The Provenance Analysis And Tectonic Significance Of Sandstones In Linxi Formation In Huolinguole-Xi Ujimqin Area,Eastern Inner Mongolia

The northeast China located at the eastern part of the central Asian orogenic belt(CAOB).In the Paleozoic,it is mainly influenced by the ancient Asian oceanic tectonic domain and the Mesozoic is influenced by the superposition of the Central Pacific tectonic domain.This region has a complex tectonic setting,the implications of our research will make a significant sense to geotectonic evolution of CAOB.In this paper,the sandstones of Linxi Formation in Huolinguole-Xi Ujimqin areas in eastern Inner Mongolia are studied.The origin of sandstones is discussed mainly by petrology,provenance characteristics and detrial zircon chronology.Combined with the regional chronological data to explore the collision and closure history between the northern margin of North China Craton and the north blocks.The study area(Huolinguole-Xi Ujimqin area)is located in the eastern part of Inner Mongolia,south-central segment of Daxinganling.Considered with geotectonic view,it is located in the north of the Ondon Sum-Xar moron River suture belt,and Hegenshan suture belt to the south.The Late Permian strata are extensively developed in this area.The lithology of the Upper Permian Linxi Formation is mainly composed of feldspar lithic sandstone and lithic feldspar sandstone.The rocks are predominantly quartz,lithic clasts,feldspar,and a small amount of micas in composition.Most of the lithic clasts are volcanic frgment,while quartz grains are mainly monocrystalline quartz.Sandstones of Linxi Formation are immature,reflecting the rapid erosion rate of these source area,with short transport distance and short transport distance.Based on the statistical analysis of the skeleton components of the sandstone,the Dickinson triangular diagram shows that the sandstone source of the Linxi Formation is mostly the opened magmatic arc.In the Cathodoluminescence(CL)images of the detrital zircons extracted from the sandstones of Linxi Formation,the zircons are mainly rounded to sub-angular,a few of them are columnar,and the zircons have a clear oscillating zonings.The rare earth elements of zircon reveals a deficit of light rare earth and enrichment of the heavy one,with the ratios of Th/U range from 0.1 to 1.8,which indicates that most of the zircons are magmatic in origin.The U-Pb data of detrial zircons show that the ages are distributed between 254 and 2573 Ma,with main peaks of 261 Ma,284Ma,315 Ma and some other older ages(409~578Ma,700~1290Ma,>1700Ma).The youngest peak age indicates that deposition of the Linxi Formation should be later than 261 Ma,the provenance of the sandstones is mainly the Early Permian volcanic rocks of Dashizhai Formation,the Sunidzuoqi-Xilinhot-southern Xi Ujimqin volcanic arc,the metamorphic basement of the surrounding region and partly from the northern margin of the North China Craton.In conclusion,the study on the tectonic setting of the provenances and the chronological characteristics of the detrital zircons of the sandstones in the Linxi Formation have shown that the northern margin of North China Craton and the blocks to the north has collided began at the end of the Late Permian.