珠江口盆地陆丰凹陷断裂构造特征及“人”字型构造成因

陆丰凹陷位于珠江口盆地珠一坳陷东北部，被陆丰中央低凸起分隔成为南、北两个洼陷带，可进一步划分出惠州5洼、惠州11洼、陆丰7洼、陆丰13西洼、陆丰13东洼、陆丰15洼等次级构造单元。地震资料解释表明，不同构造单元内发育的主要构造样式具有差异性。其中"人"字型构造样式发育在陆丰中央低凸起的西部，向东逐渐演化为共轭式（"X"型）构造样式。理论模型表明，只有在基底地垒顶面之上盖层的厚度大于共轭断层倾向交叉点的高度时，盖层中才能发育地堑，形成地堑叠加在地垒之上的"X"型构造样式，否则形成盖层地垒叠加基底地垒的构造样式。平衡演化剖面和构造物理模拟实验表明，"人"字型构造样式受先存走向非平行的基底隐伏断层控制，其经历了文昌组沉积期强烈断陷、恩平组沉积期弱断陷、珠海组沉积期断坳转换、新近纪裂后差异沉降等构造演化阶段。基底隐伏断层差异活动是导致盖层变形差异的主控因素，伸展应力方向的顺时针转变及其与基底隐伏断层之间的交角变化是产生基底断层活动差异的主要原因。

Characteristics of fault structure and the genesis of herringbone structure in Lufeng sag,Pearl River Mouth Basin

Lufeng sag is located in the north-eastern part of Zhu-I depression in Pearl River Mouth Basin, which is divided into the north and south depression zones by Lufeng Central Low Bulge region, further sub-divided into the secondary units such as Huizhou 5 subsag, Huizhou 11 subsag, Lufeng 7 subsag, West subsag of Lufeng 13, East subsag of Lufeng 13 and Lufeng 15 subsag. Seismic data interpretation results indicate that the tectonic structures developed in different tectonic units present various patterns. The herringbone structure is developed in the western of Lufeng Central Low Bulge region, which gradually evolves to the conjugate tectonics ("X" style)to the east. The theoretical model proves that only when the thickness of the cover layers on the top surface of basement horst is greater than the height of the intersection point of tilting conjugate faults, the horst can be developed on the cover to form the "X" pattern of graben superimposing on the horst. Otherwise, the tectonic pattern of cover horst superimposed on the basement horst will be formed. The balanced evolutionary profile and tectonic physical simulation results show that the herringbone structure is controlled by the non-parallel concealed basement fault, which experienced the strong rifting in Wenchang period, the weak rifting in Enping period, the fault-depression transition in Zhuhai period, and the Neogene post-rift differential subsidence. The different activity of concealed basement faults is the main control factor leading to the difference in cover deformation. The clockwise transition of the tensile stress and its angle change with the concealed basement fault are the main reasons for the different activities of basal fault.