西藏搭格架地热区天然水的水化学组成与稳定碳同位素特征

为探究青藏高原搭格架地热区地热水、湖水、河水、冰雪融水等天然水体的水化学组成及物质来源控制因子，于2014年8月对该地区进行了考察和取样。利用紫外-可见光分光光度计和ICP-OES测定了水样中各阴、阳离子含量，利用Gas Bench连接同位素质谱仪测定了水样中溶解无机碳（DIC）同位素比值。结果表明，地热水中总溶解固体（TDS）含量为977.13~1 279.50 mg/L，阳离子以K+和Na+为主，阴离子以HCO3-和Cl-为主，湖水的TDS含量为77.81~810.94 mg/L，阳离子以Na+和Ca2+为主，阴离子以HCO3-(CO32-)和SO42-为主，地热水和湖水的水化学类型为HCO3-Na型；河水和冰雪融水的各离子含量较低，水化学类型为HCO3-Ca型；地热水的DIC浓度范围为9.2~15.4 mmol/L，δ13CDIC值为-9.09‰~-0.95‰；湖水的DIC浓度为1.1~9.7 mmol/L，δ13CDIC值为-8.84‰~-0.27‰。根据水化学Gibbs分布模式图判断出区域水化学特征主要受硅酸盐岩风化控制，以钠长石和钾长石风化为主，但是地热水的水化学组分受到硅酸盐岩和蒸发盐岩共同控制。通过碳同位素比值分析对区域主要风化过程中CO2的来源示踪表明，湖区周围的硅酸盐风化其碳源主要为土壤CO2，热泉区硅酸盐水解其碳源为地球深部CO2输入。 

Characteristics of hydrochemical compositions and stable carbon isotope of natural water in the Daggyia geothermal field, Tibet, China

The objective of this work is to investigate the hydrochemical compositions of the geothermal water, lake water, river water, and ice- and snow-melt water as well as control factors of provenance in the Daggyia geothermal field of Tibet. The field surveys and sampling were conducted in August 2014. The main cations and anions of samples were measured using the ICP-OES and UV-visible spectrophotometer. The isotopic ratios of dissolved inorganic carbon (DIC) were analyzed using a gas stable isotope ratio mass spectrometer. The results show that the concentrations of total dissolved solids (TDS) range from 977.13 mg/L to 1 279.50 mg/L for geothermal water, and K+and Na+are the main cations, and HCO3-and Cl-are the main anions. The concentrations of TDS of the lake waters range from 77.81 mg/L to 810.94 mg/L, Ca2+, Na+, HCO3-(CO32-)andSO42-occupy the majority of ions. The hydrochemical types of both geothermal water and lake water are the type of bicarbonate-sodium. The ion concentrations of river and melt water are low, and the hydrochemical type is bicarbonate-calcium. The concentrations of DIC in geothermal water range from 9.2 mmol/L to 15.4 mmol/L, and that of δ13CDIC ranges from -9.09‰ to -0.95‰. The concentrations of DIC in lake water are 1.1 mmol/L to 9.7 mmol/L, the δ13CDIC values are -8.84‰ to -0.27‰. The Gibbs boomerang envelope of water samples indicates that the hydrochemical characteristics are mainly controlled by silicate rocks weathering in the area, and the major processes are the albite and potash feldspar weathering, while the hydrochemical compositions of geothermal water are also affected by dissolution of evaporation of salt rocks. The carbon sources of silicate weathering around the lakes are mainly soil carbon dioxide. Meanwhile the deep carbon dioxide input is the main source of silicate hydrolysis in hot spring areas. 