Meso-Cenozoic lithospheric dynamic evolution in the Ordos Basin, China: insight from the study on geothermal and lithospheric thermal structure 

Abstract

Research on geothermal play a significant role linking to surface processes and mantle dynamics, especially the deep process of lithospheric evolution to a certain extent. The Ordos Basin, located in the Western North China Craton (WNCC), is a significant petroliferous basin, yielding more than 60 million tons of oil and gas equivalents every year. It has been confirmed by undergoing large-scale lithospheric thinning at the end of the Early Cretaceous (130~90Ma), but investigation involving its lithospheric thermal structure in the Mesozoic and Cenozoic are limited. In addition, there are still great divergences on the understanding of the current lithospheric thickness of the Ordos Basin, some scholars believe that the basin still maintains a 200 km thick "lithospheric root" (Zhu et al., 2012), but others believe that it is only 78 km-120 km (Ren et al., 2007; Jiao et al., 2013). In this study, we employ 1-D steady-state, heat conduction equation to calculate mantle heat flow and its partitioning, Moho temperature as well as thermal lithospheric thickness of different tectonic units in the Ordos Basin based on the analysis of thermal history reconstruction and crustal layering models. The results suggest that the peak of mantle heat flow at the end of the Early Cretaceous varied between 46.65 mW/m2 and 62.97 mW/m2, far exceeded 50% of surface heat flow, which showed a typical “hot mantle and cold crust” type of lithospheric thermal structure, and the lithospheric thinning reached a minimum thickness of 50~75km. It is followed by thermal decay phase in the Late Cretaceous, and a significant vertical thickening of lithosphere occurred this period, where the lithospheric thickness increased to 78~133km by the end of Late Cretaceous. Since the Cenozoic, the ratio of mantle to surface heat flow gradually declined to less than or closely 50%. At present, the average mantle heat flow in the Ordos Basin range from 22.10 mW/m2 to 38.76 mW/m2, and the lithospheric thickness is between 81~158 km and Moho temperature entirely surpasses 600℃. In addition, we discuss potential factors and uncertainty on the thermal structure calculation. Combined with previous studies, we suggest that the lithosphere in the WNCC been thinned locally due to local asthenosphere upwelling. Acknowledgments This work was supported by the National Key Fund Project of China under Grant (No. 41630312) Reference Jiao, Y.X, Qiu, N.S, Li, W.Z., Zuo, Y.H., Que, Y.Q, Liu, F.L. (2013). The Mesozoic-Cenozoic evolution of lithospheric thickness in the Ordos basin constrained by geothermal evidence. Chin. J. Geophys, 56(9), 3051-3060 (in Chinese with English abstract). Ren, Z.L, Zhang, S., Gao, S.L., Cui, J.P., Xiao, Y.Y, Xiao, H., Tectonic thermal history and its significance on the formation of oil and gas accumulation and mineral deposit in Ordos Basin. Science in China Series D: Earth Sciences, 50(2), 27-38. (in Chinese with English abstract). Zhu, R.X., Yang, J.H., Wu, F.Y., 2012. Timing of destruction of the north china craton. Lithos 149, 51-60.