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Existing data on Quaternary shortening of the Himalayan orogen suggests that most of the Himalayan shortening has been accommodated by active folding and faulting within the Sub-Himalayan fold-and-thrust belt. It is understood that the total Sub-Himalayan shortening of 11-15 mm.a-1 in the late Quaternary timescale is actually caused by slip on the basal decollement (The Main Himalayan Thrust), into which the Sub-Himalayan faults are rooted. All of the Sub-Himalayan shortening is not consumed by the Main Frontal Thrust (MFT) since its’ initiation ~40 ka, but is partitioned among other Sub-Himalayan tectonic structures.
Here, I present a case study from the Kangra re-entrant in the Himachal Pradesh, where I show that the Jwalamukhi Thrust (an interior thrust within the Sub-Himalaya) has accommodated 5 – 7.5 mm.a-1 shortening since ~10 ka. This means 40-50% of the late Pleistocene- Holocene shortening in this sector (141 mm.a-1) is achieved not by the elsewhere predominant MFT. This Holocene out-of-sequence thrusting can possibly be related to large-scale evacuation of transiently-stored sediments from the intermontane Kangra Basin.
On the other hand, I portray another study across the high-relief orographic barrier of the Dhauladhar Range, where low-T thermochronology data provides hints about 1-3 mm.a-1 shortening accommodated by the MBT since at least ~2-3 Ma. Sustenance of such high topography in a highly-erodible environment is possible only if active uplift over a mid-crustal ramp of the MBT. Recently-published study from the Kishtwar region (Gavillot et al., 2018) supports the claim that the Lesser Himalayan Duplex is experiencing active uplift over a mid-crustal high-angle ramp which is characterized by a high-relief and frequent seismic activity over a 30-40 km wide region inside the NW Himalaya. However, morphometric analysis of the NW Himalaya suggests that the geometry of the mid-crustal ramp is variable along the length and may be affected by a lateral ramp. |