The red river fault zone and its deep structural characteristics revealed by high-resolution seismic data in the Yinggehai basin, South China sea

With the Red River Fault Zone (RRFZ) as the northern boundary, the lateral extrusion of the Indochina Block relative to the South China Block is a response and accommodation to the substantial deformation resulted from the collision and convergence of the India-Eurasia plates. However, the tectonic nature of the RRFZ remains a topic of debate. The Cenozoic Yinggehai Basin (YGHB), controlled by the RRFZ, preserves the tectonic history of the region in its thick strata. Analysis of high-resolution seismic data indicates that the RRFZ, including the No.1 Fault, Central Fault, and other basement faults, intersects the Moho, suggesting its lithospheric-scale nature. Strike-slip shearing along the RRFZ in the YGHB dates back to approximately 40.4 Ma ago, as inferred by the T83 horizon distinguished for the first time. The Moho surface exhibits uplift and gentle undulations within the Central Depression (CD), with a minimum depth less than 19 km. In the diapir zone of the CD, crustal thickness ranges from 4 to 5 km, with stretching coefficient of 5.2–6.5, indicating significant thinning and hyper-extension, evidenced by the low-angle normal faults in the lower crust. Strike-slip shearing along the Central Fault and No.1 Fault, coupled with multiple structural inversions, facilitated the development of structural inversion in the northern YGHB. A comprehensive understanding of the RRFZ is crucial for oil and gas exploration in the YGHB.