Phase relationships of the Fe-FeS system in conditions up to the Earth's outer core

Seiji Kamada, Hidenori Terasaki, Eiji Ohtani, Takeshi Sakai, Takumi Kikegawa, Yasuo Ohishi, Naohisa Hirao, Nagayoshi Sata, Tadashi Kondo

Research output: Contribution to journalArticlepeer-review

59 Citations (Scopus)


In situ X-ray diffraction experiments in the Fe-FeS system were performed up to 220GPa and 3300K using a laser-heated diamond anvil cell. Fe3S and ε-Fe coexisted stably up to 220GPa and 3300K, and thus, Fe3S is likely to be the stable S-bearing iron alloy under the Earth's core conditions. The solid iron (ε-Fe) also contained 7.6(0.8) at.% of sulfur at 86GPa and 2200K. The amount of sulfur in the solid iron increased with increasing pressure at the eutectic temperatures. If the sulfur content obtained in this study is extrapolated to the conditions at the inner core, all the sulfur in the solid inner core can be stored in ε-Fe.The eutectic composition becomes nonsensitive to pressure and seems to be constant around 20. at.% of sulfur at pressures above 40. GPa. The pressure gradient of the melting curve of the Fe-FeS system is 13.4(0.7) K/GPa. Based on our results of melting relationship, the temperature at the core-mantle boundary should be greater than 2850(100) K, assuming that sulfur is the only light element in the Earth's liquid outer core.

Original languageEnglish
Pages (from-to)94-100
Number of pages7
JournalEarth and Planetary Science Letters
Issue number1-2
Publication statusPublished - May 2010
Externally publishedYes


  • Fe-FeS system
  • High pressure
  • High temperature
  • In situ X-ray diffraction
  • Inner core
  • Laser-heated diamond anvil cell

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


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