Cenozoic rifting and inversion in Beibuwan Basin and its relationship with strike-slip motion on the Ailao Shan-Red River Shear Zone

The Beibuwan basin is located along the western margin of the Ailao Shan Red River Shear Zone (ASRRSZ), and also in the north margin of the South China Sea (SCS). This study utilizes 2-D seismic data to investigate the evolution of this basin and discuss its broad tectonic settings. Several stages of rifting and inversion occurred in the Beibuwan basin during Cenozoic: (1) During Paleocene initial rifting (66-56 Ma), the ocean-ward gradual retreat of the Paleo-pacific subduction zone created an extensional tectonic setting in the SCS region. The overall extensional tectonic setting of the northern passive margin of the SCS generated a series of Paleogene NE-striking rift basins, including the Beibuwan basin, the Qingdongnan basin and the Pear River Mouth Basin. (2) During Eocene rifting stage (56-37.8 Ma), the Pacific plate still subducted under the Eurasian plate, and soft collision started to occur between the greater India plate and the Eurasian plate. Subsequently, the NW-SE-direction extension gradually changed to N-S-direction extension, therefore, the NE-striking faults active intensively during this stage, and a small group of EW-striking faults formed in the study area. (3) During the Oligocene rifting stage (37.8-23 Ma), the India-Eurasian collision went into hard collision stage, induced the large-scale left-lateral strike-slip of the ASRRSZ. Furthermore, the subduction of the Pacific plate strengthens the left-lateral shearing of the ASRRSZ. The left-lateral strike-slip of ASRRSZ resulted in the formation of large amount of EW-striking faults in the Beibuwan and Yinggehai basins, and the opening of the South China Sea. (4) After Paleogene, several stage of inversions occurred in the study area, including the end-Oilgocene, end-Miocene and end-Plioence inversions. The regional end-Oligocene inversion is supposed related to the change from major left-lateral transtensional rifting to left-lateral transpression of ASRRSZ. The end-Miocene and end-Pliocene inversions are localized inversions, which also related to the left-lateral transpression of ASRRSZ.