珠江口盆地西江主洼低角度边界正断层特征及成因演化

西江主洼位于珠江口盆地珠一坳陷的中西部，是珠江口盆地重要的富生烃凹陷之一。为了认识珠江口盆地西江主洼边界断层（Fxj33）属性特征，基于钻井约束的高精度三维地震资料，对Fxj33断层几何学和运动学进行了综合分析。研究揭示Fxj33边界断层为低角度生长正断层，倾角5°~36°，呈NEE走向，长度约55 km，最大水平位移达9.5 km左右。在多幕裂陷演化过程中，Fxj33断层沿走向上表现为分段差异活动特征，并与两排EW向高角度断裂共同控制着西江主洼各次级洼陷的发育演化。中生代基底中发育的叠瓦状构造、残留山和先存断面等一系列构造表明Fxj33边界断层为中生代先存逆冲构造体系在新生代反转形成，并且在断陷中晚期进一步被一系列EW向高角度断面切割改造，形成现今形态。期望研究结果对被动陆缘断陷盆地边界断层的形成和演化研究有指示意义。

Characteristics and genetic development of a low-angle boundary normal fault in Xijiang Main Sag,Pearl River Mouth Basin,China

The Xijiang Main Sag,located in the west-central Zhu-1 Depression,is one of the most important hydrocarbon-rich sags in the Pearl River Mouth Basin,China.To recognize the properties of the boundary fault (Fxj33) in the Xijiang Main Sag,we comprehensively analyze the geometry and kinematics of Fxj33,using high-resolution 3-D seismic data under the constraints of well data.The results show that the boundary fault Fxj33 of about 55 km long and up to 9.5 km displacement at most,is a NEE-trending low-angle normal fault with a dip of 5°-36°.During the evolution of multistage rifting,the fault Fxj33 is characterized by differential activities of different segments along the strike,and jointly controls the evolution of the sub-sags in the Xjiang Main Sag together with the two lines of EW-trending high-angle normal faults.Various structures developed in the Mesozoic basement,including imbricate structures,residual hills and pre-existing fault planes,indicate that the boundary fault Fxj33 was developed by the inversion of the pre-existing Mesozoic thrusting system in the Cenozoic,and subsequently reformed by the EW-trending high-angle fault planes cutting into it during the middle-to-late rifting stage.The research results are expected to be of referential meaning to the study of the boundary faults during rifting in passive margin faulted basins.