The Lithophile Element Budget of Earth's Core

Bethany A. Chidester*, Simon Lock, Kellie E. Swadba, Zia Rahman, Kevin Richter, Andrew J. Campbell

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

7 Citations (Scopus)
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Abstract

The relative composition of Earth's core and mantle were set during core formation. By determining how elements partition between metal and silicate at high pressures and temperatures, measurements of the mantle composition and geophysical observations of the core can be used to understand the mechanisms by which Earth formed. Here we present the results of metal-silicate partitioning experiments for a range of nominally lithophile elements (Al, Ca, K, Mg, O, Si, Th, and U) and S to 85 GPa and up to 5400 K. With our results and a compilation of literature data, we developed a parameterization for partitioning that accounts for compositional dependencies in both the metal and silicate phases. Using this parameterization in a range of planetary growth models, we find that, in general, lithophile element partitioning into the metallic phase is enhanced at high temperatures. The relative abundances of FeO, SiO2, and MgO in the mantle vary significantly between planetary growth models, and the mantle abundances of these elements can be used to provide important constraints on Earth's accretion. To match Earth's core mass and mantle composition, Earth's building blocks must have been enriched in Fe and depleted in Si compared with CI chondrites. Finally, too little Mg, Si, and O are partitioned into the core for precipitation of oxides to be a major source of energy for the geodynamo. In contrast, several ppb of U can be partitioned into the core at high temperatures, and this energy source must be accounted for in thermal evolution models.
Original languageEnglish
Article numbere2021GC009986
Number of pages29
JournalGeochemistry, Geophysics, Geosystems
Volume23
Issue number2
Early online date5 Feb 2022
DOIs
Publication statusPublished - 15 Feb 2022

Bibliographical note

Funding Information:
The authors are grateful to Ingrid Blanchard and an anonymous reviewer for thoughtful comments on the manuscript. B. A. Chidester is grateful to Kellye Pando for help completing the piston‐cylinder experiments and Minako Righter for completing the LA‐ICP‐MS measurements. This study was funded by an NSF Graduate Research Fellowship Grant # DGE‐1144082 to B. A. Chidester and NSF Grant # EAR‐1427123 to A. J. Campbell. B. A. Chidester was also funded by NASA Solar System Workings (# NNX15AH54G), the UC Office of the President Laboratory Fees Research Program (# LFR‐17‐449,059), and by the Department of Energy, National Nuclear Security Administration under Award Number DE‐NA0003842. Support for K. Righter was provided by NASA's Planetary Science Research Program. S. J. Lock acknowledges funding from the Harvard Earth and Planetary Sciences Department, the Caltech Division of Geological and Planetary Sciences, NSF through awards EAR‐1947614 and EAR‐1725349, and UK NERC Grant NE/V014129/1.

Publisher Copyright:
© 2022 The Authors.

Keywords

  • core formation
  • diamond anvil cell
  • metal-silicate partitioning
  • lithophile elements

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