Geochemistry and petrology of Harsin–Sahneh ophiolitic complex (NE of Kermanshah—west of Iran) an evidence of Southern Neo-Tethys Ocean tectonic

Abstract

Ophiolites of the Zagros orogenic belt of Iran are part of the Tethys ophiolites, linking the Middle East ophiolites and other Asian ophiolites (e.g., Pakistani and Tibetan) to the Mediterranean ophiolites (e.g., Troodos, Greek, and East European) due to their geographical position. The nature of Harsin–Sahneh ophiolite (Kermanshah), studied in this paper, is traditionally considered as one of the Mesozoic southern branch of the Neo-Tethys Ocean, and remnants of the Peri-Arabic ophiolite system obducted onto Arabian shield (Gondwana). Petrographic evidence indicates that this ophiolitic sequence consists of both mantle and crustal suites. In this complex, generally lithologies include harzburgitic and lherzolitic peridotites, isotropic and mylonitic gabbros, dyke complex, basaltic pillow lavas, and small out crop of plagiogranite. The mineral chemistry of Harsin mafic rocks is island arc setting for this part of complex and geochemistry of mafic and ultramafic rocks of Sahneh region displaying P-type mid-ocean ridge basalt (MORB) nature. The presence of basalts with different compositions in this region can be interpreted as an interaction between MORB-type and OIA-type asthenosphere. Field relationships and geochemical evidence reveal that the studied ophiolites were a part of a rifted basin at the ocean–continent transition zone formed in the south of the Neo-Tethyan Ocean. Based on the evidence, in Late Cretaceous, the subduction of Southern Neo-Tethyan Ocean beneath itself leads to not only the cessation of Southern Neo-Tethyan subduction to the branch of Sanandaj–Sirjan block but also the formation of arc and back-arc basin and related rocks in Kermanshah ophiolite. MORB magmatism occurred in the response to slowing down of the convergence rate of Neo-Tethyan and slab retreat in the Eurasian continental margin. This would also explain both the contemporaneous occurrence of MORB-type and OIB-type magmatism, as well as the lack of a magmatic evolution from depleted to enriched rocks.