Pattern of active tectonic deformation across the Churachandpur-Mao thrust zone of Manipur Hills, Indo-Myanmar range, NE India: Inferences from geomorphic features and indices

Abstract

The Churachandpur-Mao thrust (CMT) in Indo-Myanmar Range (IMR) is known to be tectonically active, but nevertheless the extent and pattern of activities on it and effects thereof on the surrounding region has not been determined as yet. We herein present the results of our tectonic geomorphological investigations on these aspects across a long stretch of CMT zone spanning western Imphal intermontane valley and enclosing frontal mountains. The NNE-SSW trending CMT and NW-SE trending Sekmai fault have subdivided the area into four tectonic blocks. Geomorphic features in conjunction with statistically analyzed Mountain-front Sinuosity Index (Smf), Stream Length-Gradient Index (SL), Hypsometric Integral (HI), Drainage Basin Asymmetry factor (AF), and Transverse Topography Symmetry Factor (T) reveal variations in nature and extent of tectonic activities, and thus the pattern of surface deformation in these tectonic blocks. Tectonic blocks to the north of Sekmai fault are experiencing more intense activities than the tectonic blocks to the south of Sekmai fault. North of the Sekmai fault, the CMT's footwall is experiencing the most intense activity and thus severe surface deformation in the area, whereas the tectonic activity in the CMT's hanging wall here is only intense in the northern part. To the south of Sekmai fault, while the hanging wall of the CMT is experiencing relatively moderate tectonic activities, the footwall of the CMT is experiencing moderate to intense tectonic activities in different parts, being most intense close to the Sekmai fault. Tectonic activities have caused an overall southward down-tilting of the CMT's footwall to the north of Sekmai fault, and overall northward down-tilting of the remaining three tectonic blocks. Evidently, the tectonic activities and thus the pattern of active surface deformation in the CMT zone of the area is significantly influenced by the transverse Sekmai fault.