Evidence for late Quaternary brittle deformation and back thrusting within the Indus Suture Zone, Ladakh Himalaya

Abstract

Although the tectonic evolution of the southern Himalaya has been extensively studied, relatively few studies have focused on potential neotectonic activity in the most hinterland part of Himalaya, north of the region that separates the southern edge of the Tibetan plateau from the peaks of the Higher Himalayan Range. Here we use a combination of new structural and geomorphic field data, Optically Stimulated Luminescence (OSL) chronology, as well as previously published seismicity and denudation rate dataset, to suggest that the Trans-Himalaya within the region of the Indus Suture Zone (ISZ) is neotectonically active. Based on fault gouge, tilted paleolake deposits, and the chronology of deformed fluvial gravels constrained by OSL dating, the present study provides evidence for the tectonic activity along the ISZ between 78 and 58 ka. The occurrence of two earthquakes of Mw ≥ 4.0 and the focal mechanism solution of a shallow focus earthquake (Mw: 3.0, depth ~ 8 km) near the town of Upshi, shows a pure thrust mechanism. We suggest that this earthquake was likely associated with the Upshi-Bazgo thrust, a major structure which separates the mid-Miocene Indus Molasse from the Cretaceous Ladakh Batholith. It is envisaged that the fault and fold systems in the Ladakh region such as the Upshi-Bazgo thrust originated due to (1) acceleration in the northward movement of Indian plate relative to the Eurasian plate, and (2) post-collisional shortening parallel to plate convergence. On account of this, the Eocene to Miocene post-collisional sedimentary sequences, such as the Indus Molasse, rode over the now-extinct Ladakh Arc, as it acted as a rigid body, and formed a system of backthrusts, which are neotectonically active.