Structure of a mushy layer under hypergravity with implications for Earth's inner core

Huguet, Ludovic; Alboussière, Thierry; Bergman, Michael; Deguen, Renaud; Labrosse, S.; Lesœur, Germain

doi:10.1093/gji/ggv554

Cited by 33 publications

(26 citation statements)

References 124 publications

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“…For a more accurate description of the process of crystal growth, it is interesting to generalize the present theoretical approach to describe the growth of non-spherical crystals, just as was done in describing the growth of ellipsoidal particles in metastable magnetic liquids [57]. It is also of interest to make a theoretical generalization of the bulk and directional crystallization for modelling solidification processes in the presence of a mushy layer (two-phase region) that is widely encountered in various fields of physics [58][59][60][61][62][63][64].…”

Section: Resultsmentioning

confidence: 99%

On the theory of crystal growth in metastable systems with biomedical applications: protein and insulin crystallization

Alexandrov

Nizovtseva

2019

Phil. Trans. R. Soc. A.

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Section: Resultsmentioning

confidence: 99%

On the theory of crystal growth in metastable systems with biomedical applications: protein and insulin crystallization

Alexandrov

Nizovtseva

2019

Phil. Trans. R. Soc. A.

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“…The top of the mush is coincident with the ICB to be consistent with the sharpness of the seismic velocity jump at the ICB (Fearn et al 1981), and the mush is thought to be strongly influenced by convection. Huguet et al (2016) use experimental methods to suggest that mush convection is the dominant regime in the inner core, leaving a matrix with a solid fraction close to unity without the effect of compaction (a collapsing mush). If the inner core grows dendritically then a slurry layer cannot overlay a mush, since dendrites would grow to the point where the liquidus and adiabat intersect at the top of the F-layer which would have been seismically visible.…”

Section: Discussionmentioning

confidence: 99%

A Boussinesq slurry model of the F-layer at the base of Earth’s outer core

Wong

Davies

Jones

2018

Geophysical Journal International

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S U M M A R YSeismic observations suggest that a stably stratified layer, known as the F-layer, 150-300 km thick exists at the bottom of Earth's liquid outer core. These observations contrast with the density inferred from the Preliminary Reference Earth Model (PREM), which assumes an outer core that is well-mixed and adiabatic throughout. The liquid core is composed primarily of iron alloyed with a light component. A thermal boundary layer produces the opposite effect on the density profile compared with the observations, and single phase, thermochemical models do not provide a sufficient dynamic description of how light element is transported across the F-layer into the overlying liquid outer core. We therefore propose that the layer can be explained by a slurry on the liquidus, whereby solid particles of iron crystallize from the liquid alloy throughout the layer. The slurry model provides a dynamic explanation of how light element can be transported across a stable layer. We make two key assumptions, the first of which is fast-melting where the timescale of freezing is considered short compared to other processes. The second assumption is that we consider a binary alloy where the light element is purely composed of oxygen, which is expelled entirely into the liquid during freezing. We present a steady state 1-D box model of a slurry formulated in a reference frame moving at the speed of inner core growth. We ascertain temperature, light element concentration and solid flux profiles by varying the layer thickness, inner core heat flux and thermal conductivity, since there is some uncertainty in these estimates. Our solutions demonstrate that the steady state slurry can satisfy the geophysical constraints on the density jump across the layer and the core-mantle boundary heat flux.

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“…In addition to the high value of the Schmidt number, another fundamental specificity of compositional convection arises from the complexity of the chemical processes occurring at the "mushy layer" that may exist at the interface between the fluid outer core and the crystallizing inner core. Experiments conducted on model systems involving the freezing of ammonium chloride in solution (Chen and Chen, 1991;Huguet et al, 2016) showed that the gravitational instability manifests itself through eruptions of buoyant fluid in the form of chemical plumes emerging through localized "chimneys" that are spontaneously created in the mushy layer. Fluid from the bulk core percolates through the mush and becomes gradually lighter as it converges horizontally into the chimneys.…”

Section: Introductionmentioning

confidence: 99%

Chemical Convection and Stratification in the Earth's Outer Core

et al. 2019

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Convection in the Earth's outer core is driven by buoyancy sources of both thermal and compositional origin. The thermal and compositional molecular diffusivities differ by several orders of magnitude, which can affect the dynamics in various ways. So far, the large majority of numerical simulations have been performed within the codensity framework that consists in combining temperature and composition, assuming artificially enhanced diffusivities for both variables. In this study, we use a particle-in-cell method implemented in a 3D dynamo code to conduct a first qualitative exploration of pure compositional convection in a rotating spherical shell. We focus on the end-member case of infinite Schmidt number by totally neglecting the compositional diffusivity. We show that compositional convection has a very rich physics that deserves several more focused and quantitative studies. We also report, for the first time in numerical simulations, the self-consistent formation of a chemically stratified layer at the top of the shell caused by the accumulation of chemical plumes and blobs emitted at the bottom boundary. When applied to likely numbers for the Earth's core, some (possibly simplistic) physical considerations suggest that a stratified layer formed in such a scenario would be probably weakly stratified and may be compatible with magnetic observations.

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Structure of a mushy layer under hypergravity with implications for Earth's inner core

Cited by 33 publications

References 124 publications

On the theory of crystal growth in metastable systems with biomedical applications: protein and insulin crystallization

On the theory of crystal growth in metastable systems with biomedical applications: protein and insulin crystallization

A Boussinesq slurry model of the F-layer at the base of Earth’s outer core

Chemical Convection and Stratification in the Earth's Outer Core

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