TECTONO-STRATIGRAPHIC EVIDENCE FOR THE OPENING AND CLOSURE OF THE NEOTETHYS IN THE SOUTHERN PART OF THE SANANDAJ-SIRJAN ZONE, SOUTHERN IRAN

The Sanandaj-Sirjan area, the most active structural zone in Iran, is a part of the Zagros orogen which resulted from the convergence of northern part of the Gondwana, the Cimmerian blocks and the southern part of Eurasia. This zone extends from the Sabzevaran fault at its most southeastern part to the Iranian-Turkish border in the northwest and further into the Bitlis Massif in southeast Anatolia.

Study of the characteristics of different rock units and their stratigraphic relationships, as well as magmatic and metamorphic activities in the southern part of the Sanandaj-Sirjan zone, resulted in identification of different tectono-stratigraphic units based on their tectonic environments reflecting the opening and closure of the Neotethys Ocean in southern Iran. The major tectono-stratigraphic units identified in this study are as follows:

Sediments deposited in the aulacogeosyncline setting in the southern part of the central Iranian platform of Paleozoic to Middle Triassic age, highly deformed and metamorphosed by the Early Cimmerian event; Triassic volcanic rocks and turbiditic sediments; magmatic rocks related to a magmatic arc generated by a northeastwards-directed subduction of the Neotethys oceanic lithosphere beneath central Iran; low-grade flysch- type sediments of Jurassic-Early Cretaceous age deposited in a forearc basin and deformed by later stages of Cimmerian orogeny; Lower Cretaceous carbonate platform sediments; suture zone-related rocks containing ophiolite, radilolarite and glaucophane schists; Tertiary flysch-type sediments containing exotic blocks of Lower Cretaceous carbonate, ophiolite and Zagros Formations formed over the edge of the high Zagros zone; retro-arc foreland sediments which unconformably overlie the deformed rocks of the northeastern part of the area and southern part of central Iran; and finally post-orogenic molasse-type sediments resulted from post uplift erosion of the Zagros orogeny, deposited in the internal and marginal parts of the southern Sanandaj-Sirjan zone.