Determination of tectonomagmatic environment of volcanic and subvolcanic rocks in North of Shahrekord by amphiboles geothermobarometry

On the basis of geothermobarometric calculations, amphiboles in volcanic and subvolcanic rocks belong to Upper Jurassic volcanism of Sanandaj-sirjan zone in north of Shahrekord. Using Hamarstrom, Schmidt, Johnson - Rutherford and Hollister methods, amphiboles have crystallized about 635 to 715◦ c and 2.68 to 7.5 kbar at the depth about 17 to 25 km. The result of calculations has moderate accuracy. The lower FET/ (Fet + Mg) ratio in amphibles is characteristic of calc-alkaline magma suites. Calculated temperatures, pressures and depths for amphiboles is coincide with a subduction tectonical environment. The maximum depth of crystallization of amphiboles is 25km and subduction angle is lower than 45 km on the basis of 35 km distance between this volcanic belt and main Zagros fault. Aliv measures of amphiboles are higher than 1.5 that indicate an island arc suite.The presence of this old island arc had predicted in Zagros orogenic belt.