Partitioning of Oxygen Between Ferropericlase and Earth's Liquid Core

Davies, C. J.; Pozzo, Monica; Gubbins, David

doi:10.1029/2018gl077758

Cited by 20 publications

(13 citation statements)

References 47 publications

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“…This interaction could cause the partial melting of the mantle since it is well established that the presence of the FeO component results in a decrease in the melting temperature of the mantle ferropericlase (Du & Lee, 2014). Furthermore, there is the possibility that the liquid iron in the outer core absorbs large amounts of oxygen (Davies et al, 2018; Frost et al, 2010) as well as hydrogen. Such an oxygen‐rich core would also ultimately lead to an increase in the FeO component of the bottom of the mantle via elemental partitioning between the mantle and the core.…”

Section: Discussionmentioning

confidence: 99%

Chemical Reaction Between Metallic Iron and a Limited Water Supply Under Pressure: Implications for Water Behavior at the Core‐Mantle Boundary

Nishi

Kuwayama

Hatakeyama

et al. 2020

Geophysical Research Letters

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Water transportation to the deep lower mantle via plate subduction may induce a reaction between water and iron at the core-mantle boundary. Recent experimental studies suggest that such a reaction may generate FeO 2 H x-rich domains, which can explain the seismic structures of the ultralow velocity zone in this region. In this study, the chemical reaction between metallic iron and a limited water supply at~120 GPa was investigated using time-resolved in situ synchrotron X-ray diffraction measurements in combination with the laser-heated diamond anvil cell technique. Contrary to the results of earlier studies, the formation of FeO instead of FeO 2 H x without intermediate phases was observed. Considering the unlimited availability of iron in the core and the limited water supply resulting from mantle downflow, the FeO-rich layers consisted of Fe-bearing ferropericlase and postperovskite, which must have locally cumulated at the bottom of the mantle simultaneously with hydrogen incorporation into the core. Plain Language Summary Water strongly influences the structure, dynamics, and evolution of the deep Earth. Recent experimental studies suggest that hydrous phases play an important role as carriers of surface water to the deep mantle via the subduction of oceanic plates. Such deep-water subduction processes may allow the surface water to reach the bottom of the mantle, where the mantle minerals are in direct contact with the iron at the core. Thus, the purpose of this study was to provide understanding regarding the behavior of water when it meets iron at the core-mantle boundary. To investigate the reaction between water and iron at high pressures and temperatures, experiments were performed using in situ X-ray diffraction measurements in combination with the diamond-anvil cell technique. The results obtained confirmed the formation of FeO during the reaction. Thus, the deep water cycle may produce FeO-rich layers at the core-mantle boundary, which may explain the seismic characteristics of the bottom of the mantle and at the top of the outer core.

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Section: Discussionmentioning

confidence: 99%

Chemical Reaction Between Metallic Iron and a Limited Water Supply Under Pressure: Implications for Water Behavior at the Core‐Mantle Boundary

Nishi

Kuwayama

Hatakeyama

et al. 2020

Geophysical Research Letters

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“…The partition coefficient for hydrogen between solid ringwoodite and liquid iron at pressures appropriate to the CMB was measured as ~9 (mass fraction) or ~26 (molar ratio), which implies that nearly all (~97% by number) of the hydrogen in silicates should partition into metal at thermodynamic equilibrium. Experiments have not yet constrained how composition and oxygen fugacity influence this partitioning behavior, as known for other elements (e.g., Davies et al, ; Fischer et al, ), or how partitioning may slow as the metal becomes hydrogen rich. Ultimately, mantle dynamics govern the rate at which material is delivered to the relatively thin region above the CMB where redox reaction may occur.…”

Section: Introductionmentioning

confidence: 99%

Hydrogenation of the Martian Core by Hydrated Mantle Minerals With Implications for the Early Dynamo

