沉积盆地中地表实测热流值的分布特点——以华北盆地为例

THE DISTRIBUTION CHARACTERISTICS OF THE MEASURED HEAT FLOW IN A SEDIMENTARY BASIN

作者根据华北盆地已发表的实测热流数据和部分钻孔温度数据,用统计分析的方法研究了盆地内地表热流值的分布规律,并以保定—歧口地质剖面为例,介绍采用反演法求取区域背景热流值的方法。实测资料和理论计算结果说明,沉积盖层较薄的基岩隆起区地表热流值相对较高;沉积盖层较厚的基岩坳陷区地表热流值相对较低,且热流值沿深度变化,一般在热导率差异较大的两种岩层界面上热流值的变化最大。

Based on the 26 of the measured and 139 of the estimated heat flow data, and also the borehole temperature loggings published for the northern part of the North China Basin, the distribution pattern of the surface heat flow within the basin was studied by statistical analysis. The data show that the tectonic structure, i.e. uplift or depression, especially convex and concave, with the great difference in the thermo-physical properties between the very thick sedimentary cover and the basement rocks, controls the distribution of the surface heat flow. Usually, the surface heat flow of the convex area can be 1.2—1.7 times as much as that of the concave area. While the ratio of the maximum and minimum surface heat flow can be as much as 2.0. A very clear division of the three different categories of heat flow data is a necessary step for the heat flow studied in the area. Generally speaking, the surface heat flow reflects the shallow geological structures of the basin and the possible influence by groundwater; the average surface heat flow is just the statistical mean value of the measured surface heat flow; the residual heat flow is the background heat flow obtained by the correction of the measured surface heat flow for different influencing factors like that of the groundwater movement. This heat flow value indicates the regional thermal background, and therefore should be considered as an important basis for the study on thermal structure of the lithosphere and the earth dynamics. Usually, the value of the average heat flow is close to that of the back ground heat flow only when the heat flow measurements of the area are sufficient in the studied area. Taking the Baoding——Qikou geological profile as an example, this paper demonstrates the method for calculating the residual heat flow using an inverse approach. The calculated result is matched with the measured surface heat flow according to the least square root principle. Results show that the variation of the measured surface heat flow in different tectonic subregions of the basin is a result of the redistribution of surface heat flow at shallower depth of the earth's crust.