Geochemical variability among stratiform chromitites and ultramafic rocks from Western Makran, South Iran

The geochemical compositions of minerals from the Moho transition zone of ophiolites potentially can help to understand the magmatic evolution of the ophiolites, and subsequent mantle-melt interactions. The Jurassic-Late Cretaceous Makran ophiolite of south Iran comprises one of the most extensive tracts of oceanic crust which were scraped off and preserved in an accretionary complex. The Makran ophiolite records traces of MORB-OIB-type magmatism during the Jurassic, but mostly supra-subduction zone magmatic activity during the Late Cretaceous. Despite a few geochemical studies on the crustal rocks, the nature and geochemical signatures of the mantle rocks from this ophiolite remain controversial. The Sorkhband mantle-crust transition zone underlying crustal cumulates in the western Makran consists of stratiform chromitites, harzburgites, chromite-rich dunites and dunites, with crosscutting dikes of olivine websterite and olivine clinopyroxenite. Major- and trace-element compositions of clinopyroxene grains in olivine websterite and clinopyroxenite dikes indicate crystallization from melts similar to boninites and low-Ti fore-arc basalts. Spinel compositions in olivine websterite and clinopyroxenite dikes suggest crystal fractionation from boninitic or high- Mg# magmas have played a major role in the genesis these rocks.