Abstract The redox condition of magma determines the stability and composition of crystallizing and volatile phases in martian meteorites, reflecting the evolution of the martian interior. In the current study, direct analyses on the oxidation states of V, Cr, and Fe were performed based on the X‑ray absorption near-edge structure (XANES) measurements equipped with a micro-sized X‑ray beam. We first applied the micro-XANES (μ-XANES) technique to the olivine-hosted glass inclusion and groundmass glass of martian meteorite Yamato 980459 (Y98), which is interpreted as representing a primary melt composition. Mass-balance calculations and XANES spectra comparisons indicated that, while chromite and pyroxene affected Cr and Fe K-edge XANES spectra, the contribution of these minerals was minimal for V. The pre-edge peak intensity of V K-edge XANES enabled the estimation of the oxygen fugacity for inclusion and groundmass glasses. The calculated oxygen fugacity (fO2) of the glass inclusions was near the Iron-Wüstite (IW) buffer (IW-0.07 ± 0.32) for the glass inclusion, whereas it was 0.9 log units more oxidized (IW+0.93 ± 0.56) for the groundmass glasses. This result suggests that the redox condition of the parent magma of Y98 evolved during magma ascent and emplacement. Since Y98 is interpreted to have evolved in a closed system, our finding suggests that fractional crystallization and/or ascent of magma potentially induces the fO2 increase. This study shows that the μ-XANES technique enables us to determine the fO2 by only measuring a single phase of glassy compounds, and thus, it is useful to discuss the redox condition of volcanic rocks even if they do not crystallize out several equilibrium phases of minerals.

中文翻译：

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钒微XANES测定火星原始shergottite Yamato 980459橄榄石玻璃包裹体和基质玻璃中的氧逸度

摘要 岩浆的氧化还原条件决定了火星陨石中结晶相和挥发相的稳定性和组成，反映了火星内部的演化过程。在当前的研究中，基于配备微型 X 射线束的 X 射线吸收近边结构 (XANES) 测量，对 V、Cr 和 Fe 的氧化态进行了直接分析。我们首先将微 XANES (μ-XANES) 技术应用于火星陨石 Yamato 980459 (Y98) 的橄榄石玻璃包裹体和地块玻璃，这被解释为代表主要熔体成分。质量平衡计算和 XANES 光谱比较表明，虽然铬铁矿和辉石影响 Cr 和 Fe K-edge XANES 光谱，但这些矿物对 V 的贡献最小。V K-edge XANES 的前边缘峰值强度能够估计夹杂物和地块玻璃的氧逸度。计算得出的玻璃夹杂物的氧逸度 (fO2) 接近于玻璃夹杂物的铁-方铁矿 (IW) 缓冲液 (IW-0.07 ± 0.32)，而对于玻璃夹杂物而言，它的氧化程度高 0.9 log 单位 (IW+0.93 ± 0.56)地块眼镜。这一结果表明，Y98 母岩浆的氧化还原条件是在岩浆上升和侵位过程中演化而来的。由于 Y98 被解释为在封闭系统中演化，我们的发现表明部分结晶和/或岩浆上升可能导致 fO2 增加。这项研究表明，μ-XANES 技术使我们能够仅通过测量玻璃状化合物的单相来确定 fO2，因此，