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BERBERIAN AND KING 237 58 ° OMAb FIG. 13. Paleogeographic map oflran during Rhaeto-Liassic time, after the Middle Triassic orogenic movements (around 195 Ma). See Fig. 5 for paleoreconstruction. 1. Known mountainous regions formed during the Late Precambrian, Late Paleozoic, and Middle Triassic orogenic movements. The central mass and the main trend of the present mountain belts were already formed. 2. Rhaeto-Liassic continental paralic plant-beating sandstone and shale with coal-seams in Central Iran, Alborz and Kopeh Dagh, indicating a coherent continental mass after the Middle Triassic orogenic movements, in contrast to the subsiding marine basin of Zagros in the south. 3. Middle to Upper Jurassic marine carbonates of the Surmeh Formation, with thin shallow-water Liassic shaly unit at the base (Neyriz Formation) in Zagros subsiding basin. 4. Mainly carbonates and shale in the northwestern segment of the High-Zagros. 5. Mainly shale and anhydrite with minor carbonates in west Zagros. 6.Upper Triassic - Lower Jurassic volcanic activity (mainly andesite with some basalts) along the Sanandaj-Sirjan belt (SS), and in northwestern Iran (mainly tuffs andesites with sandstones and carbonates). 7. Jurassic oceanic sediments, mainly radiolarite along the High-Zagros (HZ), Sevan-Vedin northwestern Iran (Little Caucasus). Similar sediments were possibly deposited along the Central Iranian Red Sea type narrow oceanic belts (blank). 8. Triassic - early Jurassic and some Middle or Upper Jurassic calc-alkaline granite, granodiorite, diorite, and gabbro intrusions exposed at surface. 9. Middle Triassic metamorphic rocks. 10. Little Caucasian eugeosyncline. 11. Great Caucasian miogeosyncline. Principal sources of data: Vach6 (1968); Vereschagin and Ronov (1968); Stazhilo-Alekseev et al. (1972); Sborshchikov et al. (1972); Shevchenko and Rezanov (1976); Berberian (1976a and b); Muratov (1977); Saint-Marc (1978); Setudehnia Huber (1978); Berberian and Berberian (1980); Berberian (1981); and all available data from the Geological and Mineral of Iran to 1980. Lambert Conformal Conic Projection.
238 CAN. J. EARTH SCI. VOL. 18, 1981 Triassic was a time of regression under arid conditions (Murris 1978). Clastic deposits were increased in central and north Arabia, and the carbonate-evaporite platform was restricted in the Persian Gulf area and the Zagros belt. Carbonates of the High-Zagros (Fig. 12) now suggest an open marine condition along the northern margin of the Arabian platform. In some regions (i.e., central Arabia and the Dead Sea) a slight Middle Triassic transgression is recorded. Furthermore, in both Iraq and the Dead Sea region, numerous breaks without visible unconformity are known, of which the one at the end of Middle Triassic time seems important (Saint-Marc 1978). II.3---MIDDLE TRIASSIC MOVEMENTS (210-195 MA) The Mesozoic Era started in Iran without a great change in structural or sedimentary environment. The rifting of the Iranian Paleozoic platform and the sedimentary cycle beginning with Permian transgression (Section II.2.2b) continued and ended in the Middle Triassic (Figs. 4, 11, and 12; Tables 1 and 2). At the stratigraphic boundary of the Middle to early Upper Triassic rocks (post Landian -pre Norian, 210-195 Ma) there is evidence of a major compressional phase. Regional uplift, folding, metamorphism, and erosion took place and were followed by the formation of a new sedimentary basin with rapid facies changes. Apparently the Middle Triassic movements ended the late Paleozoic oceanic closure between Iran and Turan in the north and both regions became a united landmass (Fig. 5). have been considered minimum values (by a substantial margin), and a Triassic age of metamorphism has been favoured for the Barrovian-type assemblages (Watters and Sabzehei 1970; Ricou 1974). Petrographic investigations