Phase relations in the carbon-saturated C-Mg-Fe-Si-O system and C and Si solubility in liquid Fe at high pressure and temperature: Implications for planetary interiors

Suguru Takahashi, Eiji Ohtani, Hidenori Terasaki, Yoshinori Ito, Yuki Shibazaki, Miho Ishii, Ken ichi Funakoshi, Yuji Higo

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)

Abstract

The phase and melting relations of the C-saturated C-Mg-Fe-Si-O system were investigated at high pressure and temperature to understand the role of carbon in the structure of the Earth, terrestrial planets, and carbon-enriched extraterrestrial planets. The phase relations were studied using two types of experiments at 4 GPa: analyses of recovered samples and in situ X-ray diffractions. Our experiments revealed that the composition of metallic iron melts changes from a C-rich composition with up to about 5 wt.% C under oxidizing conditions (ΔIW = -1.7 to -1.2, where ΔIW is the deviation of the oxygen fugacity (fO2) from an iron-wüstite (IW) buffer) to a C-depleted composition with 21 wt.% Si under reducing conditions (ΔIW < -3.3) at 4 GPa and 1,873 K. SiC grains also coexisted with the Fe-Si melt under the most reducing conditions. The solubility of C in liquid Fe increased with increasing fO2, whereas the solubility of Si decreased with increasing fO2. The carbon-bearing phases were graphite, Fe3C, SiC, and Fe alloy melt (Fe-C or Fe-Si-C melts) under the redox conditions applied at 4 GPa, but carbonate was not observed under our experimental conditions. The phase relations observed in this study can be applicable to the Earth and other planets. In hypothetical reducing carbon planets (ΔIW < -6.2), graphite/diamond and/or SiC exist in the mantle, whereas the core would be an Fe-Si alloy containing very small amount of C even in the carbon-enriched planets. The mutually exclusive nature of C and Si may be important also for considering the light elements of the Earth's core.

Original languageEnglish
Pages (from-to)647-657
Number of pages11
JournalPhysics and Chemistry of Minerals
Volume40
Issue number8
DOIs
Publication statusPublished - Sep 2013
Externally publishedYes

Keywords

  • Carbon-enriched planet
  • Core composition
  • Deep carbon cycle
  • Oxygen fugacity
  • Solubility

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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