The Structure Styles Of Xuefeng Intra-continental Structural System And The Progressive Deformation During Indo-Chinese Epoch And Yanshanian

The Xuefeng Moutain, located in the southeastern margin of Yangtze block, together with the eastern part of the Sichuan Basin on the west, is called the Xuefeng intra-continental structural system. This structural belt covers two thirds of the Middle and Upper Yangtze region in south of China, so the study of its structural styles and tectonic processes will be about of the evaluation of the marine oil and gas potential associated with the continental geology and structure in south of China. The paper concluded systematically the predecessor's research results, and carried out regional geological survey. The structural styles of Xuefeng Moutain are studied and described, and the issues related with the structural deformation are discussed.1. The intra-continental structural belt forms an arc protruding southwestward in plain view, three different zones can be subdivided from southeast to northwest. NE-trending thrust-nappe zone widely developed in the rising basement belt of Xuefeng area, Proterozoic rock is exposed on the surface in the center; Trough like folds setting would be the obvious feature in the center zone, the syncline is closed well the anticline is wide and gentle. Triassic is exposed on the core; the Chuandong fold belt indicates ejective folds feature in the northwestern. A series of high and steep anticlines developed, the two wings become gentle suddenly when extend forward, and the layer between the anticlines is horizontal.2. S-form fold belts are discovered in the working area, and it indicates the superposition of structures from different direction. Strike-slip structures developed in this area, such as strike-slip faults and plunging vertical fold associated with thrusting and strike-slipping, it is considered to be the accommodation and transition structures caused by superposition. The superposition of structures in the trough like folds zone is considered to be a composition of earlier NE-trending structure and later NNE-trending extrusion and strike-slipping.3. Based on the structural analysis and lithology data, it is considered preliminary that slipping zone developed in the lower of Simian and Cambrian, Silurian, and Triassic. In vertical direction the structure is controlled by slipping zone in the working area. Multi-level detachment faults developed and extend in the forms of flat-and-ramp style, and control the upper structural patterns across the whole region, the depth of the slip surface reduces from southeast to northwest. The different patterns of fold developed as a result of the detachment in the different layers.4. It is considered that the Xuefeng Moutain extended from southeast to northwest during the Indo-Chinese epoch and Yanshanian. The time sequencing of the NW extending Xuefeng structure can be assumed. The structural deformation was mainly in the east of the Xuefeng Moutain in the late Middle Triassic; and extending to Huahua in the late Triassic, in the late Middle Jurassic, the structural belt reached to the Enshi-Lichuan area, and the coverage of influence is mainly in the southeastern of Lichuan, Enshi and Zigui line. The structural deformation extended to the Dianjiang area in the east of Huayingshan during the late Jurassic and the early Cretaceous. In the late Cretaceous, the Xuefeng Moutain moved westward to the Huayingshan area.