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Kermanshah Ophiolite Complex (NW Iran), located along the Main Zagros Thrust Zone, marks the ophiolitic suture between the Arabian and Sanandaj-Sirjan continental blocks. N-MORB-normalized multielement patterns and chondrite--normalized REE patterns in the Kermanshah mantle restites show depletion in incompatible elements concentrations with respect to the depleted MORB mantle (DMM). In the V vs. Yb diagram, Harsin-Sahneh-Norabad and Miyanrahan peridotites (Kermanshah Ophiolite Complex), due to their relatively low V contents, fall close to the QFM buffer. Calculated TiO 2 and Al 2 O 3 compositions in the parental melt that were in equilibrium with chromian spinel are consistent with supra-subduction zone-type compositions. Besides, calculated FeO/MgO ratios in the parental melts are comparable with those in boninites from Oman ophiolites. Olivine from the peridotite restites is highly magnesian (Fo 89-93 ) with NiO contents of 0.2-0.4 wt. %, consistent with formation in a forearc environment. This is also proven by the Cr# and Mg# values as well as TiO 2 , Cr 2 O 3 , and Al 2 O 3 concentrations in chromian spinel of ultramafic rocks. Accordingly, petrogenetic modeling indicates that the Kermanshah ultramafic rocks may represent the residual mantle after extraction of 13-23% of boninitic-type melts. Decompression, melting and melt-rock reaction related textures are widespread in the Kermanshah mantle restites. 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 Neo-Tethyan Ocean.

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. Th e na t ure o f H arsin -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.

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