天津宝坻地区地下水水文地球化学特征

Hydrogeochemical Characteristics of Groundwater in Baodi Area,Tianjin,China

天津宝坻地区地震观测井是京津冀地区的前兆敏感井,但其水文地球化学特征研究程度比较薄弱。本文选取宝坻断裂南北两侧的3个地震观测井,分析离子组分浓度、氢氧同位素组成、二氧化硅及碳同位素含量,开展水文地球化学特征研究。结果表明:(1)宝坻断裂北部的宝坻新井及周边冷水井的水化学类型以Na-SO_(4)·HCO_(3)型为主,宝坻断裂南部的王3井、王4井及周边地热井的水化学类型以Na-HCO_(3)型为主。(2)地下水来源皆为大气降水,补给区为北部燕山山地。宝坻断裂两侧的冷水和地热水位于未成熟水区,表明两者在向上运移过程中皆受到浅表冷水的混合作用。断裂南侧的地热水循环深度明显高于北侧冷水,且地热水Cl^(-)具有深部来源成因。(3)冷水和地热水的无机碳同位素表现出分区特征,断裂北侧冷水中碳酸盐矿物不饱和,断裂南侧地热水的碳来源为补给区碳酸盐矿物的淋滤作用及碳酸盐岩含水层的溶解作用。(4)宝坻断裂两侧冷水和地热水的补给区虽然同为北部燕山山地,但由于观测井所在地水文地质条件、循环路径、循环深度等差异,以及宝坻断裂对两侧地下水水文地球化学演化的控制作用,形成了断裂两侧不同类型的地下水。本文研究结果丰富了京津冀地区地球化学背景场数据,为分析区域地下流体地球化学特征提供了科学依据。

The seismic observation wells in Baodi area,Tianjin,have been the precursor sensitive wells in the Beijing-Tianjin-Hebei region,but their hydrogeochemical characteristics is less studied.In this paper,three seismic observation wells on the north and south sides of the Baodi Fracture were selected to analyze the ionic component concentrations,hydrogen and oxygen isotope compositions,silica and carbon isotope contents,and to carry out hydrogeochemical characteristics,and the results show that:(1)The hydrochemical types of Baodi Xin well and the surrounding cold-water wells in the northern part of the Baodi Fracture were dominated by Na-SO_(4)-HCO_(3) types,and the hydrochemical types of Wang 3 well,Wang 4 well and the surrounding geothermal wells in the southern part of the Baodi Fracture were dominated by Na-HCO_(3) types.Wang 3 and Wang 4 wells in the southern part of Baodi Fracture and the surrounding geothermal wells are dominated by Na-HCO_(3) type of water chemistry.The source of groundwater is atmospheric precipitation,and the recharge area is the northern Yanshan Mountains.The cold water and geothermal water on both sides of the Baodi Fracture are located in the immature water zone,indicating that both of them are mixed by shallow cold water in the upward transportation process.The depth of geothermal water circulation on the south side of the fracture is significantly higher than that of the cold water on the north side,and the Cl^(-)of geothermal water has a deep origin.The inorganic carbon isotopes of the cold water and the geothermal water show zoning characteristics.The carbonate minerals in the cold water on the north side of the fracture are not saturated,and the carbon source of the geothermal water on the south side of the fracture is the leaching of carbonate minerals from the recharge zone and the dissolution of the carbonate aquifer.(4)Although the recharge zones of cold water and geothermal water on both sides of the Baodi Fracture are the same in the northern Yanshan Mountains,different types of groundwater on both sides of the fracture are formed due to the differences in hydrogeological conditions,circulation paths,and circulation depths at the locations of the observation wells,as well as the controlling effect of the Baodi Fracture on the hydrological and geochemical evolution of the groundwater on both sides of the fracture.The results of this paper enrich the geochemical background field data in the Beijing-Tianjin-Hebei region,and provide a scientific basis for exploring the geochemical characteristics of regional subsurface fluids.