Vanadium K edge XANES of synthetic and natural basaltic glasses and application to microscale oxygen barometry
Vanadium K edge XANES of synthetic and natural basaltic glasses and application to microscale oxygen barometry
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DOI：
10.1016/j.gca.2004.10.013
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发表时间：
2005-05
影响因子：
5
通讯作者：
S. Sutton;J. Karner;J. Papike;J. Delaney;C. Shearer;M. Newville;P. Eng;M. Rivers;M. Dyar
中科院分区：
文献类型：
--
作者：
S. Sutton;J. Karner;J. Papike;J. Delaney;C. Shearer;M. Newville;P. Eng;M. Rivers;M. Dyar
描述了一种用于太阳系玄武岩玻璃的新型微型氧气压计，其基于钒 K 边 X 射线吸收近边结构 (XANES) 光谱。钒在硅质材料中丰富的元素中是独一无二的，因为它在自然界中可能以四种价态存在：V2+、V3+、V4+和V5+。因此，钒氧化还原系统是一种稳健的氧气压计，其相对于缓冲液的氧逸度覆盖至少六个数量级。该方法使用在已知 fO2 和温度条件下生产的合成玻璃标准品进行校准。使用等量合成玻璃对的 microXANES 数据对标准品和未知品之间的温度差异进行了量化校正。将该方法应用于月球、火星和陆地玻璃时，得出的 fO2 估计值从比月球玻璃的铁方铁矿 (IW) 缓冲液 (IW-1.6) 低 1.6 个对数单位，到陆地玻璃包裹体的 IW + 4.0。火星和陆地的结果与之前其他方法的估计非常一致。月球火山碎屑玻璃的推断 fO2 值比之前的估计减少约 0.5 个对数单位，但差异与分析不确定性相当。微扩展X射线吸收精细结构光谱与microXANES确定的价态一致，并为钒位点几何形状提供了额外的限制。这些结果证明了这种新型氧压计的价值，它可以无损地应用于传统薄片中的单个颗粒，具有~微米分辨率和~100 ppm元素灵敏度。
A new microscale oxybarometer for solar system basaltic glasses, based on vanadium K-edge X-ray absorption near edge structure (XANES) spectroscopy, is described. Vanadium is unique among abundant elements in siliceous materials in that it can potentially occur in nature in four valence states: V2+, V3+, V4+and V5+. Consequently, the vanadium redox system is a robust oxybarometer covering at least six orders of magnitude in buffer-relative oxygen fugacity. The method was calibrated using synthetic glass standards produced under known fO2and temperature conditions. Correction for temperature differences among standards and unknowns was quantified using microXANES data for isobaric synthetic glass couples. Application of the method to lunar, martian, and terrestrial glasses yielded fO2estimates from 1.6 log units more reduced than the iron-wüstite (IW) buffer (IW-1.6) for lunar glasses, to IW + 4.0 for terrestrial glass inclusions. The martian and terrestrial results are in good agreement with previous estimates by other methods. The inferred fO2values for lunar pyroclastic glasses are ∼0.5 log unit more reduced than previous estimates, but the differences are comparable to analytical uncertainties. Micro-extended X-ray absorption fine structure spectra were consistent with the valence states determined by microXANES and provided additional constraints on vanadium site geometry. These results demonstrate the value of this new oxybarometer, which can be applied nondestructively to individual grains in conventional thin sections with ∼ micrometer resolution and ∼100 ppm elemental sensitivity.