Late Mesozoic extension and denudation of the South China Block: Insights from low-temperature geochronology into the differential evolution of detachment faults

Late Mesozoic subduction and retreat of the Paleo-Pacific Plate constructed a vast back-arc region with numerous extensional basins and extensive magmatic activities that destroyed the east South China Craton.Widespread extensional structures are always controlled by detachment faults, which provide direct constraint ofthe precise tectonic process of craton destruction. At the westernmost end of this back-arc region, we identify a unique, two-detachment extensional system, the Yuechengling dome with the Ziyuan Detachment in the west and the Tianhu Fault at the middle. Low-temperature geochronology shows that during the extension at 100-85 Ma, the Ziyuan Detachmentevolved progressively with a north-to-south migration pattern. At the same time, the Tianhu Fault was also reactivated. Its northern segment experienced rapid cooling from 85-70 Ma, and the southern segment was in a rapid cooling stage from 70-45 Ma. This trend reflects heterogeneous evolution and exhumation related to the subduction retreat of the Paleo-Pacific. The uplift and denudation process from 10-0 Ma obtained from the thermal history inversion of the Tianhu Fault and the Ziyuan Detachment may be related to crustal thermal subsidence. According to the Airy - Heiskanen Model, combined with the regional low-temperature geochronology data, we calculated that the denudation thickness in the Yuechengling area reached approximately 2000 m. Combining with the current altitude, it is speculated that the altitude in the Yuechengling area reached approximately 2900 ± 300 m during the Late Mesozoic, and decreased after the thinning of the cratonic lithosphere of South China. Our results reveal a consistent structural and topographic change of regional extension and shed light in the coupling of deep and surface response to the cratonmodification and destruction.