Geological significance of late Cretaceous exhumation in Jiuhua Mountain: Insights from zircon (U-Th)/He dating

Jiuhua Mountain, situated in the eastern segment of the Jiangnan Orogenic Belt, is characterized by extensive granite masses, providing an ideal setting for investigating the exhumation history of the region. This study presents the first zircon (U-Th)/He thermochronological investigation utilizing an age-elevation approach for Jiuhua Mountain. Zircon (U-Th)/He analyses of six bedrock samples yielded consistent ages ranging from 89 to 74 Ma. This finding aligns with the results of thermal history simulations (90-70 Ma), indicating significant exhumation in the Jiuhua Mountain region during the late Cretaceous. Comparative analysis with adjacent orogenic belts (e.g., the Mufu and Dabie Mountains) reveals a consistent pattern: low-temperature thermochronological ages are younger than the U-Pb zircon ages. This indicates a widespread tectonic exhumation and erosion phase affecting multiple regions within the northern part of the South China Block. The rapid exhumation observed during the late Cretaceous is primarily attributed to extensional tectonics, driven by the rollback of the Paleo-Pacific slab and accompanied by thermal upwelling of the asthenosphere beneath the South China Block. These findings establish crucial temporal constraints for the exhumation history of the eastern Jiangnan Orogenic Belt, significantly enhancing our understanding of its poorly constrained Cretaceous tectonic evolution.