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TECTONICS AND GEOLOGICAL EVOLUTION OF XUEFENGINTRA CONTINENTAL OROGENE, SOUTH CHINA

Qiu yuanxi(Department of Geosciences, Zhongshan University, Guangzhou 510275)Zhang Yichang(Central Laboratory, Ministry of Geology and Mineral Recources, Wuxi 214000)Ma Wenpu (Department of Geology, Geological University of China, Beijing 100083)  
The Xuefeng Mountains are located in the southeastern margin of the Yangtze Block, South China The tectonics and geological evolution of this region have been studied and compared with the orogene and allochthonous nappes of Alpine and Appalachian types The following features are recognized: 1 The development of inter layer gliding is one of the major features of the Xuefeng Mountains The glide structures have a regional scale and are of multi layer and polycyclic characteristics Discordant folds were well developed, in which the upper layers are usually more intensively deformed than the lower layers Thrust or overthrust developed in the earlier stages, while gravity slide or extensional detachment in the later stages The basement was thrusted more intensively in its front edge and detached from the cover, forming Jura type folds, extended anticlines, imbricated thrusts, and foredeep depressions A sequence of progressive deformations developed: inter layer gliding→ inter layer folding→imbricated thrusting→overthrusting (layer cutting) →gravity sliding or extensional detachment Recoil structures formed on the hanging side of the thrusts 2 Although imbrcated thrusts developed in the Xuefeng Mountains, klippes, structure windows, duplex and recoil structures, mega recumbent folds or nappe sheets do not exist in this area. The displacement of thrust or glide does not exceed 50km The hanging side of the thrusts is allochthonous in the relatively sense, as it resided in the same paleobiogeographic division with the downthrown side The thrusting has narrowed the sedimentary facies, belts of original formations, but did not distort their sedimentary framework (platform facies → continental facies → abyssal facies) The Banxi, Xiajiang, and Danzhou groups are synchronous formations with different sedimentary facies and are not melanges. The outcrops of Early Paleozoic in southeast Guizhou Province are not in the structural windows but in synclines The Proterozoic Banxi Group does not overlay on the Early Paleozoic strata No Alpine type allochthonous nappe has been found in the Xuefeng Mountains 3 The tectonic evolution of the Xuefeng Mountains has been proceeded on the background of continental crust Since the Late Caledonian orogene, intra continental subduction had replaced the B type subduction as the major geodynamic process in the area Inter layer gliding became the dominant form of deformation When the rifts closed, the micro continental blocks collided (soft collision), and inter layer gliding occurred
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