Application of amphibole and feldspar chemistry in the petrogenetic study of the Middle Miocene granitoid complex, west of Kashan

The Middle Miocene Niyasar granitoid complex is located in west of Kashan and in the Urumieh – Dokhtar magmatic belt. Based on petrographic studies, the Niyasar complex is composed of tonalite, quartz-diorite and diorite intrusive rocks. These rocks are mainly composed of quartz, plagioclase, amphibole, biotite and K-feldspar. The amphiboles belonge to calcic group and vary in composiotion from magnesiohornblende to actinolite which is an indicative of I-type granitoids. The composition of plagioclase ranges from oligoclase to bytonite in the tonalites, albite to andesine in the quartz-diorite and oligoclase to bytonite in the diorites. Barometric studies exhibit that the hornblende pressure crystallization was 1-2 Kbar which is equivalent to 3.8-7.5 Km depth of crystallization. Hornblende-plagioclase and feldspar thermometry in the Niyasar complex show 706-756 ˚C as equilibrium temperature of minerals. Oxygen fugacity estimation, suggests that the Niyasar intrusive crystallized from highly oxidized magmas in a convergent boundary setting.