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subject to progressive subsidence and uniform thick
shallow marine sedimentation (Table 2). There are very
striking simple linear facies boundaries parallel to the
old continental margin (Figs. 5 and 14). These were
presumably normal faults formed during extensional
movement at that time.
In the north the sedimentary environment was more
complex, with rapid facies changes and unstable conditions.
There were large areas of shallow sea and small
Red Sea type oceanic basins (the sites of the Central
Iranian narrow ophiolite belts) with a few small land
areas. Presumably these basins and shallow seas were
associated with fragmentation of continental crust during
the period of movement of the continental mass from
Arabia to Asia (Figs. 4 and 5). There appears to be
evidence on which to base speculation about when and
how the Central Iranian narrow oceanic basins formed.
However, the stratigraphic evidence suggests that the
Central Iranian continental fragments were never widely
separated (Tables 1, 2, and 3; Figs. 10 to 17).
1.3.1--Late Cretaceous orogenic phases
The Late Cretaceous Epoch in Iran is characterized by
two episodes of ophiolite emplacement. The emplacement
dates and the associated change of sedimentary
conditions from oceanic to shallow marine are critical,
since they determine the time of ocean closure. Detailed
arguments outlined in Sections II.5.2b and II.5.3b constrain
the dates of these changes together with the High-
Zagros and the Central Iranian ophiolite emplacement to
be nominally around 75 Ma and 65 Ma (Fig. 6; Table 2).
The latter phase was associated with regional metamorphism,
magmatism, and extensive folding and uplift
throughout the country and is taken here to represent the
final closure of the High-Zagros Alpine Ocean. The
’High-Zagros-Oman ophiolite-radiolarite belt,’ which
was emplaced in the form of a thrust stack around 75
Ma, is apparently the remnant of the High-Zagros Alpine
Ocean extending from southeastern Turkey via
High-Zagros to Oman. The ’Central Iranian ophiolitemtlange
belts’ were emplaced around 65 Ma and resulted
from the subsequent closure of the ’small ocean
basins’ created by fragmentation after the separation of
Iran from Arabia. They form a complex system in the
country (Fig. 6). The ’Makran ophiolite-mtlange’
southeastern Iran (Figs. 1, 6, and 14) is not interpretable
as a continental closure, since subduction of ocean crust
BERBERIAN AND ~NG 217
preceded and succeeded its emplacement. It may be
speculated that it was associated with the collision of an
island arc of the eastern High-Zagros Alpine Ocean.
The Sevan-Akera and Vedi ophiolite belts of the Little
Caucasus, which were emplaced around 118-105 Ma,
were the remnants of the western part of the Hercynian
Ocean in the northwest, and presumably were emplaced
during the collision between northwestern Iran and the
Caucasus (see Section 11.5. lc).
The Central Iranian ophiolite-mtlange belts are associated
with glaucophane-schist metamorphism (along
the belt north of the Zagros fault line and in Makran),
and simultaneously the active Central Iranian continental
margin (the Sanandaj-Sirjan belt) was affected by
greenschist metamorphic overprint (see Section
II.5.3b; Figs. 6 and 14). Extensive magmatism
not
found associated with the closure of the internal ocean
basins. This could be because the volcanism is concealed
by later sediments, or because the area of ocean
crust consumed was too small to allow significant volcanic
arcs to become established. The second explanation
is a plausible confirmation of the view that the
internal ophiolites do not represent the remains of the
large ocean basins.
We take the Late Cretaceous events to represent the
disappearance of the oceanic crust between Asia and
Arabia. From this period to the present, all continued
convergence of these plates apparently has been accommodated
by processes that have progressively thickened
and shortened the continental crust and caused its gradual
emergence (Figs. 7 to 9). The compression has
been accompanied by extensive volcanism and various
tectonic episodes, but none have the characteristic of a
closure episode and no ophiolites and pelagic sediments
have been emplaced later than 55 Ma.
1.4----MIDDLE AND LATE ALPIN EVENTS
The Middle Alpine orogenic events started at the
close of the Late Cretaceous movements (65 Ma) and
ended at about 20 Ma. The Late Cretaceous movements
created the main structural features of present-day Iran
(Figs. 6 and 7). During the closure of the High-Zagros
Alpine Ocean in the south, acid plutonic activity took
place in Late Jurassic time (140 Ma) along the southern
margin of Central Iran (the Sanandaj-Sirjan belt; Figs.
and 14). Later plutonic activity and deformation in the
volcanics and the comagmatic alkali granites apparently are the products of post-orogenic rifting. 8. Approximate boundary
between different sedimentary facies. 9. Basement faults (N: Najd left-lateral fault system in Saudi Arabia; Z: Main Zagros and
High-Zagros reverse fault system in Iran; and C: Chapedony fault delineating the western part of a possible Precambrian island
arc in the eastern part of Central Iran). 10. Present continental shorelines.
Principal sources of data: Reconstruction (Mercat6r Projection) is modified from Smith et al. (1973). The Iranian
tectono-sedimentary data are based on our Fig. 10. Data outside Iran come from Abu-Bar and Jackson (1964), Wolfart (1967),
Ketin (1966), Gas and Gibson (1969), Brown (1972), et al. (1974),and Frisch and A1-Shanti (1977).