Late Quaternary deformation in parts of the Belt of Schuppen of Dimapur and Peren districts, Nagaland, NE India

摘要

Geomorphic evidences and geochronology suggest recent tectonic activity in the Belt of Schuppen of Dimapur and Peren districts of Nagaland. Multiple levels of strath terraces forming remarkable geomorphic expressions are observed along the Chathe and Jharnapani river valleys. They indicate episodic uplift of the hanging-wall blocks of the thrust systems. The major lineaments prominently trend parallel to the NE-SW regional thrusts, some being perpendicular or oblique. Active normal faults displacing bedrock and overlying fill sediments point to recent tectonic activity. The parallel and trellis drainage patterns are lineament-controlled. Uplift of the terrain is evident from successive palaeochannels of the Chathe River younging towards the southwest. Three major aggradational phases of the terrace sediments are inferred from optically stimulated luminescence (OSL) chronology, the oldest beginning around 21 ka, the second around 11-7 ka, and the youngest between 3.5 and 1 ka. A sand lens of a tilted strath terrace exposed between Kukidolong and Chumukedima is dated at 7 ka, indicating tectonic events after 7 ka. Five major phases of bedrock uplift/incision have been estimated during 20 ka (0.13 mm/year), 11 ka (0.92 mm/year), 9 ka (2.29 mm/year), 6 ka (0.67 mm/year), and 1.8 ka (2.6 mm/year). Transverse topographic symmetry and asymmetry factor data suggest tilting towards the NE and SW. Other morphometric indices, such as channel sinuosity, stream length gradient index, valley floor to valley height ratio, and mountain front sinuosity, suggest that the area is tectonically active, which corroborates field observations.