In this study we determined rubidium isotope ratios in twenty-one commonly used international geological reference materials, including igneous, sedimentary and metamorphic rocks, as well as an IAPSO seawater reference material. All δ⁸⁷Rb results were obtained relative to the NIST SRM 984 reference material. For most reference materials, Rb was purified using a single column loaded with Sr-spec resin. For reference materials containing low Rb but high mass fractions of matrix elements (such as basic rock and seawater), Rb was purified using two-column chromatography, with the first column packed with AGMP-50 resin and the second column packed with Sr-spec resin. Two methods for instrumental mass bias correction, sample-standard bracketing (SSB) mode, and the combined sample-standard bracketing and Zr internal normalisation (C-SSBIN) method, were compared for Rb isotopic measurements by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). The long-term reproducibility of Rb isotopic measurements using both methods was similar, better than 0.06‰ (2s, standard deviation) for NIST SRM 984. Significant Rb isotopic fractionation was observed among the reference materials, with an overall variation in δ⁸⁷Rb values of approximately 0.5‰. The δ⁸⁷Rb values of igneous rocks ranged from -0.28‰ to +0.06‰, showing a trend from heavier isotopic compositions in mafic rocks to lighter δ⁸⁷Rb values in the more evolved felsic rocks. The sedimentary and metamorphic rocks had Rb isotope ratios similar to those of igneous rocks. The δ⁸⁷Rb values of the reference materials related to low-temperature geological processes showed a wider range than those of high-temperature processes. Notably, the IAPSO seawater reference material had a δ⁸⁷Rb value of +0.14‰, which deviated from that of igneous rocks, and represents the heaviest reservoir of Rb isotopes found thus far on Earth. The comprehensive dataset presented here has the potential to serve for quality assurance purposes, and provide a framework for interlaboratory comparisons of Rb isotope ratios.

中文翻译：

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国际地质标准物质铷同位素比值

在这项研究中，我们测定了 21 种常用的国际地质标准物质（包括火成岩、沉积岩和变质岩）以及 IAPSO 海水标准物质中的铷同位素比率。所有 δ ⁸⁷Rb 结果是相对于 NIST SRM 984 参考材料获得的。对于大多数参考材料，铷是使用装有 Sr 规格树脂的单柱纯化的。对于含有低 Rb 但基质元素质量分数较高的标准物质（如基性岩和海水），采用双柱色谱法纯化 Rb，第一根柱填充 AGMP-50 树脂，第二根柱填充 Sr-spec树脂。比较了两种仪器质量偏差校正方法，即样品标准包围 (SSB) 模式以及样品标准包围和 Zr 内部归一化组合 (C-SSBIN) 方法，通过多接收器电感耦合等离子体质量进行 Rb 同位素测量光谱测定（MC-ICP-MS）。使用两种方法进行 Rb 同位素测量的长期再现性相似，优于 0.06‰ (2NIST SRM 984 的s ，标准差）。在参考材料中观察到显着的 Rb 同位素分馏，δ ⁸⁷ Rb 值的总体变化约为0.5‰。火成岩的δ ⁸⁷ Rb值范围为-0.28‰至+0.06‰，呈现出从镁铁质岩石中较重的同位素组成到较演化的长英质岩石中较轻的δ ⁸⁷ Rb值的趋势。沉积岩和变质岩的铷同位素比与火成岩相似。与低温地质过程相关的参考资料的δ ⁸⁷ Rb值显示出比高温过程更宽的范围。值得注意的是，IAPSO 海水参考材料的 δ ⁸⁷Rb值为+0.14‰，与火成岩的Rb值存在偏差，是迄今为止地球上发现的最重的Rb同位素储库。这里提供的综合数据集有可能用于质量保证目的，并为铷同位素比率的实验室间比较提供框架。