Plio-Plistocene in-sequence thrust propagation along the Main Central Thrust zone (Kumaon–Garhwal Himalaya, India): New thermochronological data

Abstract

The Kumaon and Garhwal Himalayas, NW-India have similar geologic, tectonic, topographic and precipitation pattern. However, low-temperature thermochronological age pattern varies significantly along the strike as well as across the strike of major faults. Here, we interpret the new set of thermochronological age data across the strike of major faults namely Vaikrita Thrust (VT), Munsiari Thrust (MT), Berinag Thrust (BT) and the Baijnath nappe along Pindari valley in the Kumaon–Garhwal Himalaya. In the present work, 18 new apatite fission track (AFT) ages of samples collected along a north–south transect have been reported. Ages in the hanging wall of VT which range from 2.1±0.2 to 4.2±0.7Ma, have been found to be becoming younger linearly with distance from north to the VT. This trend crosses the VT with significant jump in ages. In the south of the VT, ages are lying between 0.3±0.1 and 3.9±0.8Ma, and show linear variation with distance from the VT to BT. No significant jump in ages across the MT is observed and the linear trend of younging southward is continuing till the BT. The break and displacement in age pattern with youngest ages close to thrusts possibly indicate progressive late thrust movement. It reflects sequential uplift and cooling towards the south from the VT to BT which is consistent with an in-sequence style of thrust propagation. We compare our new data to the published thermochronological data from its adjacent traverses along the Goriganga and Dhauliganga valleys (~25km away from the present traverse towards east and west respectively) in the Kumaon–Garhwal Himalaya in order to understand potential along-strike variations in the kinematics. Our observations indicate a dynamic coupling between tectonic and surface processes in the Garhwal–Kumaon Himalaya and support that the geometry of crustal scale faults and their associated kinematics control exhumation pathways of rocks.