Pyroxenites from mantle section of Voykar Ophiolite – Melt/peridotite reaction and crystallization in SSZ mantle

Abstract Pyroxenites from Voykar Ophiolite mantle section provide a great record of processes happening during final stages of evolution of an ophiolite. They are represented by the complete range from clino- to ortho-pyroxenites with websterites and complex dunite-pyroxenite veins also present. Their formation is attributed to various degrees of fractional crystallization and reaction of melts and possibly fluids with host harzburgites during changing P and T conditions. Most of pyroxenite parental melts were migrating through that part of the mantle section from a more depleted and higher temperature harzburgites. Presence of subduction signature is evident from mineral and whole rock compositions. Parental melt with boninite-like trace element patterns is proposed with most likely positioning in lithospheric part of forearc mantle. Orthopyroxenites formed on earliest stages from parental melt/fluid most depleted in REE and highest in silica. As the melt reacted with residual peridotites Si content was decreasing and websterites and clinopyroxenites started to form with increase of Cpx/Opx ratio with decreasing temperature. Olivine websterites and clinopyroxenites formed from the melt saturated in olivine and therefore not reacting with residual peridotites. Formation of pyroxenites triggered minor melting of surrounding harzburgites and some of thin cm sized pyroxenites represent accumulations of such melts.