Mineralogy, geochemistry and petrogenesis of plagiogranitic intrusions from ophiolitic complex of southern Mehriz (SW Yazd)

There are small plagiogranite intrusions and veins in the ophiolitic complex of Northern Kamrod and Southern Dehshir containing feldsparꫦꮷ㾛誋抵±garnet minerals. The host rock of plagiogranites are granular and foliated metagabbro. Ragged boundary and partial replacement of pyroxene by amphibole in the massive metagabbros indicate a disequilibrium state and metamorphic origin of amphibole. In the foliated metagabbro unlike granular ones the relicts pyroxene is absent. Whole rocks geochemical evidences imply partial melting as the main process in generation of plagiogranites in a slow-spreading center of suprasubduction setting. Probably water infiltration through fractures of a spreading setting of back arc resulting of Neotethys subduction caused hydrothermal metamorphism and hydration of ophiolitic sequence gabbros, partial melting and creation of plagiogranitic melt. Alternatively it is possible that during injection of hot magmatic bodies, amphibole dehydration, partial melting and generation of plagiogranitic melt have been occurred as well. On the basis of chemical composition of clinopyroxene, crystallization temperature of gabbroic cumulate is determined between 959 to 977°C. Pressure and temperature conditions of hydrothermal stage estimated as less than 3 Kb and 750°C, owing to chemical composition of metamorphic amphibole. Based on whole rock geochemical signatures of the plagiogranites and their comparison with experimental results, the partial melting temperature is calculated as less than 850ºC. The latest stage of hydrothermal metamorphism was associated with prehnite formation under shallow conditions.