Abstract: The North Beijing Geothermal Field includes Xiaotangshan and Shahe sub-geothermal fields, distributing as a triangle in plan. It borders Huangzhuang-Gaoliying Fault on the southeast, Nankou-Sunhe Fault on the southwest, and Asuwei-Xiaotangshan Fault on the north. The thermal reservoirs are the fissure aquifers of carbonate karsts among Wumishan Formation and Tieling Formation of Jixian System, and Cambrian-Ordovician System. The cover rocks of thermal reservoir are impermeable strata of sandstone and shale of Qingbaikou system, sandstone and shale of Carboniferous-Permian and volcanic rocks of Jurassic. Its plane characteristic of geo-temperature is marked by two hyper thermal areas in Xiaotangshan and Tang11. The vertical characteristic is such that the temperature increases with depth at the rate being lower in the thermal reservoirs and higher in the cover rocks. The compositions of δD-δ¹⁸O in rainwater, groundwater and geothermal water are almost on the Craig Atmosphere Precipitation Line in the area. The diagram shows that the natural rainfall is the geothermal water source. In hydrochemical diagram of geothermal water in Beijing area, the geothermal water is under urban thermal water. It shows that the North Beijing geothermal water is closer to cold water replenished area than the urban geothermal water. The distributing of ³H in geothermal water is higher in the north and lower in the south, and the dating of ¹⁴C of geothermal water is increasing from north to south. So we can conclude that the geothermal water flows from north to south. This shows that the atmosphere precipitation infiltrating underground from the northern mountain area flows from the karst area of Ming Tombs-Taoyukou, striding over Asuwei-Xiaotangshan Fault, then circulating in the deep and being heated by geothermal. At last it flows into and is stored in the North Beijing area, forming a geothermal field. Based on the above-mentioned characteristics, the genetic model of North Beijing geothermal system is built and defined as a mid-low temperature convective type geothermal system in North Beijing.

Key words: geothermal water, geo-temperature field, hydro-geochemistry, genetic model of geothermal system, North Beijing Geothermal Field

摘要： 京北地热田包括小汤山和沙河2个次级地热田,呈三角形展布,东南部边界为黄庄-高丽营断裂,西南部边界为南口-孙河断裂,北部边界为阿苏卫-小汤山断裂。热储层为蓟县系雾迷山组、铁岭组和寒武系—奥陶系碳酸盐岩岩溶裂隙含水层,热储盖层为青白口系页岩、石炭系—二叠系砂页岩和侏罗系火山岩隔水层。该地热田地温场的平面特征是在小汤山镇和汤11井区出现2个高温区;垂向特征是随埋深加大,地温升高,但热储层内垂向增温率较低,热储盖层垂向增温率较高。该区雨水、地下冷水和热水的氢氧同位素组成基本上都落在克雷格降水线上,表明区内热水来源于大气降水。在地下水化学三线图解中,该区热水位于城区热水的下方,说明京北热水比城区热水更靠近冷水补给区。热水的³H值表现出北高南低的特点,¹⁴C年龄也由北往南逐渐增大,说明热水自北向南流动。由此认为,由北部山区渗入地下的大气降水,经小汤山以北的十三陵—桃峪口岩溶水分布区,跨过阿苏卫-小汤山断裂后发生深循环并被地热加温,流入京北地区后在该地区赋存,形成热田。根据上述特征,建立了京北地热田地热系统的成因模式并定义为京北中低温对流型地热系统。

关键词: 热水, 地温场, 水文地球化学, 地热系统模式, 京北地热田