Seismological constraints on core composition from Fe-O-S liquid immiscibility

George Helffrich, Satoshi Kaneshima

Research output: Contribution to journalArticle

64 Citations (Scopus)

Abstract

Earth's core is composed primarily of iron (Fe) with about 10% by weight of lighter elements. The lighter elements are progressively enriched in the liquid outer core as the core cools and the inner core crystallizes. Thermodynamic modeling of Fe-O-S liquids shows that immiscible liquids can exist at outer-core pressures (136 to 330 gigapascals) at temperatures below 5200 kelvin and lead to layering in the outer core if the concentrations of the lighter elements are high enough. We found no evidence for layering in the outer core in the travel times and wave forms of P4KP seismic waves that reflect internally in the core. The absence of layers therefore constrains outer-core compositions in the Fe-O-S system to be no richer than 6 ± 1 weight % (wt %) O and 2 to 15 wt % S. A single core liquid composition of 10.5 ± 3.5 wt % S and 1.5 ± 1.5 wt % O is compatible with wave speeds and densities throughout the outer core.

Original languageEnglish
Pages (from-to)2239-2242
Number of pages4
JournalScience
Volume306
Issue number5705
DOIs
Publication statusPublished - Dec 24 2004
Externally publishedYes

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Weights and Measures
Thermodynamics
Iron
Pressure
Temperature

All Science Journal Classification (ASJC) codes

  • General

Cite this

Seismological constraints on core composition from Fe-O-S liquid immiscibility. / Helffrich, George; Kaneshima, Satoshi.

In: Science, Vol. 306, No. 5705, 24.12.2004, p. 2239-2242.

Research output: Contribution to journalArticle

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abstract = "Earth's core is composed primarily of iron (Fe) with about 10{\%} by weight of lighter elements. The lighter elements are progressively enriched in the liquid outer core as the core cools and the inner core crystallizes. Thermodynamic modeling of Fe-O-S liquids shows that immiscible liquids can exist at outer-core pressures (136 to 330 gigapascals) at temperatures below 5200 kelvin and lead to layering in the outer core if the concentrations of the lighter elements are high enough. We found no evidence for layering in the outer core in the travel times and wave forms of P4KP seismic waves that reflect internally in the core. The absence of layers therefore constrains outer-core compositions in the Fe-O-S system to be no richer than 6 ± 1 weight {\%} (wt {\%}) O and 2 to 15 wt {\%} S. A single core liquid composition of 10.5 ± 3.5 wt {\%} S and 1.5 ± 1.5 wt {\%} O is compatible with wave speeds and densities throughout the outer core.",
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