Collapse of East Asia Coastal Mountains Revealed by Bedrock Geo-Thermochronology and Thermal Modelling: Impact of Low-U Mineral Grains

Late Mesozoic–Cenozoic topographic evolution along the East Asian continental margin is intimately linked to the subduction of the Paleo-Pacific Plate. To quantify the topographic response to the variable subduction dynamics, we present an integrated geo-thermochronological dataset from 28 Precambrian basement and Mesozoic plutons samples along NW–SE and NE–SW transects and an elevation profile across southeastern China. Our first evaluation of the thermochronological dataset highlights that low-U zircon and apatite grains exhibit relatively low (U-Th)/He closure temperatures, while low-U apatite and small number size in fission track and (U-Th)/He analyses show high uncertainties, requiring careful treatment. Using the geo-thermochronological dataset and latest HeFTy 2.2.0, we then performed single- and multi-sample thermal modelling of these bedrock samples to resolve exhumation processes between ca. 6–1 km while accounting for geothermal disturbances from thermal buffering, variable exhumation rate, geothermal gradient changing, and topographic development and deflection. Our results reveal significant cooling and exhumation across southeastern China during the Late Cretaceous–Early Paleogene (ca. 90–40 Ma), with a systematic spatiotemporal pattern of progressively younger and more pronounced exhumation toward the coast and a significant thermochronology age break across the Zhenghe-Dapu Fault Zone. These processes reflect tectonic and erosional exhumation associated with rollback and retreat of the subducting Paleo-Pacific slab, driven by tectonic extension and precipitation pattern, ultimately leading to the collapse of the mid-Cretaceous coastal mountain belt.