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Li L.,Jilin University | Sun F.,Jilin University | Li B.,Jilin University | Xu Q.,Shandong University of Science and Technology | And 2 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2017

To address the controversy of the Ershi'erzhan Formation sandstone formation ages in the Mohe basin of the northern Great Khingan Range, this study presents an accurate limit to its formation ages using the LA-ICP-MS detrital zircon U-Pb dating for the first time in this paper, and discusses its provenance and tectonic setting combined with the geochemistry of major and trace elements. The results show that the fragmental material in sandstone has poor psephicity and sorting, indicating that source region is relatively unstable with characteristics of rapid denudation, transportation and sedimentation. The grains of detrital zircons are big with clear oscillatory zoning, and Th/U values range from 0.35-1.07, which is indicative of a magmatic origin. Zircon U-Pb dating results show that 90 dating data are distributed in the following three periods, namely, 152-170 Ma with the peak of 158 Ma, standing for the lower limit of Ershi'erzhan Formation sedimentary rocks at Late Jurassic; 179-193 Ma with the peak of 190 Ma and 205-214 Ma with the peak of 210 Ma. The three peak ages are the evolution records of the Mongolia-Okhotsk ocean. The peak ages of 210 Ma and 190 Ma are consistent with the Late Triassic and Early Jurassic magmatic events of south margin of the basin in the Erguna massif, the peak age of 158 Ma fits the Late Jurassic magmatic event of north margin of the basin. The geochemical diagrams of major and trace elements reveal that the provenance has the background of active continental margin. Meanwhile, the zircon dating shows that there is no Pre-Mesozoic clastics in the Ershi'erzhan Formation. It suggest that these were generated within an active continental margin setting at the north margin of the Erguna massif in Mesozoic, and provided the most clastics for the Ershi'erzhan Formation. Combining with the previous studies, it is concluded that the Ershi'erzhan Formation sandstone was formed in Late Jurassic under the environment of rapid denudation, transportation and sedimentation, controlled by the uplift of the Mongolia-Okhotsk orogenic belt, indicating that the eastern Mongolia-Okhotsk ocean has already closed in Late Jurassic. © 2017, Editorial Department of Earth Science. All right reserved.

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