ofthe Aruma Formation is an eros-
. iorial contact, the thickness of this formation varies
considerably over the structure. In the downthrown
block thicknesses of more than 4,000 ft can be observed.
Wasia limestone formation (Middle Cretaceous: Cenomanian-Albian)
The Wasia Limestone Formation, as originally described
by M. Sleineke and R. A. Bramkamp, 1952,^
comprises a sandstone unit outcropping in Saudi
Arabia. In 1958 the term Wasia Group was created by
R. M. S. Owen and S. N. Nasr, comprising foi-mations
of Cenomanian and Upper Albian age in Southern
Iraq.

"jsa"
246
1000 -
2000
5000'
4000'
ITxHsAS
A'f 11' Oil Producing Regions
1^'^°"'^ . SOIL RESERVOIR ROCK
; QUDLESSPBODUCTIVEJ,
mn] WATER
e WASIA MEMBER
PWC'OIL WATERCOMTACT '
eOC'.eASOlLCOMTACT • .
, ' SECTION ACROSS FAHUD FIELD
FAMUP SOUTHWEST
OMAN
FAHUD OIL FIELD
ILLUSTR, 2
Fig.2
2470
FAHUD FIELD
CONTOURS ON TOP WASIA
(DEPTH IN FEET BELOW SEALEVEL)

p New Oil Producing Regions 247
/.'

tfirt I •!• MTfti "^-^•jiiijii f" iii^ i'litifiiiTifiMitiffrrit
P 248
' • ^ '
/:-';
A'eit' Oil Producing Regions
followed by streaks of porous pseudo-oolithic and
pellety limestones down to the base of the Thamama
Group, i!e. the top oflhe palynological zone.
Jurassic sequence {± 1,000 ft)
The only complete penetration of Jurassic and older
sediments in the Fahud structure was first obtained in
the first well, Fahud-1.
The pellety and pseudo-oolithic limestone sequence
which started in the basal part ofthe Thamama Group
continues about 900 ft downwards into the Jurassic
succession. It is followed by about 100 ft of calcareous
sikstone, marl, shale and mudstone. Some streaks of
sandstone occur in the basal part.
Permo-Triassic (±3,000 ft)
The top ofthe Permo-Triassic in Fahud-I is placed at
6,517 ft b.d.f, where the drill penetrated a white dolomite
which has the appearance of being brecciated. It is
composed of various-sized fragments of fine-grained,
dense, white dolomite, cemented in a crystalline and
partly saccharoidal dolomite matrix. This white dolomite
sequence is about 200 ft.thick. It is followed by
dolomitic marl, siltstone streaks and brownish and
slightly crystalline dolomite.
Anhydrite as a matrix to pellety dolomite occurs
about 700 ft below the top of the Permo-Triassic. Occasional
nodules of pure anhydrite can be recognized.
Il is followed by predominantly dolomites. In the lower
part the Permo-Triassic., sequence gradually becornes
calcareous and limestones and sandy limestpnes are
recorded in the lowermost 300 ft.
Palaeozoic
There are two major subdivisions to this part of the
section, i.e. a,clastic sequence and a salt/dolomite unit.
Clasiic sequence {±2,100 ft)
Immediately underlying the Permo-Triassic dolomites
and limestones is a.sequence of 2,100 ft of mudstones
and sandstones of unknown age. No fauna
whatsoever has been seen in any of the beds below the
dolomite and the age of the sediments can therefore
only be given generally as Palaeozoic.
The basal part is characterized by a chert breccia,
composed of angular fragments of chert of varying size
cemented in a sandstone matrix.
Salt and Dolomite.{± AOO ft) .• , .
At 11,817 fl below derrick floor. Fahud-1 penetrated •
30 ft of a dolomile. The nature of the contact is uncertain,
but the massive breccia above would indicate a
major sedimentary break. ,
The dolomite is followed by nodules and streaks of
white anhydrite and at aboul 50 ft below the top ofthe
dolomile, the well penelrated salt.
STRUCTURAL CONFIGURATION
The Fahud structure is at the surface a WNW-ESE.
trending asymmetric anticline forming a sausage-
'sliaped relief 45 km long and 8 km wide. The structure
has a gradual plunge at both ends. Its core has been
eroded to the Upper Cretaceous Aruma shales and the
surrounding ridges expose Paleocene-Eocene limestone
deposits.
The surface structure has a flat crestal area which
makes the precise locatipn of the axis difficult without
detailed plane table control. The rnaximum dips ofthe
north and south flank are 17° and 19° respectively;
Steeper dips have been recorded, but they occur along
small strike faults which can be associated with fault
movements in depth.
The Fahud structure has a strong surface expression
which, however, does not reflect the complexity of the
subsurface tectonics. Seismic and drilling data revealed
a major subsurface fault zone at the level of Cretaceous
strata along the crest of the structure. The aggregated
throw amounts tp about 4,000 ft and the fault zone dips
wilh about 45° to the SW. This fault zone is most probably
deep-sealed and related to basement movements,
complicated perhaps by salt influence.
The upthrown northern Wasia block of Fahud has a
closed acreage of about 27 km by 4 km. The vertical
closure against the fault is roughly 3,200 ft. The dips of
the north flank are of the order of 15 to 20^ The top of
the Wasia culmination ofthe northern block is at about
750 ft below ground elevation (about 200 ft above sea
level).
South bf the Fahud main fault zone in the downthrown
block, seismic investigations and drilling results
revealed an undulating structural unit with a culmination
at Fahud Southwest and another one at Fahud
South, The whole uriit dips to the south and is bounded
at its southern niargin by a minor fault, parallel to the
main Fahud fault zone!
The Fahud uplift compares structurally rather well
with the Natih uplift, about 20 km northeast of Fahud.
Both.structures are bounded by major fault zones,
, Fahud in the south and Nalih in the north. In fact
Fahud-Natih is a structurally high area, bordered by
faults having throws of several thousand feet on Wasia
level. Fahud-Natih can be considered a horst block
which faces deep depressions to the north and south.
, Fahud is a residual gravity maximum in a larger
Bougucrgravily minimum suggesting the occurrence of
underlying sail, of which presence was proved by

i
Fahud-1 at a depth of 11,870 fl. However, Fahud is not
a structure dircctlyTelated to salt movemcnls, allhough
these might have played a secondary role.
STRUCTURAL HISTORY
The structural history ofthe Fahud structure during
pre-Middle Cretaceous time is riot known. The first
positive indications of structural growth are seen in the
W'asia Limestone, Formation (Middle Cretaceous:
Albian-Cenomanian) and the Aruma Shale Formation
(Upper Cretaceou^: Santonian-Campariian)..The following
evidences can be listed:
(1) The following Table shows that all members of
the Wasia Limestone Formation are consistently
thinner in the southern downthrown block than in
the uplifted north block. This may indicate that the
carbonates of the downthrown soiilh block were
deposited in somewhat deeper water than in the
upthrown north block.
Thickness
in feel
Wasia Lst.
members:
a
b
c
d
e
f
. . • g
Wasia Lst.
Formation
F2
168
273
157
134
532
101
53
J.418
Jplhrown noi th block
F3
160
279
, 164
135
546
104
53
. . .
1,441
F4
197
282
166
139.
—
—'
— .
—^
F5
208
299
159
146
548
102.
55
1,517
.F&
193
309
158.
154
540
103
57
1,514
New Oil Producing Regions 249
Downthrown
south block
FS-9 FSW
173 185
216 204
.141 129
119 122
440 448
• 89 70
.44 .50
1,222 1,208
(2) When comparing the detailed lithology of the
b-member on both sides ofthe fault it appears that
shallow self-indicating wackestone'to packstone
intervals are much less numerous in the southern
downthrown block, This again is an indication that
the carbonatesin the south block were deposited in
deeper water than in the north block,'
(3) Comparison of porosities between the.nprth and
south blocks show clearly that high porosities are
predominant in the upthrown block. Moreover,
the insignificant calcite cementation found in
Fahud South and Southwest, indicates that high
porosities never existed in the downthrown block
of the Fahud fault, , . .
ll is believed that the Fahud fault already existed
during the deposition of the Wasia Limestone
Formation. The upthrown block was periodically
lifted above .sea level and was therefore exposed
much longer to sub-aerial leaching than in the
downthrown block. This phenomenon is believed
to account for the high porosities preseni in the
Wasia of the upthrown block and also for the fact
that reservoir characteristics deteriorate rapidly
below the oil-water contact. '
(4) The basal pari oflhe Upper Cretaceous Aruma
Shale Formation contains the Foraminifera
Globotruncana caririala. This is so far the only
reliable palaeontological zone, wiihin the Aruma
Shale Formation. Unfortunately Globotruncana
carinala occurs rather scarcely and therefore recognition
of the zone is rather time-consuming.
The thickness of the zone has been established in
four wells, viz. Fahud North-2: 39 ft; Fahud
Norlh-7: 77 ft; Fahud South-9: 615 ft; and Fahud
Soulhwesl-11: 571 ft.
The corisiderable differences in thicknesses of the
Globotruncana carinala zone.between the north
side (upthrown block) and the south side (downthrown
block) of the Fahud fault is an indication
that this fault was already active during eariy
Aruma time (Upper Santonian).
(5) The ArumaShale Formation oflhe downthrown
, South block is about4,000ftthick or roughly 2,500
ft to 3,000 ft thicker than in the north block. These
differences are caused ifirstly because the fault was
active during the entire Aruma time, and secondly
because of erosion which followed the deposition
of the Aruma Shale Formation.
During Tertiary time the Fahud fault was almost
non-active. Some small strike faulls.at the surface
can be observed..They are associated with the
Fahud fault zone.
In summary it can be said that all the above observations
indicate that the Fahud structure was already
•present as an uplift during the deposition ofthe Middle
Cretaceous Wasia Limestone Formation. The same is
probably true oflhe Fahud fault. The principal vertical
movements along the fault occurred during Upper
Cretaceous when the Aruma Formation was deposited.
Folding and uplift tookplace during Tertiary.
OIL ACCUMULATION CONDITIONS
The reservoirs of the Wasia Limestone Formation
provide the oil.in the Fahud structure. The oil source
rpck is probably the bituminous b-member of the
Wasia. Generation of oil may have occurred in the deep
depressions north and south ofthe Fahud-Natih horst
or inan area west of Fahud. It is speculated that migration
of oil took place shortly after the Wasia Limestone

. • / " ' • "
250 New Oil Producing Regions
Formation was deposited, viz. during the sedimentation
of the Aruma Shale Formation (Upper Santonian-
Campanian). . '
All the Wasia members are productive. The maximum
gross thickness ofthe oil accumulation amounts
to about 1,500 ft. It is overlain by a primary gas cap
which is about 360 ft high. The a-member is iri all
probability oil-wet. The b-member is mainly bituminous
non-reservoir rock and in spite of being productive
in some of the wells, is not considered an attractive
completion prospect at present.
Pressure data indicate that the reservoirs probably
have a common free water level but due to variations in
lithology the oil-water contacts may range within 50-
100 ft bpth within and between the productive zones. It
is assumed that communicatipn between reservoirs
exists.
Initial well potentials of about 5-7,000 b/d are
expected.
High porosities are not necessarily associated with
high permeabilities; Frequently the more permeable
intervals are the less porous. High permeabilities are
often found in the upper parts of the members.
The oil has an API gravity of about 33-6° and a sul­
phur content of around M 5%. Regular oil production
is expected to start during the last quarter of 1967,
The following porosities and permeabilities are observed
in the reservoirs:
Members Porosity "/^ {net pay) Permeability mD
a
b
c
d
e
f
g
32
32
30
27 ,
.25
30
29
REFERENCES
10-20,000
7
7-3,000
12
20-10,000
about 5
about 5
1. DUNHAM, R. J,, Classification of carbonate rocks, 1962,
AAPG Mem, 1, pp, 108-121.
2. DUBERTRET, L., Lexique Stratigraphique International,
Vol. Ill, ASIE, Fase. loa, Iraq.
3. H UDSON, R. G. S., Permian and Trias of Oman Peninsula,
Arabia, 1959, Geol. Mag. Vol. XCVII, No. 4. '
4. LEES, G. M., The Geology and Tectonics of Oman, 1928,
Quart. Journ, Geol, Soc, Vol, LXXXIV, part 4.
5. MORTON, D. M,, The Geology of- Oman. 1959, Fifth
. World Petroleum Congress.

288 , New. pil Producing Regions
12. HEIKKILA, H. H., 1965. Eighth Commonweahh Min,
and Metal, Cong. Australia and New Zealand, 1965,
Petroleum Paper 155,.
13. KAPEL,A., 1966, Ausl,OilGasJ.,June 1966.
14. GREER, W. J., 1965. J. Ausl. Pelrol. Expl. Ass., 65-68.
15. Esso Petroleum Aust; Inc. 1967. Bur. Min. Resour. Ausl.
Petr. Search Subs. Acts Publ., 82 (in press).
16. ,M URRAY GROVER, E., 1965. J. Aust. Petrol. Expl, Ass,
' 7-19. ,
17. WELLS, A. T., FORMAN, D. J., RANFORD, L. C, and
COOK, P, J:, 1967, Bur.Min. Resour. Bull, (in preparation).
- • ; •
Situado en la parte central de la cuenca Mesozoica
del Sahara Argelino Oriental, al sudesle del Arco de
El Agreb y Messaoud y paralelo a este, el Anticlinorium
Hassi Touareg esta caracterizado por su relativamente
grande complejidad estructural y por su historia geologica
particular ditranle tiempos post-Hercinianos. La
caracteristica mas importante es la exislencia al final
del Cretacico inferior, de una fase orogenica, llamada
fase Austriaca, la cual ha dado a las estructuras principales
sus caracteristicas o las ha acentuado profundamente;
la erosion subsecuenle a esta fase descubrio las
crestas de estas estructuras hasta diversos niveles del
Jurasico e inclusive hasta la parte superior del Triasico.
Los yacimientos productiyos estan localizados, lo
misnio.que en las areas vecinasde la cuenca Mesozoica,
18. WILLIAMS, G. K., HOPKINS, R, M., and McNAUGHtON,
D. A., 1965. J. Austr. Pelrol. Expl, Ass., 159-167.
19. A.P.C. 1961. J. Geol. .Soc. Austr., 8, Pi. 1.
20. THOMPSON, J. E., 1965. Econ. Comm. Asia and Far
East(ECAFE), Japan, 1965.
'21. JOHNSTONE, M., 1966. J. Ausl. Petrol. Expl. Ass. (in
press).
22. PLAYFORD.P.E., 1965. Eighih Commonweahh Min.and
Metal. Cong. Australia and New Zealand, 1965. Petroleum
Paper 154.
23. SILLER, C. W., 1965. Econ. Comm. Asia and Far East
(ECAFE), Japan. 1965. ; . .
ABSTRACTO
Una nueva region productiva en el Sahara Argelino:
el Anticlinorium de Hassi Touareg
bajo la cubierta salina del Triasico Superior y su distribueion
es un resultado de la historia geologica Herciniana,
la cual ha condicionado la erosion mas o
menos importante de las formaciones Cambro-Ordovicicas
y la depositacion mas o menos exlensa de areniscas
del Trias pre-sahno. Existen diferencias apreciables
en los hidrocarburos a lo largo de todo el Antichnorium;
se han descubierto en el sur algunos campos de
conderisado y campos de petroleo con casquete de gas,
siendo los mas importantes Gassi Touil y Nezla, que
pueden entrar dentro de la llamada provincia petrolera
de Touil; en el none se ha encoirando el campo petroero
Rhourde el Baguel que parece mas bien corresponder
a otra provincia, petrolera, la de Hassi Messaoud.

c
^^^:^i^ ^^-^: C^r^ Cv-

278 FIFTH WORLD PETROLEUM CONGRESS
%fc„x' Introduction —
P
.....•.-.-^; :.

56«
Ka* Musandam
nmn^nntainnmixtp
THE CEOLOOY OF OMAN
Fig. 2—«ological Map of Oman.
60°
NEOGENE
With Grovel
OLIGOCENE - PALEOCENE
Normal Marine
Howaiina Bedt
Semail
279
UPPER CRETACEOUS
MIDDLE CRETACEOUS-JURASSIC
TRIASSIC - PERMIAN
UPPER PALAEOZOIC UniJiff.
lOWER PALAEOZOIC Undiff.
SALT PLUGS
Rat ot Hadd

:D
280
Regional Geology
The territory of Oman is divisible into a mountain
zone in the northeast and an alinost featureless desert
foreland to the southvyest (Fig. 2).
The foreland is topographically and geologically a
continuation of the gently-undulating shelf which extends
eastwards from the Precambrian AraborNubian
iriass of Hed jaz [16]. The mountain zone appears
along the east coast as a detached orogenic arc with
the overall structure of a complex geanticline. It exposes
rocks, including serpentinites and radiolarites,
which have counterparts in the rhountain ranges of
S.W. Iran (Zagros), and of landward Makran [3]—
"coloured melanges."
Lees [13] suggested that the serpentinites ("Semail"),
radiolarites ("Hawasina beds"), and underiying
limestones ("Musandam," etc.), had been thrust
individually on to the Arabian foreland by Pre-Gosau
nappe movements, from some gcpsynclinal zone to the
East; but evidence will be given to show that these
formations are autochthonous [6, 8] and that their
chaotic structure is due to a region of "effusion tectonics"
[II] associated with Upper Cretaceous serpentinite
extrusions on a great scale. The milieu of
these extrusions can be studied to advantage in Oman
because subsequent compression has had relatively
slight and restricted cflfects, producing no well-defined
thrust-zone or folded foredeep comparable with those
of the Zagros range.
The regional relationships pf the Oman orogen are
still open to speculation.
It may be a quasi-independent eruptive unit [8, p.
151]; but most authors assume that it has structural
links with Iran. Thus it has long been recognized that
the N-S strike of its northern sector is in approximate
alignment with an old structural trend through Central
Iran and beyond [2, 3]; yet there is no reappearance
of the Oman orogenic zone northwards in the Laristan
province of Iran across the Straits of Hormuz.
Lees [op. cit] regarded the range as a south-trending
branch of the Zagros "nappe zone," deflected southwestward
[cf. 8, Fig. 1] under the NNW-SSE late
Tertiary folds of the Biaban Coast (although these
show no effects of a discordant Upper Cretaceous substructure),
and continumg southward to include isolated
outcrops of serpentinite along the Batain Cloast,
at Masira Island, and at Ras Madhraka.
FIFTH WORLD PETROLEUM CONORESS
However, those outcrops have no extensions to the
north, where deep drilling (Fahud; Ghaba) and geophysical
maps reveal normal foreland conditions.
Lees mentioned the possibility that the Oman orogenic
zone might swing south-rwestwards off the Arabian
Coast; but the coastal geology and bathymetric
surveys off shore lend no support to this view, and the
, serpentinites themselves are now known to be alien
elements in a foreland environment.
These observations are compatible with the results
of air and ground reconnaissance which indicate that
the Oman orogenic zone deflects wholly from a N-S
strike in the north, to a NW-SE strike in the southern
sector, where it is cut off rather abruptly by the Batain
Coast, trending NE-SW.
Previous authors have associated this NE-SW coastal
trend with large-scale normal faulting [5, opp; p. 20]
or wrench-faulting [15, Fig. 10; Henson in 4], Both
may have occurred, and transcurrent shearing along
the "Masira fault zone" is invoked to account for the
anomalous coastal outcrops of serpentinite.
In the North the range ends suddenly at its intersection
with the Pirate Coast which also trends NE-
SW; and the coastal belt is characterized by parallel
• normal and wrench-faulting and by stratigraphic variations.
Parallelism of the Batain and Pirate coasts, and the
conspicuous deflection of the Persian Gulf towards the
Straits of Hormuz, may be coincidental; on the other
hand it may be significant that their common trend is
that of the "aualitic lineament" [16] in the "rhcgmatic
shear pattern" (Sonder) of Africa and Arabia
[6]; • f
Wrench-faulting along the Batain coast may be associated
with the development or rejuvenation of NE-iSW
shearing movements responsible for this pattern
(part); and the Pirate Coast trend may have a similar
explanation, though critical evidence is now concealed
by later deppsits, parucularly in the flat foreland.
Thus wrench-faulting on a very large scale could
account for detachment of Uie Oman orogenic zone
from former connections to the north and soutli.
This speculation [6] introduces considerations beyond
the scope of the present paper, but is noted here
as a possible alternative to other hypotheses concerning
the regional relationships of the Oman orogenic zone.
Space does not permit further discussion of these
.problenas in the present synopsis.
LA

