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ABSTRACT

The Sanandaj-Sirjan zone in Iran is a part of the Cimmerian terrane, which was accreted to Eurasia in the Late Triassic. This zone was later incorporated into the Zagros orogen, which resulted from the collision of Eurasia (Iranian subplate) with the northern Gondwana margin (Arabian subplate) during the Cenozoic. Characteristics of different rock units and their stratigraphic relationships combined with evidence from magmatic and metamorphic events in the southern part of the Sanandaj-Sirjan zone, as examined in this paper, resulted in identification of 11 tectono-stratigraphic units that record different tectonic environments involved in the opening and closure of the Neotethys Ocean in southwestern Iran. During Paleozoic intraplate extension, sedimentation and igneous activity took place in aborted rift system to continental shelf settings in the southern part of the Central Iranian Platform (unit 1). Spreading of the Neotethys was associated with formation of Upper Permian (unit 2) and Lower to Middle Triassic turbidites and volcanics (unit 4) in an intracontinental rift setting, which continued up to the Late Triassic. Late Triassic subduction caused the metamorphism of the aborted rift materials (unit 3), calc-alkaline magmatism (unit 5), deposition of a turbiditic sequence and associated volcanic rocks of Early to Middle Jurassic age (unit 6), and carbonate sedimentation during the Early Cretaceous (unit 7). These subduction-related units of Late Triassic–Early Cretaceous age formed respectively in a high-temperature–low-pressure metamorphic regime, magmatic arc, forearc basin, and continental platform. The Zagros suture zone of Late Cretaceous age (unit 8), the Tertiary flysch-type sediments (unit 9), and the Oligocene–Miocene sedimentary succession (unit 10) are tectono-stratigraphic units formed during the Neotethyan obduction to Arabia-Asia continental collision phases. Finally, the young molasse sediments (unit 11) were shed from the postcollisional highlands into intramontane basins. This chapter also proposes the presence of two sutures in southwest Iran: Suture zone I marks the subduction-obduction of Neotethys toward the end of the Cretaceous, while the younger (Eocene–Oligocene) suture zone II marks the closure of the Oman Ocean between suture zone I and the Sanandaj-Sirjan zone.

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