燕山中段南麓蓟县北部常州沟-杨庄一带地质构造基本特征

在燕山中段南麓的蓟县北部山区有着中国国家地质公园，中国北方中-新元古代正层型剖面标志碑就耸立在那里。对这一地区基本地质事实和地质体真实位态的研究，不仅关系着对华北地区晚前寒武纪标准剖面可靠性的评价，也关系着燕山运动命名地的基本地壳结构的合理解析和我国北方中生代以来构造一岩浆活动序列的正确建立。本文展示的基础地质调查成果可揭示：蓟县北部常州沟-杨庄一带的地质结构构造远不是我国大多数地学学者们对此描述的那样简单。调查区约200km。面积可代表燕山中段南麓的大面积中-新元古界分布区的基本地质结构构造特征。已识别出的18条断层和由其限制的21个以上构造岩片的现实位态表明，该地区地壳上部是由多个复杂地块堆叠构成的，主体构造形成于燕山晚期，在形成方式上以大规模多次不同方向运移的薄皮构造岩片叠覆为主要特征。

The Structural Feature of the Southern Margin of Middle Segment of Yanshan, a Case study in Changzhougou-Yangzhuang Area, Jixian County

The National Geopark for stratotype profile of Mesoproterozoic strata of northern China is located in Changzhougou-Yangzhuang area of the northern part of Jixian County,Tianjin Municipality,in where the steles were erected to mark the profile.Geologically,this area belongs to the southern margin of middle segment of Yanshan belt.The published geological map of this region shows a very simple feature on geological structure,and the profile was demonstrated as a south-dipping monoclinic succession in Chinese geological literatures.However,a lot of complex thrust systems and folds have been found in this area by this research.Totally,18 major thrust faults and 21 fault slices had been identified in the 200 km~2 region around Changzhougou-Yangzhuang area.In general,the region can be divided into two parts.The northern part is composed of many shallow dipping thrusts,forming some tectonic windows and klippes;and the penetrative structures develop extensively within the thrust slices.The south-dipping imbricate thrust system occurs in the southern part.Therefore,the structural feature in the site of 'stratotype profile' is so complex that the exposed Mesoproterozoic strata belong to the stacks of thrust slices.Accordingly,essential structural feature of the research area is characterized as the stack of large-scale thin-skin nappes having different vergences.Meanwhile,it is suggested that the major faulting and folding are formed in the late epoch of Yanshanian movement.