MINERAL CHEMISTRY OF FELDSPAR AND AMPHIBOLE APPLICATION OF DIFFERENT GEOTHERMOBAROMETRY METHODS AND OXYGEN FUGACITY, DETERMINATION OF MAGMATIC SERIES, ORIGIN AND TECTONOMAGMATIC CLASSIFICATION OF SHIRKUH GRANITOID BATHOLITH, YAZD, IRAN

Abstract

Batholith of Shirkuh, Yazd, is part of the central Iranian structural zone, located southwest of the province. The lithology of this complex comprises mostly monzogranite and granodiorite and some quartz monzonite, quartz monzodiorite and syenogranite.Plagioclase, quartz, orthoclase, biotite and amphibole are the dominant minerals in these rocks. The composition of plagioclases varies from labradorite to oligoclase, and alkali feldspars belong to the orthoclase category. Amphiboles are calcic, rich in iron and Fe-Mg-Mn amphiboles, and range from ferro-hornblende to tschermakite, and tschermakite hornblende. According to various geobarometry methods using the amphibole composition, it is estimated that the calc-alkaline batholith has been formed in a supra-subduction tectonomagmatic environment at 700–900 °C and 0.8–1.5 kbar pressure under high oxygen fugacity. Moreover, based on the thermometry results of feldspars, the emplacement temperature was obtained in the 770–920 °C range by the Anderson method for the Shirkuh granitoid batholith