Pattern of active crustal deformation in a part of a Lesser Himalayan tectonic window, Himachal Pradesh, India

Abstract

Overriding the underthrusting Indian plate along the low angle detachment surface of the Main Himalayan Thrust (MHT), the entire Himalayan wedge, consisting of several allochthonous and autochthonous sheets is actively deforming due to ongoing India-Asia convergence. However, the information on active tectonics of autochthonous sheets exposed in tectonic windows has often been eluded due to lack of directed investigations. The present study pertains to the active tectonics of the eastern part of an autochthonous sheet exposed in Kullu-Larji-Rampur window of the Lesser Himalaya. Geomorphic features and statistically analyzed geomorphic indices of Drainage Basin Shape (Bs), Hypsometric Integral (HI), Stream Length-Gradient Index (SL), Transverse Topography Symmetry Factor (T), and Basin Asymmetry Factor (AF) reveal active crustal deformation in the window caused by tectonic activities of spatially varying magnitudes. While the spatial distribution of Bs, HI, and SL suggest differential uplift of the anticlinally folded autochthonous sheet along the MHT, the spatial distributions of AF and T suggest an overall southeastward preferential shifting of the trunk streams of 3rd-order drainage basins of the terrane; the hinge zone and northwestern part of the sheet are experiencing relatively faster uplift. The faster uplift in the northwest has caused an overall southeastward down-tiling of the terrane, and thus preferential stream migration in that direction. The faster uplift of the hinge zone is considered to indicate active tightening of the fold.