柴达木盆地北缘南八仙背斜深、浅断裂系统耦合分析

柴达木盆地内部发育有丰富的基底和浅层断裂，二者之间的成因机制目前还存在较大争议。文章基于高精度三维地 震反射数据和钻井资料，对柴达木盆地北缘南八仙背斜的深、浅断裂系统的几何形态和相互耦合关系进行了分析。南八仙 地区主要发育两条近EW走向的高角度基底断裂，分别为南倾的马仙断裂和北倾的仙南断裂，都是中生代晚期就开始发育 的老断裂，并在新生代重新活化。在新生界内部还发育NW走向和近EW走向两组浅层正断层体系，断距都很小。NW走向 正断层主要位于马仙断裂南侧（上盘），呈雁列式排列。近EW走向正断层范围较小，仅局限在南八仙背斜核部、仙南断裂 上部，由一系列近平行的正断层组成，在仙南断裂上部形成一个小型的地堑构造，切割了NW走向的正断层体系。分析认 为NW走向正断层与马仙断裂左旋走滑导致的尾端拉张有关，而近EW走向正断层体系与高角度仙南断裂逆冲活动导致的 浅层剪切拉张有关。综合前人研究成果认为柴达木盆地广泛存在的浅层断裂成因多变，深、浅断裂耦合关系十分复杂，先 存断裂在新生代构造活动中起到了一定的控制作用。

Structural Coupling of Deep and Shallow Fault Systems in the Nanbaxian Anticline,Northern Qaidam Basin

Abundant basement deep faults and shallow faults are widely developed in the Qaidam Basin, but the genetic mechanism between the coupling of the diverse faults is still controversial. In this paper, we analyze the geometry and coupling relationship of deep and shallow fault systems across the Nanbaxian anticline in the northern margin of the Qaidam Basin, by using high-resolution 3D seismic reflection data and drilling data. Results show that two EW-trending, high-angle basement faults are developed in the Nanbaxian area, namely, the south-dipping Maxian fault and the north-dipping Xiannan fault. They were both initially formed in the late Mesozoic and rejuvenated in the Cenozoic. Two sets of shallow normal fault systems are well developed within the Cenozoic in Nanbaxian. One is NW-striking, and mainly en echelon distributed on the southern side (hanging wall) of the Maxian fault. The other is EW-striking, and confined in the core of the Nanbaxian anticline above the Xiannan fault. This EW-striking fault cuts the NW-striking normal fault system, and consists of a series of parallel sub-normal faults, forming a small graben structure within the Cenozoic above the basement-involved Xiannan fault. We interpret that the NW-striking normal faults are related to extension at the western tail of the Maxian fault caused by the sinistral strike slip, while the EW-striking normal faults result from local extension caused by thrust of the high-angle Xiannan fault. Combined with previous research, we conclude that the widely distributed shallow fault systems are of various origins with a complicated coupling with the deep fault systems in the Qaidam Basin, and that the pre-existing faults played an important role in the Cenozoic deformation.