High-temperature crustal scale shear zone at the western margin of the Eastern Ghats granulite belt, India: implications for rapid exhumation

Abstract

A mylonitic shear zone occurs along the western margin of the Eastern Ghats Granulite belt, India. In the northern sector, it separates metapelitic and mafic granulites from the granite gneisses of the Bastar craton, while in the southern sector, it separates charnockitic gneisses and mafic granulites from the granite gneisses of the Bastar craton. This boundary shear zone is characterized by a mylonitic foliation and a stretching lineation. Microstructures characterize high-grade conditions and quartz c-axis patterns show strong point maxima close to the long axes of the strain ellipsoids, indicating dominant prism [c] slip in quartz, commonly interpreted in terms of ductile deformation at high-temperatures. Quartz c-axis patterns in the recrystallized and unrecrystallized domains also imply grain boundary migration as the principal mechanism of dynamic recrystallization at high temperature conditions. A rapid exhumation during shearing in this marginal part of the convergent Eastern Ghats orogen is indicated by decompression reaction textures and retrograde hydration reactions, presumably due to hydrous fluid ingress, in the shear zone rocks.