FUKHAIRI a^
LAKSHAIW
SHAMAL
MUSANDAM
EimiNSTONE
MIUHA
CAIL
HAGIL
BIH
H-T-H DOLOMITE
I'I 'i I LIMESTONE
l^"^! MADL
fetoJ SHALE
EE^ SAND
H'^-VI CONGLOMERATE g BRECOA
RADIOLARITES
l.V''''"Vi METAMORPHICS
iV'-'-'-i IGNEOUS
CHERTS,SECONDARY
THE OEOLOOY OF OMAN
Fig. 8—Stratigraphic Sections of Oman.
""""^•W^WWIB
FORMATION NAMES
SEE LEES, 1928;
HUDSON |TAL,I»S4 (2)
SEMAIL
HAWASINA
HATAT
281

w
282 FIFTH WORLD PETROZXUM CONGRESS
Oman Mountairis
Excellent accounts of the physiography, rocks and
structures of the Oman mountains have been given by
Lecs [12, 13], so that attention may be confined here
to nc\v information and modified interpretations resulting
from a considerable volume of later work
(Fig-2).
.Stratigraphy
The oldest exposed formations appear in a scries of
axial uplifts, the largest of which are the Jebel Hagab
thrust, the Jabal Qamar block-fold, and the Jcbcl
Akhdar and Saih Hatat domes. These provide sections
down to the Paleozoic (Fig. 3).
The stratigraphy at Hagab and Qamar has been
described in publications [8, 9] tO which the reader is
referred, and is summarized in Fig. 3, with suggested
revisions which are explained below. Descriptions
arc given here of the most complete sections available,
which are exposed in the Akhdar and Saih Hatat areas
near Muscat.
PERMIAN
Results of rapid reconnaissances by Pilgrim and Lccs
in the Saih Hatat dome, have been revised by R. Wetzel
and others (unpubl).
The lowest exposed beds arc the Hatat phyllitcs and
schists [ 13], with basic minor intrusiycs, passing southwards
(in part) to quartzites. The original sediments
were elastics and pyroclastics, with a strong limestone
member which contains Permian fossils (Oldhamia
Waagen, etc.). They arc overlain by Upper Permian
fossiliferous limestones, concordantly in the north, but
with a 5° unconformity in the south. The dynamometamorphism
is of low-grade with sehistosity parallel
to the bedding, and it decreases upwards, so that fossil
molds at 90 m. below the Upper Permian limestone
cover have survived its cff

ji.jeolina cretacea (d'Archiac); (b) pellety limej:oiivi
[109 m.] with Orbitolina cf. concava (Lapijrck);
(a) marly, silty lunestone [122 m.] with O.
ci. concava.
At Saih Hatat (Wadi Adi) the Lower and Middle'
Cretaceous cannot be recognised owing to extreme
dulomitisation of the limestones, which, however, grade
tt the top into the overlying Hawasina beds (q.v.).
' Along the Wadi Semail, between Akhdar and Saih
Hatat, the Upper Cretaceous sequence is as follows:
: Top. (c) serpentinites and gabbros [H- 1000 m.]; (d)
'rf)w grtide metamorphics with basic igneous intrusions
(155 m.]; metamorphism is most intense at top; (c)
pdiolaritcs [228 m.]; (b) finely detrital limestones,
illidfied mudstones, and microconglomcrates with rare
Globotruncana sp., and reworked Orbitolina [76 m.];
(a) marls and sandy marls, grading into breccias and
f«ng|omcratcs [94 m.].
Unit (c) represents the 'Semail* of Lees [13], while
(d-a) corresponds to his 'Hawasina' beds.
Tlic contact between unit 'a' and the Middle Cre-
Ufcous is sharp but concordant, while that between
the Hawasina beds and the Semail is also concordant,
but sli^'htly sheared to a degree vvhich, in the author's
vir\( s not indicate iinportant thrusting.
•X. .lilar succession is observed elsewhere in the
range so that it is probably normal and autochthonous;
i.id tliij view is supported by the fact that the Hawaiin.i
facies tongues westward into normal marine globir.'in.il
marls of the foreland [M. Chatton].
i Further evidence in the same direction is provided
^> geophysical surveys in^he north foreland, which
mral an exceptionally high gravity-gradient rising
• iw.irds the mountains, suggesting that the Semail ex-
"fV'ions arc dccp-rooted in iiiu.
F.rodcd surfaces of Hawasina and Semail are covered
r. both flanks of the range by transgressive Maestrichtun
conglomerates, marls and rudist reefs. The age
nr.£c of the Hawasina-Semail succession lies therefore
•'tween the Cenomanian or Turonian and the Maes-
•:. liiian, with scope for some diachronism. Since mag-
•-.itc vxins, probably the immediate after-effects of
•-it.iMion [K. C. Dunham], have been found to cross
^iinu-ichtian—Semail contacits, the Semail itself may
•'^ of Campanian-Maestrichtian age.
Tlicjc conclusions differ from those of earlier pub-'
-'..ow which assumed a considerable time interval, ,
THE OEOLOOY OF OMAN 283
with orogenic movements, between the genesis of the
Semail-Hawasina complex, and deposition of the overlapping
Maestrichtian. Hawasina beds are typically
contorted under Semail coyer, but this is attributed to
penecontemporaneous slumping, whatever their age
may be.
In the northern part of the range (Hagab; Qamar)
earlier dates (Triassic-Jurassic-Lower Cretaceous)
havd been assigned to the Hawasina [8, 9] suggesting
repetition of the facies in Oman. However, evidence
for this interpretation is under review in these two
structurally-complex areas, because, at the Jabal Agah
dome between them, the stratigraphy approximates to
that at Wadi Semail. Thus the Qamar sequence [op.
cit.] of Ais schists (cf. Unit "d") and Kharmil cherts
(cf. Unit "c") is here underlain by detrital limestones
(cf. Units a & b; (?) and Makhsur beds—part) with a
basal conglomerate resting transgressively on eroded
Upper Musandam limestone of Lower Cretaceous age
(Fig-3).
Correlation of displaced Hawasina beds is difficult
because the evidence of their radiolaria has beeii found
to be unreliable [G. F. Elliott] and they often contain
derived faunas, sometimes locally monogenetic, ranging
from Permian to Cretaceous; they also contain
numerous massive slumped blocks of the sub-strata
(the klippen of Lees). The Semail itself has entrained
blocks of underlying, sediments. Sills of serpentinite
occasionally penetrate the Hawasina (e.g. near Jabal
Agah), and basic dykes of later date cut both formations
and their contacts. Pillow lavas appear locally in
the Upper Cretaceous (Wadi Jizzi, etc.) but their relationships
are uncertain.
TER'nARV
Cainozoic marine sediments overlap both flanks of
the mountain zone, marking separate transgressions of
Paleocene-Eocene, Oligocene, and Miocene age. Some
folding movements intervened bety/een the Oligocene
and the Miocene.
Geological History
The detailed structure of the Oman Mountains (Fig.
4) is stiil imperfectly known but the main events in its
history arc indicated by stratigraphic studies. These
show that the region was a stable part of the gentle
foreland basin of Trucial and Central Oman until the
end of Middle Cretaceous times. There is no evidence

c
t
284 FIFTH WORLD PETROLEUM CONGRESS
SSW
(200*) SaiK Hotol
n~l NEOCENE
Es3 OUGOCENE • PALEOCENE
BiJUJI Normol Morins |
H Howotino » > UPPER CRETACEOUS
t?^/l Somoil i
^ MIDDLE CRETACEOUS-JURASSIC
^ TRIASSIC • PERMIAN
^ ^ UPPER PALAEOZOIC Undiff.
E ^ LOWER PALAEOZOIC Undiff.
to suggest that any Mesozoic geosynclinal zone developed
to the cast, where the Gulf of Oman subsided at
a mui::h later ( (?)post-01igocene) date.
The first movements recognisable in Oman are indicated
by metamorphism and tectonic repetition of the
Hatat phyllitcs, which are not likely to have resulted
from, or followed, the broad folding of the Saih Hatat
and Akhdar domes in which they appear. Since these ,
dynamic effects increase dowmwards in the deeper, incompetent
core of the structure, diminishing and disappearing
upwards in their competent cover, they may
have been caused by slight underthrusdng of a peneplaned
basement [Henson].
• lA>cal uplift due to this or some other case, began
Scolo in Milo»
Coot»rlad
10 20
NNE
(20»)
Muicol
NOTE 1. Abnormol opporoni ihicltnoitoi of Howotino b«d» orodwo lo contorlion.
2v Somoil Veoli* oro omillod bocovto thoir potilioni oro onknown.
• • y •
Fig. 4—Structural Gross-Sections of Oman Mountains..
at or towards the'end of the Middle Cietaceous, when
basal Hawasina breccias and conglomerates appeared
with derived faunas, indicating contemporaneous axial
emergence and erosion. In the ovieriying Hawasina
uixits, huge slumped masses of Permian—Jurassic sediments
point to more violent local disruption and probably
block movements, accompanied by premonitory
vulcanicity (tuffs; basic extrusions). Associated silica
eiuichment of the sea water favoured the deposition
of radiolarites which are often chaotically slumped and
contorted. The reg^e was evidently one of continued
regional subsidence with local uplift and archipelago
conditions in a scismically-activc orogenic zone.

yWi history culminated in the extrusion bf ophiolite
^>._ppcs" on an immense scale, and probably in a viscous
form and local low-grade dynamo-thermal metamorphism
of immediately underlying beds; and in
slight shearing of ophiolites already consolidated.
These generally rest on Hawasina beds, but at Jabal
Rann (near Qamar) they overlie a truncated, uplifted
dome or block of Rann (Ordovician) quartzites
and shales [9].
Semail extrusion, from "roots" so far undiscovered,
was probably accompanied by continued subsidence;
the upper part of the serpentinites is sometimes conglomeratic,
suggesting emplacement under submarine
conditions. However uplift and axial erosion followed
quickly, with deposition of flanking basal Maestrichtian
conglomerates, probably including the Ajma
boulder beds [9].
Apart from gentle oscillations which controlled subsequent
transgressions and regressions, there is little
evidence of further activity in the Oman range until
post-Oligoccne, pre-Mioccnc folds appeared on the
west flank. It was probably at this time that axial uplifts
were accentuated, tilting their Semail-Hawasina
cover; and that thrusting occurred on a large scale in
thf "'orth [8, 9] and on a minor scale elsewhere, to-
P with vwcnch-faulting [8, 9]. The anomalous
NV^W trend of the Jabal Nakhl [13], paralleling the
Wadi Sonail gap, is attributed to trai^current movements.
The Neogene folding on the west flank is confined
to a narrow belt of widely-spaced anticlines, some very
irregular with minor thrusts, exposing steep-dipping
Oligocene to Cretaceous formations overlapped by
gently-tilted Miocene. Trending N-S to Hafit, the
folds swing eastward in the latitude of Ras al Hadd,
terminating as they approach the mountain front.
These structures were interpreted by Lees as elements
of an independent fold-arc continuing, perhaps, towards
Sind. However, it is considered that they arc
related to endemic, deep-seated fault-tectonics in
Oman, and in some cases (Fahiid) to associated salt
diapirfsm at depth.
Geophysical surveys in the Sharjah area show that
the N-S strike swings abrupdy NE at Juweiza, into approximate
parallelism widi the Pirate Coast and the
•Dibba line' wrench-fault [8, Fig. 2]; faulting and
great thickening of sediments are indicated towards the
'm''.m''m.
THE GEOLOGY OF OMAN ;^85
adjacent coast.
General emergence of Oman followed the Miocene,
but successive erosion terraces in the mountains indicate
that the range itself imderwent differential uplift
in stages [12].
Tlie Desert
Most of the desert foreland is covered by flat-lying
marine Oligocene or Miocene deposits, or by recent
dune sands and salty mud-flats (Figs. 2, 5). However,
deeper exposures occur in coastal Dhofar [1], and in
the broad, gentle Hugf-Haushi swell, trending northwards
for 100 miles from Ras Duqm. This is an old
elevated feature with unconformable Paleozoic, Mesozoic
and Tertiary deposits converging upon its flanks.
Stratigraphy
BASEMENT
Crystalline basement outcrops only at Murbat and
the Kuria Muria Islands [1, 13], and possibly at Kalhat,
where Lees recorded foliated granite-gneiss under
Maestrichtian limestones [ 13]. Extension of this gneiss,
with associated granite, has been found recently around
Jebel Jaalan, but the context of these occurrences is
uncertain. ^
(?) CAMBRIAN -
In the Hugf area, the oldest exposed sedunents arc
as follows [7].
Top. (d) dolomite, massive to laminated, with solution
breccias and with chert bands and thin elastics at top
[224 m.]; Collenia s^.'f (c) red and green micaceous
shales, with some interbedded oolitic limestones and
platey dolomites (top), [299 m.] (b) dolomite, as in
(d), [299 m.]; (a) coarse sandstone, silty shales,
sheared gypseous shales at base [+ 315 m.].
Rare basalt intrusions of xmknown age penetrate
these beds. The strata dip gently westwards towards
flat desert with salt donies. Several of the domes appear
at the surface, exposing large blocks of gypsum and
laminated dolomites, with salt in Kebrit, Milh and
Sahma, and with conglomcradc red-beds and a litde
igneous debris in the latter. These components suggest
correladon with the Middle-Upper Cambrian Hormuz
series of the Persian Gulf salt domes [14], in
which casie the partly-evaporidc units (d) to (a) updip
to tbe east (Hugf), may well be Lower Cambrian.
J .l|.'.l. ...wm

c
d
286
SW
WNW
(300^)
Fohvd
Houthl
FIFTH WORLD PETROLEUM CONORESS
Tliin Noogono covor
Tryy-^^ r- •:. ...'..",.„.!•...••-.•..-.....: ..'• , ,. . ~zrr-r-—_
W
ED NEOCENE
^m OLIGOCENE - PALEOCENE
Normal Morinol ,,,.__•.__._.^.,,
Ho*o.ino bodi jUPPERCRETACtOUS
MIDDLE CRETACEOUS-JURASSIC
TRIASSIC- PERMIAN
^ ^ UPPEIt PALAEOZOIC Undiff.
^ a lOWER PALAEOZOIC Undiff.
Seclieni 8,C & D Vcrlicoi Scola x 2
Cantral Hvgf
NE
(35*1
ESE
020»)
Sec Iovol
rr^}mw!^/m^m'i>'a'M!i»fi. Soa Iovol
too//
W E
Duqm
Seal* in MiUt
5 to 15
Fig. Sr—Strnetoral Cross-Sections of Oman Foreland.
Soa Iovol
Soa Iovol
It is assumed that salt docs not occur at depth in the geophysical evidence suggests that salt-doming occurs
outcrop area (or in the Oman range) because it makes at depth.
no appearances under conditions which should have These observadons lend some support to the tentafavouired
extrusion. dye correlation suggested above.
ORDOVICIAN
Near Haushi, an ill-exposed sequence [550 m.] of
red sandstones and mptded shales with trilobites and
Cruziana (cf. Rann beds of Qamar), lies unconformably
on units (b) or (c) of the (?)Cambri«in. At
Ghaba to the north-west. Lower Ordovician sandstones,
siltstones, shales and mudstones [2000 m. +]
containing Didymograptus bifidus (Hall) and Cruziana,
have been drilled withoiit reaching the base; but
PLRMIAN
At Haushi, the Ordovician is overlain by clasdcs
with boulder beds, the latter containing unsorted, subrounded
blocks of granite and porphyry, wth occasional
Palaeozoic dolomites, ranging up to 2 m. diameter.
These boulder beds, composed exclusively of
Arabian rocks, are transgressive over a wide area. An
aqiia-glacial origin has been suggested [Chatton; Hudson
in 10], though other explanadons are possible. The

C-^
i
W^'
boulder beds contjun interbedded sandstones with a
brachiopod fauna, and arc overlain by 230 metres of
sandstones and red marls. The sandstones grade up
into an alternating sequence of marls and platy lunestones
[36 m.] with a rich brachiopod, trilobite and
goniaUtc fauna of Sakmarian-Ardnskian age.
TRIASSIC
Triassic rocks are not exposed in the Oman desert,
but 580 m. of dolonaite with Lingula tenuissima Bronn,
and some anhydrite, are assigned provisionally to the
Trias in a drilled sccdon at Fahud.
Jl'RASliIC
The Lower Jurassic is not represented in the Hugf,
but at Nafun, 77 metres of Bathonian limestones with
Anabacia, rest unconformably on (?) Lower Cambrian.
At Haushi, the Permian is followed by dolomites and
limestones [162 m.], ranging from Bathonian to low
Upper Jurassic age. A similar sequence was found
above the Trias in Fchud Well. There is everywhere,
at the base of the Jurassic, a thin clastic unit which
cannot be firmly dated.
CKETACEOUS
At Haushi, the Lower Cretaceous [169 m.] lies unconformably
on the Jurassic and consists of dolomitic
and pcllcty limestones in the lower part, with chalky
limestones and porous dolomitic limestoi^es above.
Orbitolina cf. disoidca occurs throughout.
The Lower/Middle Cretaceous contact is marked
by marls and sands [151 m.] with Orbitolina, etc.; and'
the overlying Middle Cretaceous is represented by
marly limestones [156 m.] with Orbitolina cf. concava.
These subdivisions can be followed with local variations
of thickness and lithology, throughout Oman.
The Upper Cretaceous with Globotruncana spp.
shows marked facies and thickness changes: Lower
Scnoni.in marls in the Hugf change northwards into
KiiKlstoncs, hut become marly again in the Fnhud area.
Campanian marly limestones in the Hugf change to
iiiiii'ls northwards.
Serpentinites outcrop sporadically along the Batain
coast, and at Masira Island where they are associated
with typical ( (?) Hawasina) radiolarites and covered
by Eocene. Shattered metamorphics (cf. Ais formation,
ficie Dunham) and serpendnites appear at Ras Madhraka
under transgressive Oligocene. Basement serpen­
THE OEOLOOY OF OMAN 287
dnites and amphibolites, striking NE-SW, occur in the
"metamorphic complex" at Murbat [ 1); but pctrological
comparisons, and the presence of familiar radiolarites
at Masira, seem to demand correlation of the S.
Oman outcrops with the Scmail/Hawasina complex
of the Oman range. However, it is unlikely that they
are in their original positions because no traces of thern,
in situ or derived, or in transitional (radiolarian)
facies, arc to be found in adjacent comparative sections
of Hugf and Haushi.
They are, therefore, believed to have been displaced
from the Oman orogenic zone by post-Crctaceous, prc-
Oligocene wrenchrfauldng along the Batain Coastal
belt.
The Macstrichdan is transgressive and outcrops
over wide areas bordering the mountains and the Hugf-
Haushi swell. It is normally characterized by orbitoidal
limestones and rudist reefs with basal conglomerates,
sands and marls. At Fahud however, the Maestrichtian
is in a marl facies which reappears in a well at Juweiza,
overlying a thick Campanian section with flysch and
conglomerates, known only at this locality adjacent to
the Pirate Coast.
PALEOCENE-EOCENE
There is generally a break, without angular discordance,
between the Maestrichtian and the Paleoccne.
At Fahud, Maestrichtian marls are succeeded by Paleocene
[122 m.], consisting of yellow marls with abundant
I.o

V
288 FIFTH WORLD PETKOLEUM CONGRESS
and limestpnes with.Nummulites fabianii Prever, Pellatispira
sp., etc.
The Eocene is believed to be well represented in a
thick Tertiary basin at Sur (Lees), and extends northwards
along dte east coast.
OUCOCENE
The most complete Oligocene section is found at
Duqni. The Lower Oligocene [125 m.] is unconfonnable
on the Eocene and comprises echinoidal chalky
limestones overlying a marl, gypsum, and dolomitic
limestone sequence, with a basal reef containing derived
Eocene nummulites, etc. Above is a section [47
m.] of chalky limestones with peneroplidae and miliolidae
dated as Upper Oligocene, which extends far to
the west. At Ras Madhraka, chalky limestones with
Lepidocyclina overlie Hawasina-Semail rocks. Thin
OHgocenc outcrops arc also known on the Batinah
Coast, and at Jebel Hafit, all in reef facics; but at
Jabal Aii and Ras Sadr on the Pirate Coast, there is
a ver/ thick Oligo-Miocenc section of marls and
evaporites similar to that oif Qishm Island.
MIOCENE
The Miocene rests unconformably On the Oligocene.
At Fahud, the Miocene can be divided into a lower
unit of limestone, chalk and marl [33 m.] of Burdigalian
age, and an upper part [+90 m.] which is
largely detrital and evaporitic and has been correlated
with the Lower Fars of Qatar and the Trucial Coast
Ostrea latimarginata Vrcdenburg, Clausinella persica
Cox, and C. amidei (Stcfani) arc present with a reworked
fauna of Lower Eocenc-Maestrichtian ages.
The Burdigalian extends south and southwest towards
Dhofar,
Late Tertiary deposits at Sur [13] have not been
studied in detail, but they differ somewhat from those
of the Oman foreland. ,
MiO-PUOCENE
Extensive deposits of coarse gravel and conglomerates
occur above the definite marine Miocene at Fahud,
and they extend along mountain pediment.
Volcanics
Basalts, probably of Quaternary or Recent age, occur
at Ras Madhraka.
Structure
The desert region can be subdivided structurally
(Fig. 5) as follows:—
a) In the south coastal belt, the broad tabular Hugf-
Haushi swell can be seen trending NNE-SSW with a
core of Lower Palaeozoics running from Duqm to Latitude
21°, and bounded on the west by a scarp exposing
Mesozoics and Tertiaries with low dip. Some of these
unconformable deposits reappear on the cast flank in
the southem sector.
Stratigraphic observations show that differential
block movements of various ages from Paleozoic onwards
have affected this feature; it is cut by numerous
intersecting faults at diverse angles, the prevailing dirccdon
being N-S. However, in its gross, structure, the
core is roughly divided into major blocks with margins.
striking ENE-WSW to NE-SW; and the latter trend
dominates geophysical survey pattems in a coastal belt
50-100 miles wide, reappearing in the geological mapping
of the Sur sector. It is considered that the prominence
of this trend is due to movements of the Masira
wrench-fault zone which may have had a long history
of rc

c
THE GEOLOGY OF OMAN
III.I, lywijif lltl.. ,I. i^wi^M ii>PH.I •.!.••. i.w n .• i|i]iMH,(;i|i .'•!1^.,t.'ii^ .J«i!"". I
y. '• .- ; • > . > . .
V,':
-^d= d/-dr^''--dM.-'d^^^^
.i^:'..- •mm
y-:J.. '.'H' ,>','•,•; " • •
d-.-. "yy•d^''-^^y\•••:•'•••
'd^-'p'''^isy:v^dP:.
v^:..fy:P-.\\\^'d •:
•^"'^^•vfil;:''/^\iir.v.v-'i .
dm ..•^'•.,B:NU^V::,
m-m:'^^- ••:.••
md-\
,;S:.:":-vv..:^H,
.,'^;
^ • - ^ • . ^ ; ; •
'W':-

