Application of pyroxene chemistry for evaluation of temperature and pressure in the Kuh-e Dom intrusion

The Late Eocene Kuh-e-Dom intrusion located in the central part of Urumieh-Dokhtar magmatic belt, NE of Ardestan. The intrusion consists of gabbroic to granitic rocks, intruded by several acidic and basic dikes. The EMP analyses of gabbro pyroxenes show the occurrence of two types of pyroxene: orthopyroxene with hypersthene and ferro hypersthene composition and clinopyroxene with augite- diopside composition. The trachybasaltic dikes have clinopyroxene with augite to diopside composition. The compostion of the pyroxenes shows that these rocks have been crystallized in a subduction zone setting. The average crystallization temperature of pyroxenes in gabbros is about 1070°C, and it seems the clinopyroxenes crystallized in the lower temperature than orthopyroxenes. While the average crystallization temperature of pyroxenes in the basic dikes is evaluated to be around 1130°C. The estimated pressure for clinopyroxenes crystallization in the studied gabbros is lower than 2 kb and 2 to 5 kb for orthopyroxenes. These data indicate that clinopyroxenes have been formed in the depth lower than 7.7 km and the orthopyroxenes in depth of 10 km. The crystallization pressure of clinopyroxenes in the basic dikes studied is calculated in the range of 2.7 to 2.8 kb which is in accordance with their formation in the depth of 10 km.