Abstract: The occurrence, petrology and geochemistry are dealt with in details for the corsite identified for the first time in the southern Altun fault, Xinjiang. The corsite appears generally in back-arc basins or on active continental margins as the mixtures derived from the consumed oceanic crust and overlying wedge-shaped (mantle)-derived rocks. The magmas of the corsite resulted from the direct melting of the consumed oceanic crust, and were often reacted with the wedge-shaped mantle-derived rocks during their migration to the surface, (accompanied) by crystallization and differentiation.