سنگ نگاري و شيمي كاني ها در سنگ هاي آتشفشاني كوه گريز، جنوب خاوري اصفهان

Petrography and Mineral Chemistry of Volcanic Rocks in Gowris Mountain, South East Isfahan

The late Miocene - Pliocene to Quaternary calc-alkaline volcanic rocks are exposed in Gowriz mountain in southeast of Isfahan. The volcanic rocks comprise basaltic andesites, andesites, dacites lava flows and domes. Geochemical studies show that they are a medium to high K calc-alkaline suite. These rocks belong to Urumieh-Dokhtar magmatic belt of central Iran structural zone. Some of rocks with dacitic and andesitic composition are characterized by disequilibrium phenocrysts assemblages and textures. Plagioclase is the dominant mineral in these volcanic rocks and has large range in composition, this mineral generally display reverse and oscillatory zoning; sieved or dusty texture. Amphibole phenocrysts are classified as calcic amphiboles. Amphibole and biotite phenocrysts have reaction rims indicating disequilibrium crystallization with surrounding magma. Quartz phenocrysts are embayed and a few have augite reaction rims. Clinopyroxenes are augite approaching the diopside composition and Orthopyroxenes are hypersthene to bronzite. The presence of normally and reversely zoned pyroxene in the same sample is another evidence of disequilibrium. These Criteria; support crystallization under disequilibrium condition and magma contaminated with other melt and suggested magma mixing as an important process in the evolution of these rocks.