Morphotectonics and neotectonic activity of the Schuppen Belt of Mokokchung, Nagaland, India

摘要

A stretch of the schuppen belt, trending NE-SW in the western sector of the Indo-Myanmar Ranges, represents a tectonically active zone. Deformed Quaternary deposits and various geomorphic features lend evidence for the same. In a portion of the footwall block of the Sanis-Chongliyimsen Thrust, the Nazira Sandstone of the Tipam Group of Mio-Pliocene age is thrust over tilted Quaternary fluvial deposits near Tzudikong, with a displacement of more than 2 m along the plane of the thrust fault. Deformed Quaternary deposits such as tilted terraces and faulted Quaternary sediments are indicative of ongoing tectonic activity in the area. The sediments are tilted towards the southeast by varying degrees (21 degrees-39 degrees) similar to the trend of stream migrations observed at four locations in and around Tuli. In some sections, faulting has not only affected the underlying bedrock but also deformed the overlying fluvial sediments. An important morphotectonic feature representing tectonic movement along the Kongan Thrust is evident from drainage migration in the hanging wall block of the thrust. The stream has migrated towards the southeast as a result of NW verging along the Kongan Thrust, which has left behind a trail of palaeochannels. Numerous palaeochannels, mostly linear in nature, associated with the scarp of the terrace, are indicative of migration of the river. Stream migrations suggest that the two anticlines noted in the study area are possibly growing in the present tectonic regime. Multiple levels of strath terraces lend evidence to tectonic pulses in the study area, each strath representing a tectonic phase. Lineaments have been extensively mapped in the area, out of which, around 70% are parallel to the regional NE-SW trend and the other 30% are approximately perpendicular to this trend. Any movement along the NW-SE plane may be normal faults. The mountain front sinuosity index of the emerging mountain front is close to 1, which is indicative of a relatively active mountain front. Steam length gradient index and steepness index correspond with each other, with high values in the thrust zones, which is indicative of a neotectonically active region.