Genesis of the heat flow anomaly in Yanqing basin, NW Beijing

Geophysical survey of basal structure is important for providing information that can help us to understand the genesis of heat flow anomaly. Using data from the recently completed regional gravity survey, the field source edge detection and density interface inversion are used to obtain the Cenozoic basement morphology and fault distribution characteristics in Yanqing basin. Meanwhile, we calculate the heat flow of 17 boreholes from its temperature logging data and the regional thermal conductivity measurement data, then analyze the tectonic setting of heat flow anomaly. The result reveals that (1) The basement relief of Yanqing basin can be divided into "one uplift, four sags and one monoclinic", including Dongwuliying uplift, Yaojiaying sag, Zhanglaoying sag, Tiansongying sag, Zhuojiaying sag and Kangzhuang-Shenjiaying monoclinic. The Yanqing basin is mainly developed by two NE-trending faults, and six nearly SN-trending faults which connect with the recharge area of south and north mountains and cut NE-trending faults, forming a crisscross shallow fault network. (2) The average value of heat flow in Yanqing basin is 65. 8 +/- 113. 0 mW . m(2), which is slightly lower than that of Bohai Bay basin. There are two abnormal areas of high heat flow, one is the convergence area of Kangzhuang-Shenjiaying fault and Jinjiapu fault, the other is the transition zone between the Xizhuojiaying sag and the Dongwuliying uplift. (3) The heat flow anomaly in Yanqing basin is mainly related to the distribution and thickness variation of the Jixian carbonates with high thermal conductivity and the heat flow redistribution promoted by groundwater thermal activity which is controlled by multi-system shallow faults, while it has little relationship with the development of FoyukouHuangbaisi fault and the intrusion of Yanshanian granite.