Garnet-Staurolite-Mica Schist from Rangli Rangliot, Eastern Himalaya: Constraints from Phase Equilibria and Thermobarometry

Abstract: Rangli Rangliot is an integral part of lesser Himalaya. The area around Rangli Rangliot consists of garnet-staurolite-mica schist and it is characterized by mineral assemblage garnet-biotite-muscovite-staurolite-quartz± plagioclase. Different reaction textures are of particular interest as they reflect discontinuous or continuous reactions under changing physical conditions. The relative XMg in the minerals varies in the order: muscovite> biotite> staurolite> garnet, and the XMn decreases in the order: garnet>staurolite>biotite>muscovite. The P-T evolution of the garnet-staurolite-mica schist has been constrained through the use of internally consistent TWEEQU programme and Perple_X software in the KFMASH model system. The combination of these two approaches demonstrates that the garnet-staurolite-mica schist experienced peak pressure and temperature at 5.8 kbar and 590 °C. The proposed clockwise P-T path implies that rocks from the study area could have resulted from thickened continental crust undergoing decompression.