Abstract:Abstract:The Mohe Basin is located in the northern margin of the Erguna microplate in the Mongolia-Okhotsk fold belt. It is located in the collision zone between the Siberian plate and the North China plate. The Ershi’erzhan Group is one of the Mesozoic sedimentary strata in the Mohe Basin. The predecessors discussed its formation age and source, but there is still much controversy. Based on the previous studies, the zircon chronology of detrital zircons and rock geochemistry again determines the age of its formation, and explores the tectonic setting of the source and source areas in this paper. The chronological study of detrital zircons shows that most of the detrital zircons in Ershi’erzhan Group are magmatic zircons, and a small part of zircon particles are hyperplastic-mixed zircons, which shows that they have undergone post-structural-thermal event modification. In addition, a small portion of the zircon particles are rounded, indicating that they have undergone multiple handling and deposition processes,suggesting that the early formation of ancient sedimentary rocks provided a source for the Ershi’erzhan group. The youngest zircon age is 134±1Ma. In the previous regional geological survey report, the fossils of the paleontology in the J3-K1 period were found, and the sedimentary limit of Ershi’erzhan Group was limited to the early Cretaceous, and it also explained the area of the early Cretaceous igneous rocks existed in the study area. The tectonic environment discrimination of the main and trace elements and provenance analysis reveal that the source of Ershi’erzhan Group is mainly the felsic upper crust and the Andesitic source area of upper crust of the active continental margin and the continental island arc environment, and is mixed with the lower crust deep matter ( Basite rock). The zircon LA-ICP-MS U-Pb dating results show that the detrital zircon in Ershi’erzhan Group has a tendency to increase the amount of zircon preservation with the age, and its age distribution can be divided into four periods as a whole: Neoarchean (2711±10Ma), indicating the existence of the basement information of the Neoarchean in the Erguna massif; the Mesoproterozoic-Palaeozoic (1238-2428Ma), indicating that the Xinghuadukou rock group is the partial sediment source of Ershi’erzhan Group;Neoproterozoic (561-921Ma) is a record of the continental magmatic arc (active continental margin) tectonic events in the study area during the subduction of the ancient Asian ocean to the Erguna-Xing"an block of the Jiningian period; the Mesozoic - Late Paleozoic (134-540Ma), a material record of the granitic magma formed during the subduction and closure of the Mongolian-Okhotsk in the study area, and the Phanerozoic granitic magma provided the most rich source for the Ershi’erzhan Group.