Detrital zircon U-Pb age and geochemistry of sandstone from the Mohe Formation in the Mohe Basin Heilongjiang and their constraints on tectonic setting

Mohe Basin is located in the north of Greater Khingan Range and Erguna Massif at the eastern end of theXing'an-Mongolian orogenic belt. Through the study of detrital zircon chronology, petrogeochemistry, modern stratigraphy, paleontology and heavy minerals in the strata of the Mohe Formation, the sedimentary age, material source and geotectonic background are discussed, providing scientific basis for the study of the evolution of the Mohe Basin. Petrogeochemistry, heavy minerals assemblage and ATi (89.51~100.00, average 98.69) and GZi (39.76~100.00, average 64.50) index show that Mohe Formation is mainly under the background of active continental margin and continental island arc, and the provenance are feldspathic rocks of the upper crust, metamorphic rocks and sedimentary rocks, mixed with basic magmatic rocks in the lower crust or mantle. The CIA (50.35~60.37, average 53.22), and ICV index (0.91~1.79, average 1.40), Rb/Sr (0.08~0.67) and Th/U (5.05~5.81, average 5.55) ratios of the rocks indicate that the provenance of Mohe Formation have undergone relatively weak weathering. The ZTR index of heavy minerals reflects that the detrital has the characteristics of proximal transport. Fossils of paleoplants from the Early Jurassic -Early Cretaceousera were found in the Mohe Formation, combined with the detrital zircon LA-ICP-MS U-Pb chronology (the minimum age was 156±3 Ma), it was determined that the Mohe Formation was depositional in the Late Jurassic. The ages of detrital zircons are concentrated in three periods: 1841~2462 Ma (n=4, Paleoproterozoic), indicating the existence of Paleoproterozoic crystalline basement in the Erguna Massif. 311~480 Ma (n=56) is a record of granitic magma formation under the extensional setting after the Erguna block and Siberian block were combined.156~242 Ma (n=48) is evidence of magma intrusion under the setting of Mongolia-Okhotsk Ocean subducted into the Erguna Massif.