Field documentation and genesis of the back-structures from the Garhwal Lesser Himalaya, Uttarakhand, India

Abstract

Abstract Collisional fold-and-thrust belts are characterized by foreland-verging thrusts. Conversely, structures with hinterland-ward vergence, known as the back-thrusts, also exist. Strain intensification, critical taper deformation and the presence of thrust ramps generate back-thrusts. This study focuses on the exposure-scale brittle and ductile structures showing hinterland-ward vergence (back-structures) from a part of the Garhwal Lesser Himalaya, NW India, mainly along the Bhagirathi river section. In our field-traverse, back-structures were found at 31 locations. Towards the north, in the Outer Lesser Himalaya, the back-structures are located on the inverted limb of the Mussoorie Syncline (Group 1). The Tons Thrust is a south-dipping thrust (i.e. back-thrust). Hence, the Tons Thrust and nearby areas show intense back-structures (Group 2). In the Inner Lesser Himalaya, back-structures have been generated by shearing related to the folded Berinag Thrust (Group 3). The back-structures at and near the Main Central Thrust Zone (MCTZ) (Group 4) can be correlated with the presence of the Delhi–Haridwar Ridge. In this way, this study establishes the back-structures to be an integral part of the Garhwal Lesser Himalaya and provides the genesis of those structures by correlating them with the (local) tectonic settings. Supplementary material : Tables listing seismic events and the GPS coordinates of the field locations, and figures showing structures at these field locations are available at https://doi.org/10.6084/m9.figshare.c.4339784