49-8 Fluvial terraces as recorders of Pleistocene-Quaternary deformation in the central Himalaya

Session: Exploring Feedbacks Between Tectonics and Climate on Lithospheric Evolution Using Multidisciplinary Approaches

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Abstract:

Rapid uplift coupled with an extreme climate gradient make the Himalayan mountains the ideal landscape to study interactions between tectonics and surface processes. Much focus has been placed on resolving the processes responsible for generating and sustaining a major topographic break in the Himalaya, which is best expressed in central Nepal. This feature, termed the High Himalayan Topographic Front (HHTF), separates the subdued topography of the Lesser Himalaya from the high relief of the Greater Himalaya. It is generally accepted that the HHTF likely requires active tectonics, however, whether it is caused by a surface breaking thrust, a mid-crustal ramp, or a mid-crustal duplex remains debated. This break is commonly attributed to focused erosion driven by monsoonal precipitation that may have led to out-of-sequence thrust faulting in the central Himalaya, however, the timing remains unconstrained. The fast uplift and incision rates of the Himalayas provide a unique opportunity to observe tectonic signals recorded by fluvial terraces. Consequentially, river terraces can be used to infer tectonic deformation from terrace warping, divergence, or tilting. We use longitudinal fluvial terrace profiles and river incision plots derived from EarthDEM 2m resolution models to investigate whether there is evidence of differential uplift across the HHTF. We leverage significant changes in terrace geometry over kilometers distance and deformation recorded by multiple terrace levels.  We conduct analyses on multiple drainages to detect a common signal while remaining cognizant that mass wasting and other landscape perturbations can influence terrace formation. Terraces within the Seti River drainage show possible deformation including folding near the HHTF and divergence above the HHTF within the highest three terraces. In the Trishuli River drainage, the oldest terrace is discontinuous near the HHTF, however the lowest three terraces show evidence of folding near the HHTF. Detailed terrace morphology data is now being coupled with geochronologic constraints on OSL and pedogenic carbonate samples collected from terraces in these drainages.  

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8271

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