Geologic Character And Tectonic Evolution Of The East Guizhou And Its Adjacent Region

Based on the geological and tectonic features of the East Guizhou and its adjacent regions,four tectonic cycles were suggested in this area, namely,the Wuling Cycle,the Caledonan Cycle(transformation from ocean to continent), the Yanshanian Cycle and the Himalayan Cycle(developed in an intra-plate orogen).Employing associated tectonic analyses methods of orogenic belt, the material frame and geometrical features of these four tectonic Cycles were analyzed in detail.We tried to divide the tectonic facies the studied area into two different tectonic facies based on the studies of material textures and features of different orogen: orogen formed during transformation from ocean and continent and intra-plate orogenics. This classification may better illustrate the tectonic evolutions of different orogens in the East Guizhou and its adjacent regions.Based on the studies of geometrical features,Typical structural patterns were found in the East Guizhou and its adjacent region including the Alps-type fold(widen and closeness),the Jurassic type fold,thrust nappe,the ductile shear zone,orogen-paralleled sliding structures,the metamorphosed core-complex (MCC))structure,extensional detachment,and horst-graben structure.Meanwhile, the main structural traces in different tectonic cycles were unique.According to comprehensive analyses of the regional geological data,we presented a tectonic evolution history as follows:the Wuling to Caledonan Cycles (represented a transformation from ocean to continent),and the Yanshanian and Himalayan Cycles(intra-plate activation).By this process,the active crust evolved into a stable one.Our researches were focused on these following areas: nature of sedimentary basins formed in different tectonic cycles and their migration; characters of typical tectonic patterns and their areal distribution; properties of unconformity surfaces, their distribution and the relationship between their lower and upper strata. Based on the above sedimentology and structure geology studies, we firstly proposed that the center of Wuling Movement is located along North Fanjingshan(in Guizhou Province)-Dayong(in Hunan province)-Yueyang(in Hunan province)-Pingjiang(in Hunan province) while the center of Caledonian Movement is located along Luocheng(in Guangxi province)-Longsheng(in Guangxi province)-Tongdao(in Hunan province) and the center of Yanshanian orogen is located along Shaoxing-Pingxiang-Beihai. The tectonic movement in this area stepped into intraplate uplifting during Indo-Chinese periods.Accordingly,a new tectonic division schedule for the study area was proposed and described below.The first-level tectonic unit was the Jiangnan Orogen, which is bounded northerly by the Shizong-Songtao-Chili-Jiujiang belt and southerly by the Shaoxin-Pingxiang-Beihai fault system.The Jiangnan orogen is bracketed by the Yangtz (Northwest) and Cathisian (Southeast) blocks, and it was subdivided into three sub-units: the southern boundary of the northern sub-unit is the Shizong-Songtao-Chili-Jiujiang belt;between the Shizong-Songtao-Chili-Jiujiang belt and the Luocheng-Longshen-Taojiang-Jingdezhen was the middle sub-unit; and south of the Luocheng-Longshen-Taojiang-Jingdezhen belt belongs to the southern sub-unit , where the Qiandong-Xiangxi and Nanning-Changsha blocks were enclosed.In conclusion,the Jiangnan Orogen is a composite one formed by multi-stages orogenesis of the Wuling northern sub-orogen,the Caledonan middle sub-orogen,and the Yanshanian southern sub-orogen.