c
%
y
290 FIFTH WORLD PETROLEUM CONGRESS
services; to K. G. S. Hudson and M. Chatton for
paleontological-stratigraphical research; and to many
colleagues who have shared in the arduous work of exploration,
particularly T. F. Williamson and D. Glynn-
Jones [1936-7], L. S. Thompson and H. Hotchkiss
[1940], R. Wetzel [1949], and R. G. S. Hudson
[1951-2]. •
K. C. Dunham and F. R. S. Henson have kindly
reviewed the manusc:ript.
References
1. Fox, C. S., "The Geology and Mineral Resources
of Dhufar Province, Muscat and Oman," Muscat,
1947.
2. Furon, R., "La Geologic du Plateau Iranien,"
Rev. gcncrale des Sciences, Vol. XLVIII, No. 2,
pp. 36-43, 1937.
3. Gansser, A., "New Aspects of the Geology in Central
Iran," Proc. 4th World Petroleum Congress,
Sect I/A/5, pp. 279-300; 1955.
4. Girdler, R. W., "The relationship of the Red Sea
to the East African Rift system," Quart. Joum.
Geol. Soc. London, Vol. CXIV, Part I, pp. 79-
105; 1958.
5. Gregory, J. W., "The Rift Valleys and Geology of
East Africa," Seelcy, Service & Co., Ltd., London;
1921.
6. Henson, F. R. S., "Observadons on the Geology
and Petroleum Occurrences, of the Middle East,"
Proc. Third World Petr. Congr., Sect. I, pp. 118-
140; 1951.
7. Henson, F. R. S. and Elliott, G. F., Exhibidon of
specimens of Collenia? from pre-Permian sediments
in South Arabia, Proc. Geol. Soc London,
No. 1561, 29th May; 1958.
8. Hudson, R. G. S., A. M. McGugan and D. M.
Morton, "The Structure of the Jcbcl Hagab Area,
Trucial Oman," Quart. Journ. Geol. Soc. London,
Vol. CX, pp! 121-152; 1954.
9. Hudson, R. G. S., R. V. Browne and M. Chatton,
"The Structure and Stradgraphy of the Jebel
Qamar area, Oman," Proc. Geol. Soc London,
No. 1513; 15di June 1954.
10. King, L. C, "Basic paleogeography of Gondwanaland
during the late Paleozoic and Mesozoic eras,"
Quart. Journ. Geol. Soc. London, Vol. CXIV,
Part 1, pp. 47-77; 1958.
11. Kiindig, E., "The position in rime and space of
the ophiolites with relation to orogenic metamorphisin,"
Geol. en Mijnb. No. 4, New Series,
18di year, pp. 106-114; April 1956.
12. Lees, G. M., "The.Physical Geography of South-
Eastem Arabia," Geograph. Joum., Vol. LXXI,
No. 5, pp. 441-470; 1928.
13. Lees, G. M., "The Geology and Tectonics of
Oman and of Parts of South-Eastcrn .'\rabia,"
Quart. Joum. Geol. Soc. London, Vol. LXXXIV,
No. 336, pp. 585-670; 1928; (widi bibliography).
14. Schroeder, J. W., "Geologie de ITle de Larak,"
Arch Sci. phys. ct nat. 5th Per., Vol. 28, pp. 5-18;
Jan.-Feb. 1946.
15. Vening Meinesz, F. A., "Shear Patterns of the
Earth's Crust," Trans. Amer. Geophys. Union,
Vol. 28, No. 1, pp. 1-61; 1947.
16. Von Wissmann, H., C. Rathjens, and F. Kossmat,
"Beitrage zur Tektonik Arabiens," Geol. Rundsch.
Vol. 33, pp. 221-353; 1942.
This paper was presented on June 3, 1959, by D.
M. MORTON.
Discussion
N. E. BAKER (Consulting Geologist, Upper Montclair,
N. ]., U.S.A.). The factual geologic data presented
by the author represents a vast amount of
arduous field work by himself and many of his col-
,leagues. This is a major contribution to the geology.
of Southem Arabia and the lower Arabian Gulf
area, ranlying along with Lccs' early work on the
geology of Oman. This present contribution embraces
knowledge gained from photogeology, surface examinations;
geophysical surveys and subsurface studies of
the results of eight deep wells drilled in the area.
Hence it constitutes a solid foundation for future
regional studies.
The speculative portion of the paper is embraced
in the discussion of the "Regional Geology," concerning
the significance of the Oman Range with
respect to its rclaUonship to the Zagros nappe zone
of Iran. As regards oil prospecting in the lower
Arabian Gulf with particular reference to the Trucial
Coast and Iran, this relationship is very important.
The author points to: 1) "effusion tectonics" as
responsible for this (Oman) "chaotic structure,"
rather than the results of thrust from the cast as con-
iimm9mi}f:tiim\muM'i

••""••
The configuration of the Arabian Gulf coast lines
of both Iran and the Trucial Coast, the parallel
structural trends in the Biaban and Badnah Coasts,
/' ^ intensity of structural c»inpression in botih the
i^.- gros and Oman belts of folding, and the presence
V^ large salt masses in the foreland areas of both
these regions are some of the conspicuoiis features
that make the direct reladonship of structural and
stratigraphic factors on both sides of the Gulf appear
to be the result of uniform and contemporaneous
condidons.
The importance of determining the relationship
of the geologic factors of these areas for purpose of
oil finding is obvious. The stratigraphy of the forefront
of the Oman Range and that of the Badnah
coastal area as related to oil prospects, the strad-
. graphy and structure of the Makran Coast and its
oil prospects, likewise the geological factors determining
the potentialities of Biaban coastal area, are
some of the important unknowns which may be related
to the effects of Oman orogeny.
If Lees' contention holds, namely that the Zagros
Cretaceous folding and subsequent deposidon extends
southward into Oman, then oil prospects in
the forefront of the Oman Range, the Trucial Coast
and die lower Arabian Gulf should be analogous to
those of southeastem Iran. Sinularly, the Makran
THE OEOLOOY OF OMAN 291
:

Q
292 FIFTH WORLD PETROLEUM CONORESS
Essendally, the Oman range has a north-south
strike in its northern part and stops abmptly at the
Strait of Hormuz. In the southern part it swings into
a northwest-southeast strike and again stops abmptly
at the Batain Coast where, to the cast, there is
another strike at right angles in this directipn. The
Batain Coast is believed to be a fault coast, some
verdcal movciiient, and also there is indicadon that
there has been wrench faulting along here.
Similariy, the parallelism of the Pirate Coast and
the studies in this area indicate that there may be
wrench faulting along this trend. In such case, the
Oman orogen itself may have a continuation elsewhere,
from whioh it is now removed.
With regard to Mr. Baker's remarks that, if the
altemadve dieories arc correct, there should be a
comparison between the Coastal Iran sediments and
thpse of Oman, to the best of my knowledge this is
not the case. We can follow our Oman foreland
deposits from the desert areas into the mountains
and the intertonguing of the radiolarites with the
marine globigerina marls of the Upper Cretaceous
seems to suggest that they are part of the same sedimentary
story.
I would like to echo Mr. Baker's remarks that perhaps
further discussion would be of great value to
all the people concerned with the geology in these
particular areas of Arabia and Iran.
Z. R. BEYDOUN (Iraq Petroleum Company, Ltd.,
London, England). I would like to add my thanks to
those of Mr. Baker and Mr. Morton for this very
interesting presentation on a previously relatively litde
known area of Arabia.
His description of the (?)Cambrian of the Hugf
area is very interesting. In the Hadramaut, where a
great deal of similar field work has been carried out,
we have found a group of old sediments which bear
very marked overall lithological similarities and unit
similarities to the Hugf beds. This suggests that the
Hadramaut beds may very Hkely be of similar (?)
Cambrian ago. However, a big unconformity occurs
above these beds, and they arc generally overlain by
Upper Jurassic or Lower Cretaceous rocks, all of the
older part of the succession being absent.
With regard to the Tertiary, the Paleocene of
Southwest Arabia extends northeastward to the Oman
with much the same facies and lithology as described
by Mr. Morton, and the break between the top of
the Cretaceous and the base of the Paleocene also
occurs in Southwest Arabia.
In view of the occurrence of salt domes in parts
of Southwest Arabia in which the age of the salt is
dated as Jurassic on the basis of fossils in the immediately
overlying shales, I would be grateful if
Mr. Morton could indicate how firm is the age dating
of the salt in the Oman.
D. M. MORTON replies. The age dating of the salt
in Oman is also tied in with the suggc:sted correlation
with the salt domes of the Arabian Gulf. In
several of these domes, the salt brings out Cambrian
fossils and overlying red clasdc beds, sometimes .salt
pseudomorphs, and a general succession has been
worked out for the Gulf area.
In Fahud, we know that the salt is certainly older
than Permian. In Ghaba, we have drilled down
through 2000 meters of. Ordovician without encountering
any evaporites in the whole well section,
and there was originally an indication, on the basis
of geophysical results, of salt tectonics at depth in
this area.
At Haushi, to the east, more than 2000 meters of
Ordovician and possibly Upper Cambrian sediments
are exposed at the surface without any signs of
evaporites, but the underlying Lower Cambrian dolomites
themselves show an approach to evaporitic conditions.
It may well be that the salt is of upper Lower
Cambrian or lower Upper Cambrian age in Oman.
E. KUENDIG (Bataafse Internationale Petroleum
Maatschappij N.V,, The Hague, The Netherlands).
1 wish to congratulate Mr. Morton for his excellent
study of what we may call a classical orogen developed
from a eugeosynclinal habitat. It links up
very well with similar studies done in Kurdistan by
Washington-Gray, in Iran by Gansser and his colleagues,
and in Anatolia by Bailey.
Lecs' original concept, that the Oman Mountains
should represent the proper nappe stmcture, has almost
disapjjcarcd .and is being replaced by the acceptance
of eugeosynclinal gravity gliding, either of
the olistostrome type or of a sheet type. This is a
typical example of what I discuss in my paper (Paper
25, Section I) at this Congress.
I have only two specific questions to ask Mr.
Morton. When he refers to the metamorphism, as far
as I understand, there is a lower series, Permian (pos-

y ^ •
d
t
THE OEOLOOY OF OMAN
sibly Triassic), which has a low-grade regional metaniorjjliisni.
This is separated by a non-metamorphic
Mesozoic interval from a low-grade Uppeir Cretaceous
mct.-vmorphic scries. The latter is probably connected
with the Semail effusiva. Distribution of this metamorphism
in the Oman mountains seems rather
strange, but it coincides with similar facts we know
of other mountain systems, such as the Alpine ophiolite
belts, where a kind of selective metamorphism
takes place.
So my question is: Are these metamorphics of the
same origin or do they represent two periods of metamorphism
and consequently two periods of mountain
formation?
D. M. MORTON replies. I would like to thank Dr.
Kuendig for his remarks and answer his question regarding
the two metamorphisms in the Oman range.
Thf lowermost metairiorphisin in the Permian
(possibly Triassic—I would say Permian) beds increases
in degree from the top downward. But it has
been suggested that it results from or could result
from underthmsting of a peneplaned basement I do
not and cannot enlarge on that theory which will be
stated elsewhere at a future date.
The uppermost metamorphism which occurs in the
Upper Cretaceous beds decreases in degree from the
top downwards, and it is believed to result perhaps
from the drag of a viscous Semail extrusion. It is
furthermore beUcved that the two metamorphisms
occurred at different dates.
F. E. WELLINGS (Iraq Petroleum Company, Ltd.,
London, England). 1 would like to say a few words
about the oil prospects in this new country of Oman.
Undl we went in there, it was entirely virgin territory
for non-Arabians including geologists. In fact, it is
the first desert country I have ever been in without
seeing somebody's previous car tracks. I would .like
to pay tribute to Mr. Morton, who first went there
with mc, for the amount of geological work they have
done in this short period of just four years.
Fnhud, the first well wc drove in the middle of the
dfsrrt, was a beautiful andclinc, an absolute natural,
which would have been drilled anytime before this
if one could have got to it. Unfortunately, it was a
dry hole except for some minor shows in the Jurassic,
Triassic and Peratiian. Because the stratigraphy was
unpromising, we did not drill the neighboring andclines
and decided to drill something geophysical
293
elsewhere. Wc knew there were a number of exposed
piercement-type salt plugs which bring up rocks
which are certainly early Paleozoic, if not Cambrian,
in age, though no fossils have been found. Wc drilled
on a seismic anticline, and that proved to be no
better.
In the neighboring Sheikdom of Dhofar, Richfield-
Citics Service did not have much better luck. They
found some oil in a sand about 2000 feet deep, but it
is so far non-commercial. They were also the first
non-Arabianis to get into this country.
The third area which we are now exploring by
geophysics is the Easi Aden Protectorate, more commonly
known as the Hadramaut. There are no oil
indications there at the surface, but we have found
some gravity anomalies and we propose to put some
seismic crews there this autumn.
The nearest discovery in this great territory is
along the Trucial Coast and in the Arabian Gulf. We
have drilled five different seismic stmcturcs along
the Tmcial Coast without getting any oil. The Arab
zone, which is the producing horizon in Arabia and
in Qatar is not typically developed there, but more
recently BP and CFB drilled a seismic stmcture in
the sea bed near the Island of Das and they discovered
oil in the Lower Cretaceous limestone, a
formation which hitherto has not been productive
anywhere in the Penian Gulf area.
We are still tesdng gas and condensate in a well of
our own at Murban.
W. PHtLLiPS| (Economic Advisor to the Sultan of
Oman, New York, N. Y., US.A.). On behalf of
Sultan Said Ben Tymour, Sultan of Oman, I want to
add one or two remarks to the very distinguished
speakers who have spoken to us this morning, and
very adequately described the geology of the Sultanate
of Oman. I want to mention two or three points
which more or less fall into my own special province
as an archaeological explorer of Oman and economic
advisor. On behalf of the Directors of the American
Foundadon for {he Study of Man, wc have conducted
extensive archaeological expeditions throughout this
endre area for many years before I introduced Cities
Service and Ricihficld into the Province of Dhofar on
behalf of the corporation of which I am president.
Cities Service and Richfield were not the first foreigners
in the Dhofar. Oman itself was extensively explored
by American missionaries beginning in 1890.

G
C:
294 FIFTH WORLD PETROLEUM CONGRESS
Dhofar is not a sheikdom but one of many prov- fortunately have had to make my living as a biblical
inces which arc ruled by the Sultan of Oman. I archaeologist. But I did want to straighten out a few
might also say that Oman has enjoyed treaty relations of these points with regard to the political and
with die United States dating from 1834, when our cultural anthropological aspect of the Sultanate of
own President Andrew Jackson helped to negotiate a Oman,
treaty with the great Said the Great. F. E. WELLINGS. My use of the word "sheikdom"
Please do not interpret these remaks as in any way for Dhofar was a slip of the tongue. I know it is a
being cridcal. I was trained as a geologist, but un- piovince of Oman.

,C!
JOURNAL OF,GEOPIIYSICAL RESliARCH, VOL. 86, NO. B4, PAGES 26fil-2()72; APRIL I0.'l'>81
Structure ofthe Sheeted Dike Complex ofthe Samail Ophiolite Near Ibra, Oman
, .JOHN S. PALLISTER'
: University of California,:Sanla Barbara, California 93106
The shecied dike complex is a regionally mappable geologic unil with a consistent position in the Samail
ophiolite stratigraphy. Discontinuous exposures of ihe complex in the Ibra area of the southeast'
Oman Mountains provide siruciural data thai allow reconsiruciiori of a paleo-spreading ridge axis of
• 347° for the region and suggests a maximum spreading widih of 275 km for the ophiolite. Contact rela- '
, tions within the well-exposed Al Ahmadi section indicate thai the complex was formed by multiple parallel
intrusion over a narrow zone at the paleo-ridge axis. Split dikes are abundant; facing directions in- '
dicaie a spreading ridge southwest of the present outcrop area, in conflict wiih other spreading axis direc-".
: tion indicators,'" '••., ':.'•• -,, ": . ; ';; ',. ;• ' '• '••.'•-. •, '•;
'• '.^ ••••'. '••••r^'-'^'i.'-IjyTRODUCTION
Mafic sheeted dike complexes are essential members of
complete ophiolite stiites, lying stratigraphically above gab-,
broic rocks and below pillowed lava flows (Penrose Conference
definition) [Gfo///w«, 1972]. They consist of series of
parallel intrusive sheets that were successively injected as
feeders for the overlying lavas. The presence of a well-developed
sheeted dike coropici = is generally regarded as prima
facie evidence of ophiolite formation at an oceanic spreading
axis [Gass, I96pfitobres.andVine, 1911, Church. 1912; Smew-{
ing et al, 1975; Coleman: 1911; Dewey and Kidd. 1911].' .
The dominant sheetlag attitude of a'dike complex iiidicates
the orientation of the paleo-spreading axis relative to the
other members ofthe ophiolite suite. This provides a relative
age framework for petrologic and geophysical studies, based .
on the seafloor spreading model. Over large regions, divergent
sheeting attitudes reveal structural discontinuities in an ophiolite
nappe, such as paleortransfonii faults [Moores and Vine,
l91l\Smewing, 1919]. '•': ' ::^' ;"/ ' r ;'
Statistical Studies of the facing directions of dike chill marr
gins in the Troodos, Belts Cove, and Smartville ophiolites,
and computer-aided simulation of dike dlsiributions [Kidd
andCann, 1914; Kidd, 1977] provide details of the ocean floor
spreading model and suggest paleo-spreading ridge orientations.
The.distribution of'one-way chilling' is used by Kidd
and Cann to deduce ophiolite symmetry (which side of a
paleo-ocean basin is represented by an ophiolite). In addition
' to one-way chilling, the orientation of diabase sheeting with
respect to other members of the ophiolite suite may be.usisd to
indicate ophiolite symmetry [Cann, 1914;'Jackson el ai, 1915].
GEOGRAPHIC, OcctjRRENCE ANC» OEOLOGIC RELATIONS
General Features ••'.:'•- •' : ,..'>':,• '
' The sheeted dike complex is a regionally mappable unit,
with a consistent stratigraphic posuion throughout the Samail
ophiolite (Figure 1). It overlies high-level gabbro and penetrates
upward into and locally feeds.subniarine pillow lava
[Glennie el ai,l91A; Hopson,et a/., 1981 J. Except for thin
zones near the'contacts the complex consists almost entirely of
parallelto subparallel dikes pf chiefly diabasic texture and basaltic
composition. In addition, leucocratic (diorite to plagiogranite),
dikes are a.minorconstitueiit of the complex. Lo-
' ' Now at U.S. Geological Survey, American Embassy, APO New
York 09697; ''' V,'. " :'^'- .•...:> ,^ ;
Copyright © 1981 bythe American Geophysical Union.
Fipcr number SOB 1613. ',;.'•,' ':'
0O48-0227/8l/O8OB-16l3$Ol,0O' • '. ' -'
cal,variations in attitude occur, but the dominant attitude is
northwesterly strike and steep dip for most outcrops measured
to date along the length ofthe Samail ophioIite-Oman Mountains
chain (Figure I)..
' The sheeted dike complex is discontinuously exposed in the
foothills ofthe mountains that rim the Ibra Valley and as ero-
. sional remnants surrounded by alluvium in the valley floor
and in the region south of Ibra. The Ibra Valley occupies the
core of a syncline (the Ibra 'Valley syncline, Figure 2) with
lower members of the stratigraphy exposed in both the north
(Jabal Dimh) and south flanks. The ophioUte.section is greatly
thinned along the southem flank of the syncline, and the
structure is complicated by a domal uplift (the Ibra Dome,
Figure 2^) possibly, related to salt Jdiapirism {Man^/uia/ii and
Cpleman\l9Sl]. ^
Luyendyk et ai (1980) suggest that the Ibra Valley syncUne
is actually a southward dipping horaocUne that is reverse
faulted along the margin ofthe Ibra dome. This model is not
consistent with the geologic outcrop pattern, and contact relations
in the Ibra valley. The southem flank of the syncline is
complicated by a faulted,contact between cumulus gabbro
and serpentinized peridotite that cuts put most of the plutonic
section of the ophiolite. However, the unfaulted sequence:
volcanic rocks —» dike complex —• plagiogranite -• high-level
gabbro ^ ciimulus gabbro, repeated in both tbe north and
south flanks of the eastern Ibra valley,,indicates a synclinal
structure (Figure la).. '••- '
The, term 'sheeted' is used following Wilson' and Ingham
(19S9] to describe the repetition of parallel dikes (geometric
..sheets) in the direction normal to the dike planes. This yields
an apparent stratified outcrop appearance (Figure 3a). Tbe
sheeted dike unit is referred to as a 'complex' because'the intrusive
sequisnce is complicated. Multiple intrusion in tbe
sarne planar orientation has resulted in dike.spUtting. Onesided
dikes are separated from their mates by younger dikes
that commonly are also split. It is possible to establish reladve
age relations at a small scale between adjacent or spUt dikes;
however, age relations can rarely be determined at a larger
scale except between the main parallercluster and rare crosscutting
dikes. : 1 , "v
The dike complex sheeting direction in most Ibra Valley
outcrops trends N-S to NW-SE such that more than 30 km of
exposure roughly perpendicular to strike is represented. However,
individual outcrops tend to be small and are commonly
elongated parallel to dike strike, limiting continuous exposures
across strike to less than 100 ra. The stratigraphic.thickness of
the dike complex is estimated to be 1.2-1.6 km in cross sec-
2661

iHiiiimM'itMi^u'mMJw^jw
2062 PALLISTER: STRUCTURE OF THE SHEETED DIKE COMPLEX
26'N
.•f
y
^y^mi
p m •';•..•.:->-.
:' 0m'dd'
•••OA
'• V '
.•;GULfOr OMAN.
V, " yr/-^•"'X
dy.^P •;:'^ -ill ^^"^'9-, f^pp •\-' •
'-.••'•'-'\:i'^ .!'.,"'..i;.,,;'---^ ' '• .'" -.Mpp^.^'''""' ••\-" '.
.SAMAIL OmiOLITE"
iTi in
Fig. I. Index mapi showing preseni outcrop area of the Samail ophi-
'• olite (stippl«d),in the Oman Mountains, Sultanate of Oman.
tions constructed through the cnistal section ofthe ophiolite
in the central Ibra Valley and Jabal Dixnh (Figure 2a). /,
\ Contdclsy.f•;.'•' :"':_•• ''''•,'/.'•''. •••••'•' ..-. • ••-.••\'y-^ • ";-
•• The upper contact ofthe dike complex with the overlyiing
pillow lava is exposed in only a few locahties io the Ibra Valr
ley (Figure 2a). Outcrops of r 100% dike rock arc separated by
only a few tens of meters from pillow lava containing few
dikes. Therefore,;the upper contact of the sheeted complex is
considered to be an abrupt transition,, In regions where the
upper section of the ophiolite is better exposed, the dikeis are
subvertical and collectively form the feeder to the overlying
bedded lavas of the, Samail ophiolite [Glennie el ai, 1974].
The contact of the'sheeted dike complex with the underlying
high-level gabbro is characterized by an abrupt transition
from —100% dikes toplutonic rock containing few dikes
over a distance of only a few tens of meters. The contact zone
is commonly intruded by small, typically oth strike and dip.
There are also domains of similar attitude, including several
groups of localities on the north side of the Ibra Valley synchne,
a cluster northwest of Batin, a group west of Al Ahmadi,
and several clusters south of Ibra. Structural control is best for
the localities in the north limb of the Ibra Valley syncline.
This group is treated as a separate subset of the data.
The structural correction procedure is illustrated m Figure

