Low temperature thermochronological analysis and geological significance in the North of the Western Margin of the Ordos Basin: A case study of the Mo'er Gou section in the Wuhai region

Abstract

The northern part of the western margin of the Ordos Basin is in the contact part of several tectonic units (Alxa Block, Hexi Corridor Transitional Zone, Ordos Block), with a special tectonic position, which makes it an ideal area for the study of the process of surface action and tectonic dynamics evolution. Since the Mesozoic, the region has experienced multiple phases of tectonic deformation and uplift. A great deal of work has been done on the tectonic features and attributes（Liu et al., 1998; Darby and Ritts, 2002; Huang et al.,2015; Guo et al., 2018）, but there is a lack of corresponding chronological constraints. In this article we carry out a low-temperature thermochronological study of six sandstones in the area, combining AFT, U-Th/He and thermal history simulations to explore the late uplift cooling process and geological response in the study area. The peak age distribution of the fission track samples ranges from 66-150Ma, all much younger than the produced stratigraphic age, and the length distribution ranges from 12.16-13.3μm, suggesting that the samples underwent an annealing cooling effect. The analysis of single particle age and thermal history simulation results indicate that the study area was influenced by the Yanshan Movement. It began to rapidly uplift from the Late Jurassic to the Early Cretaceous, reached its maximum paleogeothermal temperature in the Late Jurassic, and then rapidly uplifted to partially annealing zones. After a period of slow uplift since the Cenozoic era, it underwent the Himalayan Movement and rapidly uplifted to the surface. In summary, the tectonic evolution process in the northern western margin of the Ordos Basin is closely related to the interaction between adjacent tectonic units, and the Late Jurassic tectonic uplift indicated by thermochronology corresponds to the formation of thrust fold structures in the western margin.   Acknowledgments This work was supported by The PetroChina Changqing Oilfield Company Science and Technology Major Project (ZDZX 2021-01). Reference Liu S. F. 1998. The coupling mechanism of basin and orogen in the western Ordos Basin and adjacent regions of China. Journal of Asian Earth Sciences, 16(4): 369-383. Huang X.F., Shi W., Chen P. and Li H.Q. 2015. Superposed deformation in the Helanshan Structural Belt: Implications for Mesozoic intracontinental deformation of the North China Plate. Journal of Asian Earth Sciences, 114: 140-154. Darby B.J. and Ritts B.D. 2002. Mesozoic contractional deformation in the middle of the Asian tectonic collage: The intraplate western Ordos fold-thrust belt, China. Earth and Planetary Science Letters，205(1-2): 13-24. Guo P., Liu C.Y., Wang J.Q., Deng Y., Mao G.Z. and Wang W.Q. 2018．Detrital-zircon geochronology of the Jurassic coal-bearing strata in the western Ordos Basin, North China: Evidences for multi-cycle sedimentation. Geoscience Frontiers, 9(6): 1725-1743.