帕米尔高原东北缘中高温地热流体水文地球化学特征及成因机制

Hydrogeochemical Characteristics and Genesis of Medium-High Temperature Geothermal System in Northeast Margin of Pamir Plateau

帕米尔构造结东北缘中高温地热资源丰富,前人的研究多限于研究单个地热田,缺乏区域的系统性研究.基于帕米尔高原东北缘的地热地质特征,以地热流体地球化学研究作为认识地热资源的有效手段,根据研究区8个温泉水、1个冷泉水、11个热井水以及6个地表水的理化数据,进行了水化学成因、特征及同位素分析,揭示帕米尔北东侧区域性地热流体的热储温度特征及冷却机制的演化模式,为帕米尔北东侧地热资源勘探提供一定的地球化学依据.研究结果表明,地热水中主量离子主要受钠/钾长石、阳离子交换作用以及岩浆水的影响,热水样品B/Cl、B/Li、B/Cs、Li/Cs、Na/Cl、K/Cl的高相关性特征显示热水可能有共同的母质地热储层.氢氧同位素特征表明地热水受大气降水、雪融水及深部岩浆水补给.多种溶质温度计、硅-焓模型以及氯-焓模型重建了热水的热储温度、冷却过程及演化模式,推断出研究区下方可能存在多个热储层,其中最深部的母质热储的温度约为358~418℃,Cl含量约为300~400 mg/L.结合区域地质及地热地质条件分析,认为帕米尔高原东北缘地热异常为地壳中的熔融岩浆及高产热花岗岩共同作用的结果.

The northeast margin of Pamir tectonic junction is enriched with medium-high temperature geothermal resources.Most previous studies are limited to a single geothermal field and lack of regional systematic research.Here,it applies geothermal hydrogeochemistry as an effective method to study geothermal resources.Based on the geothermal geological characteristics of the northeast margin of the Pamirs Plateau,the hydrochemical genesis,characteristics and isotope analysis of 8 hot spring water,1 cold spring water,11 hot well water and 6 surface water in the study area were analyzed and revealed the evolution characteristics of regional geothermal fluid thermal reservoir and cooling mechanism in the northeast of Pamir.It provides a certain geochemical basis for the exploration of geothermal resources in the northeast of Pamir.The results show that the major ions in geothermal water are mainly originated from sodium/potassium feldspar,cation exchange and magmatic water.The high correlation of ratio in B/Cl、B/Li、B/Cs、Li/Cs、Na/Cl、K/Cl shows that hot water probably has a common parent geothermal fluid.The characteristics of hydrogen and oxygen isotopes indicate that geothermal water is recharged by atmospheric precipitation,snowmelt water and deep magmatic water.A variety of solute thermometers,silicon-enthalpy model and chlorine-enthalpy model were used to reconstruct the geothermal reservoir temperature,cooling process and evolution mode of geothermal groundwater.It inferred that there may be multiple thermal reservoirs under the study area,which the temperature of the deepest parent geothermal fluid storage is about 358-418°C with the Cl-concentrations about 300-400 mg/L.Combined with regional geology and geothermal geological conditions analysis,it believes the geothermal anomaly in the northeast margin of the Pamir Plateau is a result of uncooling magma in the crust and high radioactive granite.