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High-Pressure XAFS Measurements of the Coordination Environments of Fe2+ and Fe3+ in Basaltic Glasses
  • Keisuke Ozawa,
  • Kei Hirose,
  • Yoshio Takahashi
Keisuke Ozawa
Department of Earth and Planetary Science, The University of Tokyo

Corresponding Author:keisuke-ozawa996@g.ecc.u-tokyo.ac.jp

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Kei Hirose
Tokyo Institute of Technology
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Yoshio Takahashi
The University of Tokyo
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We investigated pressure-induced changes in the coordination environments of Fe2+ and Fe3+ in basaltic glasses based on the Fe K-edge X-ray absorption fine structure (XAFS) analyses for both XANES and EXAFS regions. Upon compression from 1 bar to ~15 GPa, the Fe2+-O bond length remained similar, suggesting that the average coordination number of Fe2+ increased from ~5 to 6. On the other hand, the Fe3+-O bond was remarkably elongated, which indicates that Fe3+changed from 4-fold to 6-fold coordination. Above 15 GPa, both Fe2+-O and Fe3+-O bond lengths decreased smoothly, suggesting minor changes in their coordination numbers. The data also showed that both Fe2+ and Fe3+ remained in the high-spin state up to 83 GPa and 60 GPa, respectively, in the basaltic glasses. These compression behaviors of the Fe2+-O and Fe3+-O bonds support that Fe2+ disproportionates into Fe3+ and metal Fe in a deep magma ocean.