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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.
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Powering Earth's Ancient Dynamo With Silicon Precipitation
Abstract Earth's core has produced a global magnetic field for at least the last 3.5 Gyrs, presently sustained by inner core (IC) growth. Models of the core with high thermal conductivity suggest potentially insufficient power available for the geodynamo prior to IC formation ∼1 Ga. Precipitation of silicon from the liquid core might offer an alternative power source for the ancient magnetic field, although few estimates of the silicon partition coefficient exist for conditions of the early core. We present the first ab initio determination of the silicon partition coefficient at core‐mantle boundary conditions and use these results to confirm a thermodynamic description of partitioning that is integrated into a model of coupled core‐mantle thermal evolution. We show that models including precipitation of silicon can satisfy constraints of IC size, mantle convective heat flux, mantle temperature and a persistent ancient geodynamo, and favor an oxygen poor initial core composition.
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- Award ID(s):
- 2152686
- PAR ID:
- 10589921
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 22
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1029/2022GL100692
