Late Cenozoic Foreland-to-Hinterland Low-Temperature Exhumation History of the Kashmir Himalaya

Abstract

New apatite and zircon (U-Th)/He cooling ages quantify late Cenozoic exhumation patterns associated with fault activity across the Kashmir Himalaya. Apatite (U-Th)/He (AHe) cooling ages of detrital grains from the Sub-Himalayan foreland sediments indicate significant resetting. AHe data and thermal modeling reveal cooling and exhumation initiated by 4 Ma at the deformation front and by 2–4 Ma throughout other Sub-Himalayan structures. Exhumation rates for Sub-Himalayan structures are ≥1 mm/year. In the hinterland, thrust sheet samples from the Main Boundary thrust and Main Central thrust yield AHe cooling ages between 5.1 and 21.1 Ma. Published apatite fission track cooling ages (<3 Ma) and high exhumation rates (3.6–3.2 mm/year) across the Kishtwar window further to the north are consistent with AHe data from the Sub-Himalayan structures. The pattern of cooling ages and rates indicates that exhumation occurs in association with changes in the Himalayan basal décollement ramp geometry. Hinterland zircon (U-Th)/He (ZHe) data show a pronounced abundance and probability spike in cooling ages between 14 and 21 Ma, a period when Main Central thrust motion is well documented throughout the Himalaya. ZHe single-grain ages from Sub-Himalayan samples contain a nearly identical cluster from 16 to 23 Ma. Cooling patterns across the Kashmir Himalayas do not correlate spatially with modern monsoon precipitation, suggesting that climate-related precipitation and exhumation are decoupled. Coeval translation over the basal décollement and distributed imbricate thrust deformation of the foreland in the upper plate characterizes fault-related exhumation of the Sub-Himalayan orogenic belt after 4 Ma.