Age of crustal melting in Higher Himalayan Crystalline Sequence (Darjeeling, Eastern Himalaya): Constraints from SHRIMP U–Pb geochronology

Abstract

The paper presents the petrological and geochronological studies of migmatite from an important section of Higher Himalayan Crystalline Sequence of Eastern Himalaya. Migmatites collected from the area characteristically contain biotite‐garnet‐sillimanite‐plagioclase‐K‐feldspar‐quartz as an important mineral assemblage, which has experienced extensive partial melting through dehydration melting reaction involving biotite. In this study, P–T evolution of these migmatites has been constrained through the use of multiequilibrium thermobarometry program winTWQ, conventional thermobarmetry, and pseudosection modelling in the MnNCKFMASHTO model system using Perple_X software. The unification of these three calculations demonstrates that the migmatite experienced peak pressure and temperature at 7.2 ± 0.5 kbar and 775 ± 20 °C, respectively. SHRIMP U–Pb chronological results yield the timing of crustal melting (21 Ma) in the migmatite.