Tectonomagmatic setting of the Siahbaz A-type granitoids and mafic intrusions (Northwest of Khoy

Abstract

The Siahbaz granite-gabbro-appinite outcrops from the Northwest Khoy is related to one of the complex of the Late Ordovician-Early Permian. The complex is located on the north Sanandaj-Sirjan Zone. Synchronous activities of the mafic and felsic melts indicate that hydrous mafic melts during or after injection to the crust have been able to mingle with felsic magmas produced from the base of the crust. Fractional crystallization in the magma chambers of the hydrous mafic melts caused to form appinite mafic rocks c. 25 to 60 modal percent of hornblende and gabbros. The felsic melts could form A-type granitic rocks. The mineralogical observations along with geochemical and tectonical studies show that subduction of the Paleo-Tethys under an island arc (Siahbaz) in the Northwest Iran were produced all rock types at the Late Ordovician-Early Permian. The hydrous mafic melts were produced in the mantle wedge because of the presence of subduction fluids and then transferred to the base of the island arc, formed the A-type felsic liquids as a result of the partial melting of the base. Convection in the mantle wedge in the supra subduction zone, led to the formation of an extensional setting in the region (the extensional region in the active margin); hence, the conditions for the formation of A-type felsic melts were provided