« • ; •
P
t:
I-
r
•!"••
P
PALLISTER: STRUCTURE OF THE SHEETED DIKE COMI'LEX 2603 '
. 'i Fig. 2

26(4 PALLISTLR STRUCTURL OF THI Sill ETED DIKE COMPI EX
c- ddcT
p,

'^•"., . **s s
"''•-'''"^ Sri^ac.
" '"^^^'ODiK,

.
2666:
P\LLisrr» brRuruRi or Tin Siiiini;) OIKI UIMUIX
• ry'\" :. /•:'yipy y\
^^^TTT^KTlhotivfeh) «n°^'*l wL,„ Mounuins.
H.h of the ophioliie. The |
loite3»i The .oieailu>6 «">",•;a 69 m y-ot""' :
,e„„d ..lo»B Ite'P«' »,„ ,.p„«»>. Mf ;'5.7„,,w."
. ,.esie.p.ou.eofthcshce,^aiKc^;vi^-.^,
SS.:SSS:s:?i-

""-"^^""-- -.I,:„.„„„
I' &
Fig. 3J Chifl margin of dijb

2668 PALLISTER: STRUCTURE OI TIH-. SMEETI.U DIKI- CDMIMEX
Fig. 3/. Diabase septa (indicated by the '4") between chill margins of adjacent dikes (Al Ahmadi outcrop).
The parallel dike-against-dike character, regional extent,
and basaltic composition ofthe dike complex, indicate formation
in an elongate zone of prolonged uniaxial tension and basaltic
magmatism, i.e., a divergent plate boundary. The association
of submarine pillow lavas intercalated with pelagic
sediments and overlain by Fe-Mn umbers [Hopson et al,
19K1] as well as palinspastic recon.siructions ofthe Samail and
Hawasina nappe sequence [Glennie et al, 1974; Coleman,
1981J indicate formation in a deep ocean environment, far
from conlinental margins. Together, these features are strong
evidence for ophiolite formation at a- mid-ocean spreading
ridge. The following features oflhe axial intrusion process arc
indicated by the physical characteristics ofthe Al Ahmadi section
shown diagramatically in Figure 6 and listed in Table I:
1, The complex originated by multiple, parallel-subparallel
intrusion, which resulted in dike splitting.
2. Dike splitting was not localized along the center of each
succe.s.sive dike. Two-sided dikes are common and often are
intruded between other dikes. In addition, there is considerable
variation in split dike width, suggesting that, except for
dike margins, there were no other preferred planes of weaknes.s
to localize inirusion. The process of dike splitting is
clearly not related to intrusion along the still hot, weak core of
the host dike by each subsequent intrusion. Sleep [191&\ calcu-
h ,.i\*. '^ y^ f^^^. '" ' \fW.^-'- * j%Bi'i5'°" -^-ia
Fig. 3g.. Low-angle cross-cutung dike (indicated, by the '3'). Note mottled alteration of core of dike 3 and spheruliiic alteration
of dike 5 (Al Ahmadi outcrop).

PALLISTER: STRUCTURE OF THI SUM rto DIKE CO'MPIIX 2669
.:,..,-.-.•^ys'^.-yyiy-y;':-•':••-•"•- ".''••• '••' "'»
':. Fig. 4..:; Lambert equal-area lower-hemisphere projectioiu showing poles to dike planes (a) All dikes, pnor to rotation
' (6) Nprthrlimb subset, prior lo rotation; (c) All dikes corrected (a.4iiun.j't'i IWIN..,. .^-t.
,i-80
the roof of the chamber crystallized to form the high-level
gabbro
5 The high percentage of two-sided dikes that intruded
along the margins of other dikes (—25% relative to a predicted
value of 13% [Kidd, 1977]) suggests that the dike margms were
not completely annealed at the .depth represented by the Al
: Ahmadi outcrop. Dike-niargin jointing'controlled the axis of
ihjection'for many dikes. * '. L
. 6. The apparent NE cpre-tp-margin facing preference of
chiU margins siiggests that the paleo-spreading axis, was southwest
of the Al Ahmadi outcrop. This result is in conflict with
other indicators of ophiolite symmetry such'as the inclination
of cumulus layering in the plutonic rocks [Pallister and Hopson.
1981] and dike chiU statistics from northern Oman (J. D.
Smewing, personal communication; 1980), but in agreement
with,; symmetry arguments based oh .'peridotite. petrofabrics'.
[Wrfier anrf Co/ewan, 1981]. ; 1 :. ,.
The symmetry results from the Al Ahmadi outcrop are regarded
as highly speculative, because the western: Ibra Valley
is structurally complex, and the sheeting has an anomalously
shallow dip and could conceivably be overturned. More

M^.
c
2670 PALLISTER STRUCTURE OF THL SHI FIED DIKI COMPLIX
Id'N
• plogiooranite oge locality
Strait of Hormuz
:.-.^

i'i '
p.'.
I',.
•
; •;
i)V V- 'T'^
2 /
",?"'
^:;:-%/;f.4 ,:•,:
^.,;,:.374,-;|r:i
/^l^ffi:?
PALLISTER SPRUCTURF OI TIII SHIETID DIKE COMFLFX.: • 2671
2 3 4
_J I I I L \ ,-
"•••"•'c_
•"•:,;
3
1
^
5 . 4
7b"' •,
d -..
• »c.-,..
ba 8 b ' *°
6 • 7
-I L_ L_
jirau
/'
8 , , ,:; '9:'•••• lOm
-I ' I • I ' ' 1 • u
23 25 "• 2

f'
2672 PALLISTER STRUCTURE or THE SHEETFD DIKE COMPLEX
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, 5oc./tm::£u/A, AS; 507-530, 1977. :f,;;:;^';. • Manghanani, M, H.* and R. G. Coleman, Gravity profiles across the , t •
Barrett, D. L.,:and F. Aumento, The raid-Atlantic ridge;near 45°N,', Samail ophiolite, Oman,V. Geophys. Res., 86, this issue, 1981.
XL Seismic velocity, density, and layering of the crust, Can. J.'-i
Moores, E. M., and F, J.- Vine, Troodos massif, Cyprus and other oph­
£flrl/i SCI,. 7; 1117-1124, 1970;' : ^''^'''^
iolites as oceanic crust: Evaluations and implications, Philos. Trans
Boudier, F., and R. G. Coleman, Cross section through the peridotite ' ,• R. Soc. London, Ser A, 268, 443-466, 1911.
in the Samail ophiplite, southeastern Oman Mountains, / Geophys. Pallister, J, S., and C -A, Hopsoni Samail ophiolite plutonic suite
/?w., S6,-ihis issue, 1981. •• •-:':,'••;''''r ,^ ,••':•;'. "•'' ••^' ' , Field relations, phase variation, and cryptic variation and layering,
Cann, J, R,, A model for ocean crustal structure developed,,/?. Astron. and a model ofa spreading,ridge magma; chamber, / Geophyi
'..• Soc, Geophys. J.. 39. 169-W, 1974.-:' v :• ;' •,; v ); '.•*:'' '; ,:>•/?«., S(i, this issue, 1981, , . ••'.:
..Church, W, R„ Ophiolite:, Its definition, origin as:oceanic crust, and : ;"Pallister; J. S., and R. J. Knight, Rare-earth element geochemistry of
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Coleman, R. G,, Ophiolites,'Ancient Oceanic Lithosphere?, edited by P.;; . East Pacific Rise crest, Geology. 3, 77-80, 1975, / •
•J. Wyllie. 229 pp.i;Springer!,New York, 1977?:'^ '/^y^fi^ p. 'yM ^ .;Rea, D. K.,,Asymmetric sea-floor spreading andanontransform axis
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Geop/i>j.'/?«v*(S^'this,issue, 1981,. " ;f •;'•'*':'^ , "V ip89.'s36-i44, i9m ';-p'yy'\-- '-,.•. ••fp ' •
Dewey, J F.,'and W. S. F. Kidd, Geometry of plate accretion,,Geo/. I, Schmidt,' V. AM On theiuse of orthogonal transformations in' the re-
•••' Soc, Am. Buli:.'»8i 96(^66, 1911/^'ci:; 'i'p;'pyip:i''i'i'" • "P ,- , 'duction of paleomagnetic datai/,'Gwmflg. Geoeleclr.; 26. 475-486,
, Gass. I, G., Is the Troodos massif of CyprusafragmehtofMesozoic ',''•..1974. '.';; ','•, iy.-':p':'.i'.:pp.r- • ?'• ;. •'• ' .' ' •
ocean floor?, Wo/ure;;7?p,'39-4271968.''' :^''-'.:-yi '•:^ fp-';" ./Sleep, N. H.'.'Thermal structure and.kinematics, of mid-ocean iidge
Geotimes, Penrose field;Conference on ophiolites,,/?, 24^25i 1972. ' axis, some implications to basaltic volcanism, Geophys. Res. Lett, 5,
Glennie, K. W:; M: G, A'Boeuf, M. ,W. HughsK:iarke. M. Moody- , " 4^-42S,'i91S.:'.''''.'::'-y'yp):Ti^: '••'yv'- ..• ,-':
Siuart.'W; F. H. Pilaar.'andB.M. Reinhardt, Geology of the Oman 'Smewing, J. D,, An Upper Cretaceous ridge-transform intersection in
Mounuins, Part;! (text). Part 2,(tables aiid,illustrations),,Part 3 (en- : ;;, the Oman ophiolite,'paper presented ai the International .Ophiolite
; clos\ins)ippn: Ned! Geol Mijbouwk, Genoot. Vern., 31, 423, 1974.:, ''. Symposium, Geol. Surv:Dep., Nicosia, Cyprus,-1979. ••
• Hopson; Ci'A-'ijR.G;,Coleman, R, T. Gregory,'-/. S, Pallister, and E. ; .Smewing,'J. D'., K. O. Siihonian; and 1. G. Gass,; Metabasalts from
-;,H, Bailey, Geologic section through' the Samail ophiolite and asso-;,' ,';•. -the Troodos massif, Cypms; Genetic implication deduced from pe-
'; dated rocks along a;Muscat-Ibra transect,, sputhmtcrii

,-»i^"
e
JOURNAL OF GEOPHYSICAL RLSEARCH, VOL 86, NO, B4, PAGES 2509r-2325, APRIL 10, 1981
Gravity Profiles Across the Samail Ophiolite, Oman
MuRLi H MANGHNANI ,,;"...'-'
Hawan Institute of Geophysics, University of Hawaii, Honolulu, Hawaii96822 ,v.-f "i
ROBERT G COLEMAN " '; '
U S Geological Survey, Menlo Park, California 94025 : : V; " *
Four hundred and sixty gravity stations have been established over the Samail ophiolite and adjacent
umts exposed in the Oman Mountains The Bouguer anomaly pattern follows more or less parallel to
ophiolite exposures. Along the coastal areas die Bouguer anomaly values range from -I-20 to +140 mGal
and. increase north ward. Four gravity profiles across the ophiolite are correlated with known geology and
structure. The main gravity profile extending 325 km northward from Ibra to Muscat and into the Gulf
of Oinan ishows two positive Bouguer anomalies (+85 over the southern folded ophioUte nappe and +110!mGal
near the shoreline at Muscat) that are associated with two nappes of tabular form. The nappes are
nearly continuous, and there is ho evidence that they are rooted in the mantle. The gravity high across
the southern nappe is centered over the axis ofthe synform (maximum nappe thickness); its position over
the gabbro-peridotite contact rather than over the peridotite suggests extensive serpentinization ofthe pendolite.
At the southem end ofthe profile, in the Ibra Dome area, the negative Bouguer anomaly (-10 to •
-15 mGal) is interpreted as an,Infracambrian salt piercement similar to those in the Zagros fold belt. '
Geologic modeling of the inain gravity profile provides a good correlation in terms of known thicknesses -
of the mappable ophiolite units. The nature of the gravity anomaly across the continental ihargin indicates
a transition from ~42-kni-thick continental crust to a thinner (16-18 km) oceamc crust. The two '
gravity profiles in the north Oman region show a doublet of positive residual Bouguer anomalies (+50 to -
+90 m'Oal), The anomahes, correlate ,weU with imbricated ophiolite exposures, a result of low-angle
thrusting caused by strong conipressive forces. In the absence of imbricate thrasting, the gravity profile in :
the central region has only one large positive residual Bouguer anomaly (+130 mGal). The anomalies of,.
all the four pirofiles are,further analyzed to elucidate the nappe-transport distances. ', ;-, "•-:;, , ' - v •"
INTRODUCTION; AND .GEOLObie. SE-rTING :'^;;;. •; /
The Samail ophiplite is one of the'best exposed ancient oceanic
crustal and upper mantle remnants. It forms a part ofthe
700-km arcuate Otnan Mountain chain in Northern Oman
and United Arab ;Emirates, generally trending NW-SE and
extending from Ras AI,Hadd, the most easterly part of the
, Arabian Peninsiila, to the Musandam Peninsula on the north
, (Figure 1). The ophiolitie represents nearly intact sUces of oceanic
lithosphere that were emplaced (obducted) ysouthwesterwardly
onto the margin of the Arabian platie .during
Late Cretaceous closing pf the Telhyan Ocean.'
Tectonic, emplacement of the Samail ophioUte was prob-
, ably a two-stage event initiated by detachment at a spreading
ridge followed by gravity sliding and thrusting. The thrusting
has produced extensive nappes of pelagic sediments and ophiphtes
that now overUe ,the, autochthonous shelf .carbonate
sediments (mid-Permian to Cenomanian age) and pre-Permian
basement rpcks of the Arabian Peninsula. Late Tertiary
folding and subsequent erosion has exposed ancient oceanic
crustal and upper mantle, sequences of basalt-sheeted dikes-
.gabbro-harzburgite tectonite of variable thickness.
' ,Geplogic studies of the Muscat-Ibra transect (see Figure 1)
have demonstrated that the Samail nappe was detached in an
oceanic environment during the Turonian (~90 m.y.) when
. the Tethyan Ocean began to clo.v*:. The relationships iat the
base of the ophioUte nappes indicate that formation of the.
. metamorphic sole and the; meianging of the.Havvasina pelagic
sediments probably^began on the flanks of an ancient ocean
'ridge wherie the Samail, nappe was detached and then migrated
by thrusting and.gravity sliding toward the Arabian
continerital margin which was.subsiding at that time.
Qipyrtght© 1981 by .the. American Geophysical Union.
Paper number 1B0027.
0148-0227/81/001B-0027$01 00
2509
,. -Figure 1 presents a; simpUfied regional geologic map of
Oman and its environs. One ofthe thickest and best-preserved
sections of the Samail ophiolite is exposed in the southeastern
part of the Oman Mountains. A detailed geologic transect
(r40 km wide) extending 120 km southward from the Gulf of
Oman (Muscat), across the Oman Mountains (Figure 1), has
been mapped in detail by Bailey [1981] and Hopson et ai
[1981]. Here the ophiolite 'stratigraphy' (bottom-to-top) consists
of [Hopson et al, 1981] (I) tectonized peridotite (mainly
regularly foUated harzburgite and discordant dunite) 9-12 km
thick, representing a nearly undisturbed slice' of oceanic
mantle, (2) layered gabbro (3-5 km thick) with a thin (

c
2510 MANGHNANI AND COLEMAN SAMAIL Opiiioini OR^vl^v PROIIIIS
26°-
24 c
22°-
I 1 AAoesfrichfian and Tertiary
L 1 Samail Nappe and Masirah Island
I—-J Hawasina allochthonous unit
^ M Par-autochthonous Sumemi Gp(and Muti Fm)
llJliiu.iLlJ Permian to Late Cretaceous
autochthonous rock units
L;' :,J Pre-AAiddle Permian basement
Fig 1 Simplified geologic map of Oman (after Glennie et at, 1914] The Ibra Muscat geologic transect (indicated by
rectangle) is shown m detail in Figure 5 The transects I-IV shown here represent the four gravity profiles (see also Figure
3)
conducted m northern Oman, transectmg the Samail ophiohte
at several places (Figure 2).,Four gravity profiles (1-IV) are
presented here (Figure 3); Profile I is in.the southeastern region
of the Oman Mountains.-:Profile,II, northwest of Samail
Gap, Ues in the central mountains region; profiles 11 and IV
..are In the northern, mountains region. Of;these four profiles,
one is the 400-km N-S gravity profile made up of the transect
I-I' across the Samail ophiohte from the Ibra area to Muscat
and the mtegration of it with profile I'-I", extending northward
from Muscat into the Gulf of Oman (Figure 3), based on
the gravity data of White and Ross [1979]. The objectives of
the N-S gravity transect (l-l'-I") are (I) to construct, in correlation
with surface mapped geology [Hopson el ai, 1981], a
geological model of the ophiolite body, the underlying crust.

G
MANGHNANI AND COLEMAN SAMAIL OPHIOLITE GRAVIFY PROFILES 2511
56*E
Fig 2 Gravity station location map
and upper mantle, (2) to determme if any other pan ofthe ob-
: ducted ophiohte nappes could be lymg in the Gulf of Oman,
and (3) to investigate the'gravity field'across the continental-;
• oceanic margin for delineating the structural relationship.
Besides gravhy.niodeling of tiransect 1, geological and struc-,
• tural implications of three, more gravity profiles (II, 111, and
TV),, trending :NE-SW across the Sainail ophioUte in the cen-,
tral Oman Mountain' region and ErW in the nprthernmost.
part'of Oman, will be .discussed. ..'•
The major questions addressed in this Study arc (1) do the
ophiolites, remnants;'of the pceanic Uthosphere, have any
: roots? If not, are they allochthonous (transported) slices of the
lithosphere?, (2) Is the serpentinization of peridotites deep:
seated?, (3) what is the variation in depth,to the,Moho across
the continental-oceanic margin along the Ibra-Muscat transect
(profile I)?, and (4) is there also any such remnant of oceanic
criist and.upper manikin the Gulf pf Oman? •;••
''- • ::-':•-'-':•.;•.•''•,'''^^-v.FiELD'METHODS '•;•;/ -,-'v^,^/!:':'.-:--
Gravimetry -y,' 1';^,'': '•',,.:-' ;,'''; '"^. - ,; •.•,•-.: '.'.-
During the months of February and March in 1977 and
1978, 460 stations,were established to transect the Samail ophi-.
; pUte cotnplex in: seyeral regipns in the northern parts of the
Sultanate of Oman and the United Arab Emirates (Figure 2):
By crisscrossing the Oman Mountains by four-wheel drive ve-
; hide as well as on foot along the paved and unpaved roads,
*. riverbeds (wadis), and hiU trails, fotir gravity traverses 70-150
',:km long were taken across the arcuate Samail ophioUte cpm-
' plex., For the north-south gravity profile I through Muscat and
Ibra a helicopter provided by the Omanese Defense Agency
; was used to establish five gravity stations between Saih Hatah
Mountain (south of Muscat) and Wadi Tayan (between Saih
Hatat and Ibra), which enabled a fairly continuous profile. To
minimize terrain effects in the reduction of the gravhy data
.(see next section), stations were established so as to avoid, as
' far as possible, steep reUef surroundings. ,
The La Coste and Romberg gravity meter G-144, whh a
range of over 7000 mGal,.was used,in the present study. The
meler'had a reading accuracy of ±0.01 mGal and a drift rate
of less than 2 mGal per month. All the gravity stations in
Oman and United Arab Emirates were tied to the base station
established at the Seeb International Airport, Muscat. The
value of the Seeb Station (978.9252 Gals) is based on two ties
made with the gravity station ait Santa Cruz Airport, Bombay,
India {g =• 978.6589 Gals) standardized with respect to Potsdam
{g =• 981.2740 Gals) on-the first-order international

