Whole-rock geochemistry and Sr-Nd-Pb isotope characteristics of gabbros from kahnouj ophiolitic complex (SE Iran) in the makran zone: Petrogenesis and tectonic implication

Based on new Sr-Nd-Pb isotopic and lithogeochemical data from gabbros, combined with previously published data from the Kahnouj ophiolite, we propose a tectonic model for the Kahnouj ophiolitic complex. The Kahnouj ophiolitic complex is the largest ophiolite of the Makran zone and consists of isotropic and layered gabbros with ultramafic lenses at the bottom and sheeted dikes, and basalts and pelagic limestones at the top. A cyclic succession of isotropic and layered gabbros indicates a distinct differentiation trend of early olivine and plagioclase crystallization followed by clinopyroxene and finally hornblende crystalize. Crystal fractionation and partial melting processes are also inferred by whole-rock geochemical data (e.g., fractionation recorded by the Al₂O₃/TiO₂ versus Ti/1000 diagram). Geochemically, the gabbros are subalkaline and show tholeiitic features. The εNd values of +8.1 to +9.2 and initial ⁸⁷Sr/⁸⁶Sr ratios of 0.70346–0.70371 indicate a MORB source for the gabbros. The whole-rock geochemistry of the layered and isotropic gabbros suggests that they formed in a back-arc basin setting and represent MOR-to supra-subduction type ophiolites in the Neotethys Ocean during Early Cretaceous.