Reevaluating the India-Asia Collision in the Pakistani western Himalayas: Sedimentary Evidence for a ~56 Ma Onset

The timing and sequence of the India–Asia collision along the western suture remain debated, with estimates ranging from 60 to 40 Ma. This study presents the first detailed provenance analysis of Mesozoic to Cenozoic strata in the Sulaiman-Katawaz fold-thrust belts, which preserve a continuous depositional record across the collision interval. We analyzed detrital zircon U-Pb ages and Nd-Sr isotopic signatures from Triassic to Miocene strata, complemented by zircon (U-Th)/He thermochronology data from Early Mesozoic units exposed in the hinterland region of the Sulaiman-Katawaz fold-thrust belt. These datasets collectively constrain sediment source regions, distinguishing between Indian and Asian provenance.

Detrital zircon U-Pb age spectra from the Cretaceous Pab and Paleocene Ranikot formations are dominated by Precambrian to early Paleozoic zircons (1 Ga–500 Ma), diagnostic of Indian sources. A significant shift in provenance is observed in the early Eocene Ghazij and Nisai formations, characterized by the first appearance of Early Jurassic to Eocene zircons (178–55 Ma). The Oligocene Chitarwatta and Khojak formations exhibit dominant age peaks between 194–32 Ma, along with minor older age populations, reflecting sustained input from Asian sources and nascent Himalayan tectonostratigraphic units.

A corresponding shift in εNd₍₀₎ values (from –17.2 to –8.3) and a decline in ⁸⁷Sr/⁸⁶Sr ratios from the Paleocene–Eocene transition to the Miocene further support this provenance reorganization. Integrated with Eocene ZHe cooling ages, shift in paleocurrents and sedimentary facies trends, these results indicate a major reorganization of sediment sources around ~56 Ma, consistent with a single-stage India–Asia collision in the western Himalayas.