IC
.n
'.']
-"1
.i
-1
2512
MANGHNANI AND COLEMAN: SAMAIL OPHIOLITE: GRAVITY PROPILES
gravity network [Manghnani and Woollard, 1963]. One tie'
was directly made by air travel between Muscat and Bombay,
and the second was: obtained by air travel via Dubai and
Sharjah (United Arab Emirates). The reoccupation of Sharjah
Station, WA 2075, [Woollard and Rose, 19(>3], provided a'
check on the derived 'g* value of the Seeb Airport station,
, With Seeb Airport .station as the base station, several sub-
• base stations were established for each of the traverses. The
number of ties between the Seeb and subbase stations varied
from 2 to 4. On a daily basis the'gravity stations were established
in the sequence: ABCDE:-;. A, or, whenever possible,
in a leapfrog fashion: ABCDECBA: In view ofthe very smaU
drift in the gravity meter,; both modes of gravity coverage
proved to be adequate, as jiidged from,very smaU closure er- •
Tors (less than 0.10: mGal/d.loraJitypical traverse). , pp-,. -
Altimeiry • -' ../'.iY^'yyy:p''''yi i''''. '•'••:''-Z^ h'--- .•^H'-.?'.'^";';.'
Detailed topographic maps of Oinan are not available. The
best possible general tppdgraphic information could be deprived
from British Air Force air nautical maps on a scale of
1:100,000 with a contour interval pf 100 ft (33 m). Benchmark
elevatiotis were alsp'Iacking In the'areas of interest.,jFortu-;
nately, recent highway, construction surveys provided reliable
leveling data and-benchmarks for establishing altimeiry base
stations to which;thc:gravity stations were tied. Two types of^
altimeters were ^useditp determine the elevations of all thcj
gravity stations:;,WaUace and.:Tiernan:a:nd Negretti-Zainbra'!
precision barometen. Barometric, and dry and wet biUb;tem-,
perature readings ;Wci:e taken :at each of the gravity stations,;;;
Occupa.tion of severdiiighway,engineerhig altimeiry survey;;
stations prpvided good, checks on the caUbration of the ba-('
rometer, aiding in the. reduaipn ofipiir altimeiry data.as.,ex:',
:• -plained below/'?.^;-';,.>'-' ' '"•••'- --Jy^'-i. ':',."'',--'v'" ;;r''--'••'- p}':\
,, The altimeter data .were reduced by;standard procediires,
The altitude difference between .two poinU(/ii,Aj), being a
" function of the pressure difference (PuPi), observed temperatures
and humidities (paniai pressures of water vapor), and ,
gravity (approximate latitude •> of the area), was determmed
from the formula
/i2 - A, = AA (m meters) « 18,400 log.o — (I + 0 00366/J
\P2J
(I +O378W0(I + 0 00264 cos 2(i) pressures at the two elevations: _
W'
(gJ/Pi) + (gi/Pa)
>• . 'y'2'{ • ".;••;
The terms/e,:and'cj calculated from e «=» e' T- 0.000660 (1 +
0.00115t')p{l- f)-y/herei&nd f are dry bulb readings (°C), c
andp are-ui:nullibars,;andy is the saturation vapor pressure
in milUbars. The latter is obtained from functional tables relating
saturation vapor pressure and wet bulb temperaiure. ,.
The resulting elevations of the stations are considered to be
accurate withini±5in."In the cases where the road engineering
level values areiised, the accuracy ofthe station elevadon is
within ±1 m
' Gravity Data Reduction Procedures • ' .
In reduction oflhe gravity data, first the gravimeter drift
was removed; for most traverses the drift was linear and less
Ihain 0. f mGal/d. The observed gravity values were corrected
for the earthtide variations using the Nautical Almanac and
the tidal effect tables [Damrel, 1951]. Because of lack of detailed
topographic maps, terrain corrections were not applied.
Land topography along the four gravity transects is generally
Smooth. Exaggerated topography (x20) along profile 1 is
shown in Figure 6. (Note that topography, along profiles II to
IV, shpwn in the respective geologic sections, Figures 8,9, and
10, have been verticaUy exaggerated only 2.5 times.) Highest
• elevations encountered along profiles I to IV are 910,686, 600,
and 366 m, respectively. Maximum topographic reUef encountered
was along profile 1: about 200-300 m within a radius of
400 m. The maximum uncorrected terrain eflect in such cases,
as estimated from a trigonometric method utilizing the limited
known sjwt peak and ,valley.elevations, did not exceed 3
-niGals.. • ;, ' . ' ; •:-' '••- ••"'
. For all of the land gravity, stations the frecrair as weU as
simple Bouguer anomahes were calculated. A density of 2.67
g/cih' was assumed. For the; study of the geological model
from the gravity profile T a land topography version of the
/two-dimensional computational inethod of Talwani et ai
[1959] was used. In employing this method the most direct ap­
proach woiild, be to use the free-air gravity anomaly and con-
• sider the. topography aboye.sea,level to.be one ofthe polygon
bodies! It is diflicult, however, to interpret the free-air anom-
;aly by inspection in terms of anonialpus masses below sea
level For this reason, an approximation to a 'complete' or topography-corrected
Bouguer anomaly was calculated. The
two-dimensional topography polygon gravity, effect at each
land observation site was subtracted from the corresponding
free-air anomaly. The resulting anomaly representation is easier
to interpret because the eflect of the topography above sea
level has been stripped away. This then permitted a modified
method of interpretation, in which the elevated land gravity
sues were employed in the iwp-diihensional analysis, but the
Uipography above sea level was not included as one ofthe polygons.
The 'complete', Bouguer anomaly was the pne to
which the effects of the anomalous masses below sea' level
were fitted. These complete Bouguer anomalies along the land
portion (l-F) were combined whh the free-air gravity anomalies
at sea (I'-I") to comprise the profile.corresponding to the
N-S.geologic model of the section IbrarMuscat-Gulf of Oman
(see'Figure 6).;'-^ •. ,:. .'l..;.-'';*:,:,-'? :^';;.,: ;:.':,'i;,'.;:'.^r.;---.';'
DISCUSSION'. OF'-RESULTS ''^'^•;:'".';'/'', •
Overview of the Gravity Field .;. .:Ti \ :• y. \- "-';
in Oman Mountains • • ' '.-^ '',-.. \
Figure 3 shows the regional Bpuguer anomaly map of
northern Oman based on the 460 gravity station locations
which are shown in Figure 2. In view of the regional geologic
map (Figure I), the main features of the Bouguer anomaly
map are as follows; >,;;,;;,
1. The trends of the Bouguer anomaly contours follow
more or less parallel to the Samail ophiolite exposures. The
regional gradient of the Bouguer anomaly is nearly east to
west and varies from —0.8 to — 1.2'mGal/km in the central
and northern Oman Mountains. The gravitational signatures
across tbe Samail ophioUte nappe structures are marked by
high positive Bouguer anomahes (+75 to+140 mGal).
2. Along the northern Omanese coast, the Bouguer anom-

G
.'^''
/y
M'
23'
N
22'
MANGHNANI AND COLIMAN SAMAIL OPHIOLITI GRAVITY PROFILES '•:' 2513
Bouguer Anomaly on Lond
Free-oir Anomaly at Sea
56'E 57* 58* S9«E 60' 22"
Fig 3 Map showing Bouguer anomaly contours on Und and free-air anomaly contours at sea The manne data are
taken from While and Ross (1979) Locauons of the four gravity profiles, I-IV, are also shown
aly values are positive,, ranging from +20 to as high as +140
mGal. In general,;near the northern end,bftheSamail ophiolite,
the Bouguer values along the coaist increase from +20 to
+ 140 mGal northward from Sohar to Khawr Fakkah; the
value at the coastline near Khawr Fakkah is the highest (+140
, mGal); In a;nother:localized coastal area, near Muscat (at I',
Figure, 3)jthe,,Bouguer: anomaly value is also high (+110
mGal);;.;:''. - -^ppp' P'i, -'' ";•: '"''"•"^': '-,.. "'' ••'.'''"•'•"•'
3. .Whereas in,the central region,there is one main elongated
positive Bpiigiier anomaly trending paraUel to ophioUte
exposures, there are, at least two such trends of gravity high in
the north as a result; pfiinbricatelhrusting of pphioUte nappes,
;(Figure,3).-•;-,', ,-•:i'v'.•-.;;'--• -.i'. ';>,'•,'
4. There Ls a marked break in the Bouguer anomaly contour
trends in the SamaU Gap region, between Jabal Akhdar
and Saih Hatat, and some 100 km southwest of Muscat (Figures
I and 3). This!region,,separating the southeastern and
central Om^inMoiintain areas, represents a synform on the
east flank of Jabal Akhdar (Samail Gap) such that the ophiolites
northand south of; this structure could have been connected
pnor to this pre-Late Tertiary foldmg [Glennie et al,
1974] The high positive anomaly (+120 mGal) southeast of
Samail.Gap is caused by another discoimecied ophiolite
nappe and associated igneous intrusives. Apparently this
high is related to that in the.Ibra dome area (farther, southeast);
the break and the gravity low in between ihe two highs
are pf secondary origin—i.e.,- due tp'updpming and erosion of
the underlying Saih Hatat rocks.
5. Northwest of the SamaU Gap, in the central and northem
mountain areas, traversing NE-SW landward from the
coast across the pphiolite sequence (volcanics-sheeted dikesgabbro-peridotite),
the Bouguer anomaUes gradually increase
to a maximum value of about +70 to +140 mGal over a major
section of the syncUnaUy folded ophioUte nappe (in spite
of the fact that elevation increases), foUowed by a decrease
and again an increase. Such doublets of Bouguer anomaly
(two highs and a low in between) are consistent wilh outcrop
pattern of the Samail ophioUte.
6. In northern Oman, westward of the Samail ophioUte
into the United Arab Emirates and southwestward ofthe Batinah
coast, across the central Oman Mountains into the intenor
of Oman, the Bouguer anomaUes become increasingly

.^
^
-1
" J
i'
^ji
I
2514
23«30' -
22''30'
57°30 E
GRAVITY STATION
AND SIMPLIFIED
GEOLOGICAL MAP
LEGEND
9.
FK
Quaternary
MANGHNANI AND COLIMAN SAMAIL OPHIOLITE: GRAVITY PROFILES
Late Cretoceous Tertiary
Shollow wofer L S
^'c'"] Samail nappe
, •, [< 1 Cenomanian Ophiolite
-* A 4 *
58" 58°30'"--
Hawasina nappe
Permian to Late Cretaceous
Pelagic Sediments '
Autochthonous shelf ''^
Corbonates, Perrnion to
A^id Cretaceous
Soih Holat basement
Pre-Permian
59''15'
24"
23° 30'
22* N
22'N
57'20'E 58" 58*30': 59° 59° 15'
Fig 4 Simplified geologic map ofthe Ibra-Muscat transect together with gravity station coverage and the gravity profile
negative (-50 to -100 mOal) In most cases, these negative
anomaUes can be explamed by the thick section of Late Cretaceous
sedunents deposited on. the Arabian plate margin
prior to the emplacemeiit of the Samail nappes (Figures 8-10).
Free-Air Gravity Ariomdlia.;^:o:y ...-Jl;.;'p:, :i-
•in the.Gulf of.Oman^^ypijyyyy: :.-''\^.'. ''•'•'„ r>-.'';,
.Free-air anpnialy. contours for the. pertinent area in the
western Gulf of Oman, adapted from While and Ross [1979],
-(,-.;'.
M . •'• • i ' ',;-.-• - ' ! • • - • • •' ' - y . .
23'
22° 30'
are shown in Figure 3. AU basic data for offshore gravity stations
along profile I'-I" are from the Atlantis II cruise (D.
ROSS, personal communication, 1980). The mam features of
that study mvolving gravity, magnetic, and seismic studies are
that the continental margin here is probably a passive one
with no differential movement between the (Arabian) conlinental
plate and the oceanic crust in the Gulf of Oman [ White
and Ross, 1979], The closed contours of large, negative free-air
anomalies (to -100 to -120 mGal) encountered some 120-

C 23''45
23°30
MANGHNANI AND COLEM\N SAMAIL OPHIOLITE GRAVITY PROHIES 2SI5
ss-ao E 58''45
GULF OF OMAN
23'15 23''15
23°-
22''45-
22''30N'
\ ^ ' ' ^ * " * 11*1 nil IS*. ^1 lilt I > * * » •
li'AS
23'"30
22''45'
-22°30N
0 Quaternary
(alluvium)
lA'.l.y Maestrichtian and Tertiary
Samail Nappe
1 ^J Volcanic member
(basalt)
IRD Sheeted dike
JHGJ High-level gabbro
(massive gabbro)
LSJ Layered gabbro
:,?,"] Ultramafic
(harzburgite, tectonite)
H ' Hawasina (allochthonous)
B°
(pelagic Is, shales, chert)
A A. A A A A
Autochthonous shelf
carbonates
Quartzite, dolomite
greenstone, calc-schist
;-•',.;, -'i.'. ,. -"
ppp-'i-."'---'
-"'•-,-.'•!;',. -'• ,-',:',; - ..'
P;dpiyp,p
':iiMi.
^.Late-'. 'py
(Ir'etaceo.us
\-0dpdi.
':-•' r" '...., -d-
Quartz-mica, schist + greenstone
(Preconnbrion'^)
25 km
i' '.- '• 'V •'','• .•' ' '•"'"'
'-''•;;"•• 'j. P '". •' .
5Si'3Q E SSMS
Fig 5 Detailed geologic map of the Ibra Muscat transect (after Bailey, 1981] and Bouguer anomaly contour hnes Two
contour Unes of 45 mGal are shown to enhance the detail of gravity field around the southern nappe
130 km northward from Muscat mto the gulf are m the area of trends nearly parallel to the coastline. White and Ross [1979]
^maximum; wa^r.depth (3^ thickness. : did not elaborate on the deep crustal structure in the Gulf of
Note the zero anomaly contour 50 km north of Muscat that Oman. An analysis of the deep structure wdl be made from

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COLFMAN SAMAIL OPHlOLITL GRAVHY PROHLLS
MANGHNANI AND
o
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2517

C-
IK,---
2518 MANGHNANI AND COLIMAN SAMAIL OHHIOIIII GRAVITY PROIIIIS
TABLE I Assumed Density Values in Computing the Two
."Dimensional Geologic Model for the Ibra Muscat-Gulf of
. .Oman-Transect (l-I'rll") ' ',
Unit P, g/cm^
.Ibra-Muscat:Transect (Profile J-'J!). .t
Samail ophiolite*'- .',;••'.. :,;, ^;^^ ''-" ,;'.,-."•',.'•:? •^-' -,•.• ' ' '
.:-. Basah'' • ,,••':;'.'? '••*'':•''.:'•'.yy''yl-y'y '• -'.^-^O.
.Diabase dike .':•::' •^';.'': ,0-?-^;';;.Uv'V;-;4vf-^{;?-:'-:,'' ,.; 2,80
.:'. Gabbro-- " '''''^•:-y'. .lpppjpppi.p...-. '^-OO'
,.: Peridolile (serpentinized)..i>:;;;i;;;:^;ji;f;j^^.':;r :!;' • 2.79 •
Peridolile (unserpentinized)/'';.';,if;'|?l';,:;li^!;^^ ^^^•''.' '3,3
Conlinental crust - "/•';•--. \y>:'r^:,.':i-y.^::r':. :'•'•'•••-'
Melange (underneath.the^peridptile slice abbye the r 2.42
thrust plane)-' ' ;'•'^.V/P ••*'!••'?••:; ••-'^•'•
• Hawasina pelagic sediments •;'",;•'{
Autochthonous shelf carbonates (limestone)',:;
Quartzite,,doloniite, greenstone, calc-schist .;;;
• Quartz-mica schist, greenstone (Precambrian?),-
.'•'•• • :\ ' * tCulf of Oman (Profile/': •IV-
Water ^'y i ' •t.y^:-;lpyf:ny
Top layer sedimentsl(Recent)\;Sj:;;,,v'ii^rjJS
, Deeper sediment layers,;/;;,,:.;;!; /)ion« a/.; I981J and the,deduced.regional (Figure 6) it can be seen that the. Bouguer anomaly high is
..structural relationships, [Co/eman, 1981 J. The parameters that centered over the axis ofthe synform. The.synform structural
were varied to arrive at the final model (Figure.6) were shape model is constructed from field evidence [Hopson et ai, 1981 J.
and thickness of: the individual units (within certain con­ Using estimated thickness (9-12 km) of peridotite m this area,
straints), depth of'Moho'.discontmuity, degree of serpentinir our model (Figure 6) requires extensive serpentinization of
.ization.in peridotite bodies; atid,mass distribution in the upper .the peridotite body to lower its density (p->^ 2.79 g/cm'). A
,\mantle.;jhi!adopted!densiiy values for the continental and density value of 2.79 g/cm' would imply 60% serpentinization
, oceaniccrustal'kyers,*based on thejaboratory measurements by volume, based on our measured densities [A/ang/i/»«n/ et
, on the rock samples c6l|ecte(i,in

150
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MANGHNANI AND Con MAN; SAMAIL OPHIOLITE: GHAvrrv I'KOI-ILGS , 2519
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OPHIOLITE-
RESIDUAL
FRee-AfR
AL KHABURAH
—I , , , 1—_—-^_—^_-.—, .,—~—-
Geology/rom Glenme el ol (197,4} "^ ',;
Pig 8 Pro/ile fi, showing Bouguer and free air anomalies, and simplified geologic section from Glennie el al. /I974J,
Various units ofthe Ophiolite are fc = extrusives (pillow lavas), D "f sheeted dikes, HG = bypabyssal gabbroic rock, G /i.yo«>/ a/.,' 1981]. The dcnsities;5)f theseunits are fhe
.same (~2.95-r3.0 g/cin'). There is.a gentle decrease in Bou-
.guer anomaly across the gabbroic section and a raorerapid
decrease across, the sheeted, dike complex (p = 2.8 g/cm').
This sharp decrease is probabiy,caused.by a changein density,
. form 2.95-^3.0 g/cm' (gabbro);to 2.8, g/cm' (sheeted dikesj,
and 2,6 g/ciri'(pillow lavas). Tento, twenty kilometers south-;
east of Ibra, the Bouguer apomajy, decreases to a minimum
value of —10 to —15 mGal directly over the southern synclinal
limb of peridotite. and gabbro bodies. To account for
this increase, we have assumed subsurface mass deficiency by
way of salt diapirism in the region S£ and SSE of Ibra similar
to that found in,Zagros. Glenme e/a/.f1974] describe salt diapirs
south and west ofthe Ibra area.'and it is assumed here
that at least some of these closed synforms and antiforms near
Ibra may result from salt tectonics. A,density of 2.2 g/cm' was
• f-tiyy.;-
coosi
150
100.
•50
;.0
• too
-5,0
-0 ,
-50
-100
•SL
^ 1
assumed for the salt dome at depth of-7-15 km in the model.
Near I (in the aiJochlhonous Hawasina limestones), the southeast
end of the gravity proiiJe I-/', 'he Bouguer anomaly increases
gently to values ranging from from 0 to 10 mGal.:,
N-SMarineGrayity Profile (I'I"), p ' •'•• , '..
Muscal-Gulf of Oman . \ '" ' f •
: The free-air atiomaly profile (I'-I") stretching -180 km
northward from Muscat into the Gulf of Oman (Figure 6) is
based on the gravity data obtained during the Atlantis II
cruise (1976-1977) in the Gulf of Oman [While and Ross,
1979]. In computing the two-dimensional geologic model
based pn gravity data, we have combined the Bouguer anomaly
values for the continental part, along the section I-I', Ibra
to Muscat, with the free-air anomaly values for the oceanic
part, profile I'-I", The combined 325rkm profile is shown in
Figure 6. The gravity signature oil the profile I'-I'' is interpreted
as follows. .'
A large Bouguer anomaly localized at the coast near Muscat
(V) is clearly caused by both a continental margin efi^ecl
due to thinning of the continental crust and by a peridotite
slice, a part ofthe Samail nappe resting on the coast: The
nappe has a steep (-70") northward dip. A small decrease in •

