Light elements in Earth’s core play a key role in driving convection and influencing geodynamics, both of which are crucial to the geodynamo. However, the thermal transport properties of iron alloys at high-pressure and -temperature conditions remain uncertain. Here we investigate the transport properties of solid hexagonal close-packed and liquid Fe-Si alloys with 4.3 and 9.0 wt % Si at high pressure and temperature using laser-heated diamond anvil cell experiments and first-principles molecular dynamics and dynamical mean field theory calculations. In contrast to the case of Fe, Si impurity scattering gradually dominates the total scattering in Fe-Si alloys with increasing Si concentration, leading to temperature independence of the resistivity and less electron–electron contribution to the conductivity in Fe-9Si. Our results show a thermal conductivity of ∼100 to 110 W⋅m −1 ⋅K −1 for liquid Fe-9Si near the topmost outer core. If Earth’s core consists of a large amount of silicon (e.g., > 4.3 wt %) with such a high thermal conductivity, a subadiabatic heat flow across the core–mantle boundary is likely, leaving a 400- to 500-km-deep thermally stratified layer below the core–mantle boundary, and challenges proposed thermal convection in Fe-Si liquid outer core.
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This content will become publicly available on December 1, 2024
A hydrogen-enriched layer in the topmost outer core sourced from deeply subducted water
The Earth’s core–mantle boundary presents a dramatic change in materials, from silicate to metal. While little is known about chemical interactions between them, a thin layer with a lower velocity has been proposed at the topmost outer core (Eʹ layer) that is difficult to explain with a change in concentration of a single light element. Here we perform high-temperature and -pressure laser-heated diamond-anvil cell experiments and report the formation of SiO2 and FeHx from a reaction between water from hydrous minerals and Fe–Si alloys at the pressure–temperature conditions relevant to the Earth’s core–mantle boundary. We suggest that, if water has been delivered to the core–mantle boundary by subduction, this reaction could enable exchange of hydrogen and silicon between the mantle and the core. The resulting H-rich, Si-deficient layer formed at the topmost core would have a lower density, stabilizing chemical stratification at the top of the core, and a lower velocity. We suggest that such chemical exchange between the core and mantle over gigayears of deep transport of water may have contributed to the formation of the putative Eʹ layer.
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- Award ID(s):
- 1855624
- NSF-PAR ID:
- 10513266
- Publisher / Repository:
- Nature Geoscience
- Date Published:
- Journal Name:
- Nature Geoscience
- Edition / Version:
- 1
- Volume:
- 16
- Issue:
- 12
- ISSN:
- 1752-0894
- Page Range / eLocation ID:
- 1208 to 1214
- Subject(s) / Keyword(s):
- unknown
- Format(s):
- Medium: X Size: unknown Other: pdf
- Size(s):
- unknown
- Sponsoring Org:
- National Science Foundation
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