PDF COPY - Manuel berberian

the post-Cretaceous deformation and the cause of the
Eocene volcanism are not understood; therefore the
foregoing arguments, although consistent with the stratigraphic
evidence, must be treated with caution.
A striking feature of the evolution presented here is
the apparent control of later fold episodes by the structures
formed in the earliest fold episodes. This may be
explained by regarding the early phase as introducing or
reactivating structural anisotropy that later phases have
also been forced to follow. Since these structures are
not everywhere perpendicular to the relative motion
between Arabia and Asia and since this motion has, in
any case, changed direction since Late Cretaceous time,
it follows that structures other than folds must have
played an important role in the deformation.
Many of the major faults have been inherited from
earlier periods. Those that are most easily recognized
formed facies dividers, presumably when acting as normal
faults during tensional, down-warping, and depositional
phases. The Main Zagros, I-Iigh-Zagros, Tabas,
Kuh Banan, Chapedony, Posht-e-Badam, and several
recent faults were probably major bounding normal
faults since late Precambrian time but have operated as
compressional faults during the overall shortening and
crustal thickening of the last 60 Ma.
Particular questions that require further study are the
time of onset of the late Paleozoic subduction in northeastern
Iran, the possibility of the late Paleozoic metamorphism
along the Sanandaj-Sirjan belt, the time and
manner of formation of the Central Iranian narrow ocean
basins (that became the Central Iranian ophiolitem61ange
belts), and the reason for the lack of extensive
exposure of the magmatic arc along the Sanandaj-Sirjan
belt for the late Paleozoic and Middle Triassic events.
Finally a detailed and systematic investigation of the
petrology, the radiometric ages, and the trace- and
major-element composition of the magmatic (including
ophiolites) and metamorphic rocks of the country, together
with paleomagnetic studies for certain crucial
periods and sites, will carry us further towards a true
understanding of the paleogeography and tectonic evolution
of Iran.
II--Review of the geological data
The Iranian plateau extends over a number of continental
fragments welded together along suture zones of
oceanic character. The fragments are delineated by
major boundary faults, which appear to be inherited
from old geological times. Each fragment differs in its
BERBERIAN AND KING 223
sedimentary sequence, nature, and age of magmatism
and metamorphism, and in structural character and intensity
of deformation (Fig. 1). In this section the evolution
and effects of different orogenic phases since Late
Precambrian time are reviewed and discussed separately
for each unit. A brief review of the previous paleogeographic
and tectonic reconstructions of the region is
also included (Section 11.9).
II. I--PRECAMBRIAN
The continental crust of Iran was metamorphosed,
granitized, folded, and faulted during the Late Precambrian
by what is called the Hijaz or Pan African orogeny
(around 960-600 Ma). These metamorphosed rocks,
which are scarcely exposed, form the basement of the
region (Huckriede et al. 1962; Stocklin 1968a, 1974,
1977; Nabavi 1976; Berberian 1976a,b). This orogenic
phase is considered by Brown and Coleman (1972),
A1-Shanti and Mitchell (1976), Greenwood et al. (1975,
1976), Neary et al. (1976), and Frisch and AI-Shanti
(1977) to be an episode of plate collision and arcmagmatism
terminating about 600-550 Ma in Arabia.
Following these movements the Upper Precambrian -
Cambrian Hormoz Salt (Stocklin 1968b, 1972) was deposited
in a basin(s), parts of which now lie along the
north and eastern side of the Arabian Peninsula (Fig.
10).
Since the different orogenic phases recognized in the
crystalline shield of Arabia (Greenwood et al. 1976) are
not recognized in Iran, no detailed correlation can be
made between the basements of Iran and Arabia. Hence
the consolidation of the Iranian basement is not well
understood. The Precambrian Chapedony and Posht-e-
Badam complexes of east Central Iran (Hushmandzadeh
1969; Stocklin 1972; Haghipour 1974, 1977; and
Haghipour et al. 1977), which consist of metagreywacke,
metadiorite, meta-andesite, amphibolite, pyroxenite,
serpentinite, and calc-alkaline intrusive rocks
(Fig. 10) may represent the crust of a Precambrian
calc-alkaline island arc (Berberian and Berberian
1980). The nearly north-south arcuate mountain belts in
east Central Iran may represent the original pattern of
the Precambrian arc belts. Like the Arabian basement,
the island-arc cratonization of the Iranian Precambrian
basement should have taken place prior to the deposition
of the Upper Precambrian - Lower Cambrian Hormoz
Salt and detritic sediments.
Because of subsequent orogenic movements, the few
attempts to date the Iranian basement using mainly
Principal sources of data: Reconstruction (Mercartor Conformal Projection) is modified from Smith and Briden (1977).
tectono-sedimentary data within the boundaries of Iran are based on our Fig. 14. Data outside Iran come from Vereshchagin and
Ronov (1968), and Adamia et al. (1977) for northwesternmost part, Saint-Marc (1978), and Powell (1979) for the north
part.