Whole-rock chemistry of isotropic gabbros from the Kermanshah ophiolite: Evidence for petrological and source region characteristics of ophiolitic and it's tectonic setting

The isotropic gabbros of Kermanshah ophiolite are mainly represented by, gabbro, leucogabbro, olivine gabbro, gabbronorite, olivine gabbronorite and Troctolite. The gabbros are medium grained with euhedral to subhedral plagioclase, subhedral orthopyroxenes and clinopyroxenes, olivine and together with rare amphiboles. The gabbros are characterized by high contents of MgO, CaO and low TiO2, K2O, P2O5, Zr and Y. The geochemical signature of the gabbros indicates tholeiitic affinity for the protolith, with magma generation in island arc-setting. N-MORB and primitive mantle normalized multielement patterns of the gabbros show flat patterns for HFS-elements and depletion in (P, Zr, Sm, Ti, and Y) and enrichment of LIL-elements (Ba, Rb, K, Th, Sr) with negative Nb anomalies suggesting involvement of subduction component in the depleted mantle source and formation in a supra-subduction zone tectonic setting. REEs exhibiting flat to slightly depleted LREE patterns, geochemically similar to island arc tholeiites. In general, isotropic gabbros have transitional characteristics between mid-ocean ridge basalt and island-arc tholeiite on discrimination tectonomagmatic diagrams. It is therefore proposed that these gabbros may have originated in a back-arc basin tectonic setting.