Yueqiao Zhang, Liqing Jiao, Jinhong Xiong, Erkang Qiu
• Syn-tectonic growth strata documented below the K/Pg unconformity in northern West Qinling. • Magnetostratigraphy and AFT dates constrain initial uplift in latest Cretaceous (74–71 Ma). • A proto-Tibetan plateau is proposed to form before the initial India/Eurasia collision. The timing of initial uplift in the NE Tibetan Plateau remains debated, with competing models proposed from Cenozoic magnetostratigraphic studies in foreland depressional basins. To resolve this controversy, we present new chronological constraints on syn-tectonic growth strata beneath the Cretaceous-Paleogene (K/Pg) unconformity along the northern West Qinling Range front through integrated magnetostratigraphic and apatite fission-track (AFT) analyses. A high-resolution magnetostratigraphic framework established from a well-exposed Cretaceous section constrains the basal age of growth strata to 74–71 Ma. Detrital AFT dating of Paleogene conglomerates overlying the K/Pg unconformity reveals deposition initiation at 58–50 Ma. Bedrock AFT thermal modeling further identifies two distinct uplift episodes: an initial phase (80–57 Ma) corresponding to syn-tectonic deposition below the K/Pg unconformity, and a subsequent phase (50–25 Ma) associated with post-unconformity conglomerate accumulation. Our integrated chronology demonstrates that the West Qinling Range experienced initial uplift at the latest Cretaceous (74–71 Ma), preceding Paleogene sedimentation by 13–20 Mys. By integrating our finding with others in and around the Tibetan Plateau, we suggest that significant crustal thickening occurred through thrusting along block boundaries prior to the India-Eurasia collision, potentially leading to establish elevated proto-plateau topography during the period of the latest Cretaceous to Paleocene. This pre-collisional uplift represents a far-field response to fast subduction of the Neo-Tethys oceanic slab beneath Eurasia.