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in high-grade Precambrian metamorphic rocks. A new generation of biotite is formed in the Upper Precambrian Sefid granite and granodiorite of the Saghand area during this phase (Haghipour 1974; Haghipour et al. 1977). Isotopic disturbances around 240 to 190 Ma are observed by Crawford (1977) in the rhyolite samples from the Upper Precambrian Gharadash Formation (in Azarbaijan, northwest Iran), in the Precambrian rhyolites of the Taknar Formation (in the Kerman area), in the Upper Precambrian rhyolites of the Rizu Formation (also in the Kerman area), and in the Precambrian metamorphic rocks of the Saghand area. These together with disturbances around 203 + 13 Ma observed by Reyre and Mohafez (1972) in the Precambrian metamorphic rocks of the Anarak region are apparently the effect of the Middle Triassic compressional movement in various parts of the country. The slaty and phyllitic structures observed in the upper Paleozoic rocks of the Talesh mountains (Davies et al. 1972; Clark et al. 1975) seem to be the result of the same movements in the area southwest of the Caspian Sea. Following the Middle Triassic (210-195 Ma) compressional phase, Central Iran and the Alborz region underwent tensional movements. The initiation of this extensional phase is characterized by the Upper Triassic continental alkali rift basaltic lava flows and melaphyres preceding the deposition of the Rhaetic-Liassic (200 Ma) coal-bearing continental clastic deposits of the Shemshak Formation (Assereto 1966) in Central Iran and Alborz (Fig. 13; Table 2). Two doleritic flows, about 100 m thick, interbedded in the Upper Triassic Dolaa Group of Syria (Daniel 1963) presumably belong to this extensional and rifting phase. H.3b---Zagros basin during Triassic time During the Middle Triassic orogenic movements, the whole country was folded and uplifted, except for the Zagros basin where the movements were less intense. The Zagros basin steadily subsided along faults inherited from Permian time and earlier. The marine carbonate sedimentary regime persisted throughout Permian and Early Triassic times (Dalan and Kangan Formation; Szabo and Kheradpir 1978). Regressive conditions then occurred in the Middle Triassic Epoch, resulting in the deposition of the evaporites of the Dashtak Formation, indicating hot and arid conditions (Fig. 12). The reddish green shale separating the Permian Dalan Formation from the Lower Triassic Kangan Formation was first interpreted as an unconformity by Szabo (1977). This was later corrected to a temporary cessation in carbonate deposition (Rosen 1979; Szabo and Kheradpir 1978). There are still some similarities between the Lower- Middle Triassic stratigraphic succession of the Abadeh area in Central Iran (Taraz 1974) and those in the Zagros basin (Setudehnia 1978), but the Upper Triassic rocks BERBERIAN AND KING 239 Central Iran show marked differences from those of the Zagros. The Triassic evaporite and dolomite sequence in the coastal areas of the Persian Gulf is an extension of the evaporite basin of Arabia and Iraq (Murris 1978). Towards the High-Zagros in the northeast, the evaporites are replaced by dolomites (Setudehnia 1978). The Middle Triassic movements in the Zagros (Middie-Upper Triassic unconformity) were not as intense as the movements in Central Iran. The uplift and erosion were apparently stronger in the High-Zagros belt (most of the Triassic and some Upper Permian sediments were presumably removed from the High-Zagros), while to the south erosion was less severe. The Middle Triassic evaporite beds of the Zagros (anhydrite/dolomite and red shales) are unconformably overlain by the Liassic terrigenous clastics and transitional terrigenous-to-open-madne sediments of the Neyriz Formation. No Upper Triassic beds have been found in the Zagros so far (Szabo 1977; Szabo and Kheradpir 1978), probably indicating an apparent drop in sea level owing to an eustatic sea level change (Murris 1978). The lowest part of the Neyriz Formation (sandstone, silty shale, limestone, and subordinate coaly shales in some places; James and Wynd 1965) is roughly similar to the Shemshak Formation of Central-north Iran, and represents Liassic shallow water (tidal flat) sediments. The deposits of coaly shale and carbonized plant remnants with bauxite pebbles are only found in the Dopolan area of the High-Zagros (Szabo and Kheradpir 1978). The Central Arabian hinterland and other elevations such as the Qatar arch (Murris 1978) presumably provided detrital material for the lower part of the Neyriz Formation. During the deposition of the Neyriz Formation, the Zagros basin with marine carbonate platform sedimentation became established, with the greatest subsidence being in the northeast, possibly along several faults (Figs. 5 and 13). Marine carbonate sedimentation then continued until Miocene time. This continuous episode of subsidence and sedimentation in the Zagros marginal basin was possibly an isostatic adjustment in response to the spreading of the lithosphere following the Middle Triassic movements. From Jurassic to Miocene times the subsidence possibly along inherited faults allowed up to 14 km of sediment (mainly marine carbonates) to accumulate in the basin. Some of the faults along which subsidence took place controlled the sedimentary facies in the Zagros basin. The only evidence of volcanic activity associated with rifting of Zagros is a few amygdaloidal basaltic flows of Permian age in the High-Zagros (Section II.2a. 1.3). The Middle Triassic movement affected central and southern Arabia and Oman as well as the area of the Dead Sea. There the transgressive Jurassic beds are discordant upon the Triassic beds. This unconformity and the absence of deposits in central and southern Arabia
