Onset of mountain building in the Qinling Mountains: Evidence from bedrock and detrital low-temperature thermochronology

Abstract: Hinterland mountains serve as the pivotal link that spatially and temporally couples deep lithospheric processes with surface responses in orogenic systems. The Qinling Mountains, situated in the continental interior of East Asia, form a significant natural boundary that separates China into distinct north-south climatic and geographical zones. A key unresolved issue is the origin of the Qinling Mountains-specifically, the timing and mechanisms of their initial uplift and exhumation. The basin-range structure of the East Qinling provides a natural archive for elucidating this problem, as its formation records the onset of mountain building. This study employs multiple thermochronological techniques, including apatite and zircon fission-track and (U-Th)/He analyses of both basin sediments and bedrock samples across basin-bounding faults. Through analyses of lag-time, elevation profiles, and thermal history modeling, the exhumation history of East Qinling is reconstructed. Results elucidate an early-phase cooling event during ~120-100 Ma, with a rate of 5.9-3.4 °C/Ma. Following a prolonged thermal stagnation until ~80 Ma, a renewed phase of accelerated cooling occurred between 80 and 60 Ma, with cooling rates ranging from 5.3 to 1.0 °C/Ma. Integrating these new results with existing geological evidence, we propose that the Qinling Mountains underwent multi-stage uplift and orogenic processes, driven by far-field tectonic stresses associated with the convergence of surrounding plates. The early Cretaceous rapid cooling and exhumation are correlated with intracontinental deformation stage in the eastern China during the Yanshanian period. However, prolonged erosion and planation resulted in low-relief topography in the Qinling Mountains before the late Cretaceous (~80 Ma). During the late Cretaceous-early Cenozoic, under the far-field influence of Pacific Plate subduction, the East Qinling region experienced intense hinterland extension. This process broke up the pre-existing planation surface and formed a series of alternating basins and ranges, signifying the onset of the mountain building in Qinling mountains. Furthermore, the Qinling Mountains exhibit a spatio-temporal pattern of progressive mountain growth from south to north. This study provides a typical case study for understanding the uplift and tectonic evolution of hinterland mountains.