Characteristics and Formation Mechanism of the Geothermal Field in the North China Downfaulted Basin

The geothermal field is mainly controlled by the regional tectonic framework characterized by alternationsof uplifted and depressed basement. and exhibits a similar zoned distribution of temperatures. In the upliftedarea the geothermal gradient (G) and terrestrial heat flow value(q) of the Cenozoic sedimentary cover are rela-tively high, with G=3.5-5.0℃/100m and q=63-84mW/m~2; whereas in the depressions they are rela-tively low, with G=2.7-3.5℃/100m and q=46-59mW/m~2. In the whole region, G=3.58℃/100m and q=61.5±13.4nW/m~2, indicating a comparatively high geothermal background and the presence of localgeothermal anomalies. A comparison of the results of mathematical simulation of the geothermal field with themeasured values shows a good agrecment between them. The geothermal difference between various tectonicunits is caused chiefly by the lateral and vertical variation of thermal properties of shallow crustal rocks. Thisphenomenon can be regarded as the result of redistribution of relatively uniform heat flows from the deep crustin the surficial part of the crust in the process of their upward conduction.

Characteristics and Formation Mechanism of the Geothermal Field in the North China Downfaulted Basin

Abstract The geothermal field is mainly controlled by the regional tectonic framework characterized by alternations of uplifted and depressed basement, and exhibits a similar zoned distribution of temperatures. In the uplifted area the geothermal gradient (G) and terrestrial heat flow value(q) of the Cenozoic sedimentary cover are relatively high, with G = 3.5 ? 5.0°C / 100 m and q = 63-84 mW / m²; whereas in the depressions they are relatively low, with G = 2.7?3.5°C / 100 m and q = 46-59 mW / m². In the whole region, ? = 3.581°C / 100 m and q = 61.5± 13.4 nW/ m², indicating a comparatively high geothermal background and the presence of local geothermal anomalies. A comparison of the results of mathematical simulation of the geothermal field with the measured values shows a good agreement between them. The geothermal difference between various tectonic units is caused chiefly by the lateral and vertical variation of thermal properties of shallow crustal rocks. This phenomenon can be regarded as the result of redistribution of relatively uniform heat flows from the deep crust in the surficial part of the crust in the process of their upward conduction.