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<p>Oxygen and other light elements comprise up to 5 wt% of the Earth’s outer-core, and may significantly influence its physical properties and the operation of the geodynamo. Here we report in situ X-ray diffraction measurements of Fe, Fe + 4.5 FeO (atomic proportion), and Fe<sub>2</sub>O<sub>3</sub> melts at 177-440 GPa, achieved using laser-driven shock compression at an x-ray free-electron laser. The melts exhibit Fe-O coordination numbers between 4.0(0.4) and 4.5(0.4), indicating predominantly four-fold coordination environments. These coordination states are significantly smaller than those of Fe-bearing lower-mantle phases such as bridgmanite and ferropericlase. Shorter Fe-Fe interatomic distances in compressed iron oxide melts drive the denser packing relative to ambient melts, while the structural differences between Fe + 4.5 FeO and Fe<sub>2</sub>O<sub>3</sub> melts under shock indicate that the oxidation state modulates oxygen solubility in liquid Fe. At 177 GPa (&#xa0;~&#xa0;380 km below the core-mantle boundary) and 3800 K, Fe<sub>2</sub>O<sub>3</sub> melts exhibit higher Fe-O coordination, suggesting that local variations in oxygen content could contribute to the stratification in the uppermost outer-core inferred from seismological and geomagnetic observations.</p>

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Structural evolution of iron oxides melts at Earth’s outer-core pressures

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月10日

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  • Céline Crépisson,
  • Mila Fitzgerald,
  • Domenic Peake,
  • Patrick G. Heighway,
  • Thomas Stevens,
  • Adrien Descamps,
  • David McGonegle,
  • Alexis Amouretti,
  • Karim K. Alaa El-Din,
  • Michal Andrzejewski,
  • Sam Azadi,
  • Erik Brambrink,
  • Carolina Camarda,
  • David A. Chin,
  • Samuele Di Dio Cafiso,
  • Ana Coutinho Dutra,
  • Hauke Höppner,
  • Kohdai Yamamoto,
  • Phani S. Karamched,
  • Zuzana Konôpková,
  • Motoaki Nakatsutsumi,
  • Norimasa Ozaki,
  • Danae N. Polsin,
  • Jan-Patrick Schwinkendorf,
  • Georgiy Shoulga,
  • Cornelius Strohm,
  • Minxue Tang,
  • Harry Taylor,
  • Monika Toncian,
  • Yizhen Wang,
  • Jin Yao,
  • Gianluca Gregori,
  • Justin S. Wark,
  • Karen Appel,
  • Marion Harmand,
  • Sam M. Vinko

摘要

Oxygen and other light elements comprise up to 5 wt% of the Earth’s outer-core, and may significantly influence its physical properties and the operation of the geodynamo. Here we report in situ X-ray diffraction measurements of Fe, Fe + 4.5 FeO (atomic proportion), and Fe2O3 melts at 177-440 GPa, achieved using laser-driven shock compression at an x-ray free-electron laser. The melts exhibit Fe-O coordination numbers between 4.0(0.4) and 4.5(0.4), indicating predominantly four-fold coordination environments. These coordination states are significantly smaller than those of Fe-bearing lower-mantle phases such as bridgmanite and ferropericlase. Shorter Fe-Fe interatomic distances in compressed iron oxide melts drive the denser packing relative to ambient melts, while the structural differences between Fe + 4.5 FeO and Fe2O3 melts under shock indicate that the oxidation state modulates oxygen solubility in liquid Fe. At 177 GPa ( ~ 380 km below the core-mantle boundary) and 3800 K, Fe2O3 melts exhibit higher Fe-O coordination, suggesting that local variations in oxygen content could contribute to the stratification in the uppermost outer-core inferred from seismological and geomagnetic observations.