华北地区上地幔温度及岩石圈厚度分布研究

Temperature is one of the most important key parameters which control viscosity and rheology of the Earth's material and hence the dynamic process of the mantle. Based on the correlation between mineral temperature and seismic velocity structure, we derived the upper mantle temperatures of North China at the depths ranging between 50 and 300 km by high-resolution S-wave tomography model. Defining the depth where the geotherm intersects the mantle adiabat with a potential temperature of 1300°C as the lithosphere-asthenosphere boundary, we estimated the correspondent lithospheric thickness in the North China. Using the inveted temperatures at 60 km depth as the bottom boundary constraints, we calculated the surface heat flow. The calculated heat flow agrees well with the observations at the surface, and the misfits for most regions of North China are within the uncertainty of the heat flow measurements. Three main characteristics can be observed from the distribution of temperature: (1) Upper mantle temperatures at shallow depths are consistent with the tectonic settings. At depths shallower than 170 km, temperatures under the tectonically active eastern part of North China are higher than that in the stable cratonic regions in the west. The regions with high mantle temperature include the Hehuai Basin, the Bohai Bay Basin, the boundary between the North China Plain and the central North China; hotter lithosphere can also be found at the northern margin of Ordos Plateau, including the Yinchuan-Hetao Rift Zone and the Yinshan Orogen. The lithospheric thickness in the regions with warmer lithosphere is about 80~100 km thick; (2) The lowest temperature is located under the Ordos Plateau in western North China, which is about 200 to 400°C lower than that in the eastern North China. The lithosphere in the Ordos block is also the thickest in the North China, which is about 140~150 km on average and 160 km in the thickest areas; (3) At depths below 170 km, the distribution pattern of the thermal structure is almost reverse to the shallower depths, where the temperatures beneath the western North China are higher than that under the eastern part. It may indicate that the two parts of the North China block had undergone different geological processes.