北京西山谷积山背斜地热系统成因模式及远景区预测

Genetic model of Gujishan anticline geothermal system and prediction of potential areas in Western Hills of Beijing

北京西山隆起区没有天然温泉出露。近年来,在谷积山背斜相继钻井发现了40~49℃的地下热水,但对地热系统成因尚无研究。运用地质、水文地质、地球化学等方法开展研究,结果表明热储为蓟县系雾迷山组白云岩岩溶裂隙水,热水为HCO3-Ca·Mg型,为中-弱碱性、微硬度、氟水型淡热矿水,初步称为北京西山谷积山地热田。构建了地热系统成因模式,分析热源为谷积山背斜深部隐伏的燕山期酸性花岗岩体产生的放射性元素衰变生热,为隆起山地碳酸盐岩层状热储的地热系统类型,不同于一般隆起山地导热断裂对流地热系统类型。结合西山地区广泛发育的穹窿型构造与燕山期岩浆活动特征,初步预测西山下苇甸穹窿等穹窿型构造具有形成地热系统的地热地质条件,有潜力成为地热资源的富集远景区。

There is no natural hot spring outcropped in the uplift area of Beijing Western Hills(Xishan). In the past several years,geothermal water temperatures ranging from 40℃ to 49℃ were discovered through drilling of thermal water boreholes one after another in Gujishan anticline. However, the research on geothermal origin has not been carried out yet. Geological, hydrogeological and geochemical studies show that hot rock reservoir is the karst fissure water developed in dolomite rock of Wumishan Group,Jixian System. The water geochemical type is HCO3-Ca · Mg, neutral-to-weakly alkaline, micro hardness and fluorine fresh geothermal mineral water, which is named Xishan Gujishan geothermal field primarily. In this paper, the authors put forward the geothermal genetic model, and the analytical results show that the heat source is the radioactive element decay heat from the concealed acid granite pluton at the deep dome in Yanshanian period. It is of the layer carbonatite hot reservoir type located in uplifted mountain area different from the common geothermal systems of convective type developed in heat conducting faults. Based on dome structure and Yanshanian magma characteristics, the authors preliminarily predict that the domes like Xiaweidian dome in Beijing Western Hills have conditions for the formation of geothermal system, and they can be regarded as the advantage potential areas.