Unraveling rapid exhumation: Insights into the increase of exhumation rates in the Sutlej River anticline (NW Indian Himalaya) over the last 200 kyr.

Abstract

Estimating exhumation rates on Pleistocene-Holocene time scales presents a challenge due to the scarcity of suitable low-temperature thermochronometers. Apatite helium (AHe) dating is unable to precisely differentiate cooling ages <1 Ma and whilst optically stimulated luminescence (OSL) thermochronometry resolves younger ages (104-105 years timescale), it is limited in regions with lower exhumation rates (<2-3 mm/yr). These restrictions limit our ability to accurately study exhumation rates on such time scales, thus hindering our understanding of the implications of tectonics, climate, and hydrology. To address this challenge and gain insights into the dynamics of rapid exhumation, we conducted our study in the Sutlej River valley (northwest Indian Himalaya), which features a prominent river anticline with exceptionally high exhumation rates locally reaching up to 12 mm/yr (OSL data from a previous study). For this purpose, we collected 10 samples, including 5 from a 2200 m vertical profile in the Sutlej valley, and 5 from the main tributaries. The new OSL analysis of these samples reveals high exhumation rates at lower altitudes (<2500 m), ranging from 6-8 mm/yr, 350 m above the river, and from 3-5 mm/yr, 720 m above the river. Furthermore, OSL ages of samples from lower elevations along the tributaries were not saturated, also pointing to rapid exhumation in these areas. In contrast, all samples from higher elevations (>2500 m) reach field saturation, indicating lower average exhumation rates that cannot be recorded using OSL thermochronometry. Although the vertical profile data exhibit a significant increase in exhumation rates over the past 200 kyr, this region lacks glaciated landscapes, suggesting a feedback loop within the river anticline. The river incision promotes the development of the anticline, which, in turn, amplifies the river incision, leading to accelerated exhumation over time. By demonstrating the importance of the interplay between river incision and anticline development in driving the progression of exhumation rates in the Sutlej River region, this study offers a new perspective on Late Pleistocene exhumation rates in the Himalayas.