Sedimentary Characteristics And Tectonic Setting Of Permian In The Xing'an Region Of Inner Mongolian Autonomous Region

The study area located in the middle part of the Great Xing'an Range which is in the east of Inner Mongolian Autonomous Region, and belongs to the Xingmeng Orogenic Belt(eastern segment of Central Asian Orogenic Belt) tectonically. In late paleozoic, Paleo-Asian Ocean covered this area. From Permian, Paleo-Asian Ocean decreased,then the collision between Siberia Plate and North China Plate took place which led to the formation of Xingmeng Orogenic Belt. The subjects of this study is Zhesi Formation of middle Permian and Linxi Formation of upper Permian. The study uses the theory of stratigraphy, sedimentology and rock geochemistry to analyze the characteristics of sections, rock assemblages and the skeletal component of sandstone which are enssential to research the sedimentary environments and tectonic setting.The achievements of study are as follows: Firstly, the gain size of the two formations increases from bottom to top which represents a tectonical lifting event with waters regional regression. Secondly, rock assemblages and fossil data indicate that in the early stage the tectonic setting was stable and the strata was of shallow marine facies. Then the sedimentary facies transferred to paralic as the tectonic activity strengthened. Thirdly, by using achievements and diagrams of Dickinson, Bhatia and Roser, this study analyzes the geotectonic background of provenance and the conclusions are that the Zhesi Formation is mainly of active continental margin of Andes Type which also shows some characteristics of island arc, the Linxi Formation represents island arc environment.Based on regional geologic data and works mentioned above,the thesis can draw following conclusions: (1)Siberia Plate took Southeast subduction towards North China Plate and the geosuture might locate in the southern of the study area. (2)The tectonic setting of the southern part is active continental margin,and that of the northern part is island arc. (3)The evolutionary processes of the study area in Permian is that volcanic activities were active in P1,but stoped in P2,and tectonic environment became stable, then as the collision between Siberia Plate and North China Plate took place, the ground surface elevated which caused marine regression and despair in P₃. At the end of Permian, the study area was mainly in continental environment.