Abstract:

Based on 2,706 static temperature measurements in 236 boreholes and system temperature measurements in 25 boreholes, the geothermal gradient and heat flow of Bohai basin were calculated. By setting up typical crustal structure models in this area, the mantle heat flow, deeper temperature and thermallithosphere thickness were calculated by the “stripping” method. Based on the dynamic model of the Earth, the heat flow evolution in this area was reconstructed. The results show that the background geothermal gradient is 322 ℃/km, and the heat flow is 648 mW/m2. The presentday lithosphere thickness ranges from 61 km to 69 km, and the ratio of mantle heat flow in the surface heat flow is about 60%, while the type of lithosphere geothermal structure is “hot mantle and cold crust”, and the temperature of the bottom of crust ranges from 548 ℃ to 749 ℃. The heat flow evolution coincides with the tectonic subsidence history. After three phases of heating and thinning of lithosphere, the heat flow reached the maximum (70-83 mW/m2） at the end of Dongying depositional duration. It is suggested that the basin has experienced the process of synrift phase involving the mantle and combining with multiphase alkaline basalt in the basin. As the heat flows decreasing in thermal subsidence phase, the type of basin transforms into depression.

Key words: heat flow, thermal structure of lithosphere, mantle heat flow, lithosphere thickness, tectoniothermal evolution, Bohai basin