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Tectonics of the Middle Triassic intracontinental Xuefengshan Belt, South China: new insights from structural and chronological constraints on the basal décollement zone |
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| Authors: | Yang Chu Michel Faure Wei Lin Qingchen Wang Wenbin Ji |
| Institution: | 1. State Key Laboratory of Lithopheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, 19 Beitucheng Western Road, Chaoyang District, Beijing, 100029, People’s Republic of China 2. Institut des Sciences de la Terre d’Orléans, Campus Géosciences, Université d’Orléans, 1A, Rue de la Férollerie, 45071, Orléans Cedex 2, France 3. Graduate University of Chinese Academy of Sciences, Beijing, 100049, China |
| Abstract: | In orogenic belts, a basal décollement zone often develops at depth to accommodate the shortening due to folding and thrusting of the sedimentary cover. In the Early Mesozoic intracontinental Xuefengshan Belt of South China, such a décollement zone is exposed in the core of anticlines formed by the emplacement of the late-orogenic granitic plutons. Our detailed, multi-scale structural analysis documents a synmetamorphic ductile deformation. In the basal décollement, the Neoproterozoic pelite and sandstone, and the intruding Early Paleozoic granites were deformed and metamorphosed into mylonites and orthogneiss, respectively. The metamorphic foliation contains a NW–SE stretching lineation associated with top-to-the-NW kinematic indicators. The ductile shearing of these high-strained rocks can be correlated with NW-verging folds and thrusts recognized in the Neoproterozoic to Early Triassic sedimentary cover. Monazite U–Th–Pbtot chemical dating, and zircon SIMS U–Pb dating provide age constraints of the ductile shearing between 243 and 226?Ma, and late-orogenic granite emplacement around 235–215?Ma. In agreement with recent geochronological data, these new results show that the Xuefengshan Belt is an Early Mesozoic orogen dominated by the NW-directed shearing and thrusting. At the southeastern boundary of the Xuefengshan Belt, the Chenzhou-Linwu fault separates the Early Mesozoic domain to the NW from the Early Paleozoic domain to the SE. The tectonic architecture of this belt was possibly originated from the continental underthrusting to the SE of the South China block in response to northwest-directed subduction of the Paleo-Pacific plate. |
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