Valence state of titanium in the Wark-Lovering rim of a Leoville CAI as a record of progressive oxidation in the early Solar Nebula
Valence state of titanium in the Wark-Lovering rim of a Leoville CAI as a record of progressive oxidation in the early Solar Nebula
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DOI：
10.1016/j.gca.2010.09.042
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发表时间：
2011-02
影响因子：
5
通讯作者：
K. A. Dyl;J. Simon;E. Young
中科院分区：
文献类型：
--
作者：
K. A. Dyl;J. Simon;E. Young
西蒙等人。 (2005) 报告称，与包裹体内部相比，Leoville CAI (144A) 的 Wark-Lovering 边缘 (WL) 中的富钛辉石中的 Ti3+/Ti4+ 值较低。这些电子微探针分析被解释为证据，表明 WL 边缘的生长是向氧化性更强的环境演化的表现。西蒙等人的进一步工作。 (2007) 使用 XANES 分析来论证更高的 Ti3+ 丰度，并解释了 Simon 等人的数据。 (2005) 是相邻相（特别是尖晶石）X 射线污染的结果。后期改造也被列为可能的解释。为了进一步研究 WL 轮圈中 Ti 的氧化态，我们重新分析了 Leoville 144A，以获得 Wark–Lovering 轮圈中更完整的 Ti3+/Ti4+ 值数据集。我们进行了尖晶石混合实验，以确定这是否是对 WL 轮圈中观察到的 Ti3+ 缺乏的合理解释。虽然我们在这些 WL 轮辋数据中发现的 Ti3+/Ti4+ 范围比我们最初的研究更大，但我们的新数据表明，轮辋的 Ti3+/Ti4+ 含量低于内饰的最初结论仍然有效。我们最终排除了尖晶石混合作为对我们数据的解释，并且我们发现我们的电子微探针数据和 XANES 数据之间没有明显的不一致。 CAI Ef3 的 WL 边缘也通过 EMPA 进行了分析，并与 Leoville 144A 的结果进行了比较。为了预测该假设的成分结果，我们构建了 WL 边缘中的富钛辉石、钙钛矿、Mg(g)、Ca(g)、O2(g) 和 SiO(g) 之间的反应空间。我们发现 Ti3+ 的氧化，加上钙钛矿形成造成的 Ti 损失，解释了 WL rim EMPA 分析的许多特征。我们认为，WL 边缘辉石在成分上与内部的辉石不同，并且是 WL 边缘形成过程中氧化性更强的环境的证据。
Simon et al. (2005) reported low Ti3+/Ti4+values in Ti-rich pyroxenes in the Wark–Lovering rim (WL) of a Leoville CAI (144A) as compared to the interior of the inclusion. These electron microprobe analyses were interpreted as evidence that the growth of the WL rim is the manifestation of an evolution to a more oxidizing environment. Further work by Simon et al. (2007) used XANES analyses to argue for higher Ti3+abundances and interpreted the data of Simon et al. (2005) as the result of X-ray contamination by neighboring phases, specifically spinel. Late-stage alteration was also included as a possible explanation. To investigate further the oxidation state of Ti in WL rims, we re-analyzed Leoville 144A to obtain a more complete data set of Ti3+/Ti4+values in the Wark–Lovering rims. We conducted experiments on spinel-mixing to determine whether this was a plausible explanation for the observed paucity of Ti3+in WL rims. While we found a wider range of Ti3+/Ti4+in these WL rim data than in our original study, our new data show that the original conclusion that rims are lower in Ti3+/Ti4+than interiors remains valid. We conclusively rule out spinel-mixing as an explanation for our data, and we see no clear inconsistency between our electron microprobe data and the XANES data. The WL rim of CAI Ef3 was also analyzed by EMPA and compared to the results of Leoville 144A. To predict compositional consequences of this hypothesis, we constructed a reaction space between Ti-rich pyroxene in the WL rim, perovskite, Mg(g), Ca(g), O2(g), and SiO(g). We find the oxidation of Ti3+, coupled with Ti loss via perovskite formation, explains many features of WL rim EMPA analyses. We maintain that the WL rim pyroxenes are compositionally distinct from those in the interior, and are evidence of a more oxidizing environment during WL rim formation.