Application of clinopyroxene in petrogenesis of volcanic rocks at north of East Alloun Abad village (East of Isfahan)

The study area is located in the Isfahan province and at the north of East Alloun Abad village. This area is a part of Urmia - Dokhtar belt in Central Iran. A large part of the area is formed from Eocene igneous rocks. These rocks include basaltic andesite and pyroclastic rocks of ignimbrite and tuff. These rocks show porphyritic and microlithic texture with plagioclase, amphibole and clinopyroxene as the main mineral constituents. The secondary minerals such as chlorite, calcite, epidote and iron oxide are formed due to alterations. Electron microprobe analyses reveals that clinopyroxenes are diopside - augite. The study of clinopyroxene chemistry showed that the water was between 2 to 10% during clinopyroxene crystallization. The parental magma was calc-alkaline and tectonic setting is a subduction-related environment, based on clinopyroxene composition. Geothermobarometry of clinopyroxene gives temperature range of 925-1091°C and pressures range of 2-10 kbars for the formation of clinopyroxene in these rocks.