Mineral geochemistry of clinopyroxene and its application in thermo-barometery of basaltic rocks in Ahmad-Abad, Tahmoures and Gahre-toreh volcanoes (North Qorveh-Kurdistan)

The Ahmadabad, Tahmoures and Ghareh-toreh volcanoes are part of the volcanic centers located on the Qorveh-Bijar axis and constitute a part of the magmatic outcrops of the northern arm of the Sanandaj Sirjan Zone, Hamadan-Tabriz. Volcanic rocks have basaltic composition and show porphyritic, microlithic porphyry and glomeroporphyritic textures. Major phenocrysts include clinopyroxene and olivine. The abundance of clinopyroxene is found to be lower in Ghareh-toreh basalts, olivine is major phenocryst in this center. Clinopyroxene phenocrysts show normal, in some cases, reverse zoning and gulf corrosion indicating disequilibrium with the host's melt. The results of thermobarometric calculation (temperature and pressure) using clinopyroxene mineral indicate the temperatures of 1100-11300 °C and pressures of 3 to 11 kbar for Ahmadabad and Tahmoures volcanoes, and volcanic basalts at Ghareh-toreh reveal the temperature of 800 Up to 1100 °C and pressure of 0 to 3 kbar. The high oxygen fugacity in these rocks and the coherence of the temperature and pressure of the olivine phenocryst in this region with the temperature and pressure of the clinopyroxene in Ahmedabad and Tahmoures, all show that clinopyroxene crystals of Ghareh-toreh volcano formed at a lower depth and possibly in a shallow reservoir