Iron speciation is linked to oxygen fugacity; hence the Fe 3+ /ΣFe ratio of glasses can reveal the oxygen fugacity of the system where they last equilibrated. Previous studies using X-ray Absorption Near Edge Structure (XANES) spectroscopy in silicate glasses and olivine-hosted melt inclusions have shown that arc basalts are more oxidized than mid-ocean ridge basalts (MORB) and oceanic island basalts (OIB). However, Cottrell et al. (2018) recently demonstrated that hydrous glasses can experience beam-induced oxidation during XANES analysis, leading to an overestimation of their Fe 3+ /ΣFe ratios. Here, we determined Fe 3+ /ΣFe ratios in olivine-hosted melt inclusions from various arc, MORB and OIB localities by Mossbauer and XANES spectroscopy. We carried out a careful evaluation of beam damage during XANES measurements that included detailed analysis of consecutive XANES spectra and collection of time series on hydrous basaltic and basanitic glasses using different radiation doses. Fe 3+ /ΣFe ratios obtained using both spectroscopy methods on the same sample set allowed us to confirm the oxidation state of those magmas and the reliability of our approach to avoid the effect of beam-induced oxidation during XANES analysis. Our results show that melt inclusions from MORBs, OIBs and arc basalts display mean Fe 3+ /ΣFe ratios of 0.10 ± 0.05 (2σ; n = 5), 0.13 ± 0.05 (2σ; n = 2) and 0.25 ± 0.15 (2σ; n = 19), respectively , while Mount Etna melt inclusions display a mean Fe 3+ /ΣFe ratio of 0.26 ± 0.05 (2σ; n = 7). These results confirm that arc magmas are more oxidized than those from hot spots and mid-ocean ridges.

中文翻译：

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使用穆斯堡尔和 XANES 光谱测定橄榄石熔体包裹体的 Fe3+/ΣFe

铁的形态与氧逸度有关；因此，玻璃的 Fe 3+ /ΣFe 比率可以揭示它们最后平衡时系统的氧逸度。先前在硅酸盐玻璃和橄榄石熔体包裹体中使用 X 射线吸收近边结构 (XANES) 光谱的研究表明，弧形玄武岩比洋中脊玄武岩 (MORB) 和大洋岛玄武岩 (OIB) 更容易氧化。然而，科特雷尔等人。(2018) 最近证明，含水玻璃在 XANES 分析过程中会经历光束诱导的氧化，导致其 Fe 3+ /ΣFe 比率被高估。在这里，我们通过 Mossbauer 和 XANES 光谱确定了来自不同弧、MORB 和 OIB 位置的橄榄石熔体包裹体中的 Fe 3+ /ΣFe 比率。我们在 XANES 测量期间对光束损伤进行了仔细评估，其中包括对连续 XANES 光谱的详细分析以及使用不同辐射剂量的含水玄武岩和玄武岩玻璃的时间序列收集。在同一样本集上使用两种光谱方法获得的 Fe 3+ /ΣFe 比率使我们能够确认这些岩浆的氧化状态和我们的方法的可靠性，以避免在 XANES 分析过程中光束诱导氧化的影响。我们的结果表明，来自 MORB、OIB 和弧形玄武岩的熔体夹杂物的平​​均 Fe 3+ /ΣFe 比率为 0.10 ± 0.05 (2σ; n = 5)、0.13 ± 0.05 (2σ; n = 2) 和 0.25 ± 0.15 (2σ; n = 19)，而埃特纳火山熔体夹杂物的平​​均 Fe 3+ /ΣFe 比值为 0.26 ± 0.05 (2σ；n = 7)。