Mineral chemistry, tectonic setting and thermo-barometry of the gabbro-diorite intrusive body (south of Tikmehdash), East-Azarbaijan

The Bostanabad-Hashtrood gabbro-diorite intrusive body in the south of Tikmehdash has intruded the Eocene volcanic-sedimentary rocks. The chemistry of the constituent minerals in this intrusive body shows that the plagioclases and clinopyroxenes have labradoritic and diopsidic composition, respectively, and are accompanied by the subordinate amounts of Mg-rich biotite and gangue minerals. The chemistry of the existing diopsides in these rocks indicates that their parent magma belongs to subalkaline magmatic series with a continental arc tectonic setting. The thermometric considerations showed that the clinopyroxene was crystallized at temperatures around 1200°C. Based on AlVI content (0.048-0.102) in the crystal lattice of the clinopyroxenes, it was ascertained that this mineral was formed under the pressure range of 6 to 9 kbars equivalent to depths between 19 and 28 km. Additionally, this study revealed that the clinopyroxenes in these rocks were formed from a magma which contained 10% water. The presence of some ferric iron in these clinopyroxenes with titanomagnetite is indicative of high oxygen fugacity in the parent magma.