| 湘黔桂边区溆浦—三江断裂带平移运动的初步研究 |
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| A PRELIMINARY STUDY ON THE HORIZONTAL DISPLACEMENT OF THE XUPU-SANJIANG FAULT ZONE IN THE BORDER REGION OF HUNAN GUIZHOU-GUANGXI PROVINCES |
| The steeply dipping(65°-80°)Xupu-Sanjiang fault zone lies in the border region of Hunan-Guizhou-Guangxi provinces. It may be traced about 700 km, with a strike from NNE to NE, and assuming an‘s'shape. There are various wrench structures within the fault zone, such as echelon folds, splay fractures, regional stretching, cleavage belt and steep beds. These wrench structures have proved that the fault zone has undergone left-lateral horizontal displacement. On the other hand, the formation of the wrench structures was controlled by shear stress and the distribution displayed the general tectonic pattern of the wrench fault zone.The strata cut by the fault zone include the Proterozoic Lengjiaxi Group up to the Carboniferous, thus revealing the vertical deformation zoning and also its horizontal variations. Three vertical deformation facies and zones have been distinguished in the fault zone. In the top level deformation fades, brittle shear is the main destructive mechanism. It was dominated by fault breccia and fault gouge etc., and there was no ductile structures. Some marginal faults which controlled the Messozoic red-basins and the faults within the red basins are considesed as typical structures. The second shallow level facies was domineted by brittle and brittle-ductile transitional deformation, to which belonged the upper Sinian and the Paleozoic. At its upper leve cataclastic rocks were the principal tectonites. However, it can be seen that such rocks series coexisted with the mylonite series in the lower part of this facies. Ductile deformation was very typical in the third mid-deep level deformation facies, which often occurred in the lower Sinian and much older formations. Mylonites were the main tectonites. In addition, ductile flow structures, syntectonic foliation and lineation were also well developed. These three deformation facies weve resulted from different strain mechanism and have showed that the factors (e. g. temperature and hydrostatic pressure etc. ) controlling tectonism varied with the depth of the crust and the size of stress difference. Therefore they resulted in the different wrench effects in the regional tectonics. Different deformation patterns and different horizontal displacements of the paleolithofacies belts deformed by the wrench fault zone occurred at various depths. In general, the lithofacies belts were distorted by ductile shearing and there was no brittle offset. In contrast to it, the lithofacies belts of the shallow facies suffered both brittle offset and ductile distortion or complete brittle offset. The horizontal displacement increased progressively from the lower to the upper level of the fault zone.The formation and evolution of the Xupu-Sanjiang fault zone constiuted a considerably complex process. Based on the fact that fault zone deformed he pre-Mesozoic lithofacies belts and controlled the Mesozoic basins and according to some isotope age data of magmatic bodies which appeared along the fault zone, the author has come to the conclusion that the whole Xupu-Sanjiang fault zone formed in the Mesozoic, in which might include some pre-existing faults. The fault zone suffered a great left-lateral horizontal displacement immediately after its birth. The greatest displacement, being more than 300 km, took place during the early Yanshan movement in the Middle Jurassic, and deformed all the pre-existing structures in the western part of South China. The primitive E-W trending structural system was reoriented and rotated to NNE-NE. In the early Cretaceous there was tensional faulting along the fault zone, at one side of which the tensional basins often formed. Some secondary faults and folds occured within these basins. After the Late Cretaceous the fault zone has been characterized by a minor right-lateral displacement. |
| LIU Qing.1986.A PRELIMINARY STUDY ON THE HORIZONTAL DISPLACEMENT OF THE XUPU-SANJIANG FAULT ZONE IN THE BORDER REGION OF HUNAN GUIZHOU-GUANGXI PROVINCES[J].Acta Geoscientica Sinica,8(2):1-11. |
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