,2520 MANGHNANI AND COLEMAN; SAMAIL OPHIOLITR: GRAVITY PROFILES
the.Bouguer anomaly just north of the coastline could result. The gravity expression of transition is smooth and takes place
from relatively shallower eflTect: pervasive serpentinization , within a rather short distance (50-100 km).
and a seaward thinning of the peridotite nappe. On the basis The overall pattern ofthe gravhy profile, i.e., gravity first
of such a large Bouguer anomaly near the shore and some- decreasing steeply from a positive value (—I-100 mGal) sea­
. what smaller positive free-.air gravity offshore north of Muscat ward from Muscat to the Gulf of Oman (150-210 km) and
in the Gulf of Oman [White and Ross, 1979], it is interpreted then gently increasing lo zero (210-325 km), is attributed lo
that the peridptite.slice doesextend some distance northward , the transition from the continental area (thicker crust) to the
into the Gulf of Oman. However, the sUceis interpreted to be oceanic area (thinner crust), as depicted in the model. In our
slightly thinner (about 5-7; km) and less extensive (~50 km in . , model (iFigure 6) the crustal thickness changes from ~42 km
the N-S direction) than that m the Ibra area and that most of on the continental side to 16-18 km pn the oceanic side.
it is serpentinized (see model, Figure 6). We also interpret that An 'edge effect' due to the transition al Uie continental-oce­
the peridotite nappe.exposed albng the coast at Muscat is not anic margin is widely revealed in several free-air and isosiatic
rooted in the oceanic liihosphere of the Gulf of Oman. The gravity profiles across the western coast of the United Stales
thrust fault shown in Figure 6 at the base ;of the northern Sa- ; and several other continental margins [Iforze/, 1974; Rabi-
mail nappe represents,the initial emplacement surface during . nowilz, 191A', Drake et a/., 1959]. In a situation of complete
Late Cretaceous now covered by younger sediments. Under­ isostatic compensation the, positive anomaly inshore from the
neath the nappe is the; Hawasina ;melange. Recent sediments continental margin (water depth of ~2 km) shoulcl be mini­
(p ~1.95 g/cm'). 1-2 km thick, as evidenced from seismic re- ' mized, and the negative anomaly offshore extended over a
flection study [miite;:andRoss,;l919\,Ueiu^ over^ wider area, i.e., more gentle seaward gradient. Although such
• theiperidotite slicer';;:rv'v-'::"---':^. "'•'V;'^;.;: '.•'••'••''., ' ^',,- •'•', a trend in gravity profile is suggested along the profile I'-l",
The free-air gravity value decreases northward from ~110 the observed gravity cannot be fit with a model that is in com­
mGal at Muscat (at'13,8 km* on the profile I'-FO to abouit 50 - plete isostatic compensation; In ,order to establish the degree
mGal (at r;160.km) and then increases to 70 mGafover a , pf isosiatic compensation, if any,, additional gravity data for
. short distance (^5,irkin). The iiiitial decrease in the free-air '. the Gulf of Oman areneeded. ,
anomaly can be attribiited to the lensUke sediment layer (< I "^j In the following we discuss three gravity profiles across the
km thick) at the edge of the contmental margin with some', Samail OphioUte tn central and northern Oman. The purpose
, .contributioii also^ froni the thinning of the peridptite body.., here is also to correlate,the gravity field across the ophiolite
The sharp increasiB: to -70 mGal' may be inferred to be:-; with known surface geology and deduced siructure. We must
caused by a sUght thickening of the peridotite body and per-'i emphasize, however, that we have riot carried out any geohaps
also by the presence of unserpenlinized lenses, tn the pe- .< logic mapping in these areas. We have only utilized Glennie et
' ridotite body, as showii^inthe model (Figtire 6).The dike land,, a/.'s [1974] geologic cross sections that are approximately
sill system (Figure 6) represents magmatism relatedto the ini- , coincident with our gravity profiles. These geologic section
lial rifting of the Tethyan seaway during .Permian and Triassic were deduced by Glennie et al. by reconnaissance methods,
times. We have shown this diabase dike and sill complex at' and as a result, stratigraphic thicknesses and attitudes of indi­
the boundary of the continental, and ocean crust on the specvidual units coiild be modified by future work. For instance,
ulation that i early rifting within;the Tethyan ocean during; we note, that in profile I the gravity anomalies over the Samail
Permian and Triassic times was marked by block faulting and. nappe, appear to represent greater thicknesses than those
invasion of diabase 'dikes ancl siUs as suggested by Coleman- shown by Glennie et al. • • v.,.;- r''^ ,
[1981]. Although "therer is :no; geologic evidence of diabase ,.
dikes and sUls. in, the basement just south of Muscat in Saih
Hatat, diabase dikes of unknown age intrude the basement Gravity Profile II-II'. Al Khqburah-Ibri .
rocks exposed near.,Jabal Ja'alan some 240 km southeast of: The lOO-km NE-SE profile across the Samail ophioUte in
:'Muscat (Figure 1).- • •••y y •:•;:•,/':'• ';.••'• '^', ;'' ,A; the central Oman Mountains region (Al Khaburah to Ibri) is
Note that the free-air, anomaly decreases farther northward / shown in Figure 8. The profile transects the Batinah coast, aU
and reaches a minimum value of ~-110 mGal. This is over ' the major mappable units of the ophioUte nappe, the under­
the abyssal area (water depth ~3:2 km) in the Gulf of Oman ; lying Oman melange (OM) and Oman Exotics (EX), the
where an active accretionary sedimentary prism is forming by; ^ southem,ipart oflhe Hawasina window (also shown in Figure
northward subduction as interpreted from seismic reflection 1), a thin veneer of another ophiohte nappe, and the aUoch-
: studies [White and Ross, 1979). We have modeled the conflgu-^^^ , thonous Hawasina pelagic sediments (see Figure 8). The tran­
ration of the sedimentary layers by combining the seismic and ;, sected Hawasina pelagic sediments, in top to bottom strati­
gravity data. The uppermost pediment layer (p =• 1.95 g/cm'); graphic order, are HaUw Fm (Ha), Al Ayh Fm (Ay), and
is thickest (:£2.5 km), and the underlying sediment layer (p =.' vWahrah Fm (Wa), belonging lo the Upper Hawasina, and
2.1 to 2.3 g/cm') and the supposed Hawasina sediments (p =, • Flamarat. Duru Group (HD), belonging to the Lower Hawa­
2.42 g/cm') are not as thick here. The gradual mcrease in free- .
sina, These formations,- respectively, consist, mainly of radio­
air anomaly from 215 to .325 km along the profile is inter- „
larian cherts and.siUcified limestones, turbiditic quartz sand-'
preted to be caused,,maihly by decreasing water depth and in-;
stone, limestone and calcareous, mudstones, and internally
creasing depth to the 'Moho- discontinuity toward the Makran
imbricated limestones. The latter (HD) is the thickest unit (~ I
km). The density of these formations varies from 2.3 to 2.6 g/
(Iran) coast to the north.; .;:/;.^,/ ' :-, :v. v .,,;/'•
cm'. The Hawasinas are intercalated between the underlying
: autochthonous and par-autochthonous Mesoieoic sediments of
Gravity Anomaly Across the Conlinental Margin
the Arabian Continental Margin and the Samail ophioUte
The transition from.oceanic to Continental crust, as revealed nappe [Glennie et ai, 1974]. In some places along ihe profile
by Bouguer and free-air anomaly profiiles, is simple (Figure 6).
the updomed Mesozoic shelf slope sequences of the Sumeini

C
MANGHNANI AND CoLiMAN SAMAII OPHIOIHI GRAVHY PRO/HIS 2-,2l
m'
Geology from Glenme ef ol (1974) ^
.^V- RESIOUAI
/ \^^ FREE A/R
OPHlOlllE
SAMAIL NAPPE
E ~ banc eirrusivet
D - Dioboie dilei
HC-Cabbroid
-v.-- hypobys foci
G - Gobbro
P - Pe'ioolite
pan serpsnl
5 Slroflgly sheared
sdfpeni pendofile
Fig 9 Profile III, showing Bouguer and free-air anomalies and simplified geologic section adapted from Glenme et al
-- - JI974J LR HAW represents lower Hawasina
Group (Mu = Mutl Formation) pierce the Hawasma cover as
found in this section (Figure 8)
The Bouguer and free-air anomalies as welt as the residual
anomalies along profile II are shown in Figure 8. The regional •
gradient is about.-p.8;;mGai/km.in NE-SW direction. The '
Bouguer aiiomalyiiear. the .coast is -tSO mGafand increases?,
;to the south across.the extrusives (basalt), diabase dikes and •gabbro,
reachin^.a inaxunum. value of;+ll5 mGal over the-
-lOD
- 50
(United Arab Emirates) are depicted m Figure 9 Overall the
two profiles have similar patterns, the small deviations, of
course, are due to topography The regional Bouguer gravity
igradient'is —1,3 mGal/kni in nearly £-W direction. The residiial
free^air and Bouguer anomaly proxies'and the simplified
geologic section (Sohar-Burairai), adapted from
.Glennie etal f 1974], are also shown in the figure. The Bouguer
; anomaly increases first slowly and then rapidly in traversing
gabbro-peridotite; cpntact (at. 25 krn) dipping northeastward.; • westward across the coastal aliuvjuih (()-20 km) and in ap-
The residual Bouguer abomalyneai: the contact is about +120 , .proaching the ophiohte nappe. The rapid increase in Bpuguer
mGal. There is.-aiSharp decrease in the residual Bouguer;;; anomaly is attributed to the higher-density units in the nappe
anomaly in „ tra versing-across the serpentinized peridotite,. >' (structure; /The total Bouguer anomaly increases from a value
which has lower density (p,~2.79 g/cm^) than gabbro (/> r3,0; of about +25 mGal near the coast to about +100 mGal near
g/cm'). The residual-JBouguer anomaly reaches nearly zero' the contact between basit; extrusives (E), consisting of basaltic
over, the Hawasina; window (45 to 70 km) where the lighter lava flows, and gabbro (G). The maximum residual Bouguer
Hawasina (Oman Exotics' arid/Hafflarat; Duru formations, p. anomaly at 30-40 km is of the same magnitude (+95 mGal).
~2.42 g/cm') and the autochthonous platform calcareqiis, Along the Sohar-Buraimi section, the peridotite is partly ser­
, sediraenLs (liinestones and cherts,./? -^2.42 - 216 g/cm') are expentinized (P) or strongly sheared (S) due to prevailiiig imbriposed
(Figure 8). There.is a slight increase in the residual cate thrusting indicated by Glennie etal [1914], The decrease
Bouguer anomaly (to +-20! mGal) over the ismall peridotite in the Bouguer anomaly between 35 and 60 km along the sec­
exposures (65-70 km). No appreciable increase in gravity is . tion III-III' (a minimum value of-25 mGal is reached near
observed toward the southwestward end of the profile where Hail) is therefore attributed to lower density of the near-sur­
the Hawasina consisting of cherts and shales (Hamarat Duru face strongly serpentinized peridotite (~2.79 g/cm') as well as
Group) is exposed. Along prpfileTI, we thus! find good corre­ to thinning of the nappe. The increase in Boiiguer anomaly
lation between'gi^yity and gebiogy-C?^f€''" ' ' ;..,-''•••'. from westbf Hail between 60 and 75 km, reaching +10 mGal
Gravity ProfilpIIpIIJ'.Sohp-Burafmip.- , .^ 4 ;
at 75 km, is again caused by thinning and disappearance of
the nappe. The residual Bouguer anomaly due to this nappe
The Boiiguer; and- free-air anomaly profiles along the 120- structure is smaller (~+50 mGal) than over the eastern
fcm E-W transect from Sohar on the Gulf coast to Burauni nappe. A sharp decrease in Bouguer anomaly from 90 to iOO
0
100
-50
50
St
100

2i22 MANGHNANI CND COLIMAN SAMAII OPHIOHU GK'VVITY PROHILLS
D
O)
E
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100
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50'
100
« 50
>-
<
o
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<
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\u
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-50
-100
SL
\
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90 80 70 60 50 40 30 30 20 '10 .'. ' Q,-
I ( I I 1 I 1 1 I I I I 1 1 1 1, r .1 ;, ,r ,, i, , i -i—y 1~
°"-—,
+
p-—-o-,.
y y—*\
FREE-AIR^, /
.—o -O-^.^y'
- - * " " ~ ^ - - •-'••• y
„'^ ^^^p-s RESIDUAL' ',«'--^
^,'^ ^^^ \ ^ FREE-AIR ... .. •
. / RESIDUAL
BOUGUER
' - ' . /
.i^^'
-^^
a.«^'
/ o>oy\y^
s/dimmm.
• ..; OPHIOLITE ' y ',
'• SAIAAILHAPPE ;' '
E - Basic extrusives'.
D '- Diabose dikes .,',
Gr' Gobbro \ ,
,P -' pBtidolite,: '"':' •••.
'• port, serpent.,
, S -' StrotiQly sheared
•:'•;: 'serpent, peridotite'
3 1 1 1 1 1 r-
Gaology Irom Glennie et QI (1974) "^ i ,
Fig to Profile W, showing Bouguer and free-air anomalies and simplified geologie map a4apu!d from Glennie et ah
[19741 Horuonial scale is represented by km marks on x axis, vertical exaggeration of geolo^c section is 2.5 limes. The
.allochthonous Hawasina units ate Hf -Haifa Fm and Ar "Al Aridh Fm..Umis belonging to ihe Sumeini Group are Mh
\a Mayhah Fni and.Mq;«» Maqan FI«L Horizontal .scale is represented by km marks on x.wus; vertical exaggeration of
' gMlogic'sectioii is'2.5 times.''•'.";.';'-,, , '•"••''. '•.•^•..Py. y.i-y'~'-'iy'^^y,. i'.,'' : -=.' •'v'''v^' . f; - . •-••.,'•. '.-
km isprobably caused by thtt; thinning and disappearance of The, maximum^Bouguer anomaly (+140 mOal) along the
the nappe (Figure 9)..The farther westwa.rd decrease in the to- • , E-W profile IV is found near about 25.kitj (Figure 10) and octal
Bougucr anomaly fto TTSO mGal) b caused by lower den-, ; curs,over the thickest section ofthe nappe. It is also of interest
siiy (p »»! 2.2 ,to,2.3 6/cm'),lower-H^^
to note that the gravity high appears to be,oyer the gabbroic
••;.Vi/adi-Tenrace'-niateriais.,; •; '-' --r'.'-,-.'•.•;>:.'!:'".'•;',- '.'-,. •(G) and gabbro-peridotite (PG) exposures and not over the
''• -The overall.features df the Boviguer profile 111, then, are peridotite section. Between 20 and 45 km along the profile, the
that therc.is a doublet In the anomaly and that the magnitudes Bouguer anomaly decreases steeply (to +20 mGal). This de­
. of the two residual positive anomalies are about .+95 and +50 crease is partly caused by the presence of Ughler aUoch-
mGal and^ are separated by a distance of 45 km. There apthohouS sediments (Ar and Hf formations) wedged between
pears to be a good correlation between the observed gravity the two nappe structures. The Al Aridh (Ar) and Haifa (Hf)
anomaUes and geologic structure. The imbricate nappe struc­ formations consist of reefal limestone conglomerates and
ture jconsisiing of ;t.wo;ovcithnisl OphioUte sequences; is con- cherts, respectively, and the density of these materials varies
• fiLTtned,by .doublet positive gravity anomaUes, . -p;. ,'„..' from 2.2 to 2,5 g/cm'. ..
}:'Pr(!!^Ic,I}(^/K^'i4i^Iiina2-I)ufc

2.S24. MANGHNANI AND COLLMAN; SAMAIL OPHIOLITI;: GRAVITI PKOI-ILLS
Sumail ophioUte nappes is reflected-by high positive gravity the Quebec Appalachian ophioUte zone are much smaller, of
anomaly doublets that reflect a distinct separation between the order of +50 to +65 mGal, and those over the Zhob ophi­
the nappes, ll is not clear whether the individual nappes were olite even smaUer (+22 to -12 mGal) [Farah and Zaigham,
at one time connected'and emplaced as one huge nappe or .1979). The negative residual Bouguer anomalies uniquely re­
whether there were a sequential series of nappes^ In the northported in .this case are localized only in the area and are
ern parts of Oman, G/enni'e et ai [1974] show some imbrica­ ' caused by the exceptionaUy low .density of harzburgites (p ~.
tion and repetition of these nappes (Figures 8 and 9), whereas 2.5-2.6 g/cm') as a result of intense serpentinization. In sum­
in the Ibra-Muscat transect (Figure 6) there is no evidence of mary, most of the residual Bouguer anomaUes encountered
imbrication; This may be explained by tectonic thinning or ; over the ophiolites surveyed so far range from +50 to +125
thickening during earlier detachment or during emplacement mGal; the more positive anomalies signify proximity to the
by thrusting or gravity sliding onto .the Arabian platforin ; upper mantle (i.e., thinner crust as in Troodos).
[Coleman, 1981]., y-pp'^- ' , ,' '•"; • , ,
'„.!-.-'•--
It is difficuh to relate the positive gravity anomalies directly
•,-'•"., .CONCLUSIONS •"..'.''. ;'-. •;to
the exposed sections of the Samail ophioiile because we I, Samail ophioUte nappes are nearly continuous and weU
had no control on the subsurface extent of serpentinization. In ,: preserved segments of the ancient oceanic Uthosphere that
fact, petrologic investigations have revealed that much ofthe '? were detached near a mid-Cretaceous spreading center at the
surface peridotite was lip to 80% serpentinized [Boudier and •;Tethyan ocean, Complete Bouguer anomalies of the order of
Coleman, 1981] and that ihost of this serpentinization had .+75 to +140 mGal are encountered in traversing the uidividtaken
place after .emplacement [McCulloch el ai, 1980). The . ual nappes of pphiolite. Thegravity data support the field evi­
lack of large areasof sheared serpentinite rislated to the basal dence eoncerning the slratigrajphic relationships between
thrusts, which would have resulted in low or- even negative I mantle andtcrust and estimated thicknesses of the nappes as
anomaUes, such as those encountered in some localized areas , weU as their geologic structure; The gravity data presented
Ul the Zhob ophiolite complex, Buluchistan [Farah and Zaig- here support the concept ihaf these ophioUte nappes are rootham,
1979], provides further evidence; thai the Samail ophioless and have been transported southward on to the conlinenlite
nappes underwent .piostemplacemenf serpentinization lal margin of Arabia. Futut'e detailed geophysical and struc-
[Hopson elal.,'l9i\]yp'i'pp::,,.,,:- .'-^--V ''.P\-''-''''. t tural, work wiU provideimtirc precise information'relative to
The presence of pre-Permian sah in the eastern Arabian ; the actual tectonic conditions accompanying obduction ofthe
platform at,the;base of the shelf carbonates has been com­ ' Samail ophioUte nappes.; .»' ¥ t. ,
mented on and described by several authors [e.g., Glennie et (2, iThe gravity high in the Ibra area, where a complete
a/., 1974], The domal patterns east of Ibra may be due to sah oceanic crust stratigraphic^ seijuence is preserved, centers
dome tectonics. .Even;though our*negative,enclosed gravity ".:... around the thickest sectionof the ophiohte nappe over the pe­
anomaly (--10 to ^15 mGal) is asynunetric to the Ibra dome, ridotite-gabbro conucl. To: some extent the displacement of
we suggest that it maylbe related to salt diapirism whhin the ,'J'the gravity high from the peridotite may be caused by ser­
shelf carbonates after the emplacement of the Samail ophio­ pentinization. Similar relationships are observed for the grav­
Ute nappe. It is not possible'to relate these postemplacement idity profiles ip the central and.northemOma;n Mountain restructures
.;to any other reasonable tectonic origin. ',.,:,.: J'j ^''gions.-;- ••;-,••' • ';•'' '-:''^'-y'y.pyy'- ••'••-.
,; ,,3^ The gravity signatures ^of the traverses acrpss the individual
ophioUte nappes in central and northern regions of
•;. COMPARISON WITH; OTHER OPHIOLITE ANOMALIES ^
:, Oman are represented, by a doublet of positive residual Bou­
Gravity surveys of at least four other ophiolite complexes guer anomaUes of 50-100 mGal. The wavelength ofthe douhave
been reported: TrobdoSiMassif, Cyprus [Gass and Mas- - blef decreased northward as, a result of imbricate thrusting
son^Smith,-1963]; Papua^New Guinea [St. John. 1910;-Mil- caused by relatively stronger E-W.lateral compression forces,
som, 1913a, b; Kroenke et a/, 1976]; Zhob OphioUte, Baluchis-; ,; 4. No convincing evidence can be found to indicate that
tan [Farah and Zaigham.; 1919];, and the ophioUte. belt. in these Samail ophioUte nappes are rooted in the Tethyan oce-
. Quebec Appalachians [Seguin,, 1979]. The largest Bouguer : anic Uthosphere oflhe Gulf of Oman. ,•
anomaly is reported for Troodos Massif (+100 ,to:+250 , -5. -The gravity'transect across the'continental margin of
mGal) [Gass and Masson-Smilh 1963]. Although the thick­ Oman indicates a continental crust of ~42 km thick decreasness
of the, Troodos Massif from the top of piUow lavas; to the ; 'ing to an oceanic crust less than 18 km thick. A geologic cross
base of plutonic gabbroicVrocksXie.; to Moho) is only 4 km, section developed from the gravity data and mapping allows
such a high positive anomaly has-been interpreted by. Gass , an iiiterpretation that shows a passive continental margin de­
and Masson-Smith [I9(i}] to bt caused by an underlying thick velopment similar to that suggested for the AUantic. Thus a
(~10 km), unserpenlinized sequence of ultrabasic rocks (p ~ ' would appear that oceanic Uthosphere slabs had been em-
3.3 g/cm'). The Bouguer anomaUes reported over tbeophio- ; placed across a subsiding passive' continental margin during
.'lite complex inPaptia-NewGuineia, which- is the thickest the closing of the Tethyan sea in Late Cretaceous time.
known ophiolite complex consisting of r4-^ thick basalts ~4
km thick gabbro, and ~4.5-6.0 km thick underlying mantle
Acknowledgments. We dedicate this paper to the late George P,
ultramafic rocks [Davie.;, 1971], are also quite large, of the orr Woollard, who inspired us lo go where we went; he was indeed a
der of +100 and +150 mGal [Milsom;, 1963a, b\ Kroenke et guiding force in this projecl. The projecl was jointly supported by the
a/./19761. In terms of the magnitude of the residual Bouguer National Science Foundation (grant EAR 75-15212 AOl) to the Uni­
the values encountered over the Samail OphioUte (~l-2 km versity of Hawaii, the Defense Mapping Agency, and the U.S, Geological
Survey, The authors express gratitude to the Ministry of PetropiUow
lavas plus sheeted.dikes and 9-12 km of harzburgite . leum and Minerals of the Sultanate of Oman for their, generous
tectonite) are comparable to, those in Papua-New Guinea. In support and guidance in this survey.-Special thanks are due Mocomparison,;
the maximum; fesidual Bpuguer anomaUes over - hammed Kassim, Khalifa Al Hiiia, Ismail E'l Boushi, and A, E. Rus-

Ci
(:.,:,
- ..
.MANGHNANI AND,COLEMAN: SAMAIL OPHIOLITE: GRAVITY FKOHILES 2525
sell We deeply appreciate Wayne Lau's sujjerb assistance in all
phases of ihc field iheasurements; without his help the gravity work
would not have been so extensive. We also acknowledge the help and
guidance of .Clifford, Hopson, Ed Bailey, and John Pallister in the
field and thank Valerie Godley and Nirmal Devnani for their invaluable
assistance in data reduction and model compulation, J. C.
Rose provided the computer program used in the two-dimensional
geologic modeling. We thank D. A, Ross and R. S. White for the At-'
laniis li cruise data. We deeply appreciate the discussions with J. C.
Rose, G. H. Sutton, R. Mobcrly, and W. Sager.. A. Griscom, C.
Bowin, and an uimamed conscientious reviewer read the manuscript
critically and offered a number of helpful suggestions to improve it.
Thanks are also,due R. Pujalet for the editorial help and Oksana Fuller
and Richard Rhodes for drafting.' This publication has been authorized
by the Director,-U. S. Geological Survey. Hawaii Institute bf
'Geophysics contnbuUM^120:,;-,.y,(-;Vt-.V''';:;'' ,' .,-. tiS'-i i:'..;':'
•' '.'., ;•- •;.,•;V'''Ci;:$-t';-il,--R.EFEkENCEs-,'"': 'i.-' --' -y^p'Pi.;. -;•
Bailey, Ei H. (Compiler), Geologic map of Muscat-Ibra area. Sultanate
of Oman, pocket,map,:/ Geophys. Res., 86 this issue, 1981,
•Boudier, F., and R. G. Coleman, Cross section through die peridotite
in the Samail ophiolite, southeastern Oman Mountains,v! Geophys,'
•;• VfM., ; i..':-J ,, .:'-,.-.' '. ''--^
.Gass, 1, G., and D. Masson-Sinith, The geolpgy and gravity anomalies
of the Troodos Massif, Cyprus, i'Ai'/of.;-7>onj. /t Soc. London,
'. .255..4n-467,1963:.:':'-I'-'y-.i••:•-•••• -^yy -i-''.'
Glenme, K. W., M. O. A) Boeuf, M?W. Hughes-Clark, M Moody-
Stuart, W F H Pdaar, andB M Reinhardt, Geology of the Oman
Mounuins, Kon Ned. Geol Mijnbouwk Genoot Verh., 31, 423 pp,
1974,
Hopson C A, R G Coleman, R T Gregory, J S Pallister, and E
H. Bailey, Geologic section through the Samail ophiolite and associated
rocks jilong a Muscat-Ibra'transect,. southeastern Oman
Mountains,/ Geophys Au, 46, this issue, 1981
Kroenke, L. W., M. H. Manghnani, C. S. Rai, P, Fr>er, and R, Ramananantoandro.
Elastic properties of selected ophiolitic rocks
; from Papua-New Guinea: Nature and composition of oceanic
.,. lower crust and upper mantle, in Tlie Geophysics ofthe Pacific Basin
, ;'and Its Margin, Geophys. Monogr. Ser., vol. 19, edited by G. H. Sutton,
M. H, Manghnani and R. Moberly, AOU. Washington, DC,
,'-1976. •••':.-,- •'•'•. .•/:':':: , '.
Manghnani, M. H,, and (3. P. Woollard, Establishment of north-south
gravimetric calibration line in India,'/ Geophys. Res.,-68, 6293-
, 6301, 1963. ; , ',. <
Manghnani, M. H., J. Hornbcck, J. S. Pallister, and R. G. Coleman,
, Velocity structure of the Samail ophiolite, Oman: Nature of the
' layer 3.and upper mantle; submitted to / Geophys. Res., 1981,
McCulloch, M.T., R. T: Gregory, G. J. Wasserburg and H. P. Taylor,
, Jr;, A neodymium, strontium, and oxygen isotopic study ofthe Cretaceous
Samail ophiolite and implications for the petrogenesis and
seawater-hydrothermal alteration of oceanic criist, Earth Planet.
5ci.JLe«.,.>6, 201-211, 1980.
Milsom, J., Gravity field of the Papuan peninsula, Ceo/. ^^lyntouH',
'• 52. 13-20, 1973fl. ' • :. . , ' '
Milsoih, J:, Papuan ultramafic belt: Gravity anomalies and the em­
placement of ophioUtes, Geol Soc: Am. Bull, 5< 2243-2258, 1913b.
-Pallister, J. S,, and C. A. Hopson, Samail ophiolite plutonic suite:,
...Field observations, phase variation, cryptic variation and layering,
• and a model of a spreading ridge magma chamber, / Geophys.
-. ilei, «

