Cretaceous exhumation history of the southwestern South China Block: Constraints from fission‐track thermochronology

Abstract

To detect the exhumation history of the southwestern South China Block (SCB), we performed fission track (FT) analysis on zircon and apatite grains in granitoid and sedimentary samples. From east to west, the study area includes the Yunkai Massif, Lingshan granitic belt, Shiwandashan Basin, and eastern margin of the Youjiang Basin. The granite sample of the Yunkai Massif has two peaks of 75 and 92 Ma for zircon FT dating. The Lingshan granitic belt samples yield zircon FT central ages from 135 to 132 Ma. The Permian bauxite samples of the Youjiang Basin yield zircon FT central ages from 109 to 93 Ma and display age peaks at ~97–93 Ma. The Yunkai Massif granite sample has two peaks at 74 and 104 Ma for apatite FT dating, while the Lingshan granitic belt sample has two peaks at 81 and 111 Ma. The cooling paths of the Yunkai Massif sample started with an Early Cretaceous (~120–100 Ma) cooling event that brought the granitoids into the apatite partial annealing zone (PAZ). Through comparative studies, we suggest that the southwestern SCB underwent three periods of crustal uplift during ~135–132, ~111–92, and ~ 81–74 Ma, respectively, which is consistent with the regional stratigraphic unconformity and crustal extension. Only the Yunkai Massif and Lingshan granitic belt were uplifted during ~135–132 Ma. During ~111–92 Ma, the southwestern SCB experienced crustal uplift, and the basal conglomerate began to deposit in the Shiwandashan Basin. Late Cretaceous uplifted occurred during ~81–74 Ma, and the Yunkai Massif was uplifted throughout the Cretaceous. From 97 to 92 Ma, the Permian bauxite deposits in the Youjiang Basin were uplifted, which provided the basis of the later transformation to Quaternary bauxite.