Sedimentary Characteristics And Tectonic Significance Of The Permian In The Zhuolunyinnuoer Area,Southern Sonid Zuoqi

The study area is located in Zhuolunyinnuoer area in the southeast of Sonid Zuoqi,Inner Mongolia.The tectonic structure is located in the northwest of Xing-Meng orogenic belt(XMOB).The Early Paleozoic tectonic evolution of XMOB is generally considered to be characterized by southward and northward subduction,while the Late Paleozoic tectonic evolution is still debated.Therefore,the identification of sedimentary paleogeography of the Late Paleozoic is one of the effective ways to resolve the above disputes.Therefore,this paper selects the clastic sedimentary rocks of the Middle Permian Zhesi Formation in the Zhuolunyinnuoer area as the research object,and analyzes the sedimentary profile,lithofacies palaeogeography and zircon chronology test results to find out the formation age,sedimentary environment and material sources of the strata,and explore the tectonic environment and evolution process of the Late Paleozoic in the XMOB.The Zhesi Formation can be divided into siltstone-shale member in the lower part and conglomerate-sandstone member in the upper part in Zhuolunyinnuoer,southern Sonid Zuoqi,Inner Mongolia,representing overbank deposit of middle fan subfacies and proximal rapid deposition of inner fan subfacies,respectively,implying a paleogeographic framework characterized by alluvial fan in intracontinental basin with the shallow water and oxidation conditions.Geochronology research of detrital zircon reveals a complex provenance containing the Xing'an-Ailigemiao block,the early Paleozoic arc belt and late Carboniferious and early Permian plutons.The youngest detrital zircon peak age of 281 Ma from the Zhesi Formation and another age of 248±3Ma from diorite porphyrite intruded into the Zhesi Formation have been obtained in study area,which constrain that formation age of the Zhesi Formation was between the middle Permian and early Triassic.Regional geology analysis reveals that there were the middle to late Permian terrigenous clastic sedimentary basins in the central and western parts of the XMOB.They were isolated each other and with different sedimentary sequences,suggesting “basin-and-ridge” structure style and intracontinental extensional tectonic setting during the Permian in the XMOB.