Cenozoic rifting and inversion of Beibuwan Basin and its linkage with the strike-slip movement along the Ailao Shan-Red River Shear Zone

The Cenozoic Beibuwan Basin is located along the eastern margin of the Ailao Shan Red River Shear Zone (ASRRSZ). The rifting and inversion processes of this basin provide important clues to the mechanism by which extrusion tectonics drive continental rifting and inversion development. However, the rifting and inversion of this basin remain ambiguous. Here, we employ seismic data, information about the time and displacement of faulting, syn-rift fault and isopach maps to analyse the Cenozoic rifting and inversion of Beibuwan Basin. Our results demonstrate that three stages of rifting and inversion occurred in this basin: (1) During the Palaeocene initial rifting, a series of NE-striking isolated half-grabens formed, which indicated that NW-SE extension dominated in this basin, and the southward slab-pull of Proto-South China Sea (SCS) was the likely cause of the extension. (2) During the Eocene rifting stage, besides significant motion on NE-striking faults, a small number of E-striking faults started to become active, which indicates that the extensional stress field shifted from NW-SE to N-S. (3) During the Oligocene rifting stage, the E-striking faults intensified, and controlled the distribution of the sediment depocentres, which implies that N-S extension dominated the deformation during this stage. The left-lateral strike-slip movement of the ASRRSZ and the slab-pull of the Proto-SCS are suggested to explain the extension stress field shift from NW-SE to N-S during the Eocene to Oligocene. (4) End-Oligocene, end-Miocene and end-Pliocene inversions have been recognized in this basin. The regional end-Oligocene inversion was stronger in the western area than the eastern area of the basin, which suggests that the compression caused by the left-lateral shearing of the ASRRSZ gradually decreased towards the east. In addition, the localized end-Miocene and end-Pliocene inversions occurred in the Haizhong sag.新生代北部湾盆地位于哀牢山-红河剪切带（Ailao Shan Red River Shear Zone, ASRRSZ）东缘。该盆地的裂陷与反转演化过程，为揭示挤出构造驱动大陆裂陷与反转发育的机制提供了关键线索。但目前学界对该盆地的裂陷与反转过程仍缺乏清晰认识。本文利用地震数据、断层活动时间与位移数据、同裂谷断层（syn-rift fault）及等厚图（isopach maps），对北部湾盆地的新生代裂陷与反转过程开展系统分析。研究结果显示，该盆地共经历三期裂陷与反转演化阶段：（1）古新世初始裂陷期：盆地内形成一系列北东向孤立半地堑，指示当时区域伸展应力以北西-南东向为主，古南海（South China Sea, SCS）南向板片拖拽可能是该伸展作用的驱动成因；（2）始新世裂陷期：除北东向断层发生显著活动外，少量东西向断层开始活化，指示区域伸展应力场由北西-南东向转为南北向；（3）渐新世裂陷期：东西向断层活动强度进一步加剧，并控制了沉积中心的展布，指示该阶段盆地变形以南北向伸展为主导。研究认为，哀牢山-红河剪切带的左旋走滑活动与古南海板片拖拽，共同解释了始新世至渐新世期间伸展应力场由北西-南东向向南北向的转变过程。盆地内已识别出渐新世末期、中新世末期及上新世末期三期反转构造，其中区域性渐新世末期反转在盆地西部地区的强度大于东部，表明哀牢山-红河剪切带左旋剪切引发的挤压应力自西向东逐渐减弱；此外，海中凹陷（Haizhong sag）还发育局域性的中新世末期与上新世末期反转构造。