Petrology and geochemistry of south Mahin volcanic rocks in Tarom-Hashtjin magmatic zone

Mahin village is located in Alborz-Azerbaijan area in Tarom-Hashtjin magmatic- metallogenetic sub-area. According to petrographic studies done around the south of Mahin, the outcrop rocks include trachyte andesite, andesite, basaltic andesite, pyroxene andesite, pyroclastic, and porphyritic gabbro, affected by the alteration process. In geochemical studies, the samples are located in the basalt, alkaline basalt, andesite, and basaltic andesite domains. All rock samples are in the magmatic series of calc-alkaline to high-potassium calc-alkaline (shoshonite). The primary magma is alkaline in nature. Amphibole and mainly phlogopite have been present in the original melt. Accordingly, the primary magma was probably formed at a depth of about 70 km. The composition of high-potassium calc-alkaline, the decrease of FHSE elements, especially Zr, the high ratios of Nb / U, Th / U, Ba / Nb, Nb / Th, and the low ratio of Ce / Pb and the diagrams all confirm the existence of active continental. Arc island evidence in some diagrams, and the association and simultaneity of igneous rocks with green tufftite and sedimentary rocks in and around the area, all confirm the existence of continental(ensialic) back-arc basin. According to these indications, there might have been active normal continental arcs and ensialic back arc simultaneously in the area.