A revised model for the NW-trending faults and Cenozoic basins in the coastal area of southeast China

The Southeast China Block hosts many basins resulting from extensional tectonics during the Mesozoic and Cenozoic. Previous studies mainly focused on the NE-NNE-trending inland basins and ascribed them to the subduction dynamics of the Paleo-Pacific Plate. The fact that a few younger W-NW-trending basins truncate the NE-NNE basins in the coastal area of Zhejiang Province was slightly mentioned in previous papers, but detailed researches are lacking. Considering that existing knowledge of extensional basins in the SCB is principally based on Mesozoic geology, which fails to provide appropriate constraints on the younger coastal basins, a revised model concerning the Cenozoic tectonics is needed.

The widespread NW-SE-trending faults and accompanying basins in the coastal area of Fujian Province (e.g. Fuzhou basin, Zhangzhou basin, and Shantou plain) provide us with a chance to further detect the formation mechanisms and geodynamic implications of these structures. Field-based structural analyses in the Zhangzhou region identify two-stage deformation in the Cenozoic. The early stage was dominated by normal faulting and mafic intrusions. The structural configuration was differentiated as a graben in the estuary area and linear ridges in the western mountains, representing outer arc extension caused by orthogonal flexure of the coast. Late-stage deformation turned early-stage normal faults into sinistral strike-slip faults and induced a transtensional setting that greatly facilitated the evolution of the basin. The tectonic dynamics are attributed to far-field effects of the west Pacific subduction zones. Additionally, a strike-slip fault-controlled scissor-like structure is proposed to demonstrate the mechanism of the redefined, fan-shaped basin.

Widespread NW-SE-trending faults and Cenozoic basins in the coastal area of Fujian Province demonstrate unique tectonic deformations from the influence of the modern arc-trench system on the adjacent continent. To expand the validity of our model built on the Zhangzhou region to a larger area (i.e. the general coastal area of southeast China), we conducted a two-dimensional viscous-elastic-plastic numerical modelling. The results verify our observations in the Zhangzhou region and can be used to predict the regional tectonics in the southeast China.