临界区硅同位素的解释

IF 1.9 3区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
P. Frings, M. Oelze, Franziska Schubring, D. Frick, F. von Blanckenburg
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引用次数: 7

摘要

金属和准金属稳定同位素比率已成为临界区风化、元素循环和输出的潜在有力指标。这些同位素比率的最简单的解释框架有三个参数:(i)经历风化的母体矿物的同位素比率,(ii)溶质和新次生相之间的元素分配,以及(iii)与新次生相形成相关的分馏因素。以硅为例,我们展示了这三个参数是如何沿着花岗岩类基岩上三个地点定义的侵蚀率和风化层停留时间的梯度变化的。这些地点从瑞士阿尔卑斯山脉中部动力学有限的罗纳河谷到构造不活跃且供应有限的斯里兰卡高地,内华达山脉是中等风化强度的地点。在每个地点,初级矿物比30Si/28Si的比值跨度>0.4‰。这些矿物的天气不同,因此从岩石中溶解的硅的同位素比值在三个地点不同,不一定等于整体基岩成分。硅在次生粘土和溶质之间的分配反映在粘土的矿物学和化学成分中:更强烈的风化产生贫硅粘土。因此,粘土组合物包括对任何分馏因子可以表达的程度的一阶质量平衡控制。最后,与粘土形成相关的硅同位素分馏因子随粘土矿物学系统地变化:硅贫化粘土矿物的形成与较大的分馏因子有关。分馏的程度可能与铝的相对可用性在机制上有关。这些发现提供了使用硅同位素比率作为定量指标来探索硅循环和重建现在和过去风化所需的框架。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Interpreting silicon isotopes in the Critical Zone
Metal and metalloid stable isotope ratios have emerged as potentially powerful proxies for weathering, element cycling and export in the Critical Zone. The simplest possible interpretative framework for these isotope ratios has three parameters: (i) the isotope ratio of the parent minerals undergoing weathering, (ii) the partitioning of the element between solute and the new secondary phases, and (iii) the fractionation factors associated with the formation of new secondary phases. Using the example of silicon, we show how all three of these parameters vary along a gradient of erosion rate and regolith residence time defined by three sites located on granitoid bedrock. These sites run from the kinetically limited Rhone Valley in the Central Swiss Alps to the tectonically inactive and supply-limited Sri Lankan highlands, with the Sierra Nevada mountains as a site of intermediate weathering intensity. At each site, primary mineral specific 30Si/28Si ratios span >0.4‰. These minerals weather differentially, such that the isotope ratio of silicon solubilised from rock differs at the three sites and is not necessarily equal to bulk bedrock composition. The partitioning of silicon between secondary clay and solute is reflected in the clay mineralogy and chemical composition: more intense weathering produces Si-poor clays. The clay composition thus comprises a first-order mass-balance control on the extent to which any fractionation factor can be expressed. Finally, the Si isotope fractionation factor associated with clay formation varies systematically with clay mineralogy: the formation of Si-deplete clay minerals is associated with larger fractionation factors. The magnitude of the fractionation may be mechanistically linked to relative aluminium availability. These findings provide the framework needed to use Si isotope ratios as a quantitative proxy to explore Si cycling and reconstruct weathering in the present and past.
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来源期刊
American Journal of Science
American Journal of Science 地学-地球科学综合
CiteScore
5.80
自引率
3.40%
发文量
17
审稿时长
>12 weeks
期刊介绍: The American Journal of Science (AJS), founded in 1818 by Benjamin Silliman, is the oldest scientific journal in the United States that has been published continuously. The Journal is devoted to geology and related sciences and publishes articles from around the world presenting results of major research from all earth sciences. Readers are primarily earth scientists in academia and government institutions.
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