O’Rourke

Shim

2019

JGR Planets

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Mars lacks an internally generated magnetic field today. Crustal remanent magnetism and meteorites indicate that a dynamo existed after accretion but died roughly four billion years ago. Standard models rely on core/mantle heat flow dropping below the adiabatic limit for thermal convection in the core. However, rapid core cooling after the Noachian is favored instead to produce long‐lived mantle plumes and magmatism at volcanic provinces such as Tharsis and Elysium. Hydrogenation of the core could resolve this apparent contradiction by impeding the dynamo while core/mantle heat flow is superadiabatic. Here we present parameterized models for the rate at which mantle convection delivers hydrogen into the core. Our models suggest that most of the water that the mantle initially contained was effectively lost to the core. We predict that the mantle became increasingly ironrich over time and a stratified layer awaits detection in the uppermost core—analogous to the E′ layer atop Earth's core but likely thicker than alternative sources of stratification in the Martian core such as iron snow. Entraining buoyant, hydrogen‐rich fluid downward in the core subtracts gravitational energy from the total dissipation budget for the dynamo. The calculated fluxes of hydrogen are high enough to potentially reduce the lifetime of the dynamo by several hundred million years or longer relative to conventional model predictions. Future work should address the complicated interactions between the stratified, hydrogen‐rich layer and convection in the underlying core.

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“…( Davies et al, 2018;Pozzo et al, 2019). Since the chemical potentials are completely determined, this formulation can be shown to be equivalent to equation ( 17) by separating the chemical potentials as…”

Section: Chemical Equilibrium At the Cmbmentioning

confidence: 99%

“…Fischer et al, 2015;Badro et al, 2018;Pozzo et al, 2019). If I i < 0 then light elements leave the mantle, which almost certainly results in chemical stratification below the CMB since the chemical anomalies associated with core convection are minute and are hence unable to mix the anomalously light fluid downwards (Buffett and Seagle, 2010;Davies et al, 2018Davies et al, , 2020. Conversely, I i > 0 implies that light elements precipitate out of solution (as oxides) and underplate onto the base of the mantle; the residual fluid, slightly iron-rich compared to the fluid below, will sink via Rayleigh-Taylor instability thus helping to drive core flow (O'Rourke and Stevenson, 2016).…”

Section: Introductionmentioning

confidence: 99%

Thermo-Chemical Dynamics in Earth's Core Arising from Interactions with the Mantle

Davies¹,

Greenwood²

2021

Preprint

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Thermo-chemical interactions at the core-mantle boundary (CMB) play an integral role in determining the dynamics and evolution Earth's deep interior. This review considers the processes in the core that arise from heat and mass transfer at the CMB, with particular focus on thermo-chemical stratification and the precipitation of oxides. A fundamental parameter is the thermal conductivity of the core, which we estimate as k = 70 − 110 W m −1 K −1 at CMB conditions based on consistent extrapolation from a number of recent studies. These high conductivity values imply the existence of an early basal magma ocean (BMO) overlying a hot core and rapid cooling potentially leading to a loss of power to the dynamo before the inner core formed around 0.5 − 1 Gyrs ago, the so-called "new core paradox". Coupling core thermal evolution modelling and calculations of chemical equilibrium between liquid iron and silicate melts suggests that FeO dissolved into the core after its formation, creating a stably stratified chemical layer below the CMB, while precipitation of MgO and SiO 2 was delayed until the last 2−3 Gyrs and was therefore not available to power the early dynamo; however, once initiated, precipitation supplied ample power for field generation. We also present a possible solution to the new core paradox without requiring precipitation or radiogenic heating using k = 70 W m −1 K −1 . The model matches the present inner core size and heat flow and temperature at the top of the

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Partitioning of Oxygen Between Ferropericlase and Earth's Liquid Core

Cited by 20 publications

References 47 publications

Chemical Reaction Between Metallic Iron and a Limited Water Supply Under Pressure: Implications for Water Behavior at the Core‐Mantle Boundary

Chemical Reaction Between Metallic Iron and a Limited Water Supply Under Pressure: Implications for Water Behavior at the Core‐Mantle Boundary

Hydrogenation of the Martian Core by Hydrated Mantle Minerals With Implications for the Early Dynamo

Thermo-Chemical Dynamics in Earth's Core Arising from Interactions with the Mantle

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