The Lower (Lesser) Himalaya

Abstract

Litho-tectonic set-up and inverted metamorphism are described. A large number of curvatures in the trend of the Main Boundary Thrust are attributed to oblique fault ramps formed during the pre-Himalayan tensional regime. The pre-Himalayan origin of the curvatures differentiates it from arcuate structures observed in other fold and thrust belts of the world. A model is proposed for arcuate geometry of the Mandi-Karsog Pluton. The Kangra recess is the longest oblique ramp of the Himalaya. The structural evolution is proposed using a three-dimensional model. A comparison is made between petrofabric and magnetic strains measured in the region. Reasons for low magnitudes of magnetic strain are mentioned. Geometrical relationships are established between displacement along oblique fault ramps and displacement out of the tectonic transport plane. Models are proposed for allochthonous (Simla) and pop-up klippen (Satengal, Banali, and Garhwal) models along with field examples. The new evidence suggests that the actual thrust displacement is much less than the previously conceived large amounts. Using the structural data from the Uttarkashi area (Garhwal Himalaya) a model is proposed for simultaneous development of thrust and normal faults at different structural levels.