Abstract: The structural style of the Pearl River Mouth Basin (PRMB) at the northern continental margin of the South China Sea (SCS) is quite complex, showing significant spatio-temporal differences influenced by the basement-involved faults striking in NNE, NE, NW and near E-W directions. Based on the structural style changes according to seismic data interpretation, we conclude that the middle section of the PRMB develops a ramp-flat detachment fault that slowly dips to the south; and the Paleogene basin structure is taken as an extensional system of the supra-detachment. The Xijiang Sag in the northern PRMB lies in the head region of the extensional system, from where the boundary normal fault extends to the deep detachment fault in listric geometry, restraining the Paleogene to form a half graben faulted structure. The Panyu Low Uplift in the middle is situated in the low-angle fault zone of the detachment fault, where extensional displacement of the supra-detachment leads to its overlying with the Enping Formation on both sides. The Baiyun Sag in the south overlays on the ramp of the detachment fault; and the Paleogene filling in the sag is characterized by a synform-type “faulted-sag” structure. The Southern Uplift is located in the deeper flat of the detachment fault controlling the Liwan Sag by its branch faults, with a complex “faulted-sag” structure of the Paleogene. Geometry and kinematics of the detachment fault and branch faults on the extensional system control the basin structural style and evolution in different tectonic units. The model demonstrates that both supra- and under-detachment are extensional deformations that could occur in different crustal layers. However, spatio-temporal differences should be expected for different deformation styles and stretch strain distributions. In general, the supra-detachment deformation features brittle extensional structure and the uneven stretch strain distribution is mainly concentrated in the listric normal faults linked to the detachment fault, but the footwall of the detachment is predominantly of ductile stretching deformation with relatively uniform distribution of stretch strain. In the head region of the detachment system (Xijiang Sag), the supra-detachment extension is greater than the under-detachment counterpart; however, the opposite is true in the root region (Baiyun and Liwan sags). The master boundary faults on the northern edge of the Xijiang Sag are listric normal faults striking NE in the Wenchang period as the head of the detachment fault, but cut off by high angle normal faults striking near E-W in the Enping period so that the head of the detachment fault is abandoned or migrated to the Panyu Low Uplift from the northern edge of the Xijiang Sag. The spatio-temporal differences in basin structure style and deformation are influenced by many factors such as pre-existing basement structure, lithosphere rheology, and scale of extension and so on, but the main factor is the response to lithospheric stretching deformation and lithosphere thermal change due to asthenosphere flows. A dynamic model, i.e. the speed up flow of asthenosphere from northwest to southeast drags the overlying lithosphere to divergent motion and causes the continent rifting, can reasonably explain the structural formation and evolution in the middle section of the PRMB. That is, the asthenosphere one-way flow drags the overlying lithosphere to its simple shearing extensional deformation and forms the detachment fault, while the relatively uniform stretch strain of the under-detachment, with diminishing toughness from south to north, is passed onto the supra-detachment with non-uniform brittle extensional deformation enhanced gradually from south to north.

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