藏南隆子县模麓温泉群水文地球化学特征及成因机制研究

Hydrogeochemical Characteristics and Genetic Mechanism of the Molu Geothermal Springs in the Longzi County, Southern Tibet

关键词:  模麓温泉  水文地球化学  热储温度  补给来源  成因机制

Key words:  Molu geothermal spring  Hydrogeochemistry  Geothermal reservoir temperature  Recharge source  Genetic mechanism

摘要:

藏南地区地热资源丰富，是喜马拉雅地热带的重要组成部分，有望成为新的地热资源开发靶区。本文以藏南桑日-错那活动构造带内模麓温泉群为研究对象，以水化学和氢氧氚同位素为研究方法，分析模麓温泉群的水岩作用、热储温度、补给来源及径流时间，揭示了地热水的成因机制。模麓地热水pH在6.6~7.2之间，TDS为1908mg/L~2326 mg/L，水化学类型以HCO₃·Cl-Na型和HCO₃·Cl-Na·Ca型为主。地热水中主要阴阳离子来源于硅酸盐矿物的溶解和少量地球深部物质。利用硅-焓方程法和硅-焓图解法计算的初始热储温度为198℃~256 ℃，冷水混入比例为68%~85%。此外，对地热水中的Li、B、F等微量元素分析得出，研究区温泉水中微量组分除来自水-岩作用外，应该还与深部流体的混入有关，且该地区的氢氧同位素特征表明地下水补给主要来源于大气降水，补给高程为5652m~5664m，模麓地热水中的氚含量＜0.5TU，表明其地热水为老水，有更长的径流时间，为水-岩作用提供了充足的时间，而宿麦郎曲河水为新水，补给径流时间短。研究区地热水与围岩遮拉组砂板岩发生水-岩作用，进行离子交换作用，在地下水运移过程中加热形成地热水，最终在有利构造部位出露形成温泉群。本次研究初步揭示了藏南模麓温泉的成因机制，可为藏南地热资源开发利用提供理论参考。

Abstract:

The geothermal resources in southern Tibet are abundant, being an important part of the Himalayan Geothermal Belt, is expected to become a new prospective area for geothermal resource development. In this paper, we analyzed the water-rock interaction, geothermal reservoir temperature, recharge source and runoff time of the geothermal springs in the active tectonic zone of the Sangri-Cuona in southern Tibet, and then revealed the genesis mechanism of geothermal water by hydrochemistry and hydrogen-oxygen-tritium isotopes. The pH values of the Molu geothermal water ranged from 6.6 to 7.2, and the TDS values were 1908 mg/L to 2326 mg/L. The hydrochemical types were mainly HCO₃·Cl-Na and HCO₃·Cl-Na·Ca types. The main anions and cations in geothermal water were originated from the weathering of silicate minerals and minor deep materials. The initial geothermal reservoir temperatures calculated using the silica-enthalpy equation method and silica-enthalpy diagramming method were 198℃~256 ℃, and the cold water mixing percentages were 68%~85%. In addition, the analysis of Li, B, F and other trace elements in geothermal water showed that the trace components in geothermal water in the study area were not only from water-rock interaction, but also related to the mixing of deep thermal fluids in geothermal water. The hydrogen and oxygen isotope characteristics of the area show that the groundwater recharge was mainly from atmospheric precipitation, the recharge elevation is 5652 m~5664 m, and the tritium content in the geothermal water in the foot of the model was less than 0.5TU, indicated that the geothermal water was old water. It showed that there was a longer runoff time, which provided sufficient time for water-rock interaction, while the Sumai Langqu River water was fresh water and the runoff time was short. The geothermal water in the study area had water-rock interaction in the diabase rocks of the Zhela Formation, and ion exchange was carried out. In the process of groundwater migration, geothermal water formed by heating and then exposed as geothermal springs in beneficial structural positions. This study preliminarily reveals the genetic mechanism of geothermal waters in southern Tibet, which can provide theoretical reference for the development and utilization of geothermal resources in southern Tibet.