Geomorphic evolution of Medziphema intermontane basin and Quaternary deformation in the schuppen belt, Nagaland, NE India

摘要

The Medziphema intermontane basin developed in the schuppen belt of Nagaland, Northeast India, has been studied to understand its tectonic and geomorphic evolution on the basis of field evidence and morphometric parameters. Major part of the basin is covered with aggradational landforms such as fan and terrace deposits. The development of this linear basin within the schuppen belt is the result of initiation of displacement of Paleogene rocks over the Neogene rocks along the Sanis-Chongliyimsen Thrust during Late Miocene and later displacement of Neogene over the Sub-Recent to Recent sediments along the Naga Thrust after the deposition of the Dihing sediments during the Lower Pleistocene. The schuppen belt is a distinct tectono-geomorphic unit, 20-25 km in width and similar to 400 km in length that is truncated at the northeast by the Mishmi Thrust and in the southwest by the Dauki Fault. The Medziphema intermontane basin, 16.5 km in length and 11 km in width, is one of the most accessible valleys of the Naga-Patkai-Mizo Hills. Late stage tectonic activities are imprinted in the Quaternary fluvial deposits in the form of truncation of terraces and tilting of fan and terrace deposits. Most of the rivers and streams draining into the Neogene hills are structurally controlled. Lateral displacement of rivers has been attributed to active strike-slip faults resulting in the formation of shutter ridges. Thrusting of the Surma sediments over the Quaternary Brahmaputra alluvium has resulted in narrowing of river channels at their exits from mountains. Strath terraces, suggesting tectonic uplift in the region, are observed along river sections within the intermontane basin.