Stable silicon isotopes of groundwater, feldspars, and clay coatings in the Navajo Sandstone aquifer, Black Mesa, Arizona, USA.
Stable silicon isotopes of groundwater, feldspars, and clay coatings in the Navajo Sandstone aquifer, Black Mesa, Arizona, USA.
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DOI：
10.1016/j.gca.2009.02.005
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发表时间：
2009-04
影响因子：
5
通讯作者：
R. B. Georg;Chen Zhu;B. Reynolds;A. Halliday
中科院分区：
文献类型：
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作者：
R. B. Georg;Chen Zhu;B. Reynolds;A. Halliday
我们提出了一些地下水中溶解硅（Si）稳定同位素组成的初步分析。选取美国亚利桑那州黑梅萨地区纳瓦霍砂岩含水层的地下水样品，分析了该含水层中碎屑长石和次生粘土包覆层的Si同位素组成。采用高分辨率多收集器电感耦合质谱（HR- mc - icp - ms） （Nu1700和NuPlasma HR）测量硅同位素组成。石英为主的块状岩石和长石分选物的δ30Si值相近，分别为- 0.09±0.04‰和- 0.15±0.04‰（±95% SEM），粘土分选物的同位素比长石轻0.4‰。从同位素质量平衡的考虑，共存的水溶液的δ30Si值应该比原生硅酸盐重。仅在浅层含水层中发现了正的δ30Si值，其中Si同位素最有可能在长石溶解和随后的粘土矿物形成过程中分馏。而δ30Si沿流道递减，从0.56‰降至- 1.42‰，是迄今为止发现的天然水体中最负的溶解Si同位素组成。我们推测28si的富集是由于纳瓦霍砂岩中部分次生粘土矿物和低温硅质颗粒的溶解作用所致。δ30Si值沿地下水流动路径的大范围和系统变化的发现说明了稳定Si同位素在破译沉积盆地Si循环、追踪流体流动和评估全球Si循环方面的潜在用途。
We present some of the first analyses of the stable isotopic composition of dissolved silicon (Si) in groundwater. The groundwater samples were from the Navajo Sandstone aquifer at Black Mesa, Arizona, USA, and the Si isotope composition of detrital feldspars and secondary clay coatings in the aquifer were also analyzed. Silicon isotope compositions were measured using high-resolution multi-collector inductively coupled mass spectrometry (HR-MC-ICP-MS) (Nu1700 & NuPlasma HR). The quartz dominated bulk rock and feldspar separates have similar δ30Si of −0.09±0.04‰ and −0.15±0.04‰ (±95% SEM), respectively, and clay separates are isotopically lighter by up to 0.4‰ compared to the feldspars. From isotopic mass-balance considerations, co-existing aqueous fluids should have δ30Si values heavier than the primary silicates. Positive δ30Si values were only found in the shallow aquifer, where Si isotopes are most likely fractionated during the dissolution of feldspars and subsequent formation of clay minerals. However, δ30Si decreases along the flow path from 0.56‰ to −1.42‰, representing the most negative dissolved Si isotope composition so far found for natural waters. We speculate that the enrichment in28Si is due to dissolution of partly secondary clay minerals and low-temperature silcretes in the Navajo Sandstone. The discovery of the large range and systematic shifts of δ30Si values along a groundwater flow path illustrates the potential utility of stable Si isotopes for deciphering the Si cycling in sedimentary basins, tracing fluid flow, and evaluating global Si cycle.