Age and provenance constraints for the geodynamic evolution of the Indus Suture Zone during the Cenozoic

• The ISZ only records syn- to post-collisional sedimentation in the foreland basin. • The Nindam Fm deposited during the Late Eocene not the Cretaceous. • Last marine deposits do not constrain the timing of collision. The timing of the India-Asia collision and the multi-stage tectonic control on the development of Himalayan sedimentary basins has remained controversial for over half a century. In particular, it remains unclear whether the stratigraphic record of the Indus Suture Zone (ISZ) in Ladakh, NW India, 1) preserves pre-collisional trench deposits, 2) whether the cessation of marine sedimentation reliably marks continental collision, and 3) how provenance and depositional ages inform on the geodynamic evolution of the orogeny. This study re-examines the tectonostratigraphic evolution of the Indus Basin in the region by leveraging new biostratigraphic data (radiolarians, dinoflagellates) and detrital zircon U-Pb ages. We further integrate whole-rock and clay-size fraction geochemical and Nd isotopic data to constrain provenance changes and their relationship to major tectonic events pertaining to the collision between India and the Kohistan-Ladakh intra-oceanic arc (KLA). Results show that the stratigraphic record in the region exclusively preserves the Paleogene-Neogene syn- to post-collisional foreland sedimentation (< ca. 54 Ma). Deposition, sediment supply, and drainage patterns were largely controlled by 1) the Spongtang ophiolite obduction (64–42 Ma) onto the Indian margin, 2) the collision-induced uplift of the KLA (53–40 Ma), and 3) the exhumation of the Tso Morari complex (45 Ma). Importantly, the diachronous cessation of plain marine conditions between the northern (50 Ma) and southern (40 Ma) margins of the Eocene foredeep warns against relying on the last occurrence of marine units as a uniquevocal marker for continental collision onset. Instead, the oldest foreland deposits only provide a minimum age constraint (ca. 54 Ma) for the India-KLA collision. These results highlight the relevance of applying a multi-proxy approach for reconstructing the evolution of collisional orogens. Furthermore, we demonstrate that palynological analyses in the Himalayas and adjacent basins constitute an effective dating method to accurately time tectonostratigraphic events.