歧口凹陷沿岸带新生代构造特征及其形成机制

歧口凹陷沿岸带是一条分隔歧口凹陷陆上和海域不同构造体系的NNE-NE的复杂构造变形带。在其两侧，盆地结构分别表现为半地堑和地堑式。在平面上，自南向北歧口凹陷沿岸带可以分为三个具有明显不同的新生代构造变形组合特征的区段：南部的斜列式走滑变形带，体现为一系列阶梯状展布的张扭断层，同时伴有岩浆活动和滑塌浊积体发育；中部的宽缓挠曲变形带，构造样式简单，地层只有微弱变形，但仍然伴随强烈的火山活动；北部的复杂断裂褶皱带是受基底走滑断层影响而形成的古近纪重力滑脱断层和新近纪花状构造的有机结合体。总体上，沿岸带复杂的构造组合特征是受到深部向北隐没的新生代右旋基底走滑断裂活动的控制，是渤海湾盆地内兰聊断裂通过歧口凹陷时的构造表现。歧口凹陷沿岸带在不同区段的构造变形特征，也造成了不同区段的油气成藏模式的差异性。

Features of the Cenozoic structure of the coastal zone in Qikou Sag and its formation mechanism

The coastal zone in the Qikou Sag was a NNE-NE trending belt with complex tectonic deformation that separated the continental structure system from marine one in the basin. The configuration of the basin was showed as a half graben in the western onshore and a graben in the eastern offshore, respectively. From the south to north, the coastal zone could be laterally divided into three different segments based on their Cenozoic deformed structure assemblages. A strike-slip deformed belt with echelon normal faults in the south represented a series of step-shaped tenso-shear faults and was accompanied by magma activities and developed fluxoturbidites. A wide and gentle flexure deformed belt in the middle had simple faults and slightly deformed strata, but was also accompanied with intense volcanic activities. And a complex faulted-fold belt in the north was formed under the influence of basal strike-slip faults that combined the Paleogene gravitational detachment faults with Neogene flower-like structures. As a whole, the complicated Cenozoic structure assemblage of different segments of the coastal zone was controlled by deep Cenozoic dextral-shear basal strike-slip faults that plunged northward, and it represented structures of the Lanliao fault in the Bohaiwan Basin that passed through the Qikou Sag. Structure deformations in different segments of the coastal zone in the Qikou Sag also resulted in the difference of various hydrocarbon accumulations.