U-Pb dating of detrital zircons and geochemical characteristics of Linxi Formation in the Kundu area of Ar Horqin Banner, southern Da Hinggan Mountains, and their geological significance

The Qiaoluotu geological section of the Linxi Formation in the Kundu area of Ar Horqin Banner in Da Hinggan Mountains is a set of yellowish green debris feldspar fine sandstone, yellowish green lithic siltstone, grayish black siltstone crust rock assemblage. The age of the section is the Late Permian according to rich bivalves and plant fossils. According to the study of LA-ICP-MS detrital zircon U-Pb in the lower sandstone of the Qiaoluotu geological section of the Linxi Formation, the authors hold that the ages of ²⁰⁶Pb/²³⁸U zircons are mainly concentrated at 267Ma, 299Ma, 484Ma, 726Ma and 933Ma, with the youngest ²⁰⁶Pb/²³⁸U zircon age being 256Ma, which indicates that the maximum deposition age of Linxi Formation in this area was not earlier than that of Late Permian Wujiaping period. Geochemical characteristics of sandstone in Linxi Formation show that the source of the Qiaoluotu geological section was characterized by the felsic materials, and the water body during the sedimentary period was a freshwater environment. Combined with paleontology, petrology, geochemistry and isotopic chronology research, it is inferred that the ancient Asian Ocean in the study area was closed in the Late Permian, the sedimentary environment of Linxi Formation was continental lake basin, and the sedimentary source had complex and diversity characteristics, suggesting that the main source area was from the Xingmeng orogenic belt, with a small amount probably from the North China plate.