走向平行之共轭式断层成因模拟及其在南堡凹陷中的应用

Physical Simulation for the Origin of Parallel Conjugate Faults and its Application in the Nanpu Sag

两组倾向相反、走向平行或非平行的正断层在剖面上相互交叉组成共轭式断层。理论模型证明走向平行的共轭式断层在平面上不发育交叉点,在剖面上发育的倾向交叉点的连线构成一条水平直线,其距离基底地垒顶面的高度(H)随着基底地垒顶面的宽度(Wh)和基底地垒边界断层的倾角(α)增加而增大。构造物理模拟结果表明,基底地垒顶面之上直接覆盖砂层时将产生标准的"X"型共轭式断层,其倾向交叉点之下砂层遭受不同程度的损失;基底地垒顶面之上直接覆盖滑脱层时产生的共轭式断层结构复杂,盖层地堑内部次级断层发育,地层产状发生明显旋转;当盖层内部夹有滑脱层时,地堑与地垒分层叠加,地堑内部次级断层发育,地层产状相背倾斜,构成低幅度的"背形负花状构造"。地震剖面解释与物理模拟结果对比表明,渤海湾盆地南堡凹陷2号构造带内发育走向平行的共轭式断层组合样式,经历了沙河街期(Es)地垒发育、东营期(Ed)地堑发育、馆陶期(Ng)背形构造发育、明化镇期(Nm)"背形负花状构造"形成四个阶段。盖层内部发育的东营组底部泥岩滑脱层是形成"背形负花状构造"的主控物质因素。

Two sets of parallel or non-parallel normal faults dipping in opposite directions are referred to as conjugate normal faults. The theoretical modelling demonstrated that parallel conjugate faults do not develop intersections on the plane, whereas the lines connecting the intersecting points on the section form a horizontal line. Moreover, the height from the crest of basement horst to the intersecting points increases with the width of the basement crest and the dip angle of basement faults. Results of our physical simulation results showed that the typical "X" shape of conjugate fault will develop with the loss of layers under the intersecting points when the sand layers directly cover the basement horst. In the presence of a ductile layer between the cover and basement such intersection patterns do not form, however, some secondary faults and rotation of sand layers will develop within both the horst and the graben. Otherwise, in the presence of a ductile layer in the middle of the cover layer, some secondary faults in the graben will cause the sand layers to dip in opposite directions and form a lower negative flower structure. Comparison of seismic profile interpretation and physical simulation shows that the parallel conjugate fault assemblages developed in the second fault-belt of the Nanpu Sag in the Bohai Bay Basin underwent four stages of development, which include the development of the horst in the Shahejie Formation(Es), the development of the graben in the Dongying Formation(Ed), the development of antiform in the Guantao Formation(Ng), and the development of the negative flower structure in the Minghuazhen Formation(Nm). The ductile layers of mudstone distributing close to the bottom of the Dongying Formation are responsible for development of the negative flower structure.