Ab Initio Prediction of Potassium Partitioning Into Earth's Core

Xiong, Zhihua; Tsuchiya, Taku; Taniuchi, Takashi

doi:10.1029/2018jb015522

Cited by 21 publications

(25 citation statements)

References 45 publications

(87 reference statements)

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“…Temperature is generally considered to be an essential factor affecting the partitioning behavior of elements (e.g., Chabot et al., 2005; Righter, 2011; Xiong et al., 2018), while the simulations in this work were conducted at a constant temperature of 5,000 K. Here, we extrapolated the metal/silicate partition coefficients of He and Ar to lower temperatures based on the Boltzmann relation (Text ). The results show that D He and D Ar decrease by approximately one order of magnitude (Figure ) as temperature decreases from 5,000 to 3,500 K. On the other hand, the density of the outer core is ∼10% lighter than pure liquid Fe, due to the presence of light elements( x ) such as H, C, O, S, Si, etc.…”

Section: Resultsmentioning

confidence: 99%

Helium and Argon Partitioning Between Liquid Iron and Silicate Melt at High Pressure

Xiong

Tsuchiya

Orman

2021

Geophysical Research Letters

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Whether Earth’s core is a significant repository of noble gases is an open question because their partitioning between liquid metal and silicate melt during core formation is poorly known. Here we calculated the He and Ar partition coefficients (D) between liquid Fe and MgSiO3 melt from 20 to 135 GPa at 5,000 K using ab initio molecular dynamics combined with thermodynamic integration. Our simulations show that DHe does not change significantly with pressure, while DAr increases strongly with increasing pressure. Furthermore, we found that the metal/silicate partitioning behaviors of He and Ar are controlled by their atomic size and the charge density properties of the host compositions. These results indicate that Earth’s core is a plausible reservoir for 3He and could possibly account for the high 3He/4He ratios in the OIBs that associated with deep‐rooted plumes, but the core is unlikely to be a significant source for 36Ar.

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Section: Resultsmentioning

confidence: 99%

Helium and Argon Partitioning Between Liquid Iron and Silicate Melt at High Pressure

Xiong

Tsuchiya

Orman

2021

Geophysical Research Letters

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“…DFT‐MD simulations give potential energy ( U ) and pressure ( P ) but not entropy ( S ) of the system; combining DFT‐MD with the thermodynamic integration method provides a general scheme for computing the Helmholtz energy ( F ) difference Δ F = F B – F A of two systems containing the same number of atoms which are governed by different potential energy functions U B (target system) and U A (reference system) (e.g., Alfè et al, 2000; Vočadlo et al, 2008; Wahl & Militzer, 2015; Xiong et al, 2018). For the metal and silicate liquids considered in this study, we use the ideal gas as reference, for which F can be calculated analytically.…”

Section: Computational Detailsmentioning

confidence: 99%

Strong Sequestration of Hydrogen Into the Earth's Core During Planetary Differentiation

Yuan

Steinle‐Neumann

2020

Geophysical Research Letters

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We explore the partitioning behavior of hydrogen between coexisting metal and silicate melts at conditions of the magma ocean and the current core–mantle boundary with the help of density functional theory molecular dynamics. We perform simulations with the two‐phase and thermodynamic integration methods. We find that hydrogen is weakly siderophile at low pressure (20 GPa and 2,500 K), and becomes much more strongly so with pressure, suggesting that hydrogen is transported to the core in a significant amount during core segregation and is stable there. Based on our results, the core likely contains ~1 wt% H, assuming single‐stage formation and equilibration at 40 GPa. Our two‐phase simulations further suggest that silicon is entrained in the core‐forming metal, while magnesium remains in the silicate phase. This preferred incorporation of silicon hints at an explanation for the elevated Mg/Si ratio of the bulk silicate Earth relative to chondritic compositions.

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“…to enable positive E J before inner core formation. The drawback here is that experiments and simulations suggest that little 40 K partitioned into the core during formation (Chidester et al, 2017;Xiong et al, 2018). Precipitation provides another potential solution, though as we have seen it introduces a number of uncertain parameters and is difficult to constrain from available observations (though see Helffrich et al, 2018).…”

Section: Towards Resolving the New Core Paradoxmentioning

confidence: 92%

“…below. We have also neglected radiogenic heating since potassium 40 is not thought to partition significantly into the core (Xiong et al, 2018). In this section we also ignore Q p and E p , but will reintroduce them when considering precipitation in Section 5.…”

Section: Evolution Of Thermal Stratificationmentioning

confidence: 99%

“…attempted to overcome the new core paradox by invoking additional effects such as a significant amount of radiogenic heating (e.g. from 40 K, Driscoll and Bercovici, 2014) or gravitational power provided by the precipitation of MgO (O'Rourke et al, 2017) or SiO 2 (Hirose et al, 2017), though the viability of all of these processes has been questioned (Xiong et al, 2018;Du et al, 2019;Arveson et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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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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Ab Initio Prediction of Potassium Partitioning Into Earth's Core

Cited by 21 publications

References 45 publications

Helium and Argon Partitioning Between Liquid Iron and Silicate Melt at High Pressure

Helium and Argon Partitioning Between Liquid Iron and Silicate Melt at High Pressure

Strong Sequestration of Hydrogen Into the Earth's Core During Planetary Differentiation

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

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