Testing Models of MCT Reactivation vs. Duplex Formation in the Kumuan and Garwhal Himalaya, India

We present preliminary results of the thermochronologic, microstructural and metamorphic evolution of the Kumaun and Garhwal Himalaya in the vicinity of the Alaknanda and Bhagarathi rivers, northern India. Samples of quartzite, schist and gneiss were collected from the Lesser Himalayan and Greater Himalayan sequences to explore the sequence of thrusting. We find that within the duplex of Lesser Himalayan rocks (Srivastava and Mitra, 1994), microstructures suggest that temperatures (and/or strain rates) during deformation did not vary significantly in the transport direction. Thermometric estimates from carbonaceous material are consistent with this observation. In contrast, the upper Lesser Himalayan sequence and MCT zone show strong gradients in quartz microstructure, metamorphic grade, thermal structure and age of textural development, with extensive reworking of earlier kyanite grade fabrics. In order to assess the conditions and sequence of thrusting, within and beneath the MCT zone, a series of thermochronologic measurements (40Ar/