Late Mesozoic–Early Cenozoic deformation history of the Yuanma Basin, central South China

Abstract

The Yuanma Basin, situated in central South China with more than 800km far away from the active plate boundaries, is a key region in deciphering the Late Mesozoic–Early Cenozoic tectonic evolution of South China. Based on a field analysis of fault–slip data collected from different rock units, we document polyphase tectonic stress fields and address the changes in the orientation of the principal stresses, and finally establish a five-phase stress evolution of the basin during the Late Mesozoic–Early Cenozoic. The earliest one with E–W compression and N–S extension occurred in the Mid–Late Jurassic and resulted in regional folding and west-directed thrusting along the eastern margin of the basin. This deformational event constrains the timing of the significant intracontinental orogeny in South China to be Mid–Late Jurassic. The subsequent NW–SE extensional regime was responsible for the initial opening and sedimentary infill of the basin during the earliest Cretaceous, which occurred coevally with the extensive Early Cretaceous magmatism, volcanism and extensional doming in South China. The tectonic regime then changed, in the late Early Cretaceous, to a compressional one with NW–SE compression and NE–SW extension, causing the inversion of this extensional basin. This compression affected the whole South China, leading to an apparent magmatic quiescence at ~108–117Ma and sinistral strike–slip faulting on the NNE-trending faults. The N–S extension prevailed in the Late Cretaceous, and activated the east-trending normal faults that controlled the Late Cretaceous subsidence. This extensional phase seems to have lasted through the Early Paleogene and ended in the Late Paleogene by a compressional regime with NE–SW compression and NW–SE extension, as attested by the stratigraphic unconformity at the base of the Neogene in the Jianghan Basin. The temporary evolution of these tectonic stress fields documented in the Yuanma Basin provides a new insight into the influences of different plate tectonics exerting on the South China Block over the Late Mesozoic to Early Cenozoic time. We infer that the Yuanma Basin was influenced, in the Middle Jurassic–Early Cretaceous, by the process of westward subduction of paleo-Pacific plate; and in the Late Cretaceous–Early Paleogene by a combined effect of the subduction along the west pacific margin and in the Tethyan domain; and finally in the Late Paleogene by the far-field effects of India–Asia collision.