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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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On the Timescale of Magma Ocean Solidification and Its Chemical Consequences: 1. Thermodynamic Database for Liquid at High Pressures
Abstract We present a new method to construct an internally consistent thermodynamic model using a compilation of high‐pressure melting experiments. The steepest descent method and Monte Carlo sampling are combined to constrain all model parameters simultaneously instead of determining each parameter sequentially from relevant experiments. Our approach is applied to the published melting experiments on mantle materials to obtain the thermodynamic parameters of the MgO‐FeO‐SiO2ternary system. Inversion with the subsets of experimental data is conducted as well to investigate the source of discrepancy among existing studies, and the key parameters are found to be the thermal expansivity of SiO2and the excess volume of mixing between MgO and SiO2. Mixing between FeO and SiO2is only constrained with large uncertainty, which could also imply that oxides with low concentrations have minimal effects on melting. Constraining the thermodynamics of MgO and SiO2will be important for a better understanding of mantle melting at high pressures.
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- Award ID(s):
- 1753916
- PAR ID:
- 10453815
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 124
- Issue:
- 4
- ISSN:
- 2169-9313
- Page Range / eLocation ID:
- p. 3382-3398
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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