Using of mineral chemistry to determine the formation conditions of Boroujerd granitoid complex and its metamorphic aureole

The composition of Boroujerd granitoid varies from quartz diorite, granodiorite to monzogranite associated with acidic dykes intruded into the Hamedan phyllite and developed a metamorphic aureole. On the basis of mineral chemistry the biotites have different compositions and their parent magma has subalkaline to calc-alkaline nature. The studied amphiboles are classified as calcic (magnesio-hornblende) which point to the I-type nature of the Boroujerd granitoid. Plagioclases vary from andesine-oligoclase to labradorite, alkali feldspars occur as orthoclase and those in pegmatites are sodic (albite) and potassic (orthoclase). The changes in feldspar composition in different units are normal indicating magma differentiation. In all samples, garnet displays zoning and is almandine-spessartine in composition. Also, garnet in hornfelses and granodiorites is cogenetic and nonmagmatic, but in pegmatites it has magmatic nature. Al-barometer accounts that the pressure of amphibole crystallization is 0.43 to 1.61Kbar and Altotal versus Fetotal/(Mg+Fetotal) accounts the pressure between 1 to 3 Kbar. Hornblende - plagioclase thermometer shows 653 to 732 °C for equilibrium of these two minerals and garnet-biotite thermometer shows 472 °C for garnet-biotite in hornfelses. The estimated oxygen fugacity (log O2 varies between -18.3 to -15.6) imply an oxidation magma (confirms magnetite and enrichment of Mg in amphibole) and its formation in convergent plate boundary.