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

Abstract

Summary. The Medziphema intermontane basin developed in the schuppen belt of Naga-land, Northeast India, has been studied to understand its tectonic and geomorphic evolution onthe basis of field evidence and morphometric parameters. Major part of the basin is coveredwith aggradational landforms such as fan and terrace deposits. The development of this linearbasin within the schuppen belt is the result of initiation of displacement of Paleogene rocksover 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 afterthe deposition of the Dihing sediments during the Lower Pleistocene. The schuppen belt is a distinct tectono- geomorphic unit, 20–25km in width and ~400km in length that is truncatedat the northeast by the Mishmi Thrust and in the southwest by the Dauki Fault. The Med -ziphema intermontane basin, 16.5km in length and 11km in width, is one of the most acces-sible valleys of the Naga-Patkai-Mizo Hills. Late stage tectonic activities are imprinted in theQuaternary fluvial deposits in the form of truncation of terraces and tilting of fan and terracedeposits. Most of the rivers and streams draining into the Neogene hills are structurally con-trolled. Lateral displacement of rivers has been attributed to active strike-slip faults resultingin the formation of shutter ridges. Thrusting of the Surma sediments over the QuaternaryBrahmaputra alluvium has resulted in narrowing of river channels at their exits from moun-tains. Strath terraces, suggesting tectonic uplift in the region, are observed along river sectionswithin the intermontane basin.