Hydrochemical and isotopic characteristics of geothermal fluids in Tongzhou District,Beijing,and their geothermal significance
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    Abstract:

    Tongzhou,as a sub-center of Beijing city,is rich in geothermal resources and has a huge demand for clean energy for regional construction.This paper aims to grasp the hydrochemical isotopic characteristics of geothermal fluids in the area,understand the recharge,circulation,and thermal storage temperature distribution of the Jixian karst geothermal system,and provide scientific support for the development and protection of geothermal resources in the city.Methods: Based on a full understanding of the tectonic and geological conditions in the study area,this paper uses water chemistry and 2H,18O,3H,14C,and n(87Sr)/n(86Sr) isotopic tracers to carry out the work.Results:In the western part of Tongzhou district,within the Daxingdian uplift tectonic unit,the water age increases from northwest (18 ka) to southeast (27 ka) with a transport rate of about 1.5 m/a,and the reservoir temperature increases from 57.4 ℃ to 86.5 ℃.The Xiadian fault in the southeast is a hydraulic and thermal conductivity fault on which the geothermal water age decreases to 8.4 ka,while the reservoir temperature increases to 107.8 ℃.Both strontium content and strontium isotope values in geothermal water increase along the direction of groundwater runoff, revealing the superimposed effects of two processes: dissolution of strontium in Jixian system carbonates and decay of 87Rb,the latter showing a significant time-accumulation effect,which is more evident in the southeastern part of the study area.Conclusions: The recharge source is atmospheric precipitation in the northwestern or northern mountainous areas of Beijing,with an average recharge elevation of 1510 m.The age and temperature of geothermal water in the thermal reservoir show obvious tectonic control characteristics. Regionally,changes in strontium content and strontium isotope values can effectively trace the transport of geothermal fluids and the degree of water—rock interaction.

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YUAN Lijuan, ZHANG Jinping, HE Yuncheng, KONG Xiangjun, GAO Jian.2021. Hydrochemical and isotopic characteristics of geothermal fluids in Tongzhou District, Beijing, and their geothermal significance[J]. Geological Review,67(5):1545-1556.

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History
  • Received:April 12,2021
  • Revised:June 28,2021
  • Adopted:
  • Online: September 20,2021
  • Published: September 15,2021