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BERBERIAN AND KING 249 FI~. 16. Paleogeographic map of Iran during Oligocene-Miocene times, after the Late Eocene movements (around 30-15 Ma). See Fig. 8 for paleoreconstruction. 1. Mountainous regions, area of erosion and non-marine sedimentation. 2. Oligocene-Miocene marine carbonates: Qom Formation in Central Iran; and Asmari back-reefal neritic carbonate facies in Zagros. 3. Sandstone, shale, and back-reef limestone in the Persian Gulf region. 4. Continental littoral sandstone (Ahwaz sandstone delta). 5. Continental red beds Central Iran; and Razak red silty marls with subordinate silty limestone and sandstone in Zagros. 6. Flysch-molasse sediments. 7. Molasse (Zeivar Formation and Maikop Series composed of conglomerate, clay, and tuffaceous sandstone) in northwestern Iran, and Vindobonian marls in the Caspian region. 8. Volcanics in Little Caucasus (northwestern Iran); and in Central Iran (basalt, andesite, dacite, tuffs). 9. Acidic and basic intrusive rocks exposed at surface (Upper Eocene - Oligocene Zabol-Baluch, central and south Afghanistan; and Miocene in Central Iran and northern Afghanistan). 10. Platform basins in the Turan plate (northeastern Iran). Principal sources of data: Gansser (1955); Milanovsky and Khain (1963); Abu Bakr and Jackson (1964); James and (1965); Mina et al. (1967); Grossheim and Khain (1968); Sampo (1969); Ahmed (1969); Stazhilo-Alekseev et al. (1972); Zakhidov (1972); Dimitrijevic (1973); Ricou (1974); Berberian (1976a,b); Shevchenko and Rezanov (1976); et al. (1977); Kotanski (1978); Huber (1978); Murris (1978); Berberian and Berberian (1980); Berberian (1981); and all the data from the Geological and Mineral Survey of Iran to 1980. Lambert Conformal Conic Projection.
250 CAN. J. EARTH SCI. VOL. 18, 1981 not believe it to be trench related. A similar substantial gap between the end of subduction and the beginning of igneous activity exists in the Old Red Sandstone extrusive and intrusive activity of the northern British Isles. It has been suggested that the Lower Old Red Sandstone volcanics of Scotland and northern England (about 2 km thick olivine basalt, andesite, dacite, and rhyolite; Rayner 1967; Groome and Hall 1974; Gandy 1975) were developed during the major Devonian sinistral wrenchfaulting movements of the region (Morris 1976) and may indicate a genetic connection (Leake 1978). Takin (1972), Milanovskiy (1974), Amidi (1975, 1977), and Conrad et al. (1977) related this volcanism the melting or mobilization of sialic crustal material during a rifting process. The widespread volcanic activity following the high erosion rate of thickened continental crust during a considerable development of the Late Cretaceous folding and mountain-building phase could indicate the rising of the geotherms and onset of volcanism due to high erosion and peneplanation. However, the composition of the volcanics, which include basaltic members as well, does not suggest remobilized sialic crust being the only process involved. To produce the basaltic members some of the mobilized material must be approaching the composition of mantle rocks, since there is general argumenthat basaltic magma is a product of partial melting of ultramafic material in the upper mantle (Presnall 1969; Carmichael et al. 1974; Ringwood 1975; Yoder 1976; Kushiro 1979). The volcanic activity cannot easily be ascribed to plumes rising from hot spots fixed in the deep mantle (Bailey 1977), since the Iranian crust moved a considerable distance with respect to the mantle during the volcanic period. The Eocene period of volcanism in Central Iran was followed by Late Eocene (37 Ma) movements, represented by a regional unconformity at the base of the Oligocene rocks. During this phase the Lut zone in east-Central Iran underwent uplift (major Lut uplift) and no Oligocene-Miocene sediments were apparently deposited (Berberian and Soheili 1973; Berberian 1974, 1977a; see Fig. 16 and Table 3). The Upper Oligocene transgression of the sea deposited the Upper Oligocene - Lower Miocene marine carbonates of the Qom Formation (Bozorgnia 1966) Central Iran (Fig. 16 and Table 3). No Eocene-Oligocene deposits were laid down along the northern flank of the Alborz mountains while the southern part was subsiding (Figs. 15 and 16). The Upper Oligocene beds rest unconformably on the Eocene rocks in the Alborz region, indicating the Late Eocene movements in northern Iran (Stocklin 1968a; Nabavi 1971; Berberian 1976a). ll.6c--Zabol-Baluch and Makran flysch basins during Middle Alpine time The Late Cretaceous subduction zone of the eastern High-Zagros Alpine Ocean along the Makran active margin of southeast Central Iran was shifted southwards during Eocene time. This created new basins to the south of the obducted Upper Cretaceous ophiolite-m61ange zone of the Makran (in the southeast) and to the east the Zabol-Baluch ophiolites (in the east), in the form marginal seas, with a branching arm extending along the northern margin of the High-Zagros (Fig. 15). Olistromatic flysch deposits with terrigenous and turbulent clastic rocks from the emergent east-west ophiolitem61ange source north of the Makran basin, and northsouth mountains of the Zabol-Baluch east of the Lut, indicate rapid erosion and sedimentation in an active tectonic environment during an orogenic period along the continental margin of the Makran and Lut. In the Makran the tectonic unrest (oceanwards episodic thrusting) accompanying the voluminous flysch deposits gradually shifted the main axes of the Makran basin towards the south (Huber 1978). The southwards shifting of the Markan basin axes and therefore development of younger flysch and molasse in the south, the northward increase in elevation, and the formation of the Jaz Murian depression north of the Makran range, indicate an ’accretionary prism’ from Early Tertiary time to the present. The prism is presumably formed on top of the subducting oceanic crust (eastern part of the High-Zagros Alpine Ocean) with subsiding ’upper slope or fore-arc basin’ (the Jaz Murian and Mashkhel depressions) and an "uplifted lower slope" across which the accreted sediments become younger towards the trench (Farhoudi and Karig 1977). The strongly deformed Eocene-Oligocene Lower Flysch (Falcon 1974) and the Panjgur units (Ahmed 1969) are therefore interpreted as "trench-fill deposits" forming a narrow ribbon of turbidites at the base of the continental slope (Farhoudi and Karig 1977). No rocks older than the Upper Cretaceous ophiolitem61ange have been recognized underlying the Eocene- Oligocene Makran flysch. The presence of conglomerates with serpentine boulders together with exotic blocks of ophiolite-m61ange in the Lower Flysch (wild flysch), and the transgression of the lower sandstone and conglomerate of Eocene flysch over the ophiolite-m61ange in the Jagin valley and Fanuj area of the Makran (Falcon 1974; Huber 1978) have been used as evidence to suggest that this flysch basin is floored by ocean crust. The present Gulf of Oman is assumed to be floored by oceanic crust (Farhudi and Karig 1977) because of its depth, the acoustic character and velocity of the basement (White and Klitgord 1976), the possible easttrending magnetic anomalies (Taylor 1968), and the strongly positive Bouguer gravity field (USSR Academy of Sciences, 1975). A Deep Sea Drilling Project hole bottomed in Paleocene basalt on the crust of the Gulf of Oman (Whitmarsh et al. 1974).
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