Instrumental mass fractionation during sulfur isotope analysis by secondary ion mass spectrometry in natural and synthetic glasses
Instrumental mass fractionation during sulfur isotope analysis by secondary ion mass spectrometry in natural and synthetic glasses
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通过二次离子质谱法对天然和合成玻璃中的硫同位素进行仪器质量分馏
DOI：
10.1016/j.chemgeo.2021.120318
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发表时间：
2021
期刊：
影响因子：
3.9
通讯作者：
Taracsák Z
中科院分区：
文献类型：
--
作者：
Taracsák Z
硫同位素比值是地球化学中最常研究的同位素体系之一。虽然硫同位素比分析的材料，如散装岩石样品，气体和硫化物颗粒常规进行，原位分析的硅酸盐玻璃，如那些在岩浆系统中形成的是相对稀缺的文献。尽管近年来尝试了一些分析硫同位素比率在火山和实验玻璃的二次离子质谱（西姆斯），仪器质量分馏（IMF）在分析过程中的影响仍然知之甚少。在这项研究中，我们使用超过600硫同位素分析的9种不同的玻璃，以消除基质效应，在硫同位素分析的玻璃西姆斯。样品的主要元素组成，硫含量和硫同位素比值的独立的方法进行了表征。我们的玻璃含有500和3400 ppm之间的硫，并涵盖了广泛的组成范围，包括低硅碧玄岩，流纹岩和响岩，使我们能够调查组成依赖的IMF。我们使用西姆斯在多收集模式与法拉第杯/电子倍增器检测器配置，以实现测量的δ 34 S的不确定度为0.3‰至2‰（2σ）。在高硫含量下，我们的西姆斯分析的分析误差类似于批量分析方法，如气源同位素比质谱。我们发现，IMF造成的偏移量为-12 ‰至+1‰之间的散装硫同位素比值和西姆斯测量。仪器质量分馏与玻璃硫含量非线性相关，并与玻璃Al，Na和K含量相结合的多元回归模型。ln（S）和Al-Na-K模型都能够以良好的准确度预测IMF：在应用成分相关IMF校正后，我们的分析的84%（ln（S））和87%（Al-Na-K）可以在2σ组合分析不确定度内重现。推动货币基金组织的进程很难确定。在我们的数据集中，玻璃S含量和IMF之间的非线性相关性类似于先前记录的在通过西姆斯进行D/H比分析期间玻璃H2O丰度和IMF之间的相关性，并且可以归因于32 S −和34 S −离子产率随着S含量和玻璃组成的变化而变化。然而，在我们的数据集中不能确定S离子产率和S含量之间的明确相关性。我们推测，在西姆斯火山口底部的碱积累可能是成分依赖IMF的主要驱动力。尽管如此，其他目前未知的因素也可能影响西姆斯分析玻璃S同位素比期间观察到的IMF。我们的研究结果表明，使用多种，以及具有广泛的组成范围内的特点的标准是需要校准西姆斯仪器之前，未知的硅酸盐玻璃的硫同位素分析。基质效应与玻璃铝钠钾含量是特别重要的长英质系统，碱和铝的含量可以变化相当多的镁铁质岩浆。
Sulfur isotope ratios are among the most commonly studied isotope systems in geochemistry. While sulfur isotope ratio analyses of materials such as bulk rock samples, gases, and sulfide grains are routinely carried out, in-situ analyses of silicate glasses such as those formed in magmatic systems are relatively scarce in the literature. Despite a number of attempts in recent years to analyse sulfur isotope ratios in volcanic and experimental glasses by secondary ion mass spectrometry (SIMS), the effects of instrumental mass fractionation (IMF) during analysis remain poorly understood. In this study we use more than 600 sulfur isotope analyses of nine different glasses to characterise the matrix effects that arise during sulfur isotope analysis of glasses by SIMS. Samples were characterised for major element composition, sulfur content, and sulfur isotope ratios by independent methods. Our glasses contain between 500 and 3400 ppm sulfur and cover a wide compositional range, including low-silica basanite, rhyolite, and phonolite, allowing us to investigate composition-dependent IMF. We use SIMS in multi-collection mode with a Faraday cup/electron multiplier detector configuration to achieve uncertainty of 0.3‰ to 2‰ (2σ) on measuredδ34S. At high sulfur content, the analytical error of our SIMS analyses is similar to that of bulk analytical methods, such as gas-source isotope ratio mass spectrometry. We find IMF causes an offset of −12‰ to +1‰ between bulk sulfur isotope ratios and those measured by SIMS. Instrumental mass fractionation correlates non-linearly with glass sulfur contents and with a multivariate regression model combining glass Al, Na, and K contents. Both ln(S) and Al-Na-K models are capable of predicting IMF with good accuracy: 84% (ln(S)) and 87% (Al-Na-K) of our analyses can be reproduced within 2σcombined analytical uncertainty after a correction for composition-dependent IMF is applied. The process driving IMF is challenging to identify. The non-linear correlation between glass S content and IMF in our dataset resembles previously documented correlation between glass H2O abundance and IMF during D/H ratio analyses by SIMS, and could be attributed to changes in32S−and34S−ion yields with changing S content and glass composition. However, a clear correlation between S ion yields and S content cannot be identified in our dataset. We speculate that accumulation of alkalis at the SIMS crater floor may be the principal driving force of composition-dependent IMF. Nonetheless, other currently unknown factors could also influence IMF observed during S isotope ratio analyses of glasses by SIMS. Our results demonstrate that the use of multiple, well-characterised standards with a wide compositional range is required to calibrate SIMS instruments prior to sulfur isotope analyses of unknown silicate glasses. Matrix effects related to glass Al-Na-K contents are of particular importance for felsic systems, where alkali and aluminium contents can vary considerably more than in mafic magmas.
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