NEOTECTONIC STRUCTURAL AND LANDSCAPE EVOLUTION IN THE FRONTAL HIMALAYA: INSIGHTS FROM THE GORUBATHAN RECESS, DARJILING HIMALAYA, INDIA

The Himalaya, hinged between two syntaxes in the east and west, marks the ~2500 km boundary between the Eurasian and the Indian plates. The Himalayan Mountain front is defined by the Main Frontal Thrust (MFT). However, in the Gorubathan Recess of the Darjiling Himalaya, the mountain front is defined by the Ramgarh Thrust and the width of the Himalayan arc is merely ~65 km between the foreland (27°05'41"N, 89°52'28"E) and the Tibet Plateau (27°40'41"N, 89°07'03"E). South of this Mountain Front several fan surfaces were deformed by blind faults resulting in geomorphic scarps over a ~40km zone making the Gorubathan Recess ideal for studying neotectonic deformation in the Himalayan belt. Geomorphic Indices computed using the Real Time Kinematic Global Navigation Satellite System (RTK-GNSS) corrected 1-arc SRTM heights indicate that the central part of the recess has been tectonically most active and anomalous Stream-Length Indices occur along drainage sub-basins near the major fault zones. RTK–GNSS derived digital topographic profiles were used for Boundary Element Method based Dislocation Modelling of topographic growth and the observed warping of fan surfaces by active thrusting and fault-propagation folding. Results indicate activity along the Ramgarh Thrust, an imbricate in its hanging wall and a rejoining splay in footwall, as well as the Main Boundary Thrust. Compared modelled and measured topographic profiles point to erosion of the fault-related scarp-tops in the deformed alluvial fans on the southern windward side. The deformation in the Gorubathan recess differs from the adjoining Dharan salient where an imbricate fan in the Siwalik section characterizes the frontal deformation and the two are separated by the Gish Transverse zone. Our integrated methodology delivers a novel approach for improved understanding of neotectonic deformation in the frontal Himalaya that may be applied more broadly across the entire Himalayan front.