Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Ali Moradpour, Reza Zarei Sahamieh, Ahmad Ahmadi Khalaji, Ramin Sarikhani

Textural records and geochemistry of the Kermanshah mantle peridotites (Iran): implications for the tectonic evolution of southern Neo-Tethys

Journal of Geosciences, volume 62 (2017), issue 3, 165 - 186

DOI: http://doi.org/10.3190/jgeosci.244

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 TiO₂ and Al₂O₃ 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 the boninites from Oman ophiolites. Olivine from 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 TiO₂, Cr₂O₃, and Al₂O₃ 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.