Southern Extension of the Dauki Fault System: Implications for Décollement Propagation Associated with Subduction Beneath the Shillong Plateau

Abstract

The Dauki Fault is a major reverse fault system along the northern margin of the Bengal Basin, yet its geometry, kinematics, and the role of Indian Plate underthrusting beneath the Shillong Plateau remain poorly constrained. This study integrates geomorphological and geophysical data to characterize the architecture and recent activity of the Dauki Fault system and its contribution to ongoing deformation along the basin margin. We identified and mapped six principal fan and terrace levels within the Surma Basin that are interpreted to range in age from the Pleistocene to the Holocene. These geomorphic surfaces are uplifted between 1.5 and 72 m above the present riverbed and yield a preliminary uplift rate estimate of approximately 1.5 mm/yr. The Dauki Fault System extends for nearly 320 km in an east–west direction and consists of two subparallel reverse fault splays. The Northern Dauki Fault is responsible for the ~2 km topographic relief of the Shillong Plateau and the development of monoclonal folding within the Garo–Jaintia–Khasi Hills. The southern splay, referred to as the Jamuna–Lubha Fault, is associated with the uplift of Pleistocene–Holocene terraces and hillocks between the Jamuna and Lubha rivers. The structural relationship between these fault splays suggests the presence of a southward-propagating décollement system consistent with active crustal shortening and underthrusting beneath the plateau margin. The observed geomorphic deformation and fault geometry indicate that the Dauki Fault system remains tectonically active and accommodates ongoing strain accumulation, representing an active phase of orogenic growth along the northern margin of the Bengal Basin.