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Xni conclualon, tbe only alQcral target of apparent latereat in the '
Oman Nountaiaa la chreadte. Known •ccurreaeea are not •eononlc but no
£ priori baala axlata for ^ueatlenlng the poaalble occurrence of larger
depoalta. In order to BaxlaU.se thia poaaibility, the entire area of the
•eoall aeriea In Oaan Mountalna should be considered and any llnltatlon of
possible investigations, i.e. by political boundaries, would reduce the
;^sibilltifts of aueeess proportionately.
CoBsidoring tbe hl|^ anbiliaation oad eKploration oost to be sotpected,
a tingle'target lovestigational prograai ia a restricted portion of the Oman
Mountains Is aot •ttroetive on any tanu at tba present ciae.
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Attachcaents
tiehard itrong

c
i )
» - '^^ ' -• :
THE NEW YORK TIMES. MONDAY, JULY lii, WI •
iSix Persian Gulf Emirates A f[ree to a Federation
SpKliI to Thl New Tork Times
BEIRUT, Lebanon, July IS—
Si.x Persian Gulf emirates announced
today that they had
reached asreement to establish
a fedei-ation before the British
leave the area at the end of
the year.
The announcement carne after
a week of talks in Dubai by the
rulers of the emirates. A seventh
emirate, Ras al Khaima,
declined to Join.
A statement said the emirs
of Abu Dhabi, Dubai, Sharja,
Ajman, Umm al Quiwain and
Fujaira had agreed to a fcdcra-j
tion that would have a Supreme;
Council of the six rulers, a cab-;
inct and a Icgislatu.'c to bcj
known as the Consultative As-i
senibly. . I
The agreement is the f:r:tj
outcome of a thrce-jear effort -
. C»TA??T.i..V,
X^y:Pdii^.
•' ^->>^
'AbuOhabi
to bring about a union of a'lirnaubtion of little less than
the nine Arab emirates on.thc;200.f00. The poorer cmiratesi
gulf. .1— •
The two bigger states. Qatar . -•
and Bahrain, are expected to;
announce their independence
between now and the end of
the year,
British Tliere 130 Years
This, however, did not stop
the seven remaining emirates,
known as the Trucial States
after their truce agreement
with Britain 1.50 years ago, to
seek unity. The British, v.-ho
have been running their foreign
affairs and often their internal
affairs, announced a policy of
disengagement from east of
Suez in 1968.
The federation would have a
(7,
Tl.« Kcw York Timci Jcly l», l»;i
The shaded states agreed
to cstPblish a fcdcratiou.
would benefit from the oil
wealth of Abu Dhabi and Dubai,
as 10 per cent of the oil
income of the emirates would
be used to finance the federation's
budget.
Abu Dhabi and Dubai, the
bigscst and richest of the six,
would dominate the ffderation.
Sheik Zayed bin Sultan, the
ruler of .Kb\i Dhabi, is expected
to be the first president of the
Supreme Council.
In the 34-member legislature,
Abu Dhabi and Dubai |
would have eight seats cach.|
Sharja, the third in size, would,
have si."« scats and the three re-|
maining emirates would have!
four seats each.
Ras Al Khaima's request forj
equal privilege in the Council
v/j>c r#>ipffn(^ h" the f'.y »"T

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8ULTAWATE OF MUSCAT AND OMAN y
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froa May io October. Teaperaturea aeldoa drop below $4 in the
cold aeasoB.
Populeilon
The giopnlailoB of ihe Sulianaie ia esilaaied ai five io ais
bnadred ibouaand. A general oatlaaie would be a ioial of one
bnadred ibouaand for ibe principal iowna (Matrah l^OUO, Sur 60U0,
Kinaa SOOU and Maacai 3000)| three hundred and fifty ibouaand fur
ibe saaller towns and Tillagea and one hundred ihoasand noa&dic
or ooai-aoaadlo tribes. The population la predealnantly Arab
ozeepi oa ib« Batinah Coaai where ibere are aaay Baluch and Negro
oleaeats* la Muscat aad Matrah, Kbojas, Ryderabadia, Hlndue, and
Baluch predoaiaaie.
Coaaunications
Moiorable roads aad tracks run froa Muacat along ihe Batinah
Coast io Sohar and ihence io ibe Trucial Coast. There are unpaved
•oiorable' roada io Niswa aad Sur, vbllsi a auaber of feeder roads
bare been constructed and are still being developed. Dhofar can
also be reached by a aotorable land route. There is a landing
ground for aaaller aircraft aear Muacat and a auaber of eaergency
strips olsewbero la ibe oonairy. Larger alrcrafi can laad ai
Adbalba, iSasirab &ad Salalab bat the aeraal aeibod of oairy into
ibe Buliaaaie is by aoa or air Tia Mnacai aad peraission is required
for the use of other air fields or ports or to travel on roads
beyond a eertain diataaea of Muacai. Meaera. Cable k Wirelesa
operate both a public telegraph and telephone service at Muscat,

c.
•^,.-
and there is also a Poat Office with aoraal *lf and aurface letter
and parcel aerviees to any part ef ihe world.
At preaent Oulf Aviation, a BUAC subaidlary run a bi-weekly
passenger air-servioo eoaneetlag Muscat with ihe International
Air»pori of Bahrain aad with all ibe Shalkdoas ia ibe Persian Oulf.
British ladla Sieaa Navigation aail aad passenger Steaaers also
oall regularly entering aad leavlag ihe Oulf, whilst Strick Line
aad other eargo ships froa Kurope, Australia and ihe Far-East call
> • ' - . . . -
at apprezlaately aonihly intervals.
ftovernaent
Oaan is aa ladepeadeai aoaarchy aad ibe Saltan, Said bin
Talaur, born on 13th August 1910t ezcerclses absolute power. The
succession has been hereditary since the beginning of the present
al-bn-said dynaaty. The Sultan Is aaslsted In the capital by a
Minister of the Interior, a Peraonal Adviaer and a auaber of
Secretariea of Depariaents including External Affairs, Defence and
Oevelopaent. Walla (or Oovemora) are appointed by the Sultan for
all ihe ehief tewas and diatricta throughout the Sultanate and tbe
irlbaa supply giiarda or aakara though not neceeaarily froa the
•aae dietrlci. A Joint Municipality of Matrah aad Muscat towns
aaaaged by aa Bxeeuilve Officer advised by a Coaaliee of leading
bnslaess-aoa, aador ibe goaoral ooairel of aa official appointed
by ibe Sultan takea care of local govemaent.

c
v^
The Econoay
- 5 -
The econoay is aleost entirely dependent upon tbe cultivation
and ozport of datea, but arled fieh, liaee, poaegranatea and fire­
wood repreaent other oxporta. Lm^orts are aalnly of wheat, rice
and ioxiiles, bui with Increaaing wealth of ibe popnlation, aore
so-called Inzury goods are finding their way iutu ihe aarketa*
The Fulian is planning developaent of ihe country and hopes
are ohiefly vested in ihe exploitation of the countries oil reaervea•
Be ia also known to be favourably disposed to geological exploration
providing the right approach can bo aade.
faxation
There is ao incoae tax, nor any Sultanate taxation other than
ihe Cuatoaa iaport duty and aakat (religious tax on produce) which,
in ihs Sultanate, la collected at 5f where Irrigation is carried
on through wella, and at IC^ where it is by "falaj". A email
Municipal Tax ia alao levied on tbe value of iaporta, and exports
through the ports of Muscat and Matrait, which provides the chief
aource of Incoac for the Joint Municipality of thoae two towna.
aeveoue
The revenue of the Sultanate la alaoat entirely derived froa
eusioaa loviea, which vary trom 7%% on essentials such as wheat,
rieo, oagar, eoffoo aad ooiton piece goods, io 73)( so dru4.s such
as opiua. There is also a levy upon exports of locally produced
eoaruoditiea Halted to 9^. There are no restrictions on export.

a

* . - ,' , 'W , -l
C • -•'-
.'t OEULOGY OF OMAN
') Pre vi ona Work
Little detailed work bas boon earried out within Oaan and that
wbleb bas boon oaderiakoa baa beea aiaed largely at fiading oil
tfopoaiia. Leea (1928) waa ihe firat io foraulate any substantial
I account of the geology of Oaan. He recogniaed the Bawasina aeriea
i . .
overlain by tbe Seaail Igneoua aeries, the two rock foraatiuna that
fora the bulk of ihe Oaan aouataln range. Leea believed that the
Bawaaina and Seiuail rocks foraed aajor eoaponents of a vast thrust
nappe eoaplex.
Further work of a stratigraphic and structural nature waa
carried out by aeabera of ihe Iraq Petroleua coapany during the
period l^kO io 19b0* Puhliahed accounta of investlgationa in the
Oaan aountain range have been provided by Budaon McOugan and Morton
- (1994)» Budaon Browne and Chatton (19d^)» Budaon and Chatton (19^9)
and BndsoB (190).
An excellent synthesis of ihs geology of Oaan is recorded by
Morion (1939) who gives ovidsnce for believing that Lees* ideas of
H ibrusiing of ihs Bawasina aad SsaMil oato the Arabian foreland froa
ihe oast aro ao leager ieaable aad thai iheae foraations ars
aaioehienoBs. Morton suggestsd ibat ibe ebaotic structures typical
of tts oorpoailae aad radiolarites of ibe Boaall aad Bawaaiaa series
~~ derlvs through "offusioa iscionlos" associated with Upper Cutaceous
r serpentine extrusions.

c

aq> ax pedoxaaep ^eeq eq o^ XxaqxT "T nvao jo x«Ttnsfod x«x**>dep etxsiojqo xt*"8
•eWowj OTw^onoa avao eq^ jo ^jwd w jo x^Ttoa^ed x*

L
• 't
- 9 -
ia ihs Seeail aad Bawasiaa reck ssrios.
•bell Oils activitiee ia flawa leadlag to ihe developaent of
prodmeilTO oilfields were alao instrmasnial in producing ihe aoat
ooaprebeaslve geological aap of Oaan. Although auch of iheir wnrk
was oenflned io ihe desert foreland iheir geologists traversed the
Oaaa aountain range aad carried out a photogeological interpretation
of ihe aonniain aass. This resulted ia ibe accurate delineation
of ^e Seaail and Bawaaina rock series. As ihs Seaail foras the
bulk ef ibe aonnialaous arsa aad is composed of serpentinite and
ultrabaaic rock types ibe Shell geologists were act too interested
in the econoaic iapllcailona ef auch roeka. However Sheila un-
pahllahed aap of Oaan reaalaa ibe beat effort io date and a copy of
ii would prove a aoat valuable baela to any aineral exploration
pragraaaa.
Begional Oeology
OBMn is divisible into a north east aountain range and a south
weat foreland adjoining the Arabian Shield.
The Foreland
Oligocene io Miocene oedlasnts sever aoat ef ihe foreland
iogether wiih recent done aands aad salty and flats*
la ihs oouib west pari of ihe forolaad a core of Lower Palosoroic
rocks foras ibe Boff-Bansbi swell. Rsrs Caabriao doloaites shales
and sandstones are intruded by rare baaalt djkes and sheets and
pierced by salt doae structures. Ordovician aandstones and shales

s
?
•B
r
e
B
f
.1
ti!' n

e
"-.a-
:-'t
•I
- 10 -
overlie ibe Caabrian nncenfenaably aad geophysical investigations
indicate salt doae structures ai depth.
Ai Bausl peraian boulder beda aapercede ihe Ordorician. The
benlder bede appear io be derived froa Baeeaeni roeka and contain
swbaagnlar blocks of graaite, gaelss aad porphyry. The boulder
beda iraaagreaa widely aad grade upwards laio sandatonea and reddiah
aarls.
f shown.
AiteBuaied Triassle and jrurasslc ssqneiices are present locally
Boi always foralag surface outcrops. Cretaceoua rocks rest uncon-
foraably upon Jurassic sedlaents although a siallar lithology ia
aalntalned. Mid-Cretaceous rocks bscoae aore arenaceoua whilst
•arly liaesioass dealBaie ibe oalcareous reek series. Marls and
llaestones wiih pronounced lateral changes in faclee and ihickness
oontlaue lato ihe Upper Cretaceous.
MaesirlchtlaB liaeaionea and auirla crop out over auch of the
foreland particularly close to the Bugf-Bauahi swell and the foothills
of ibe Oaan aountala range where their transgressive nature is well
I Tertiary liaMatones, chalks, auurls and evaporite aequences alao
fy
are wideapread ever ike Oaan forelaad. It ia ibe foreland areas that
bave provided ibe siruciurss aad rock ijrpes suitable for the
ievolopaeai of produclag oil fielda. Little ia kaowa regarding
their aetallic aineral content bat ibis is aasuaed io be rather poorly
represented.

c - 11 -
w 4
y.
The Oaan MonniaJB Hanae
la ihe Oaan aouataia range ibe oldest oxposed foraations are
Poralaapbylliies, basic iatrnsives aad qoariKlies overlaia by Upper
Foraaia liSMsiooes.
^esiloaablo Triassic sodiaoais eoaiiaoe ihe ealcareoua rock
•equence and grade upwards into JBrassic aarlS and doloaites.
Tbe Lower and Middle Cretaceous ascilons are represented largely
by doloaliic, radiolarian and crinoidal llaeabones. nie Upper
Cretaceoua is well developed and foras the bulk of ihe Oaan Mountain
range. According to Morton (1939) the Upper Cretaceoua consiata of
ihe oalcareous-aciaaorphlc ssqusnce of ibe Bawasina Ssrles overlain
by over 1,000 aetres of ibe Seaail Igaeons asriss. According io
Dr. Hewelljm of University ColIsge, London, and foraerly on Shells
aiaff in taan, ihe Seaail uaderlle ihe Bawasiaa a view generally
agreed with by Oreenwood and Loney (I968). The Seaail ia coapoaed
of a suite of plutonic, ultraaafic rocks together with iheir
bypabyssal and extrusive repres«ntati%ea. reridotitea, dunites,
pyrexenitos, gabbroa aad dioritea all occur. Oenerally they are
anbordinate io the vaat aaaa of serpentinite, auch of which has
dsrlved froa ihe ultraaukflc roeka.
Oreoawood aad Loaey (19B) bo Hove thai ibo gabbrosi ultra­
aafic rocks aad aorpoailaitos ars all coapoaeais of a pssudostrailfori
alplns porldeiile-gabbro coaplsx. They believe ihe serpentinite
derives froa plutonic ultraaafic roeka r

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- 12 -
raodoa occurrence of chroaite blocks and lens at different vertical
levels. The Bawaaina Seriea is eloaely associated with the Seaail
aad ihe Lower Bawaaina coapoaed of cberta and radiolaritea is inter­
bedded with Seaail latruslTS aheeis. Tbe Upper Bawasina generally
overlies ibe Seaail aad foras a.diaiiaci lithological group of low
grade aetaaorphie roeka. Chlorite, opldoie aad garnet occur widely
ia either predoalaantly arenaceous or oalcareous aetaaorphie rock
suites.
Manganiferoua cherts are characteristic of ihe Bawaaina as is
ihe wideepread occurrence ef oxidiaed eopper ainerala.
ylneral Beaourcea
Little la known of ihe econoaic aineral reaonrcea of Oaan,
ihe oapbaais of its liaited exploration being placed on petroleua
prospsctlag. Apart froa scattered travellers descriptions of coal
depoalta and biatorical archaeological accounta of ancient copper
workings, little can be gleaned froa puhliahed aaterlal.
Fortunately recent aiudiea of the neighbouring Trucial Oaan
Baage do allow a ceriaia knowledge of ihe Oaan aountain range by
iaferoace. Aa far as base aetal aiaeralisation goes ihe Seaail
aad Bawasiaa aeries are ibe obvious best rocks. As these aake up
ibo bulk of ibe Oaaa Monaiaia range then ii is ibis aonnialaous
aroa ibat offers ihs grsaioSt prospoois for diseovery of baae aeial
deposits.
OrssBwood aad Loneys (19^8) reconnaissance of ihs aineral
reconrces of Trucial Oaan indicate ihe preaance ef aubstantial if

c
- 13 -
•'S iselaied, ioanages of chroaite, widesprsad iracee of copper ninerali-
aaiioa aoae of oconoalc ionor, aaagaalferous cherts, and several
feocheaioally aaoaalons acnes for nickel aad aolybdenua. They
do bowever siaie thai aoae of ibe alaeral deposits ao far found in
Trucial Oaan are econoaic propositions under prsssnt conditions.
'li As iheir work waa confined io approxlaaiely one fifth of the total
f
area of Seaail aad Bawasina roeka the cbancas of discovering
siallar bodiea in Oaan is probabalistically auch greater.
Chroaite aad alckel are likely to be present in ihe Seaail
uliraaafios wbilat copper and aMBgaaeae aay be expected in ihe
h:- Bawasina Series. Ths possibility of aolybdenua occurring in
econoaic proportions is not great but ainor acid intrusions are
known and ibe preaance of dlorlio stocks does noi preclude the
developaent of porphyry copper type aineraliaation.
The Oaan aountain ophiolite suite probably corrolates with the
altrabasie belts of Cyprua aad Turkey where aiailar rook types have
given rlss to econoaic ehroae and asbestos deposits.
At Cyprus Chroae coapanya workings on Troodoa, ihe extreaely
irregular shape aad lack of coasiaacy of ibe ore pockets, prsseoted
iroBoadous osplorailoa aad aiae doTolopaeai probleas and ore reaerves
aoTcr looked good. Bvoa ao over ibo period froa I931 io I937 over
170,000 ioaa of chroae ore was aiasd.
These figures are givea to iBdioate thai Greenwood and Loneys
eaiiaates of iadividual depealts coBtaining up to 3>700 aetric tons

^:
c
1
-14-
of ehroae ore ia Trucial Oaun aight be auch aore encouraging than
ibey supposed particularly aa iheir eetiaatea were hot based on any
drilling results aad ia view of ihe typically erratic distribution
of obroae ore*
All thai can be said, at ibe pressnt state of knowledge in
Oaaa, with regard io ecoaoaic alaeral potential is that eonaiderable
areas of rock types occur that are known io be favourable to
cbroalie platinua, aickel, copper and asbestos foraatlon but that
ihe delineation of econoaic deposits could only eoae after a well
developed aad probably expeneive exploration caa^paign.
jpineral ^pportunitiea in Oaan
Due io ita relatively unexplored stats aad ibe pressBce of a
waat aass of differentiated ultrabaslcs, Oaan remains one of the
aost llksly placss io find scenoaic deposits of chroae ore. Its
known association in the past with copper soeltlng and the recorded
preaance of sub-aurglnal eopper in Trucial Oaan provide favourable
pointera towards the aearoh for eopper in this region.
Bowever in its preaent undeveloped state Muacat and Oaan
obviously provides oxtreae challenges io successful aining ventures.
Ths lack of road and transport facilitiee, ihe lack of trained seal
akllled labour force, the eoaplete absoacs of aay fora of aining
code ABd the lack of any foraal goveraaental procoedures aight appear
io ailliate againat aocceeaful ventures in this territory. One
•ould however argue that ihe eoaplete lack of a aining code could

c
t^,-
- 15 -
allow favourable aegoiiatipns of an equable arrangeaent with the
Sultan. The recent discovery and exploitation of coamercial oil
depoaiia bas provided a source of revenue ihai could be ihe spring­
board for ibe devolepaeni of Oaan.
Aocording io ihe Sultan*s I966 pronounceaents and ay discussions
wiih bis consul in London and several of bis consultants the present
is an extreaely opportune tlae io discuss aineral exploration
activities as ihe Sultan is particularly iaterested in raw aaterial
developaent, hawing at last ihe financial gaina of the twenty years
of oil exploration.
Ai present aineral eoacessioas ars held by Woadell Phillips
for ihs Ihofar Proviace aad ihs reaaiader of ihe Sultaaate ia
covered by a eoaceasioB granted to Shell Oil* Whether Shell Oil
aro iBiercsied ia bass asial prospection reaains open but in view
of diversification trends it is highly unlikely that ibey would
willingly give up their aineral concessions.
They auy, of course, be willing to eooperaie in a Joint
exploration venture and ahould U.S. Steel continue its interest in
Oaaa, then the poaaibilitiea of ouch a aove ahould be carefully
•onsldered. Shell Oils oxpertlss in Oaan, the coapoaics facilities
for iraaspori, siorags aad accoaaedatioa and its close ties with ihe
Saltan would bo •xirSaely favourable features of aay cooperative
voBturo.

