Stratigraphic age of the Mohe Formation in the western margin of Mohe Basin and tectonic environment discrimination of provenance

The Mohe Formation is widely developed in Mohe Basin which is located in the northern part of the Da Hinggan Mountains. Its formation age, provenance characteristics and tectonic background are of great geological significance for the study of the formation and evolution of the basin. Two interbeds of tuff were discovered in the Mohe Formation in the western margin of Mohe basin, Enhe-Hada area. Zircon U-Pb dating by LA-ICP-MS U-Pb method yields the weighted average ages of (158±1) Ma and (157±2) Ma respectively, indicating that the Mohe Formation rocks were formed in early Late Jurassic. The geochemical analysis of Mohe Formation sandstone shows that the content of SiO₂ is high (70.20%-76.13%), the value of SiO₂/Al₂O₃ is 4.99-5.87, and the value of K₂O/Na₂O is 0.59-1.62. In the chondrite-standardized diagram of rare earth elements, the curve is consistent with that of the active continental margin. In the high field strong elements and large-ion lithophile elements, the samples are enriched in Th, Hf, Rb and K, and deficit in Nb, Ta, Ti, P, Ba and Sr. The cobweb curve of trace elements is similar to that of the active continental margin. The geochemical source analysis and tectonic background discrimination show that the parent rocks of the Mohe Formation sandstone were mainly originated from the mixing of the quartzite sedimentary rocks and the acidic volcanic rocks. The ages of the detrital zircons in the sandstone coincide with the ages of the Precambrian basement and granitic rocks in the southern margin of the basin. The formation age, provenance characteristics and tectonic setting of the Mohe Formation, which is widely developed in the Mohe Basin in the north of the Great Hinggan Mountains, are of great significance to the study of the formation and evolution of the basin.