Petrography and mineral chemistry of tephritic dykes and associated xenoliths, the northeast of Meshkinshahr (the northwest of Iran)

The studied area is located in Ardabil province and the northeast of Meshkinshahr city and structurally in Alborz-West-Azerbaijan zone. Tephritic dykes have pyroxenite and gabbro xenolites. Mineralogy of tephritic dykes and xenolites includes plagioclase, clinopyroxene, analcime, amphibole, olivine and phlogopite. Porphyric, microcrystalline, granular and cumular microlytic textures are their main textures. According to the mineral chemistry data as well as the presence of shaped, homogeneous and coarse analcime crystals, it can be concluded that the analcime crystals are secondary and as a result of delayed magmatic reactions under hydrothermal conditions have been formed on the primary leucite crystals. The composition of olivine in gabbro xenoliths is chrysolite. The chemical composition of pyroxene mineral in tephritic dykes and gabbro xenolites is diopside. The studied clinopyroxenes with alkaline composition show good adaptation to the tectonic environment of the magmatic arc. Clinopyroxenes are also formed at low to medium pressures, indicating their crystallization during magma ascent and at different depths. The amount of ferric iron in clinopyroxenes indicates high oxygen fugacity of magma. Clinopyroxenes of Tephritic and Gabbroic dykes are formed at 10 and 12 kbar pressure, temperature between 950 and 1100 ° C and depth between 35-35 and 40-50 km. The chemical composition of amphiboles related to pyroxenite xenolite is  calcic and magnesiohastingsitic amphiboles type . The average geometry of the barometer based on the amount of aluminum for pyroxenite xenoliths is 7-9 kbar. Thermometric studies indicated that the amphiboles were formed at 900-950 ° C. The chemical composition of mica is phlogopite, and the number of magnesium in mica is 0.77.