Terrestrial heat flow of Jizhong depression, China, Western Bohai Bay basin and its influencing factors

Abstract

The Jizhong depression in the western Bohai Bay Basin has a high thermal state. Heat flow is one of the most important parameters in geothermics, its measurement can help obtain a better understanding of the regional lithospheric thermal structure. In this study, continuous steady-state temperature logs were obtained from 14 deep boreholes. 136 core samples were measured for thermal conductivity and radiogenic heat production. The temperature data indicated that heat transfer within the sedimentary layer was dominated by heat conduction, with a geothermal gradient of approximately 31.5 ℃•km−1. The gradient value was almost 0 ℃•km−1 in the dolomite strata, due to their abnormally high thermal conductivity and permeability. Average thermal conductivity values was 2.46, 5.51 and 3.21 W•m−1•K−1, and the radiogenic heat production were 1.05, 0.26, and 0.74 μW•m−3 for the sandstone, dolomite and metamorphic rocks, respectively. Higher heat flow in the Jizhong depression is mainly distributed around the subsurface structure of sub-uplift region, which is near the fault between the sub-uplift region and the sub-depression region, and the value can reach 120.0 mW•m−2. With an increase in the dolomite buried depths or an increase in the overlying sandstone thickness, the surface heat flow value decreases. Finally, we discuss the factors influencing the shallow temperature: the lateral sediment thickness variations can markedly influence the temperature distribution. The influence of magma activity that happened long ago can be neglected.