Petrology and geochemistry of amphibolites from the Nellore-Khammam schistbelt, SE India

Amphibolites from the Nellore-Khammam schist belt, Khammam district, Andhra Pradesh were metamorphosed at 700+/-50 degrees C, 1.1+/-0.1 GPa. Bulk-rock chemical characteristics for relatively immobile clement ratios (e.g. Zr-Y -Ti) of the amphibolites suggest two different tectonic settings: oceanic i sland Nc and continental margin island are affinities. Coexistence of rocks for two different tectonic settings in the schist belt can be explained by accretion at trench as protoliths of the high-pressure metamorphic amphibo lites. Because the Nellore-Khammam schist belt is located between two terra ins, such as Dharmar Craton and Eastern Chats Granulite Terrain, their mode of occurrence implicitly suggests that formation of the Nellore-Khammam sc hist belt was related to the continent-continent collision tectonics. Conse quently, the Nellore-Khammam schist belt may have formed at least in two st eps: (1) accretion of the rocks originating from different tectonic setting s at trench and (2) subsequent high-pressure metamorphism and exhumation of the rocks caused by collision tectonics.