松辽盆地南部梨树地区走滑-逆冲构造的成因——以小宽断裂带为例

多个构造带的复合叠加过程及其形成的地质结构是陆内构造变形研究的前沿问题。松辽盆地南部梨树断陷处于古亚洲洋构造域与太平洋构造域的交接位置,是研究这一问题的良好窗口。小宽断裂带是梨树断陷内具有代表性的构造单元,与区域内的油气藏关系密切,其地质结构和演化过程仍存在争议。研究通过开展三维地震数据解释和地震相干切片分析厘定了小宽断裂带的地质结构和演化过程;通过总结前人认识和区域大地构造演化背景分析了走滑-逆冲活动的成因机制及其油气地质意义。研究结果认为:(1)小宽断裂带整体向西倾,可分为南段、中段、北段3部分;(2)在早白垩世,小宽断裂带经历了早期伸展构造变形和末期左行走滑-逆冲构造变形,断裂带的走滑-逆冲构造活动导致梨树断陷中央构造带内形成多个背斜;(3)小宽断裂带形成于中国东北地区由古亚洲洋构造域主导向太平洋构造域主导的转换过程,受控于早白垩世晚期古太平洋板块的加速俯冲;(4)小宽断裂带走滑-逆冲构造活动所形成的背斜构造是梨树断陷中央构造带内油气富集的重要构造。小宽断裂带南段发育封闭性良好的背斜构造,生-储-盖条件较好,具有成为梨树断陷下一步勘探方向的潜力。

Origin of strike-slip thrust structure in Lishu area,southern Songliao Basin: a case study of Xiaokuan fault belt

The complex superposition process of multiple structural belts and their geological structures are the frontier issues in the study of intracontinental structural deformation. Lishu fault depression in the southern Songliao Basin is located at the junction of the Paleo-Asian Ocean tectonic domain and the Pacific tectonic domain, which is a good window for studying that issue. Xiaokuan fault belt is a representative structural unit in Lishu fault depression; it is closely related to the oil and gas reservoirs in this region, but there are still disputes on its geological structure and evolution process. This study determines the geological structure and evolution process of Xiaokuan fault belt by carrying out 3D seismic data interpretation and seismic coherence slice analysis. Through summarizing previous knowledge and the regional geotectonic evolution background, this paper analyzes the genetic mechanism of strike-slip thrust activity and its significance of petroleum geology. The study results show as follows. (1) Xiaokuan fault belt dips to the west as a whole and can be divided into three parts: the south, middle, and north sections. (2) In the Early Cretaceous, Xiaokuan fault belt experienced early extensional structural deformation and late sinistral strike-slip thrust deformation, and the strike-slip thrust tectonic activity of the fault belt led to the formation of multiple anticlines in the central tectonic belt of Lishu fault depression. (3) Xiaokuan fault belt formed in the transformation process from the Paleo-Asian Ocean tectonic domain dominant in northeastern China to the Pacific tectonic domain, which was controlled by the accelerated subduction of the Paleo-Pacific plate in the late Early Cretaceous. (4) The formation of anticline structure due to the strike-slip thrust tectonic activity of Xiaokuan fault belt is an important structural factor for forming hydrocarbon enrichment areas in the central tectonic belt of Lishu fault depression. The anticline structure with good sealing property developed in the southern section of Xiaokuan fault belt has good generation-reservoir-cap conditions, indicating the next exploration direction of Lishu fault depression.