and analysis of mineral paragenesis of the Sanandaj-Sirjan metamorphic rocks led to the conclusion that there were two syntectonic regional metamorphic phases during the middle Triassic movements. The first phase could be older, and more work is needed to date and separate the events. The first phase was Barrovian in type and low grade (lower amphibolite facies), and the second phase was a retrograde metamorphism (Sabzehei and Berberian 1972; Ricou 1974; Sabzehei 1974; Alric and Virlogeux 1977). The Middle Triassic syntectonic metamorphism was associated with strong isoclinal folding and axial plane schistosity (Sabzehei and Berberian 1972; Berberian 1977a). The metamorphic rocks are covered transgressively by non-metamorphic Jurassic volcano-detritus and flysch-type deposits with basal conglomerate. Compressional movements that closed the Hercynian Ocean in the north now created a subduction zone along the southern margin of Central Iran, with compressional components along the active margin represented by regional metamorphism, folding, thrusting (Fig. 5), and accompanied by acid plutonic and intermediate to basic volcanic activity (Fig. 13). The Sikhoran basic to ultrabasic complex of probable Triassic age in the southeastern segment of the Central Iranian active continental margin (east of Hajiabad in Fig. 2), represents a sequence of layered intrusive rocks (dunite, harzburgite, pyroxenite, gabbro) originating from a basaltic magma of tholeiitic composition. They produced a hot metamorphic aureole of pyroxene-hornfels facies and were covered by the Jurassic sediments (Sabzehei and Berberian 1972; Sabzehei 1974). H.3a~Central lran during Triassic time A syntectonic regional metamorphism of greenschist facies, indicative of ’strong compressional deformation,’ developed along the southern margin of Central Iran (along the Sanandaj-Sirjan belt), in the Saghand (Haghipour 1974), and probably Deh Salm (Berberian 1977a) regions of east Central Iran (Fig. 13). The linear metamorphic belt of the Sanandaj-Sirjan could have resulted from subducting High-Zagros Alpine oceanic crust beneath the Central Iranian active continental margin. The area west of Sirjan (at the southeastern part of the Sanandaj-Sirjan belt) is characterized by two distinct The Triassic Sikhoran ultrabasic complex, the upper Triassic (Carnian-Norian) tuffs, andesitic and basaltic lava flow in the Abadeh area (Taraz 1974), the Jurassic andesitic-basaltic lavas and tuffs with some acid volo canics in Sirjan, Hajiabad, Borujerd, and Deh Bid area, the late Triassic - Jurassic granitic intrusions all along The Central Iranian active continental margin (Dimitrijevic 1973; Berberian and Nogol 1974; Berthier et al. 1974; Sabzehei 1974; Alric and Virlogeux 1977), together with the Jurassic granitic batholith of Shirkuh, metamorphic regimes. In the immediate vicinity of the and the Upper Jurassic diorites and the Cretaceous Main Zagros reverse fault line, there is a metamorphic granites-diorites of Alvand (Valizadeh and Cantagrel belt of thrust slices containing metamorphosed basic and ultrabasic rocks and widespread Barrovian-type metamorphic assemblages (Watters and Sabzehei 1970). Two middle Paleozoic ages (362 + 7 and 404 -+ 8 Ma; K/Ar biotite) were found using biotite-bearing quartzofeldspathic gneisses from the Kor-e-Sefid mountain, west of Sirjan (see Fig. 2 for the location). The ages 1975) could all be considered as arc-type magmatism along the Sanandaj-Sirjan belt (Berberian and Berberian 1980; Figs. 5 and 13). The Middle Triassic regional metamorphism in the Saghand area of east Central Iran (Fig. 13) is characterized by one metamorphic phase of a low-grade greenschist facies in Paleozoic-Triassic rocks (with an eastwest b-lineation and maximum temperature estimated to have been about 500°C), and retrograde metamorphism
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