Textural records and geochemistry of the Kermanshah mantle peridotites (Iran): implications for the tectonic evolution of southern Neo-Tethys
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Abstract:
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 0.2-0.4wt.%, 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.