ON THE EXISTENCE OF VAKRITA THRUST (MCT-I) IN NORTH-EASTERN KUMAUN HIMALAYA EVIDENCE FROM STRUCTURAL ANALYSIS IN THE MUNSIARI-DHAPA SECTION

Abstract

The Main Central Thrust (MCT), an orogen parallel tectonic boundary has been attempted to map using various criteria in different regions of the Himalayas. Different workers place this tectonic boundary at different levels within the Higher Himalayan Crystallines. Mapping in the north-eastern Kumaun Himalaya reveals a gradual increase in grade of metamorphism from biotite to staurolite in the rocks sandwitched within the MCT shear zone, which questions the position of Vaikrita Thrust higher upward in the Higher Himalayan succession, established based on metamorphic break. The heterogeneous zones of phyllonite both within the Lesser Himalayan Tejam Group and Higher Himalayan Crystallines suggest that the zone of high strain is distributed in a discrete pattern throughout the area. There is a structural concordance in terms of structural style with four phases of recorded deformation throughout the succession and tightness of later folds gradually increasing from south to north. I conclude from the above observations that Munsiari Thrust (MT), the boundary between relatively undeformed Lesser Himalayan Tejam Group of rocks and Gneisses of Higher Himalayan should be defined as the MCT.