Tectonic Implications of Small-Scale Structures in the Main Central Thrust Zone of Garhwal Higher Himalaya

In the Garhwal Himalaya, the Main Central Thrust Zone (MCTZ) is bounded by the Main Central Thrust (MCT) in the south and Vaikrita Thrust (VT) in the north. The MCTZ along the Alakhnanda, Bhagirathi and Yamuna valleys is marked by different small-scale structures and are classified as early structures i.e. pre-thrusting, structures due to progressive ductile shearing (syn-thrusting) and late structures (post-thrusting). The detailed study of small-scale structures/kinematic indicators such as sigmoidal foliations, shear band (S-C) structures, asymmetric porphyroclast tails, intergranular faults, folded layering and sheath folds suggest top to SSW sense of movement in the rocks of MCTZ of Garhwal Himalaya. The strain studies and crystallographic preferred orientation of quartz reveal that mesoscopic ductile shear zones grow in a narrow zone in response to very high strain, which deformed the internal crystallographic fabric of rock. The study of compressive stress from several mesoscopic sigmoidal foliations suggest that, in MCTZ the maximum compressive stress direction acted in the NNE-SSW direction horizontally synchronous to the northward movement of Indian Plate.