Thermochronological constraints on the exhumation of the tectonic wedges in the Higher Himalayan Crystalline and Lesser Himalayan Sequence along Yamuna Valley, NW- Himalaya

Abstract

The NW Himalayas exhibit significant spatial variability in exhumation patterns, shaped by complex tectonic and climatic interactions. This study reconstructs the Mio-Pleistocene exhumation history of the Yamuna Valley, Uttarakhand, focusing on the Purola Klippe and Kharsali Window, using twenty fission track ages. Along a ∼40 km transect, apatite fission track (AFT) ages in the Kharsali Window range from 3.6 ± 0.5 to 5.3 ± 1.0 Ma, while in the Purola Klippe, they span 3.9 ± 0.6 to 6.2 ± 1.1 Ma. The zircon fission-track (ZFT) ages show a range, varying from 4.4 ± 0.3 to 6.0 ± 0.3 Ma in the Kharsali Window and from 9.2 ± 0.5 to 13.2 ± 0.4 Ma in the Purola Klippe. Exhumation rates derived by employing age2Exhume modeling suggest significantly higher exhumation in the Kharsali Window at the Pliocene (5 to 4 Ma), while the Purola Klippe has experienced relatively steady exhumation since the Late Miocene (∼11 Ma). At 4 Ma, reactivation of the Main Boundary Thrust (MBT) resulted in uniform vertical uplift and uniform exhumation along the Yamuna Valley, reflecting consistent uplift dynamics governed by duplexing and climatic feedback mechanisms. Our study provides a refined understanding of the tectonothermal evolution of klippen and windows in the NW Himalaya, shedding new light on its orogenic evolution and dynamic landscape development. © 2025 Elsevier Ltd