Petrography and mineral chemistry of Eocene volcanic in the southwest of Jandaq (northeast of Isfahan)

In the south west of Jandaq area, the Eocene volcanic rocks crop out, near the Doruneh Fault in a large area. These rocks are composed predominantly of basalt, quartz andesite, andesite, dacite and latitewith porphyritic, microliticporphyritic and hyaloporphyric textures. The main constituents are plagioclase, amphibole, clinopyroxene, quartz, minor alkali feldspar and biotite and opaque minerals as accessory minerals. The secondary minerals are opaque, sericite, calcite and chlorite. The composition of the plagioclase ranges from andesine to labradorite, the clinopyroxene is diopside-augite and the amphiboles are magnesio-hastingsite some plagioclase phenocrysts show oscillatory zoning. The study of chemical composition of clinopyroxenes classifies these rocks as sub-alkaline series and volcanic arc. The geothermometry of clinopyroxene reveal the temperature of 941-959 ºC for pressure of 1-10 kbars. Clinopyroxenes barometry point to their formation in defferent depths during their ascending. The Hlb-Plg thermometry shows the temperature of 858-941 ºC for pressure of 1-10 kbars. The high volume of water in the crystalization environment of the pyroxenes as well as variations on AlIV+Na/ AlIV+2Ti+Cr diagram indicate the high oxygen fugacity of the environment. Field observations and some petrographic evidences demonstrate traces of hydrothermal alteration.