Features and Evolution of Deep Structures in the Xuefeng Intracontinental Tectonic System
|School||Ocean University of China|
|Keywords||the Xuefeng intracontinental tectonic system MT and seismic interpretation numerical simulation deep thrust-nappe structure dynamics|
The Xuefeng intracontinental tectonic system, also named as Jiangnan xuefeng - Huaying Mountain tectonic belt, is located in the west of the interface between Yangtze block and Cathaysia block. It’s one of the classic area to investigate tectonics in South China. Many well-known experts and scholars have made pioneering and innovative research here. However, due to the lack of geophysical data, its deep structures have not been done very well, and the dynamic mechanism has not been made clear yet. Through a series of specific gravity, magnetic, MT, seismic interpretation and geochemical data, especially the establishment of the finite element numerical simulation, this paper analyses the deep structural geometry intensively, and systematically discusses their dynamic genesis and development. Six conclusions have been made, as follow:1. According to the time of mountains’uplifting around the Sichuan Basin, we can infer the Wuling mountain gravity belt should have formed since 37Ma. This shows the deep structures are not necessarily the result of pre-existing deformation.2. From aeromagnetic anomalies,there may be two basements in this area: the one is the single-crystalline basement composed of Archean and Paleoproterozoic stratum; the other is the double-folded fold basement consisted of Mesoproterozoic and Neoproterozoic stratum.3. The thrust-nappe structures in our work area are very complicated but well-regulated. The shallow level is the westward-directed arc-like imbricate structures thrusting, and the deep level is the eastward-directed imbricate structures, so the overall structure like a fish bone. Nevertheless, the final uplifting of Xuefeng mountain is due to fan-shaped back-thrusting due to opposite-directed thrusting of the two fault systems, and leading to proterozoic strata being thrusted up to the surface.4. The bottoms of Neoproterozoic and Cambrian are extremely important detachment layers in our study area, which determine the basic structural pattern of the Xuefeng intracontinental tectonic system. These detachment layers gradually become lower and lower from southeast to northwest, and the corresponding ages also become younger.5. The Jurassian thin skinned structures develop very much. The fold styles, from west to east, vary from ejective folds to trough-like folds. Their genetic mechanism is different, but is controlled by fold-related faults. The former is a result that the contols of the high-angle eastward-directed reverse faulting to the westward-directed nappe-structure thrusting resulted in a close anticline on the top. The latter is a result that the plastic strata collapse along fault, shaping a narrow syncline.6. The kinetic factors of structural deformation are discussed on the basis of geochemical data and numerical simulation. The Yangtze block and Cathaysia block collided and formed a unified continental block in the Jinningian; And in the Caledonian-Indosinian, westward-progressively compressive structures developed resulting from the Cathaysia block with the Yangtze block, named intra-continental deformation. However, the Pacific tectonic domain play a main role in the Yanshanian; Indian plate convergence with the Eurasia plate has possibly an important role in the Himalayan.