Buikin Alexei Ivanovich, Kuznetsova Olga Vitalievna, Velivetskaya Tatiana Alexeevna, Sevastyanov Vyacheslav Sergeevich, Ignatiev Alexander Vasilievich
Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Kosygin str. 19, Moscow, 119991, Russia.
Far East Geological Institute, Far Eastern Branch of the Russian Academy of Sciences, Prospect 100-letya Vladivostoku 159, Vladivostok, 690022, Russia.
Rapid Commun Mass Spectrom. 2020 Nov 30;34(22):e8923. doi: 10.1002/rcm.8923.
The study of multi-isotope systematics of fluid inclusions is of great importance for understanding of the sources and evolution of fluid phases in mantle rocks and ore deposits. The most appropriate technique for such investigations is a (stepwise) crushing method that is widely used for noble gases and nitrogen. However, because of the possible influence of mechanochemical reactions and back sorption, analyses of the isotope composition of water extracted by crushing from fluid inclusions are challenging.
An isotope ratio mass spectrometry (IRMS)-based method for hydrogen (and oxygen) isotopic analysis in sub-microliter volumes of water extracted from fluid inclusions by crushing is presented. The verification of the possible influence of adsorption processes and mechanochemical reactions on the results of isotope analysis was performed for the first time. For that a series of parallel analyses of hydrogen isotopic ratios from water inclusions in quartz applying physically different extraction methods (crushing and thermodecrepitation) was conducted.
Four series of quartz aliquots were analyzed: three series extracting water by crushing (two series for δ H values and one for δ O values) and one by thermodecrepitation. The mean value for the crushing results is δ H = -85.3 ± 3.6 ‰ (1σ, n = 11), which coincides well with the thermodecrepitation data (-86.3 ± 2.0 ‰, 1σ, n = 5), suggesting that our methodological approach allows the influence of back sorption or mechanochemical reactions during the crushing experiment to be minimized. The reproducibility of the oxygen isotopic ratios is ±0.9 ‰ (1σ, n = 5).
The conducted experiments have shown that the influence of back sorption or mechanochemical reactions during crushing on isotopic results is not crucial for our method. The developed IRMS-based method for hydrogen (and oxygen) isotopic analysis in sub-microliter volumes of water is well applicable for multi-isotope investigations of gases extracted from fluid inclusions. As an application a well-defined Ar/ Ar-δ H correlation in mantle rocks is presented for the first time.
流体包裹体的多同位素系统研究对于理解地幔岩石和矿床中流体相的来源及演化至关重要。进行此类研究最合适的技术是（逐步）压碎法，该方法广泛用于稀有气体和氮的研究。然而，由于机械化学反应和反向吸附的可能影响，通过压碎从流体包裹体中提取的水的同位素组成分析具有挑战性。
提出了一种基于同位素比率质谱（IRMS）的方法，用于分析通过压碎从流体包裹体中提取的亚微升体积水中的氢（和氧）同位素。首次对吸附过程和机械化学反应对同位素分析结果的可能影响进行了验证。为此，对石英中水样的氢同位素比率进行了一系列平行分析，采用了物理上不同的提取方法（压碎和热爆裂）。
分析了四组石英试样：三组通过压碎提取水（两组用于δH值，一组用于δO值），一组通过热爆裂提取水。压碎结果的平均值为δH = -85.3 ± 3.6‰（1σ，n = 11），与热爆裂数据（-86.3 ± 2.0‰，1σ，n = 5）非常吻合，这表明我们的方法可以将压碎实验过程中反向吸附或机械化学反应的影响降至最低。氧同位素比率的重现性为±0.9‰（1σ，n = 5）。
所进行的实验表明，压碎过程中反向吸附或机械化学反应对同位素结果的影响对我们的方法而言并不关键。所开发的基于IRMS的亚微升体积水中氢（和氧）同位素分析方法非常适用于流体包裹体中提取气体的多同位素研究。作为一个应用实例，首次展示了地幔岩石中明确的Ar/Ar - δH相关性。
