Mesozoic–Cenozoic tectonic–palaeogeographical evolution of Bayingobi Basin: response to subduction and collision of the Mongol–Okhotsk Ocean plate

The structures, sedimentary fill and magmatic rocks of sedimentary basins are the products of regional tectonic evolution and are crucial to studying the basin's tectonic–palaeogeographical environment and regional tectonic evolution. The present study discusses the zircon U–Pb dating of volcanic rock samples, in situ Hf isotope and whole-rock geochemistry analysis, and the palaeogeographical, sedimentary filling and tectonic background of the Bayingobi basin through outcrop and core descriptions of Meso-Cenozoic strata, stratigraphic correlation and lithofacies analysis. The U–Pb age of the volcanic rocks is 132–102 Ma, and the in situ Hf isotopic values range from −20.99 to +29.48. The 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopic ratios of the volcanic rocks are 0.707049–0.879761 and 0.511846–0.512540, respectively, and the Nd isotopic values range from −0.62 to −6.83. The volcanic rocks in the basin have the characteristics of continental margin island arc volcanic rocks (CAA) with loss of Nb and Ta and enrichment of Pb, originating mainly from dehydration melting of the subducting plate. The lower Cretaceous Bayingobi, Suhongtu and Yingen Formations developed specifically delta–lacustrine deposits. The lower and upper member of the Bayingobi Formation was deposited in the Berriasian to Valanginian and Valanginian to late Aptian, respectively. The Suhongtu Formation was deposited during the late Aptian to early Albian and was controlled by the strike of the Engeer Us fault. The Yingen Formation was deposited in the late faulted depression stage in the late Albian. Because of the subduction of the Mongol–Okhotsk Ocean plate in the Early Cretaceous, several depressions (sags) were formed in the Bayingobi basin, accompanied by the eruption of continental plate margin island arc magmas. With the closure of the Mongol–Okhotsk Ocean in the late Early Cretaceous, the basin was uplifted as a whole and the Upper Cretaceous Ulansuhai Formation was deposited. Supplementary material : Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.7105807