Geologic Structure And Tectonic Evolution Of The Karamay-Baikouquan Overthrust Belt At The Northwestern Margin Of Junggar Basin

The study area included the Ke-bai fault zone, which is located at the northwest edge of Junggar Basin, the Zaire mountain on the north and the western Mahu slope on the south. Kebai fault zone beolongs to the middle part of the overthrust belt in the northwestern margin of Junggar Basin with NNW trend. Since Paleozoic this area has experienced multistage tectonic movements, resulting in the very complicated geological structure performance. Previous studies using a variety of methods to study the structure feature of the overthrust belt in the northwestern margin and achieved fruitful results. While the structure feature of this area is so complicated that the seismic imaging is unclear, there still exist several confuses when we study the geological structure of a single zone in this area; the precise process and exact time of the tectonic evolution haven’t been achieving a common understanding as well. This paper starting the research by making full use of the latest seismic data, boreholes and field outcrops undering the conducting of the structural geology and the fault related folding theory. Based on the lastest methods of modern structural geology, we study and analyze the geometry features and kinematics pattern of this area, and gain several understandings as follows:1. According to the unconformity contact between lay ers, the binding characteristics of sediments in western Mahu slopes in Kebai Region,we divide the sedimentary strata with five different tectonic sequence: Carboniferous tectonic sequence,Middle- Lower Permian tectonic sequence,Upper PermianTriassic tectonic sequence,Jurassic-Cretaceous tectonic sequence and Cenozoic tectonic sequence. We also conclude that the Kebai Region is composed of four structure belts based on the difference of structure deformation and stratigraphic. These four structure belts include a Carboniferous nappe structure belt, a covered nappe structure belt, a monoclinal structure belt in the fault front and a covered Permian fold belt.2. Kebai area development several covered thrusts faults which control the movement of the Carboniferous nappe. Dip of these thrust faults vary from steep to gentle from the shallow position to the deep position, and end in the floor-fault in the Carboniferous layer.Complex duplex structure develop under thrust faults in the study area.3. According to seismic data and drilling data, we can identify multiple sets of unconformity surfaces and growth strata.4. The structure deformation of the Kebai Region started at the Early Permian period and continued to the late Jurassic.