Geothermal fluxes of alkalinity in the Narayani river system of central Nepal
Geothermal fluxes of alkalinity in the Narayani river system of central Nepal
复制标题
DOI：
10.1029/2004gc000719
复制
发表时间：
2004-08-25
影响因子：
3.5
通讯作者：
France-Lanord, C
中科院分区：
文献类型：
--
作者：
Evans, MJ;Derry, LA;France-Lanord, C
在尼泊尔中部喜马拉雅山脉前的陡峭的峡谷中有许多温泉。温泉流体的总溶解固体（TDS）高达7000 mg/L，Na+和K+通常占阳离子电荷的50%以上，表明高温硅酸盐蚀变是温泉碱度的主要来源。HCO3-通常是主要阴离子。锶同位素比值从热液流体中发现的值的范围相似的寄主岩石，并意味着显着的流体-岩石相互作用与当地岩性。为了确定热液溶质负荷对当地和区域河流化学的影响，我们使用化学质量平衡方法来量化温泉流量。泉水普遍富含锗（Ge），具有高但可变的Ge/Si。喜马拉雅河上游的温泉区Ge/Si系统像其他未受污染的河流，但下游，他们是高度异常的，与Ge/Si从2到20 μ mol/mol。Ge和Si在泉水和河流混合过程中表现保守，河流和泉水[Ge]和Ge/Si比值之间的巨大差异使锗成为温泉输入的有效示踪剂。我们使用Ge/Si质量平衡来估计各个河流系统的春季通量。我们的研究结果表明，整个纳拉亚尼流域的季风前春季流量约为2 m（3）/s（不确定性系数为2），或总纳拉亚尼河流量的0.5%。我们估计，在10月至5月的低流量季节，泉水为纳拉亚尼系统提供了25（+/-15）%的硅酸盐碱度。现有的季风季节数据表明，季风期间春季通量增加了2 - 3倍，但这种增加的流量被总体河流流量增加高达10倍所稀释。纳拉亚尼的年河流流量加权平均泉流量为3.0 +/-1.2 m（3）/s;热液蚀变对这一大型河流系统的硅酸盐碱度年流量贡献约为10%。
Numerous hot springs flow within the steeply incised gorges of the central Nepal Himalayan front. The spring fluids have total dissolved solids (TDS) up to 7000 mg/L and Na+, and K+ typically comprise >50% of the cationic charge, indicating that high-temperature silicate alteration is the dominant source of hot spring alkalinity. HCO3- is normally the dominant anion. Sr isotope ratios from the hydrothermal fluids are similar to the range of values found in the host rocks and imply significant fluid-rock interaction with local lithologies. To determine the impact of the hydrothermal solute load on the local and regional river chemistry, we use a chemical mass balance approach to quantify the hot spring discharge. The springs are ubiquitously enriched in germanium (Ge) with high but variable Ge/Si. Himalayan rivers upstream of the hot spring zones have Ge/Si systematics like other unpolluted rivers, but downstream they are highly anomalous, with Ge/Si from 2 to 20 mumol/mol. Ge and Si appear to behave conservatively during mixing of spring and river, and the large disparity between river and spring [Ge] and Ge/Si ratios makes germanium an effective tracer of hot spring input. We use the Ge/Si mass balance to estimate the spring flux to individual river systems. Our results show that the premonsoon spring flow over the entire Narayani basin is about 2 m(3)/s (with a factor of 2 uncertainty), or 0.5% of the total Narayani river discharge. We estimate that the springs provide 25 (+/-15)% of the silicate-derived alkalinity to the Narayani system during the low-flow season from October to May. Available monsoon season data indicate that the spring flux increases during the monsoon by a factor of 2-3, but this increased flow is diluted by the up to 10 x increase in overall river flow. The annual river discharge-weighted mean spring flux is 3.0+/-1.2 m(3)/s for the Narayani; hydrothermal alteration contributes similar to10% of the annual flux of silicate alkalinity to this large river system.