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<p>Lunar mare basalts are often rich in titanium, hosted predominantly within the mineral ilmenite (Fe<sup>2+</sup>Ti<sup>4+</sup>O<sub>3</sub>). Here, we examine ilmenite in a &#xa0;~&#xa0;3.8 billion-year-old mare basalt (Apollo rock 75035) using high-resolution electron microscopy and electron energy loss spectroscopy. A key finding is that 75035 ilmenite is itself enriched in Ti, beyond the end member of the conventional solid solution series. Using energy loss near-edge spectroscopy, we determine that the excess Ti is trivalent, with Ti<sup>3+</sup> accounting for 13% of the total Ti content. This discovery confirms the presence of trivalent Ti in lunar ilmenite, long hypothesized based on the Moon’s reducing environment. Accounting for the change in implied stoichiometry, a review of literature data suggests that Ti<sup>3+</sup> may be present in ilmenite across a wide range of lunar samples. We extrapolate known relationships from the literature to connect Ti<sup>3+</sup> to redox conditions, estimating the oxygen fugacity during crystallization of 75035 to be below the iron-wüstite buffer, <i>Δ</i>IW≤&#xa0;−&#xa0;1.6. Further quantifying the relationship between Ti valence state and oxygen fugacity would allow Ti<sup>3+</sup>-bearing ilmenite to serve as an oxybarometer able to access the reducing conditions found on many planetary bodies.</p>

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Trivalent titanium in high-titanium lunar ilmenite

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月27日

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  • Advik D. Vira,
  • Katherine D. Burgess,
  • Emily C. First,
  • Mengkun Tian,
  • Keyes M. Eames,
  • Roshan S. Trivedi,
  • Gabriella K. Dotson,
  • Dean M. Kim,
  • Tyler P. Farr,
  • Harrison Lisabeth,
  • Nobumichi Tamura,
  • Emma R. Livernois,
  • Brant M. Jones,
  • Thomas M. Orlando,
  • Zhigang Jiang,
  • Phillip N. First

摘要

Lunar mare basalts are often rich in titanium, hosted predominantly within the mineral ilmenite (Fe2+Ti4+O3). Here, we examine ilmenite in a  ~ 3.8 billion-year-old mare basalt (Apollo rock 75035) using high-resolution electron microscopy and electron energy loss spectroscopy. A key finding is that 75035 ilmenite is itself enriched in Ti, beyond the end member of the conventional solid solution series. Using energy loss near-edge spectroscopy, we determine that the excess Ti is trivalent, with Ti3+ accounting for 13% of the total Ti content. This discovery confirms the presence of trivalent Ti in lunar ilmenite, long hypothesized based on the Moon’s reducing environment. Accounting for the change in implied stoichiometry, a review of literature data suggests that Ti3+ may be present in ilmenite across a wide range of lunar samples. We extrapolate known relationships from the literature to connect Ti3+ to redox conditions, estimating the oxygen fugacity during crystallization of 75035 to be below the iron-wüstite buffer, ΔIW≤ − 1.6. Further quantifying the relationship between Ti valence state and oxygen fugacity would allow Ti3+-bearing ilmenite to serve as an oxybarometer able to access the reducing conditions found on many planetary bodies.