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The active tectonic aspects of the Indo-Myanmar Range (IMR) have not yet been studied in detail in spite of the fact that it's seismically active. In the present study qualitative and quantitative geomorphic analyses have been carried out to understand the active tectonic evolution of Nungba, and Barak- Makru thrust sheets (NBTS and BMTS) in the central part of IMR. The focus of the study is on understanding the active spatial growth pattern of adjacent thrust sheets in an evolving mountain range and providing baseline data for further detailed seismotectonic and seismic hazard vulnerability analyses. Drainage characteristics, disposition of landforms and statistical analyses of Normalized Steepness Index (ksn), Hypsometric Integral (HI) and Transverse Topography Symmetry Factor (T), computed for a total of 164 4th-order drainage basins, reveal that both of these adjoining thrust sheets are actively uplifting. Higher values of ksn (mode = 111) and HI (mode = 0.46) in NBTS suggest its faster uplift than the BMTS, which has comparatively lower values of ksn (mode = 56) and HI (mode = 0.43). Moreover, the northern parts of the both the thrust sheets are uplifting faster than their southern parts due to along-strike variations in the movement on their basal thrusts, as a result of which the NBTS has been south-southeastwardly down-tilting and the BMTS is south-southwestwardly down-tilting. The study reveals that both the adjacently lying NBTS and BMTS have almost the same spatial growth patterns that are mainly controlled by the movements on their basal thrusts. [ABSTRACT FROM AUTHOR]

The NE–SW trending and SE dipping Thoubal‐Chandel Thrust (TCT) in eastern Manipur Hills of the Indo‐Myanmar Range (IMR) places the Thoubal‐Chandel thrust sheet over the Churachandpur‐Mao thrust sheet. Despite being seismically active, the active tectonic aspects of the major structural discontinuities within the IMR, including TCT, are not yet studied in detail. The present study aims to examine the active tectonics of the TCT and other associated faults, with particular focus on deformation of the Churachandpur‐Mao, and Thoubal‐Chandel thrust sheets. Association and disposition of landforms, and statistical analyses of Mountain‐front Sinuosity Index (Smf), Stream Length‐Gradient Index (SL), Hypsometric Integral (HI), Drainage Basin Asymmetry Factor, and Transverse Topography Symmetry Factor (T) reveal that both of these adjacently lying thrust sheets are actively uplifting due to oblique‐slip movement on their basal thrusts, but with spatially variable rates. In general, higher SL (mode = 219) and HI (mode = 0.527) in large parts suggest faster uplift of the Thoubal‐Chandel thrust sheet than the Churachandpur‐Moa thrust sheet, which has comparatively lower SL (Mode = 140) and HI (mode = 0.416). However, differential along‐strike uplift rates have caused tilting of both the thrust sheets. Faster uplift of the northern part of Thoubal‐Chandel thrust sheet has caused its overall southward down‐tilting, whereas faster uplift of the southern part of Churachandpur‐Mao thrust sheet has caused its overall northward down‐tilting. The study brings out that the deformation pattern of even the adjacent thrust sheets of growing orogens could be at stark variance albeit the same stress regime. [ABSTRACT FROM AUTHOR]

Intermontane basins make a distinct category of sedimentary basins, but nevertheless, the depositional processes and sedimentation patterns therein are not well understood. Quaternary sediment‐filled Imphal Basin in the Indo‐Myanmar Range provides us with an excellent opportunity of lending insight into these sedimentological aspects of an intermontane basin. Detailed facies analysis brings out that five distinct facies associations ("FAA"–"FAE") have developed in different parts of the basin, each one of which indicates a specific subenvironment of deposition. Facies characters and spatial distribution of facies associations reveal that the basin fill records interlinked lacustrine, fluvial, and alluvial fan processes. Comprising mud and peat, the facies association "FAA" represents deposits of a lake and lakeshore swamp. The facies association "FAB" comprises mud interfingered with crudely bedded gravel and represents suspension fallout in a lake with intervening gravel‐rich, hyperconcentrated flows that diffusively plunged into the lakebed. The sand‐dominated facies association "FAC" and gravel‐dominated facies association "FAD" were deposited in fluvial domains of meandering and braided streams, respectively. Rimming the basin margin, the gravel‐dominated facies association "FAE" was deposited in the alluvial fan–interfan areas. Widespread development of the lacustrine facies ("FAA" and "FAB") around the Loktak Lake along with extensive peat development over the lacustrine mud suggests lakeshore regression and development of vast swamps under humid conditions. The regression under humid conditions could be a result of fast and enhanced influx of finer sediments into the lake that transcended the creation of accommodation space and ultimately led to faster infilling of the lake margins favouring development of vast swamps in due course of time. [ABSTRACT FROM AUTHOR]