240 CAN. J. EARTH SCI. VOL. 18, 1981 appear to be the effect of the Middle Triassic movements, later extended to west Siberia (Beznosov et al. 1978). In which presumably led to the emergence of most Middle Jurassic time a marine sedimentary regime of central and southern Arabia. The unconformity is not overcame the lagoonal-fluviatile environment, and an reported from northern Arabia and Syria (Powers 1968; Saint-Marc 1978). Lower Liassic marine deposits have been reported in Iraq and Oman, and the widespread Jurassic transgression in Saudi Arabia began with the deposition of the marine Toarcian Marrat Formation (Powers 1968). Upper Triassic rocks are believed to ammonite-beating limestone was laid down. The Liassic coal and the Jurassic limestones rich in fauna indicate the position of Iran in an equatorial belt. Davoudzadeh et al. (1975) inferred another orogenic phase, of Middle Jurassic age (pre-Middle Bajocian, around 176 Ma), responsible for the metamorphism of unconformable on the Middle Triassic in all known the Rhaetic-Liassic sediments of the Mashhad area localities in Iraq (Bellen et al. 1959). (northeastern Iran) and the intrusion of the Mashhad granitic batholith. However, as discussed earlier in Section II.2.2a), Majidi (1978) related this metamorphic H.3c--Kopeh Dagh basin during Triassic time The Kopeh Dagh sedimentary basin was established and magmatic activity to the Hercynian movements. A after the Middle Triassic orogenic movements, when the Middle Jurassic orogenic phase is therefore questionable. closing process between Iran and the Turan had apparently ended (Fig. 5). During Liassic time, the (coherent) Iranian - Kopeh Dagh - Turanian landmass was (195 to 140 Ma) is indicated by the tholeiitic basaltic The ’late Triassic - late Jurassic volcanic activity’ covered unconformably by the Shemshak (coal-bearing) lava flow that preceded the deposition of the Rhaetic- Formation and the unconformity is visible in the Liassic Shemshak Formation in Central Iran and Alborz, Aghdarband region of the eastern Kopeh Dagh (Fig. the Middle Jurassic basic volcanics and tuffs at the top of 13). The basal conglomerate contains detdtal rock fragments of diabase, granite, mica-schist, Triassic sediments (red quartzose sandstone, tuffs), and basic dykes (Madani 1977). The Kopeh Dagh basin started sinking along major longitudinal faults, forming a subsiding basin in northeast Iran. Afshar-Harb (1979) recognized four major basement faults (Khorkhud, Nabia, Takal Kuh, and Maraveh Tappeh), which were active at least since the Jurassic Period. In most cases the blocks north of these longitudinal basement faults subsided more than the blocks on the southern side. The faults changed their character from normal to reverse during later compressional phases. Similar cases indicating reversal of fault motion during tensional and compressional phases are also documented in Central Iran and Alborz (Berberian 1979, 1980b). II.4----LATE JURASSIC MOVEMENTS (~ 140 MA) The period of the Late Jurassic movements is presumably known to be the time of separation of India (extrusion of basaltic flows), Australia, and Antarctica from Africa, and the real opening of the Indian Ocean (Le Pichon 1968; McElhinny 1970; Veevers et al. 1971; Zonenshayn and Gorodnitskiy 1977). During this period Iran underwent some compressional movement. H.4a~Central and north lran during Late Jurassic time As a result of the Middle Triassic movements, the sedimentary environment in Central and north Iran changed from shallow marine to lagoonal-fluviatile conditions. The latter produced the coal and detrital sediments of the Rhaetic-Liassic Shemshak Formation. During the Liassic Stage, Central Iran, the Alborz, and the Kopeh Dagh were covered by dense forests with Asiatic flora (Assereto et al. 1968). These were the source of the coal. The Liassic coal-bearing deposits the Shemshak Formation in the Ramsar area (Annells et al. 1975), and the Upper Jurassic basic lavas in the Lahijan region (Annells et al. 1975). There are two Upper Jurassic - Lower Cretaceous volcanic series consisting of diabasic andesites and pyroxene diabase flow in the Deh Sard region of southeastern Sanandaj- Sirjan belt (Berberian and Nogol 1974), and the Upper Jurassic - Lower Cretaceous augite olivine diabasic flows (melaphyres of the Gypsum-Melaphyre Formation; Allenbach 1966; Steiger 1966) in the Alborz. Their stratigraphic position is not clear because of uncertainties about their real age. The Lower-Middle Jurassic andesite, dacite, basalt, and rhyolitic tuffs southeast of the Sanandaj-Sirjan belt (Dimitrijevic 1973; Berberian and Nogol 1974) could be related to the subduction zone, but more detailed petrochemical and geochronological work is needed to understand their relationship. The late Triassic to late Jurassic tensional regime in Central Iran and Alborz came to an end during the late Jurassic (140 Ma) compressional movements. The sea regressed from many parts of Central and north Iran and many continental areas emerged (Table 2). The boundary of the Jurassic and Cretaceous Systems is generally marked by an unconformity, significant hiatus, or by red continental detritus (Garedu Red Beds, Ruttner et al. 1968; Bidou Formation, Huber and Stocldin 1954, and Huckriede et al. 1962; Red Terrestric Formation, Stocklin 1961), and evaporitic sediments (Gypsum-Melaphyre Formation, Allenbach 1966, and Steiger 1966; Upper Jurassic Salt Beds, Stocklin 1961). The movements were accompanied by a few granitic intrusions (Lut magmatism in east Central Iran; Stocklin et al. 1972; Berberian and Soheili 1973; Berberian 1974, 1977c), lava flows (Gypsum-Melaphyre Formation), and slight metamorphism in some parts of the country. A
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