北部湾盆地海中凹陷断裂发育、演化特征与成因机制OA

The Haizhong Sag in the Beibu Gulf Basin has undergone superimposed modification by multi-phase tectonic activity,resulting in a highly complex and interlaced fault system.Clarifying the fault orders,assemblage patterns,differences in fault activity,and spatiotemporal evolution is of great significance for hydrocarbon exploration in the Haizhong Sag.Based on merged 3D seismic data,this study systematically determined the fault assemblage patterns,plan-view distributions,and hierarchical characteristics,and elucidated the regional disparities and genetic mechanisms of fault evolution.As indicated by the research results,(1)the faults in the sag were classified into five orders and were mainly NE-,NEE-,near-EW-NWW-,and NW-trending,among which the NEE and nearly WE-NWW striking faults are predominant and exhibit stratification-dependent differences.To be specific,the near-EW-NWW-trending faults prevail in the northern sub-sag;NWW-and NE-trending faults dominate the northern steep-slope zone;the NEE-and near-EW-NWW-trending faults are interwoven in the southern gentle-slope zone.(2)Four fault styles were identified:extensional faults,strike-slip faults,composite extensional-strike-slip faults,and inverted faults.(3)Significant temporal disparities exist in fault activity sequences:the NWW-trending faults were mainly active during the Late Oligocene,whereas the NEE-trending faults experienced long-term activity from the Paleocene to the Oligocene,with their activity intensity decreasing from northwest to southeast.For instance,fault No.3 intensified its activity during deposition of the Liushagang Formation,peaked during deposition of the 4th and 3rd members of the Weizhou Formation(Wei 4 and Wei 3 members),and gradually weakened during deposition of the 2nd and 1st members of the Weizhou Formation(Wei 2 and Wei 1 members).(4)The fundamental mechanism underlying the differential spatiotemporal fault activity in the Haizhong Sag lies in the transformation of stress field properties and directions driven by regional tectonic events,while the inherited reactivation and selective activation of pre-existing basement faults serve as critical controlling factors for differential fault evolution.(5)Differential fault activity was concentrated in four key evolutionary periods:the Paleocene-Middle Eocene,Late Eocene-Middle Oligocene,Late Oligocene,and the end of the Middle Miocene.Their core driving forces were derived from five key tectonic factors:India-Eurasia plate collision,Pacific plate subduction,subduction and extinction of the Paleo-South China Sea,South China Sea spreading,and strike-slip movement along the Ailaoshan-Red River Fault Zone.By regulating the evolution of the regional stress field and its synergistic interaction with pre-existing basement faults,these tectonic factors jointly controlled the spatiotemporal distribution,activity intensity,and evolutionary patterns of the faults in the Haizhong Sag.