Mineral chemistry of gabbro- dioritic xenoliths in Monavvar volcanic rocks (Northwest of Tabriz- NW Iran)

The studied area is located in the northwest of Iran within the western Alborz- Azerbaijan zone. The host rocks of the studied xenoliths are basaltic andesite and andesite. Xenoliths in volcanic rocks include gabbroic and diorite xenoliths. The main minerals of xenoliths include plagioclase, amphibole and clinopyroxene with minor minerals including biotite, orthopyroxene and opaque minerals. The main texture of xenoliths is granular and microlithic porphyric. Based on mineral chemistry, the composition of plagioclase, amphibole, pyroxene and biotite is oligoclase to andesine, chermakite to hornblende, augite and stonite respectively. Based on AlIV value (less than 1.5), amphiboles of xenoliths are placed in the active subduction-related continental margin. The thermo-barometric measurement of xenoliths, using the amount of total aluminum cations, indicates a pressure of 5.8 ± 0.6 kbar and a temperature of about 802°C in the crystallization environment. The studied clinopyroxenes with sub-alkaline composition show good compatibility with magmatic arc tectonic environment. Also, clinopyroxenes are formed in low to medium pressures, which indicates their crystallization during magma ascent at different depths. The amount of ferric iron in clinopyroxenes indicates the high fugacity of oxygen magma. The clinopyroxenes of diorite-gabbroic xenoliths were formed at a pressure of 12 kilobars and a temperature of about 1050°C.