The Mesozoic Structural Framework And Evolution In The Eastern Segment Of The Yanshan Intraplate Orogen

The Yanshan orogenic belt, which is located at the northern margin of the North China plate, has often been referred to as the cradle of Chinese geology. It is famous among Chinese and foreign geologists from its strong intraplate deformation in Mesozoic and Cenozoic. From the beginning of the last century, many researchers have been done on the geology and tectonics from both Chinese and foreign geologists in this area,many achievement have been acquired, but it was disputed about the deformation sequence and deformation mechanism in eastern segment of the Yanshan orogenic belt in Mesozoic.Since the crystalline basement concreted, many times of different mechanism and direction deformation have been occurred in study area, thrust, extensional tectonics and strike-slip fault have been found on field, such as transmeridional Qinglonghe strike-slip fault, northeast thrust and extensional fault, northwest Lengkou fault. All of the three fault system have been deformed many times since they were formed, the Mesozoic deformation history in the eastern segment of the Yanshan orogenic belt has been recorded in these fault system, so it is worth studying them.The main method of this thesis is structural analysis, through geological surveying, the author disassembled the complex and different scale deformation, analyzed the geometrical, kinetic, dynamic characters, environment, sequence of the structure in study area, then found the evolution, principle and mechanism of the structure in the eastern segment of the Yanshan orogenic belt.The main advancements achieved from the thesis are as followings:1. The northeast thrust formed in early Yanshanian, it caused by the extrusion from northwest to southeast, in the phrase Lijiawopu-sandaohezi fault was formed, the kinetic character of the fault is reverse-right-parallel strike slip. After extrusion, the tectonic environment changed into extension, the Lijiawopu-Sandaohezi fault was extended in some degree, moreover, the stratum in the hanging wall also extended at the same time, though the Mazhuangzi-andashi fault was formed.2. The transmeridional Qinglonghe fault, which formed in Archean, moved again in Mesozoic. In Indosinian its kinetic character was extrusion form south to north; in early Yanshanian was extrusion form northwest to southeast; in late Yanshanian was extension form northwest to southeast. The most obvious record is right-parallel character formed in early Yanshanian.3. The northwest extended Lengkou fault, a special fault is Yanshan belt, was formed during the Yanshan crystalline basement cracking. It moved again in Mesozoic. The movement record of Lenkou fault is very detailed, the movement sequence can be divided into fowling period: thrust form south to east in Indosinian, left-parallel strike slip in early Yanshanian, rotate movement in late Yanshanian, thrust form northeast to southwest in Himalayan.4. The three different direction fault system in eastern segment of Yanshan belt moved in different mode and direction, but the tectonic environment of their deformation is same. The reason is these faults are formed in different age, in Mesozoic they move again followed the primary fault plane, they formed different kinetic characters.