Petrology of Eocene volcanic rocks in the SW of Choupanan (Central Iran, NE of Isfahan Province) and their transitional nature

Eocene volcanic rocks in SW of Choupanan are exposed along the Choupanan fault as lava with andesite, trachyandesite to dacite composition and pyroclastic rocks. This area is a part of Central Iran (Yazd block). Andesite is the most predominant rock unit of the area and is composed of feldspars (andesine, oligoclase, and sanidine), amphibole (magnesio hastingsite, magnesian hastingsite, magnesio hornblende, and ferropargasite), mica (biotite and phlogopite), quartz, clinopyroxene (diopside, augite), garnet, opaque minerals (ilmenite, magnetite, titanomagnetite, and hematite), zircon, sphene and apatite. Minerals which are produced by alteration are calcite, chlorite (diabantite), and prehnite. SiO2 content of these rocks ranges 55.1 to 61.1 wt% and LREEs exhibit an evident enrichment. These volcanic rocks present a transitional affinity (between calc-alkaline and shoshonitic) and geochemically are similar to the volcanic arc rocks. The field, petrography and geochemical studies reveal that the studied andesites are formed by same petrogenetic processes and affected by magma mixing and contamination during crystallization.