• TOs^S •S*Q ^ataoqe ja^^ex w je ^dxaaea aodn 'l 'ji aopael *tJino9
^jaqxf *l 0/0 m\^ o^ a^T

:C" • ^
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" 17 -
inioresi in Oaan the oonaul will infora the Sultan accordingly.
As ths Sultan apparently la in daily Telex coaaonication with
bla London advlaers and spends froa 3 io 6 aonths of the year in
London, a proapt reply should be forthcoaing.
Appendix A.
Geology and Mineral Eesourcss of ibe Trucial Oaan Bange
by I. Oreenwood aad P» Loaey*

I
Until recently the sultanate of
Oman was the most secluded
and least known country in
the Arabian Peninsula. Now, with
the discovery of oil within its borders
and with world attention focused
on the Middle East, Oman is
emerging from its isolation. The
same, however, is not as true for the
Ibadiles, an Islamic sect whose
members make up a large part of
Oman's population and shape much
of its religious and social life.
Throughout the Islamic world,
which stretches over broad areas of
Asia, Africa, and Europe, the
Ibadites are regarded as an indrawn
and mysterious people.
The smallest ofthe three Islamic
sects, the Ibadites number no more
than half a million followers, while
the other two sects—the Sunnites
and the Shiites—together number
perhaps half a billion. The antecedents
of Ibadism go back to the first
century of Islam (the seventh century
A.D.), when a band of extremely
strict Muslims accused Aii,
the head of the Islamic community,
of deviating from the fundamental
principles of the new faith. Even
though he was the son-in-law of the
Prophel Muhammad, they left his
camp, earning themselves the designation
of Kharijiles ("outgoers" or
"seceders").
This secession took place in Iraq,
All having moved the capital of Islam
there from Medina. The partisans
of Aii, the future Shiites, then
lost out in a conflict with other rivals,
the future Sunnites, who
founded the first Islamic dynasty,
with Damascus as capital. The dissident
Kharijiles energetically, resisted
Sunnite rule, particularly in
the Arabian Peninsula. In time,
however, they split into divergent
branches, of which only the Ibadiles
have survived. The name Ibadite
is taken from Abdallah ibn
Ibad, an Arab theologian who is regarded
as the founder of the
branch.
A basic cleavage between the
three sects is the question of who
should head the Islamic community
as successor to ,the Prophet. The
Shiites require that the head, whom
they term imam, be a direct descendant
of the Propliet through his
daughter Fatima and her husband.
58
Aii. The Sunnites, allowing greater
latitude, stipulate that the head,
whom they term caliph, must be a
member of the Prophet's tribe, the
Quraish (Koreish). The Ibadites,
however, maintain that any Muslim,
provided he meets the prescribed
standards of character, piety, and
leadership, can be chosen as
imam—"even an Abyssinian slave
whose nose has been cut off" (none,
however, has yet been elected by
them).
While the Sunnites and the
Shiites have leaned toward dynastic
succession, the Ibadites adhere to
the original Islamic principle of
election. Choosing a new imam is
the prerogative of "the people who
bind and loose," the influential
members of the community whose
choice the common people should
ratify by acclamation. Ibadite doctrine
also holds that if there is no
qualified candidate, an interregnum
in the imamate is acceptable.
To escape the long arm of the
Sunnite caliph, many of the early
Ibadites migrated from Iraq and settled
in Oman on the eastern edge of
the Arabian Peninsula. From there
missionaries and merchants carried
Ibadism down to the coast of East
Africa and the offshore islands, especially
Zanzibar. Other Ibadites
moved westward and created isolated
centers in North Africa, where
their antiauthoritarianism appealed
to Berbers restless under the rule of
Arab conquerors. Small Ibadite
groups, following their traditional
beliefs, still live in the mountains of
Libya, on the island of Jarbah off
the Tunisian coast (sometimes identified
with Ulysses' Land of the
Lotus Eaters), and in oases along
the northern fringe bf the Algerian
Sahara. Scattered as these eastern
and western Ibadite settlements are,
they have maintained contact with
each other over the centuries.
Oman is the largest and most significant
Ibadite refuge and stronghold.
There a rugged mountain
range, traversed by only a few difficult
passes, seals the interior from
the coast. Some Ibadites live on the
seaward side of the range, but the
main body of believers is found in
inner Oman, where water brought
down from the mountains by underground,
Persian-type aqueducts irri­
gates fertile plantations of dates and
other crops. Here the Ibadites have
pursued their way of life with little
or no contamination by detested
alien influences.
The supreme goal of Ibadism is
the establishment and maintenance
of an Islamic society modeled after
the original Islamic community of
the Prophet Muhammad. Accordingly,
such a community should be
ruled by the prescriptions of the
Koran, the divine revelations transmitted
through the Prophet, and
guided by the examples provided by
the Prophet's own words and acts.
This has not always been easy to
achieve. For centuries before Islam,
Arab tribes were embroiled in bitter
rivalries, such as the one between
the southern and the northern
Arabs. Islam's revolutionary doctrine
that piety, not birth or ancestry,
is the touchstone of nobility
in the sight of Allah Only partially
undermined the tribesmen s pride
in their lineage. Ibadite Islam has
had to contend with this same powerful
force of tribalism in Oman,
where southerners and northerners
have frequently been at odds.
Every Ibadite imamate in Oman
has also had to contain another ageold
and deep-rooted rivalry dividing
the Arabs, that between the nomads
and the settled people. The larger
nomadic tribes range in the interior,
where their members often
penetrate into the sandy wastes of
the Empty Quarter, the great southern
desert of Arabia. When peace
prevailed, the nomads would trade
in the town markets, but time and
again the calm was shattered by nomad
raids on the town dwellers.
The first Ibadite imam in Oman
was elected in the eighth century
A.D. Many imams succeeded him,
although there were interludes
when the community existed without
a.head. In the second half of the
eighteenth century the imamate was
bestowed on the ancestor of the
Eresent ruling family of Oman, the
ouse of Said. The grandson of this
imam, apparently lured by the commercial
wealth of the seaports, took
the drastic step of transferring his
capital to the coastal town of Muscat,
where the consequent exposure
of the rulers of the house of Said to
heretical ideas and practices es-

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• JBi mh MShaiMliMwi.«^—fci«

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Although the 1970 coup gave
Omani women the right to
an education, they still lead
highly restricted lives
filled with such chores as
carrying water, bottom, and
washing utensils in streams,
left. Many still cover their
faces in public, but the
distinctive masklike veils
of Baluchi triheswomen, below,
are rarely seen today.
A bride, far left, acquires
some of the family jewels
when she marries.
63

64
During the thirty-eight-year
reign of Said ibn Taimur,
which ended in 1970, education
and trade were discouraged.
Today, imported cars cause
traffic jams in Matrah,
right, and children, top,
attend newly built schools.
Above and left: Small
groups of. men, their ornate
khanjars ("daggers") tucked
into their cartridge belts
or sashes, rest during
the heat ofthe day.

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65

Continued from page 60
Development is taking place in
many areas—agriculture, fishing, oil
exploitation, education, and transportation.
At the same time,
Oman's political profile has been
raised, and it has joined the Arab
League and the United Nations.
In today's world, it is probably
impossible for any country to mainlain
the isolation and seclusion that
for, so many years characteri'ied
Oman. Like the other Arab states,
Oman has become an arena for the
playing out of international politics.
For the past ten years a group of
guerilla fighters, the Popular Front
ibr the Liberation of Oman and the
Arabian Gulf, has been holding territorv
in the mountains of Oman's
Dliotar Province. Led by men
trained in the People's Republic of
China, the Soviet Union, and East
Germany, aided by the People's
Democratic Republic of Yemen and
by Iraq, and fighting with Sovietmade
rifles and rockets, the guerillas
are trying to bring the entire
gulf region under their control. The
sultan's effort, in turn, has been
supported by Britain, Jordan,
Libya, and Iran; Iran is reported to
have recently sent in several thousand
troops, about thirty helicopter
troop carriers, and some artillery.
At present Oman is not only
caught in the mesh of international
rivalries, it also remains beset bv internal
divisions. Ibadites and Suniiili'S,
nomads and townspeojile, inhabitants
ol the coast and people of
the interior—all have struggled for
cenluri(;s to mainlain llicir disparate
ways of life. Although the
sultan is striving to reconcile these
different groups, their old traditions
will not die easily. •
66
The loose, heavy clothing
worn by Bedouin
camel drivers keeps them
comfortable during the
day by absorbing
perspiration and allowing
air to circulate.

,, To:; File
11
d.
Subject: Mineral Possibilities
Oman Mountains,. Oman
General ;;,,-•:':• -> :
United
btates
Steel
Corporation
Interorganization Correspondence
Date: February 18, 1982
From: M. Haddadin ' .
Prior to the year, 1928 little detailed geological investigation was carried
out in Oman. However, Lees (1928) was the first to study and formulate any
substantial account of;the geology in the area. He recognized the Hawasina
and the overlying Samail igneous series, which form the bulk of the Oman
Mountain ranges,..as majorcomponents of a thrust complex. Lees regarded the
Oman Mountain ranges as a southern extension of the Zagros Mountains of Iran.
In 1959 Morton,, in a-synthesis of the geology of Oman, gave evidence for
believing that the idea of thrusting of the Hawasina and Samail onto the Arabian
foreland from the east is incorrect. He suggested that the chaotic structure,
which is typical of the serpentine and radiolarites of the Samail and Hawasina
series, was derived through "effusion tectonics" associated with Upper Cretaceous
serpentine extrusions. .•;;:: ' ^
Detailed studies of the Ophiolites in the Middle East, especially in the past
ten years, demonstrated that some geodynamic process such as oceanic crust or
some type spreading center was accountable for their formation. Recent geologic
studies proposed several emplacement models for the Ophiolite in Oman. The most
favored theory considers.the Samail Ophiolite and the associated pelagic sedimentary
deposits of the Hawasina group to have been formed in the Tethyan Sea
and later emplaced ;onto the Arabian continental margin.
Geologic Setting ' '''py-:yy.;'' *; "
The Oman continental margin is one of four geographic segments that relate to
separate geologic histories. These segments include the Saudi Arabian platfonn,
the Zagros fold belt in Iran, the Markan continental margin and the Gulf of Oman.
The Oman continental margin forms a double arc concave southward with the Persian
Gulf on the west and. the;Gulf of Oman to the.east. The mountains of Oman which represent
the margin of the Arabian Continental Platform extend from the Musandam
peninsula to Ras Al, Hadd Fig. 1;. However, they form a chain of mountains
geologically distinct from the rest of the Arabian peninsula. The Oman mountains
contain great thickness of carbonate rocks that correlate with those of Saudi
Arabia and of the Zagros fold belt of Iran. However, the pr'esence of extensive

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(. pelagic sedimentary deposits and ophiolites overlying these shelf carbonate
rocks presents a geologic situation unique to the area. Late Tertiary folding
and subsequent erosion exposed these rocks revealing the total sedimentary
section as well as the metamorphic basement. These basement rocks, in the Saih
Hatat area, were metamorphosed to greenshist facies. The metamorphic event for
these rocks was 327+16 m.y. ago.
Overlying the pre-Permian metamorphosed, and deformed basement are 3,700 meters
of Middle Permian to Middle Senonian carbonate rocks, referred to as Hajar Supergroup.
• - •-•; •.,;' , ' -; . ' ; .'
Overlying the Hajar Supergroup is a sequence of thin imbricated sedimentary rocks
that range from radiolarian chert through Limestone turbidites. The sequence is
the Hawasina unit (Permian to Senonian): The site of deposition for the Hawasina
was a deep ocean whose south boundary was the Arabian continental margin and extended
northeastward to a spreading ridge in the Tethyan Sea.
Accompanying and overlying the pelagic Hawasina, are the Samail Ophiolites, a
gigantic mass of ancient oceanic crust formed in the Tethyan during Cretaceous
spreading. The Ophiolite mass is considered to represent a slice of oceanic
crust estimated, to be 15 km thick that was emplaced upon the Hawasina. The mass
consists mostly of peridotites, layered gabbro, sheeted dikes and pillow lava.
The composition of the peridotite, which constitutes the major part of the
/'•, Ophiolite (9-12 killometers), is as follows Fig.\2. The bottom few hundred
[ , meters are composed of harzburgite with porphyroclastic texture altered with
" ; mylonite bands. The zone is generally foliated with some interbeds of dunite.
Spinel lineation is also present in this zone, however, it tends to decrease
„ in, abundance upward. The harzburgite contains some orthopyroxene bands.
Overlying the base zone is a sequence, approximately 11 killometers thick,
consisting mainly of foliated harzburgite with minor clinoproxene. Orthopyroxene
bands, parallel to the foliation, in addition to concordant and discordant
bands or bodies of dunite are present in the harzburgite. Podiform
chromite bodies commonly are present in this sequence.
Overlying this sequence is a thin transitional zone, approximately one killometer
thick, consisting of harzburgite and dunite. This zone seems to grade into a
zone of pure dunite. ^
The harzburgite in the Oman ophiolite has a mineral composition of olivineforsterite
( 74%), enstatite ( 24%) and spinel ( 2%). Clinopyroxene is rarely
present in. the harzburgite, however, when present it appears to be chromium
diopside. The olivine .in the concordant and discordant dunite bodies is commonly
forsterite and is always accompanied by 2-3% spinel in addition.to some orthopyroxenes
and clinopyroxenes. Almost all the peridotites in Oman exhibit
pervasive degree of serpentinization where lizardite and clinochrysotile are
dominant. In general serpentinization averages 62% by weight in the harzburgite

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c and 81% in the dunite.. -^Several diabase and gabbiro dikes cut the harzburgite,
however, there is no indication for their being the feeder, for the overlying
layered gabbro, from the magma chamber.
The average composition of harzburgite and dunite from Oman ophiolite compared
with other occurences is shown in Table 1.
The overlying layered gabbro reveals a history of gravitational crystallization
and consists mostly of calcic plagioclase, clinopyroxene, olivine and minor
amounts of orthopyroxenes.. Trace amounts of apatite and magnetite are usually
present. ' ''-y;y .'^ -
The sheeted dikes, above the gabbro, consist almost entirely of diabasic texture
and basaltic composition. Minor leucocratic dikes of diorite to plagiogranite
composition are present. The sheeted dikes in turn are capped by a layer of
olivine basalt pillow lava. , ;
The Hawasina and Samail Ophiolites were covered unconformably by shallow water
limestone and/or reworked laterite and conglomerates. These overlying strata
were deposited until the end of Miocene time. Deformation and uplift of the
Oman Mountains, nearly contemporaneously with the Pliocene phase of the Zagros
fold belt, resulted i,n, the extensive domal uplifts of the mountains of Ahkdar
:and Saih Hatat.'.'/:--;_;:':,,

c
,
TABLE 2.
SiO}
A1,0,
FcO
MgO
CaO
0,0,
NiO
Mg/(M8 + Fr»*>
atom%
Average Composition of lUrtburgite and Dunite From Cross Seciion Compared tu Otlier
OccufTcnces
Oman
43 9
087
72
462
091
051
036
Q92
Harebiir$ite'
Burro
Mountain Caudeto
440
094
78
460
06
0.43
0 32
091
440
0 78
82
43 3
050
042
0.31
091
Troodos
43 5
047
81
45 7
077
0 39
027
091
Oman
40.6
0,6)
7,8
48,6
0 59;
0.54
043
0.92
Ounitc
Buno
Mouauin
40,6
0.49 '
7.7
^. ;:-so.6 :\':
V 0.60 :
.''': -0.37-:,';
•;v'.,0.92:--":
.,'
Average ot 23 pcRdouiet and (6 dunitea, oomparative data from Coleman (1977).
Twin
Sisters
40.5
024
, 8.3 -
49.8
0.15
:• 0.58; ;
: 0.29
;0.91 r
Troodo
40,4
0.14
: 8.8
49.1
0.18
0.41
024
0.91

-7-
usually concentrated .in the dunite arid harzburgite portion of the peridotite.
Such deposits are found in the Philippines, Egypt, Sudan and the Canadian
.Appalachians. - ' .'
The platinum group metals have been reported in the ultramafic rocks of deposits.
Some dunite pipes or bodies in the Bushveld complex (a stratiform type deposits)
are reported to contain commercial concentration of platinum averaging as high
as 15-31 ppm. In connection with chromite mining, the Acoje mine of the
Philippines recovered a total of 5,500 oz of platinum from concentrates of disseminated
sulfides in-the serpentinite.
The second group of deposits is the massive sulfides of Cu, Ni, Zn, Co and Fe.
This group of sulfides usually occur in the volcanic rocks (pillow lava) of
the ophiolite assemblage and associated sediments. The deposits are probably
formed by reactio,ns between volcanic hydrothermal solutions from deep seated
volcanic sources,"between eruption of successive flows, and the sea water.
The Cyprus massive sulfide deposits are often quoted as examples of the ophiolite
associated massive sulfide deposits. The deposits are usually found in the lower
portion ofthe pillow lava within the ophiolite assemblage which is composed
dominantly of olivine basalt. Many of the deposits in Cyprus have a pipe-like
stockwork zones beneath the massive ore. The stockwork zones extend downward
for several hundred meters and have diameters less than that of the orebodies.
These zones are usually marked by low-grade mineralization and pervasive
hydrothermal alteration. It should be noted here that the massive sulfide deposits
within the ophiolite assemblage seldom occur singly and have characteristic grouping
patterns.,,-V ,',;:• ';''•'.••;•;„'- .:y: .y!•/.•-.y--- '.'•.;.••
Massive sulfide deposits of this type have been reported to contain significant
concentration of silver and gold. Silver and gold (as high as 1.6% gr/ton Au and
5.7 gr/ton silver) have been produced from gossans in the stockworks zone of some
Cyprus massive sulfide deposits. = . ,-.
The striking similarities between the ophiolite assemblage in Oman Mountain ranges
and those ophiolites found In Philippines, Cyprus, Turkey, Iran, Italy and the
Canadian Appalachians could indicate them to be a potential target for sizable
orebodies. The mineral targets, which could be of apparent Interest, in the
mountain ranges should include chromite, copper, nickel, cobalt, platinum, gold
and silver: however, it seems obvious from the available data on Oman mineral
resources that chromite and copper are the only mineral s reported in known
occurrences. ' : ,
Chromite occurs as podiform lenses usually small, elongated and Irregular, in
serpentinite derived from peridotite. The largest of the occurrences, north
of the capitol city of Muscat, is described to be not more than 60 meters long
and 8 meters in width and exposed to a depth of 3 to 5 meters. The estimate of
chromite tonnage in this lense amounts to 5,000 metric tons. Samples taken from
this lense contain as high as 56.5% Cr203 with Cr/p^ ratio in excess of 2.8/1.0.

C
V
1
'-.V
-S-'
The largest known copper mineralization reported in Oman include the Lasil ,
Aarja and the Bayda which are located north of Muscat. These deposits exhibit
most of the Cyprus-type characteristics and are located between two pillow
lava units. The deposits are associated with faults, usually elongated and
discontinous. The pre-production reserves is approximately 15 million tons
with a copper grade of 2.1%. It should be noted here that in 1978 Coleman,
in describing the Samail ophiolite in Oman, mentioned that over 150 cupriferous
massive sulfide prospects have been discovered throughout the assemblage. These
prospects are usually fault related.
At our present state of knowledge in Oman, commercial deposits of platinum,
gold or silver have not been reported in the ophiolite rocks; however, several
samples of harzburgite and dunite were analysed for nickel. The results indicate
the nickel values to be within the theoretical threshold values, averaging
2500 ppm and 3000 ppm nickel in the harzburgite and dunite respectively. It is
therefore, believed that nickel could constitute geologically plausible target
in the Oman ophiplite.; ^ . '. -
Reported occurrences of gold in Cyprus ophiolite and platinum in the Philippines
ophiolite, which compositionally resemble the Oman ophiolite, indicate that the
Oman ophiolite could ,be a potential target fpr platinum and gold discoveries.
In conclusion, chromite and copper are the most likely minerals that could be
found in sizable commercial deppsits in Oman. In.^ order to maximize this possibility,
the entire area of the Samail ophiolite should be considered.
Considering the rock types in, the area, the potential of discovering platinum,
nickel, gold and silver with the chromite and copper is also likely.

c
2584
TABU I. CrowSoctipo
3«00
3100
1800
4300
3000
3500
3700
2800
3100
2900
3300
2500
3100
3700
2600
2VX)
7WX)
2100
3200
2700
5300
7200
43
36000
3500
2600
3000
33CO
610
2O00
2600
2700
2300
2700
2400
2600
2600
poo
2J0O
2200
2500
2500
2500
2500
2400
2100
2400
2600
110
2300 '
3100 MO
3400 120
3500 100
3500 no,
2600 no
2900 110
3500
too
2600 95
I9g0 110
100
100
2300 lUO
4200 too
2500 88
2300 90
too
110
120
110
.120
120
120
140
100
110
98
too
110
96
97
7
II
15
18
30
11
9
32
9
31
25
30
7
16
3
6
'
In pMW per annum.
^ i ^ for vertical pwnuoc of each lampte
€-209
C-208
C-207
C-205
C-210
C-2fi3
C.204
C-20tt
C-196
C-197
C.199
om
oxn
C-«90
C-IS9
C-188
C-182
C-180
C-178
13
18
II
4
38
13
. 5
3
46
79
37
43-
4
4
48
28
44 •
40,
53
49
, SO
60
50
43
46
53
49
44
20
37
15
20
28
32
.38
59
100
15
18
62
42
10
10
21
„ M m» nion in olivine from >