LATE PLEISTOCENE EXHUMATION OF THE HIGH HIMALAYA TOPOGRAPHIC FRONT ALONG THE SUTLEJ RIVER VALLEY, NW HIMALAYA

Where the Sutlej River crosses the physiographic transition to the High Himalaya, rapid rock exhumation, high relief, a deep gorge, and >10 km-scale structural patterns are correlated with the river’s course. Existing studies focus on rock exhumation histories here over timescales of 10⁶–10⁷ years, but exhumation variations here over glacial / interglacial timescales (10⁴–10⁵ years) remains unexplored. Here, we use feldspar multi-optically stimulated luminescence thermochronology to constrain the cooling history of rocks along the Sutlej River valley across the zone of rapid exhumation defined by very young published apatite thermochronometric ages, which also correlates with a ~20 km long knickzone along the Sutlej River. Our findings show that this knickzone experienced three cooling modes over the last 0.5 Myr: (1) the western end records slow cooling from 30-20 °C over the past ~ 0.15 Myr with an exhumation rate of maximum 1 km/Myr, (2) the eastern end cooled from 50–30 °C over the past 0.2–0.1 Myr with exhumation rates of 2–3 km/Myr, and (3) the central area experienced rapid cooling from 80–70 °C over the past 0.01 Myr with exhumation rates of 10–14 km/Myr. The cooling phases recorded by the first two modes may be related to a focused erosion-dominated processes, which caused eastward propagation of a knickpoint during the development of the ~20 km long knickzone. The central area’s rapid cooling phase locally perturbed knickzone development and correlates with the end of the Last Glacial Maximum and potentially with a period of monsoon intensification across the northwestern Himalaya. The 0.01 Ma signal is also consistent with a period of increased erosion of the Lesser and Higher Himalayan rocks reported in previous studies across the Himalayan range. Collectively, these findings suggest that exhumation was modulated by focused river erosion processes during 0.5-0.1 Myr, whereas climate-controlled processes dramatically enhanced exhumation since the Last Glacial Maximum. The center of the knickzone represents one of the few places on Earth with sufficient baseline tectonic and focused-erosion controlled exhumation to record this additional 10⁵-year timescale, climate-driven exhumation signal via in-situ low-temperature thermochronometry.