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

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