Sedimentary And Geochronology Study On The Xuniwusu Formation From Tugurige Area,Inner Mongolia And Paleogeographic Significances

The Central Asian orogenic belt,as a hot spot of global orogenic belt research,has always been the focus of people's attention.The part of the central Asian orogenic belt in China is called Xing-Meng orogenic belt.In the central part of Inner Mongolia,there is a tectonic evolution process from the extensive development of the Paleoasian Ocean to the formation of the South orogenic belt and North orogenic belts.In the early Paleozoic,the subduction of the Paleoasian Ocean formed a wide trench-arc-basin system in the South orogenic belt.The Tugurige area in this paper is a typical area of the early Paleozoic trench-arc-basin system in the South orogenic belt.The Xuniwusu Formation in Tugurige area belongs to the tectonic unit of back-arc basin,Its sedimentary rock interbedding is frequent.It is very stable laterally and has a large accumulated thickness.Its Flysch formation shows typical turbidite sedimentary characteristics.This paper focus on the westen segment of the sounthen Xing-Meng orogenic belt.Sedimentary facies studies on flysch formation of Xuniwusu Formation in Tugurige area,western Inner Mongolia reveal that the formation generally shows Bouma sequences with different thickness and types,in line with turbidity current sedimentary facies.According to turbidite facies model,it can be categorized into middle fan subfacies and contains three microfacies such as braided channel,inter-braided channel and central fan front margin microfacies.Xuniwusu Formation is speculated as the early-middle Silurian according to the regional stratigraphic correlation and the youngest peak of detrital zircon ages(437.9�2.7 Ma).Provenance analysis of Xuniwusu Formation revealed that it came from the early Paleozoic island arc belt in the north and the basement of North China plate in the south,respectively.In addition,the strata comparison of Tugurige,Damaoqi and Bainaimiao areas suggests that a Back-arc Basin,representative of prevailing Xuniwusu Formation and Talingong Group,located in the south orogenic belt and extended about 400 km in East-West direction.Such a wide trench-arc-basin system in early Paleozoic might formed in relation to Paleo-Asia Ocean subduction and thus determines an Andean type active continental margin along the north edge of North China plate.