Shear fabrics reveal orogen-parallel deformations, NW Lesser Garhwal Himalaya, Uttarakhand, India

Shear deformation along the Himalayan belt is poorly understood unlike that across the orogen. Field observations and structural analysis along Bhagirathi river section along the National Highway 34 reveals NW Lesser Himalaya (Garhwal region, India) suffered both compression and extension parallel to the orogenic belt and thus forms a unique venue of great structural and tectonic interest. Meso-scale ductile- and brittle shear fabrics, such as S-C, C-P, Y-P, Y-S; are emphasized describing such deformations. Extensional shear fabric strikes N43oE and compressional shear fabrics N39.5oE, which are at a low-angle with the orogenic trend. Our study reviews orogen parallel deformation, both extension as well as compression, taking examples from other part of the world (e.g., Central Andes, N Apennines and SW Alps) and from other terrains in the Himalaya. Proposed models are evaluated and compared with the study area. The results shows that the pre-existing remnant structures (e.g., the Delhi-Haridwar ridge) on the under-thrusting Indian shield/plate plays a vital role in modifying thin-skinned tectonics along with migration of the eastward extrusion of the Tibetian plateau (hinterland deformation) into the Himalayan foreland.