Late Mesozoic to Cenozoic exhumation of the SE South China Block: Constraints from zircon and apatite fission-track thermochronology

Abstract

The late Mesozoic to Cenozoic tectonothermal history of the basin-and-range system within the Cathaysia Block in the southeastern South China Block remains poorly constrained, despite its significance in the tectonic and topographic evolution of eastern China. Zircon and apatite fission-track thermochronometers were applied to reconstruct the cooling histories of NE-trending mountain ranges mantled by late Mesozoic granites and older basement rocks in southwest Fujian. New zircon and apatite fission-track data record post-magmatic cooling of the sampled granites since their emplacement of ~164–118 Ma. Thermal modeling of the thermochronology data revealed two episodes of accelerated cooling events at ~110–85 Ma and ~40–25 Ma. The late Early Cretaceous initiation of an accelerated cooling event at rates of ~6 °C/Ma was considered to be the cause of the formation of the basin-and-range system in a back-arc extensional setting related to the rollback of the Paleo-Pacific Plate. The second cooling event at ~40–25 Ma at a rate of ~20 °C/Ma, reflected by the youngest apatite fission track ages (~25–20 Ma), was likely ascribed to headwater erosion along the drainage divide related to the intensification of the East Asian Monsoon and extensional tectonism. The sharp discrepancy in apatite fission track ages across the Zhenghe-Dapu Fault zone implies that the collapse of the late Mesozoic coastal magmatic arc in the early Eocene (51.4–45.6 Ma). This is attributed to the northward propagation of extension related to the rollback of the Paleo-Pacific Plate that formed the eastward-dipping topography. Furthermore, the long-lasting extension due to the rollback of the Pacific Plate since the ridge subduction of the Izanagi-Pacific at ~50 Ma likely drove the exhumation of the Cathaysia Block and opening of the South China Sea.