Fe Kα XANES, Fe Kβ HERFD XANES and EPMA flank method determinations of the oxidation state of Fe in garnet
Fe Kα XANES, Fe Kβ HERFD XANES and EPMA flank method determinations of the oxidation state of Fe in garnet
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Fe Kα XANES、Fe Kβ HERFD XANES 和 EPMA 侧翼法测定石榴石中 Fe 的氧化态
DOI：
10.1016/j.chemgeo.2024.121937
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发表时间：
2024
期刊：
影响因子：
3.9
通讯作者：
Newville, Matthew
中科院分区：
文献类型：
--
作者：
Holycross, Megan;Cottrell, Elizabeth;Ague, Jay;Lanzirotti, Antonio;Newville, Matthew
石榴石的铁与总铁的比值（Fe 3 +/∑Fe）可以与热力学矿物活性模型配对，以量化含石榴石岩石的氧逸度。然而，具有高分析和空间分辨率的技术是必要的，以区分石榴石Fe 3 +/∑Fe比率在百分比水平上的差异，并准确地测量被分区或包含夹杂物的石榴石。通过常规Fe Kα和高分辨能量荧光探测（HERFD）、Fe Kβ X射线吸收近边结构（XANES）谱和电子探针侧面法对27个橄榄岩和榴辉岩石榴石样品进行了分析，并用穆斯堡尔谱测定了Fe 3 +/∑Fe比值，以评价每种方法的精度。我们检查了三个XANES光谱特征的能量和强度随Fe 3 +/∑Fe比的变化：1）两个后边缘特征的强度比（I比;仅Fe Kα）; 2）Fe边缘在90%归一化强度下的能量（E0.9;仅Fe Kα）和3）前边缘质心能量（Fe Kα和HERFD Fe Kβ）。与前人的工作一致，我们发现石榴石边缘前心的能量对Fe ~（3+）/∑Fe比值相对不敏感。橄榄岩和榴辉岩石榴石的I-比率在低Fe 3 +/∑Fe比率（≤0.13）时相互抵消; I-比率石榴石XANES校准是成分特异性的。的E0.9功能是独立的石榴石的主要元素组成的光谱已被校正的自吸收的影响。我们根据E0.9特征的变化产生两种Fe Kα石榴石XANES校准;一种校准包括所有石榴石参考材料（Fe 3 +/∑Fe高达1.0;“所有石榴石校准”），另一种校准特定于具有低Fe 3 +/∑Fe比率的石榴石（“低铁校准”）。根据八种石榴石参考物质的最多25次侧边法测量的平均值计算的Fe 3 +/∑Fe比值与穆斯堡尔法测量的Fe 3 +/∑Fe比值的一对一相关性的绝对值在4%以内。经三次分析，侧翼法计算的Fe ~（3+）/∑Fe比值的标准误差与穆斯堡尔法测定的Fe ~（3+）/∑Fe比值的标准误差在3%以内接近。侧面法的精度在更高的束流下得到提高，然而，在这里测试的任何微探针分析条件下，侧面法的精度都没有接近XANES的精度。石榴石参考资料详细介绍这里可通过要求史密森学会。
The ferric to total iron ratios (Fe3+/∑Fe) of garnets can be paired with thermodynamic mineral activity models to quantify the oxygen fugacity of garnet-bearing rocks. However, techniques with a high analytical and spatial resolution are necessary to distinguish differences in garnet Fe3+/∑Fe ratios at the percent level and to accurately measure garnets that are zoned or contain inclusions. We acquired conventional Fe Kα and high-resolution energy fluorescence detection (HERFD) Fe Kβ X-ray absorption near edge structure (XANES) spectra and electron microprobe flank method analyses on a suite of 27 peridotitic and eclogitic garnets with Fe3+/∑Fe ratios previously determined by Mössbauer spectroscopy to evaluate the precision of each technique. We examined variations in the energy and intensity of three XANES spectral features as a function of Fe3+/∑Fe ratios: 1) the intensity ratio of two-post edge features (I-ratio; Fe Kα only); 2) the energy of the Fe edge at 90% normalized intensity (E0.9; Fe Kα only) and 3) the pre-edge centroid energy (Fe Kα and HERFD Fe Kβ). In accordance with previous work, we find the energies of garnet pre-edge centroids are relatively insensitive to Fe3+/∑Fe ratios. The I-ratios of peridotitic and eclogitic garnets are offset from each other at low Fe3+/∑Fe ratios (≤0.13); I-ratio garnet XANES calibrations are composition-specific. The E0.9feature is independent of garnet major element composition in spectra that have been corrected for the effects of self-absorption. We produce two Fe Kα garnet XANES calibrations based on variations in the E0.9feature; one calibration with all garnet reference materials included (Fe3+/∑Fe up to 1.0; “all garnet calibration”) and another calibration specific to garnets with low Fe3+/∑Fe ratios (“low ferric calibration”). Fe3+/∑Fe ratios calculated from the mean of up to 25 flank method measurements on eight garnet reference materials fall within 4% absolute of a one-to-one correlation with Fe3+/∑Fe ratios measured by Mössbauer. The standard error of the mean Fe3+/∑Fe ratio calculated from flank method approaches the Mössbauer-determined Fe3+/∑Fe ratio within estimated error (3%) after three analyses. Flank method precision is enhanced at higher beam current; however, the precision of the flank method does not approach the precision of XANES under any microprobe analytical condition tested here. Garnet reference materials detailed here are available by request to the Smithsonian Institution.
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影响因子：
3.1
作者：
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DOI：
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期刊：
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影响因子：
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影响因子：
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作者：
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影响因子：
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通讯作者：
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