The Tectonic Background Of The Lower Permian Shoushangou Formation In Dashizhai-West-Ujimqin Area,Inner Mongolia

The study area is located in the eastern part of the Central Asian Orogenic Belt,which is located in the combination of the Siberian and the North China cratons.There is no consensus on the final closure time of the Paleo-Asian ocean.The Shoushangou Formation is considered to be the lower section of Permian strata,and it has been a consensus in the fields of geology.The Shoushangou Formation records important information about the evolution of Paleo-Asian Ocean.It can effectively identify the evolutionary stages of development of Paleo-Asian Ocean by restricting the stratigraphic age of Shoushangou Formation and studying its composition,Stratigraphic thickness,paleontological characteristics,sedimentary environment and provenance characteristics,etc.in early Permian.This thesis takes the geochronology data and provenance analysis of the Shoushangou Formation were studying sample,section analysis,zircon U-Pb dating in the West-Ujimqin and Dashizhai areas.Studied the characteristics of sedimentary environment and sedimentary facies combining with palaeontological informations.The whole distribution of the Shoushangou Formation is characterized by NE direction and zonal distribution in the study areas.To taking stratigraphic correlation I had measured the stratigraphic profile of Shoushangou Formation on the basis of precedent achievements,and studied the lithology,sedimentary facies,sedimentary environment,spatial distribution and contact relationship of the Shoushangou Formation around the study areas.It is concluded that the rock association of the Shaoshangou Formation have the characteristics of littoral-neritic sedimentary facies.Among them,the mudstone belongs to carbonate type of littoral-neritic sedimentary facies,indicating the littoral-neritic sedimentary facies environment.Incomplete bauma sequence can be seen in silty slate of West-Ujimqin area,where DE sections is more common,and ADE sections can be seen in some rocks.Bauma sequence Characterized by low density turbidity flow,it should also belong to the shallow-subabyssal sedimentary facies,which may be the depositional product of submarine fan.According to the sedimentary rules and characteristics of the stratum,the tectonic background of the early Permian in study area was the state of extended after the collision.The detrital zircon U-Pb dating of the Shaoshangou Formation was carried out in West-Ujimqin and Dashizhai area respectively and The detrital zircon dating is 273±2Ma and 281±1Ma.Moreover,measured the detrital zircon dating U-Pb in the dacite,and the test results is 305.7±1.3Ma.It is believed that the Shaoshangou Formation are forming in the early Permian.Based on the age-dating analysis of the samples,the age informations of the detrital zircons from the north China plate basement and the north of the ErenhotHegenshan suture zone was founded in the age composition of the detrital zircons in the Shaoshangou Formation,and concluded that the Paleo-Asian Ocean was closed before the early Permian.