Clinopyroxen mineral chemistry for evaluation of temprature - pressure and genesis of matasomatic basaltic rocks of the Hormuz Formation in Gachin and Hormoz Island salt domes, south of Iran

Gachin and Hormoz island salt domes are composed of the Hormoz Formation and both are located in Hormozgan province and folded Zagros zone. Based on petrography, minerals of basaltic rocks formed in two stages: first magmatic minerals include in quartz, feldspar, pyroxene, amphibole, and then metasomatic minerals: tremolite - actinolite, chlorite, epidote, calcite, biotite, albite and iron oxide. Metasomatism changed rock forming minerals but most of clinopyroxenes are fresh compared to other minerals. Mineral chemistry of clinopyroxene is used for recognition of magma nature and tectonic settings of parent magma of the Hormoz Formation. The average composition of clinopyroxens of Gachin salt dome is augite (Wo27.66 En45.44 Fs26.91), clonopyroxens of Hormoz Island salt dome is augite –diopsid (Wo43.36 En32.71Fs23.93). These minerals are Ca-Eskola. Geochemical diagrams based on clynopyroxens composition show that the background of Hormoz salt dome samples are volcanic arc basalts and Gachin salt dome samples are intraplate tholeiitic basalts and they had sub-alkaline nature. Their forming temperatures of clinopyroxens are 875oc for Hormoz clinopyroxenes and 997oc for Gachin clinopyroxenes and forming pressure is less than 2kb.