Petrology and geochemistry of amphibolites from the Nellore-Khammam schist belt, 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 island 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 amphibolites. Because the Nellore-Khammam schist belt is located between two terrains, such as Dharmar Craton and Eastern Chats Granulite Terrain, their mode of occurrence implicitly suggests that formation of the Nellore-Khammam schist belt was related to the continent-continent collision tectonics. Consequently, the Nellore-Khammam schist belt may have formed at least in two steps: (1) accretion of the rocks originating from different tectonic settings at trench and (2) subsequent high-pressure metamorphism and exhumation of the rocks caused by collision tectonics.