Asymmetric Exhumation Across the Western Himalayan Syntaxis: Implications for the Tectonic Evolution of Orogenic Wedge

The western Himalayan fold-and-thrust belt exhibits variable fault kinematics and exhumation patterns. Our thermochronological (AHe) data reveal a broad zone of consistent cooling ages (~4–6 Ma) across the Potwar Plateau and Salt Range. This spatially uniform pattern suggests a temporally limited phase but spatially extended region of synchronous exhumation. We interpret this as deformation localized along a low-friction salt detachment enabling wedge translation on the emergent SRT/HFT without significant internal reorganization. In contrast, the eastern flank of the syntaxis (Kashmir Himalaya) exhibits significantly younger and spatially variable AHe ages (~0.9–7 Ma), with young ages (0.9-3.5 Ma) concentrated in the frontal and rear ends, and older ages in the center. This spatial and temporal variability in exhumation, interpreted along with the geological, geophysical, and geomorphic evidence, suggest that orogenic wedge is segmented, where exhumation is driven by rock displacement along active roof backthrusts in the frontal zone, and internally by out-of-sequence faulting facilitated by focused erosion and reactivation of inherited basement structures. Based on our analyses, we propose that exhumation in the Kashmir Himalayas occurs via distributed, diachronous uplift, reflecting a mechanically heterogeneous and internally reorganized orogenic wedge.This contrasts with the synchronous and spatially uniform exhumation pattern in the western limb. These contrasting patterns and wedge behaviors suggest an asymmetric structural architecture and differing thicknesses of sedimentary parts (salt vs. clastic) in the foreland, modulated by feedback between erosion, fault kinematics, and wedge strength. Understanding this coupling is crucial for unraveling young orogenic wedge evolution and assessing seismic hazard risk.