摘要
宝坻断层是渤海湾盆地西北缘的边界正断层,地处燕山褶皱带与渤海湾盆地耦合的关键部位。宝坻断层处在古亚洲构造域与太平洋构造域的交叠部位,经历了复杂的构造演化过程,其在中生代-新近纪的构造活动控制了武清凹陷的沉积和构造演化。宝坻断层整体走向近EW向,延伸长度约68km,最大位移达14. 2km,滑脱面深度约10～15km。横向上其主体断面及滑脱面均存在较明显的分段性,通过3个垂向转折轴面可划分为4段。剖面上该断层大部分呈上陡下缓的犁式正断层特征,中段部分区域为"坡坪式"结构。宝坻断层整体位移在横向上的变化与其几何学上的分段有着较好的相关性,表明其现今多次转折的结构与其生长过程密切相关。古近系底面、东营组底面及新近纪底面位移-距离曲线特征表明,沙河街组沉积期,各个断层在相对独立发育后,因横向生长而逐渐发生硬连接,至东营组沉积期之前形成整体断面,其活动于新近纪逐渐减弱,所控断陷规模萎缩。中生代以来,武清凹陷-燕山褶皱带主要受三叠纪、早中侏罗世、中晚侏罗世、白垩纪、古近纪和新近纪-第四纪6个构造演化阶段的影响,其中,三叠纪-侏罗纪末期,武清凹陷与燕山褶皱带经历了相似的构造演化过程,而自白垩纪以来,两者的构造-沉积响应出现了明显的分异。因此对宝坻断层及武清凹陷的构造解析对厘定燕山构造带陆内变形的时空范围及其与渤海湾盆地的耦合关系有着重要意义。
The Baodi fault,as the boundary normal fault of the northwestern margin of the Bohai Bay Basin,is located at the coupling area of the Yanshan Fold Belt and the Bohai Bay Basin. It controlled the Mesozoic to Cenozoic sedimentary and tectonic evolution of the Wuqing sag while being influenced by both the Paleo-Asian tectonic domain and the Pacific tectonic domain,and experienced a complex tectonic evolution process. The Baodi fault strikes generally EW for 68 km,with the detachment reaching 10 ～15 km at depth. The architecture of the main surface as well as the detachment of the Baodi fault can be subdivided by three vertical axial planes into four segments,most part of the fault surface exhibits listric normal fault characteristic while the middle part shows a sigmoidal shape. The overall displacement-distance( D-X) profile of the Baodi fault is also obviously segmented while being in good correlation with its geometric segmentation,which suggests that its multiple lateral turns is highly related to its growth history. The DX profiles of the base Paleogene,the base Dongying Formation and the base Neogene indicate that it was gradually linked from several fault segments during the sedimentation period of the Shahejie Formation,and the integral fault surface was formed before the sedimentation period of the Dongying Formation. Its activity gradually weakened in the Neogene,causing the scale of the rift it controlled to shrank during the same time at the same time. Since the Mesozoic,the Wuqing sag and the southern Yanshan Fold Belt experienced 6 main periods of tectonic evolution,i. e.,the Triassic,the Early-Middle Jurassic,the Middle-Late Jurassic,the Cretaceous,the Paleogene,and the Neogene-Quaternary respectively,among which apparent differentiation appears in the structuralsedimentary response of the two areas since the period of Cretaceous. Therefore,the study of the Baodi fault and the Wuqing sag is of great significance in determining the time and space of the intracontinental deformation of the Yanshan Orogen as well as its coupling relationships with the Bohai Bay Basin.