Heat partitioning in terrestrial planets during core formation by negative diapirism

Samuel, Henri; Tackley, P. J.; Evonuk, M.

doi:10.1016/j.epsl.2009.11.050

Cited by 37 publications

(42 citation statements)

References 22 publications

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“…Thus, we argue that previous models of chemical and thermal equilibration processes can only be accurate in a statistical mean sense (e.g. Rubie et al, 2003;Samuel et al, 2010). On the basis of our simple equilibration model, we still predict a complete equilibration before reaching the core, but at a significantly deeper depth.…”

Section: Conclusion and Open Questionsmentioning

confidence: 86%

“…As in Earth, the heat brought by the conversion of gravitational and kinetic energy during accretion is not negligible (see e.g. Tonks and Melosh, 1992;Samuel et al, 2010), it would now be interesting to study the strong coupling between the heating by viscous damping of the intense flows caused by the fall of iron diapirs, the changes in the ambient viscosity induced by this thermal evolution, and the corresponding evolution of the drop size distribution.…”

Section: Conclusion and Open Questionsmentioning

confidence: 99%

“…The same kind of interrogation can be held against interpretations of the U/Pb proxy, and for the coefficients of partition between metal and silicate, which strongly depend on the details of the smallscale processes at the iron-silicate interface during sedimentation. Actually, these interfacial dynamics influence every mechanism of equilibration by diffusion, such as diffusion of heat and diffusion of momentum by viscosity, both leading to indetermination on the initial thermal state of the mantle and the core, and on the repartition of the energy between these two (Monteux et al, 2009;Samuel et al, 2010). Thus, in order to model the evolution of both Earth's core and mantle, it is important to understand the fluid dynamics at the drop scale during the iron sedimentation (Solomatov, 2000).…”

Section: Figmentioning

confidence: 99%

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Laboratory experiments on the breakup of liquid metal diapirs

Wacheul¹,

Bars²,

Monteux³

et al. 2014

Earth and Planetary Science Letters

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The validity of the iron rain scenario, i.e. the widely accepted model for the dynamics of iron sedimentation through a magma ocean during the latest stage of the Earth's accretion, is explored via a suite of laboratory experiments. Liquid gallium and mixtures of water and glycerol are used as analogs of the iron and the molten silicate respectively. This allows us to investigate the effects of the viscosity ratio between iron and silicate and to reproduce the relevant effects of surface tension on the fragmentation dynamics. While the classical iron rain scenario considers a population of purely spherical drops with a single characteristic radius that fall towards the bottom of the magma ocean at a unique velocity without any further change, our experiments exhibit a variety of stable shapes for liquid metal drops, a large distribution of sizes and velocities, and an intense internal dynamics within the cloud with the superimposition of further fragmentations and merging events. Our results demonstrate that rich and complex dynamics occur in models of molten metal diapir physics. Further, we hypothesize that the inclusion of such flows into state of the art thermochemical equilibration models will generate a similarly broad array of complex, and likely novel, behaviors.

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Section: Conclusion and Open Questionsmentioning

confidence: 86%

Section: Conclusion and Open Questionsmentioning

confidence: 99%

Section: Figmentioning

confidence: 99%

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Laboratory experiments on the breakup of liquid metal diapirs

Wacheul¹,

Bars²,

Monteux³

et al. 2014

Earth and Planetary Science Letters

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“…In detail, the energy released by core formation is not distributed uniformly: a large fraction of energy is partitioned into the sinking iron-rich material. In this scenario, the planet at the end of accretion has a superheated core [30]. Cores form easily even in bodies as small as the Moon or Mars before the onset of silicate melting via diapiric instability of the denser iron-rich material [31].…”

Section: −2β Pmentioning

confidence: 99%

Melting in super-earths

Stixrude

2014

Phil. Trans. R. Soc. A.

104

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We examine the possible extent of melting in rockiron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of superearths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of superearth interiors based on existing experimental and ab initio results and scaling laws. We construct superearth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

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“…It is small enough to ensure efficient chemical equilibration between the droplets and the surrounding magma ocean (Rubie et al, 2003). Iron finally migrates through the solid part of the mantle toward the forming core by diapirism, initiated by Rayleigh-Taylor instabilities within the liquid pond (Karato & Murthy, 1997;Monteux et al, 2009;Samuel et al, 2010;Stevenson, 1990), diking (Stevenson, 2003), or percolation (Stevenson, 1990). No further equilibration is expected at this stage owing to the solid state of the underlying mantle and the large size of the diapirs.…”

Section: Introductionmentioning

confidence: 99%

Small‐Scale Metal/Silicate Equilibration During Core Formation: The Influence of Stretching Enhanced Diffusion on Mixing

Lherm

Deguen

2018

JGR Solid Earth

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Geochemical data provide key information on the timing of accretion and on the prevailing physical conditions during core/mantle differentiation. However, their interpretation depends critically on the efficiency of metal/silicate chemical equilibration, which is poorly constrained. Fluid dynamics experiments suggest that, before its fragmentation, a volume of liquid metal falling into a magma ocean undergoes a change of topology from a compact volume of metal toward a collection of sheets and ligaments. We investigate here to what extent the vigorous stretching of the metal phase by the turbulent flow can increase the equilibration efficiency through what is known as stretching enhanced diffusion. We obtain scaling laws giving the equilibration times of sheets and ligaments as functions of a Péclet number based on the stretching rate. At large Péclet, stretching drastically decreases the equilibration time, which in this limit depends only weakly on the diffusivity. We also perform 2‐D numerical simulations of the evolution of a volume of metal falling into a magma ocean, from which we identify several equilibration regimes depending on the values of the Péclet (Pe), Reynolds (Re), and Bond (Bo) numbers. At large Pe, Re, and Bo, the metal phase is vigorously stretched and convoluted in what we call a stirring regime. The equilibration time is found to be independent of viscosity and surface tension and depends weakly on diffusivity. Equilibration is controlled by an efficient thermochemical stretching enhanced diffusion mechanism developing from the mean flow and entraining the surrounding silicate phase.

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Heat partitioning in terrestrial planets during core formation by negative diapirism

Cited by 37 publications

References 22 publications

Laboratory experiments on the breakup of liquid metal diapirs

Laboratory experiments on the breakup of liquid metal diapirs

Melting in super-earths

Small‐Scale Metal/Silicate Equilibration During Core Formation: The Influence of Stretching Enhanced Diffusion on Mixing

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