Mineral composition and geothermobarometry of Mata basaltic rocks (SouthKerman): An indicator of magma type and tectonic setting

Basaltic volcanic rocks with pillow structures are exposed at the southeasternmost extremity of the Sanandaj-Sirjan zone.They belong to volcanic-sedimentary complexes that formed in a general northwest-southeast to north-south trend. In this research, the mineral chemistry of clinopyroxene and plagioclases are employed to study physicochemical conditions and paleo-tectonic setting during generation of basaltic rock. Basalts with plagioclase and clinopyroxene, as the major constituents, have porphyritic texture, which groundmass marked by fine grained plagioclase, clinopyroxene, apatite, opaque minerals and chloritized glass with intergranular to intersertal textures. Electron probe micro-analyzer (EMPA) data indicate most of the feldspars are calcic plagioclase with bytownite composition and clinopyroxenes are augite. High Al and low- Ti and Fe3+contents in clinopyroxenes show the major role of Tschermak’s components, specially CaAlAlSiO6 and minor presence of acmite component. Low TiO2 and Na2O and high SiO2 content indicate their tholeiitic affinity. Based on thermobarometric approaches Mata clinopyroxenes were formed at temperatures of about 1150-1200 ˚C and pressures in the range of 5–6 kbars, which approximately corresponds to a crystallization depth of 15-18 km. Clinopyroxenes have geochemical characteristics similar to ones generated in an extensional environment related to back-arc basin setting.