Provenance Constraints on Early India–Asia Collision: Evidence From the Late Cretaceous–Early Cenozoic Sulaiman–Katawaz Basin Fill

Abstract

The timing of the India–Asia collision along the western margin of the Indian Plate remains highly debated, with estimates ranging from 60 to 40 Ma, associated with different models for the sequence of collision events. To examine the collisional record along the western margin of the Indian Plate, we integrate detrital zircon U–Pb ages and Nd–Sr isotopic signatures with zircon and apatite (U–Th)/He and apatite fission track thermochronology. Late Cretaceous to Palaeocene strata (Pab and Ranikot formations) are characterised by detrital zircon populations dominated by Precambrian to early Palaeozoic grains (1 Ga–500 Ma), together with highly negative εNd₍₀₎ values (−17.2 to −12.6) and radiogenic ⁸⁷Sr/⁸⁶Sr ratios, indicating derivation from Indian-affinity sources. Across the Palaeocene–Eocene transition and into the Early Eocene, the first appearance of younger zircon populations (178–55 Ma) in the Ghazij and Nisai formations coincides with a shift toward less negative εNd₍₀₎ values (−12.0 to −8.3) and lower ⁸⁷Sr/⁸⁶Sr ratios, recording the initial addition of Asian-affinity material to a system still dominated by Indian-margin sources. The proportion of younger zircon populations is low in the Early Eocene Ghazij Formation of the Sulaiman (∼1%–3% Cretaceous–Paleogene grains), but is higher in coeval Nisai strata of the Katawaz (∼13% 55–96 Ma population), and increases further in Oligocene units (Chitarwatta and Khojak formations), where Jurassic–Oligocene zircon populations (194–32 Ma) become more prominent. This progressive increase is matched by sustained trends toward less negative εNd₍₀₎ values and lower ⁸⁷Sr/⁸⁶Sr ratios, indicating an increasing contribution from Asian-affinity sources through time. These observations are further supported by shifts in paleocurrent directions, changes in sedimentary facies, and Eocene ZHe cooling ages from the Sulaiman hinterland. The first arrival of Asian-affinity detritus on the Indian Plate provides an important sedimentary constraint on the timing of India–Asia collision in this sector. Our results indicate that collision was likely underway by the Palaeocene–Eocene transition (~56 Ma), followed by continued convergence and progressive integration of sediment-routing systems during the Eocene and younger intervals. These findings are consistent with an early Paleogene initiation of a single-stage collision along the western margin of the Indian Plate and are difficult to reconcile with models proposing significantly younger or strongly diachronous collision.