Estimation of physicochemical properties and tectonic environment of gabbro masses from‏ ‏south of Germi city (Ardabil province)‎ based on the chemistry of clinopyroxene crystals

Abstract

The studied gabbroic rocks, trending northwest- southeast, outcropped in the south of Germi, northwest of Iran. These rocks composed of plagioclase, clinopyroxene and iddingsitic olivines. Mineral chemistry studies reveal that these clinopyroxenes have augitic to diopsidic composition and are classified as Ca - Mg and Fe clinopyroxenes. These clinopyroxenes have igneous nature and belong to the alkaline- shoshonitic series from tectono-magmatic setting. Moreover, normal and oscillatory zoning are observed in these phases. Crystal chemical composition studies show that variable, different oxidation conditions, and oxygen fugacity have had the greatest effect in zoning of the clinopyroxenes studied. Thermo-barometry studies indicate these clinopyroxenes crystalized at temperature of up to 1200 °C and calculated pressure ranges from 9 to 13 Kb, on the base of 0.04VI contents in mineral structural formula. The presence of ferric iron in the core of clinopyroxenes can be ascribed to high oxygen fugacity in the source of magma.

Keywords

• mineral chemistry
• clinopyroxene
• thermo-barometry
• gabbro
• germi
• talesh zone