Metapelitic migmatites from Pangidi Granulite Complex, Eastern Ghats Belt, India: Petrological constraints on crustal melting and tectonic exhumation

Metapelitic migmatites in the Pangidi Granulite Complex, Eastern Chats belt preserve a range of high-grade mineral assemblages that vary with bulk composition. Reaction textures preserved in the migmatites indicate that the crystallized granitic melt was formed in situ by biotite dehydration-melting reactions. Decompression occurred during an episode of partial melting and melt crystallization, and was synchronous with exhumation of migmatites along shear zones. Retrograde reaction textures and the calculated positions of the mineral reactions and discrete P-T points obtained by thermobarometry reflect similar to 3 kbar (11 km) of exhumation from near peak P-T conditions of similar to 9 kbar and 950 degrees C. Decompression has been traditionally ascribed to be the cause of dehydration melting in many orogens, but the bulk of melting reactions in Pangidi were ultimately driven by elevated temperatures. Simple pressure release during exhumation did not force melting reactions, instead as the present study reveals, it is more likely that the presence of melt triggered deformation in the migmatites and facilitated exhumation.