摘要
福建省地处华南陆缘高热流地热异常区,揭示区域地热成藏机制对指导地热科学高效利用具有重要意义.基于福建省地热地质分区,结合全省208件地热样品水化学特征与自组织神经映射与K-means耦合聚类机器学习方法,剖析了地热流体的水化学形成变化与水岩作用机制,探讨了地热系统的热源类型.结果表明,福建省内陆由隆起山地补给区至山间河谷与盆地中部地热流体水化学类型由HCO_(3)-Ca和HCO_(3)-Na·Ca型演化为HCO_(3)·SO_(4)-Na和HCO_(3)-Na型.闽中隆起山地至闽东火山断坳盆地与滨海平原深部,地热流体水化学类型呈现由HCO_(3)-Ca和HCO_(3)-Na·Ca型至HCO_(3)·SO_(4)-Na和HCO_(3)-Na型,再到ClNa·Ca和Cl-Na型演化特征.SOM-KM耦合聚类将省域地热温泉水样划分为三大类,有效区分识别了浅循环低焓低矿化度地热水、高温高氟富磷富硅深循环与海水混合补给型深循环成因地热水的空间分布.其中,浅循环低焓低矿化度地热流体受地表水与浅层地下水混合影响较大,主要分布于闽西北隆起带与闽西南碳酸盐岩-碎屑岩断陷盆地区.高氟富磷富硅深循环地热水分布于闽东火山断坳带张扭性NW向导水断裂与压性NE向阻水-导热断裂、环状火山机构放射性断裂带交汇处与火山断陷盆地中部,水化学形成受火成岩内生水及深大断裂与火山机构古封存流体的升流混合影响较为显著.海水混合补给型深循环地热水循环过程中经历了与深部海水的第一次混合以及升流过程中与浅部冷水的第二次混合过程.区域侵入岩-火山岩地热储层水化学的长期供应端元为斜长石,矿物水热蚀变指示的热储温度集中在100~150℃,在橄榄石、辉石和钙长石等优先溶解形成的方解石饱和沉淀-碳酸缓冲平衡体系制约下,热储层流体向高pH、富Na、低Ca的HCO_(3)-Na型地热水演化.从地热流体水文地球化学论据来看,福建省地热系统为无岩浆热源的深循环水热系统.
Fujian Province is one of the most important geothermal anomaly areas in China.It is of great significance for the scientific utilization of geothermal resources to reveal the formation mechanisms of geothermal system in the region.The changes in hydrochemical formation and water-rock interaction mechanism of geothermal fluidsin each hydrogeochemical zonewas clarified based on the implication of hydrochemical characteristics of 208 geothermal water samples and the machine learning methods of self-organizing map-K-means(SOM-KM)clustering.The results show that the water types of geothermal fluids from the uplifted mountainous recharge areas to the low-lying valleys and deep basin axis evolved from HCO_(3)-Ca and HCO_(3)-Na·Ca to HCO_(3)·SO_(4)-Naand HCO_(3)-Na in each intact groundwater system in inland areas.While from the central mountainous areas to the eastern volcano-graben basin and coastal plain,the water types of geothermal fluids evolved from HCO_(3)-Ca,HCO_(3)-Na·Ca to HCO_(3)·SO_(4)-Na and HCO_(3)-Na,and then Cl-Na·Ca,Cl-Na type.The SOM-KM analysis identified the spatial distribution of low-enthalpy and low-salinity shallow circulating geothermal water,high-enthalpy and P-F-SiO2 enriched deep circulating geothermal water,and deep circulation geothermal water with seawater mixing at the provincial scale effectively.Among them,the low-enthalpy shallow circulating geothermal water was significantly affected by the mixing of surface water and shallow groundwater,and mainly distributed along the steam systems of northwestern uplifted mountain region and the carbonate-clastic sedimentary basins of southeastern region.The hydrochemistry formation of high-enthalpy deep circulating geothermal water was significantly influenced by the upwelling mixing of endogenous water in igneous rocks,deep-seated faults,and ancient sealed fluids in volcanic edifice,and mainly distributed at the intersection of regional northwestern water-conducting faults with the northeastern thermal-conducting faults and the radioactive faults of the circular volcanic apparatus in eastern volcanic depression zone.The deep circulation geothermal fluid affected by seawater recharge undergone the first mixing process with the deep high-salinity seawater and the second mixing process with shallow cold water during the upwelling stage.The long-term supply end member of hydrochemistry in regional intrusive-volcanic geothermal reservoir is plagioclase,and the reservoir temperature indicated by mineral hydrothermal alteration is concentrated in the range of 100-150℃.The geothermal fluid tended to evolve towards HCO_(3)-Na water with high pH,low-Na concentration and high-Ca concentration under the constraints of super saturation precipitation of calcite-carbonate buffer equilibrium system due to the preferential dissolution of olivine,pyroxene,and anorthite in the plagioclase.The geothermal system in the bulk horizons is turned out to be deep-circulation hydrothermal systems without magmatic heat source from the hydrogeochemical evidence.
作者
孙厚云
马峰
王贵玲
朱喜
张薇
陈礼明
Sun Houyun;Ma Feng;Wang Guiling;Zhu Xi;Zhang Wei;Chen Liming(Institute of Hydrogeology and Environmental Geology,Chinese Academy of Geological Sciences,Xiamen 361021,China;Technology Innovation Center of Geothermal&Hot Dry Rock Exploitation and Development,MNR,Shijiazhuang 050061,China;Fujian Institute of Geological Survey,Fuzhou 350013,China)
出处
《地球科学》
北大核心
2025年第8期3241-3269,共29页
Earth Science
基金
中国地质科学院基本科研业务费项目(No.SK202328)
中国地质科学院青年英才项目(No.YK202305)
厦门市自然科学基金项目(No.3502Z202471066)
中国地质调查局项目(Nos.DD20230501,DD20230019)。
关键词
地热温泉
水化学
水岩作用
成因模式
自组织神经网络
福建省
水文地质
geothermal water
hydrogeochemistry
water-rock interaction
formation mode
self-organizing map
Fujian Province
hydrogeology
