Research Projects

The Sub-Himalayan fold-and-thrust belt situated at the southern fringes of the Himalayan arc accommodates the majority of the crustal shortening driven by Indo-Eurasian collision since at least Quaternary. For example, in the Sikkim-Darjeeling Himalaya, the piedmont fan system at the southern front accommodates 13 - 16 mm/y out of total 20 – 21 mm/y convergence. The remainder however is not well-traced. Speculations remain if a small yet significant fraction of the cumulative Himalayan crustal shortening is being accommodated at the interiors of the orogen by out-of-sequence faulting along pre-existing fault/s. The structural attributes of the Sikkim Himalaya exhibit a half-window formed by north-bound warping of the Main Central Thrust (MCT) exposing the Lesser Himalayan metasediments within the Darjeeling-Sikkim window (DSW). Debates exist whether the MCT bordering the north of DSW is a single 30 km-wide shear zone or are there two exclusive MCTs, viz., MCT-I (Mangan Thrust) and MCT-II (Chungthang Thrust). Terrain analysis done using a 30 m digital elevation model shows that the hanging walls of MCT-I and MCT-II are steeper than the rest. While MCT-I receives focused rainfall, MCT-II is situated in a rain-shadow. The steep landscapes ensure faster exhumation/ denudation of the MCT zone with respect to the surroundings. The question is how a landscape sustains oversteepened hillslopes unless it undergoes sustained exhumation or uplift. This fundamental question on decoupling tectonic and climatic forcing on landscapes define my present research proposal. The steep landscapes in Sikkim Himalaya could be driven by active uplift and/ or climate-driven faster exhumation. To decouple this, I plan to obtain exhumation patterns across 102 - 106-year timescales. For million-year timescale, I will use detrital Apatite-Helium (U-Th/He) thermochronology and for shorter timescales, luminescence thermochronology and 10Be-26Al-based catchment-averaged denudation rates will be estimated from selected catchments. If the exhumation/ uplift is sustained across timescales, we would expect similar rates and similar trends in thermochron data. For tectonically-active landscapes, differential erosion/ incision rates are expected across active faults. For example, the hanging wall ramp of an active thrust would denude faster than the footwall. I further plan to use isotopic fingerprinting (using Sr-Nd) and Thermoluminescence sensitivity of the eroded sediments to find out the erosion hotspots. A successful execution of this project proposal will not only help us to constrain potential fault activity rates in the interiors of the Sikkim Himalaya, but also help us to map and quantify erosion hotspots as well as to predict future natural hazards caused by multiple factors, such as landslides, glacial lake outburst floods or cloudbursts.