Metal-silicate mixing by large Earth-forming impacts

Landeau, Maylis; Deguen, Renaud; Phillips, Dominic; Neufeld, Jerome A.; Lherm, Victor; Dalziel, Stuart B.

doi:10.1016/j.epsl.2021.116888

Cited by 31 publications

(45 citation statements)

References 53 publications

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“…For example, 129 Xe may have been produced in the core after accretion by decay of its parent isotope 129 I, since iodine tends toward siderophile behavior at high pressures (C. Jackson et al., 2018) and may have been deposited in the core during accretion. However, magma ocean mixing of stable and unstable isotopes with diverse metal/silicate affinities is a complex dynamical phenomenon (Deguen et al., 2014; Landeau et al., 2021) and requires additional constraints and assumptions beyond those used here for primordial helium.…”

Section: Discussionmentioning

confidence: 99%

Primordial Helium‐3 Exchange Between Earth's Core and Mantle

Olson

Sharp

2022

Geochem Geophys Geosyst

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Volatiles from the solar nebula are known to be present in Earth's deep mantle. The core also may contain solar nebula‐derived volatiles, but in unknown amounts. Here we use calculations of volatile ingassing and degassing to estimate the abundance of primordial 3He now in the core and track the rate of 3He exchange between the core and mantle through Earth history. We apply an ingassing model that includes a silicate magma ocean and an iron‐rich proto‐core coupled to a nebular atmosphere of solar composition to calculate the amounts of 3He acquired by the mantle and core during accretion and core formation. Using experimentally determined partitioning between core‐forming metals and silicate magma, we find that dissolution from the nebular atmosphere deposits one or more petagrams of 3He into the proto‐core. Following accretion, 3He exchange depends on the convective history of the coupled core‐mantle system. We combine determinations of the present‐day surface 3He flux with estimates of the present‐day mantle 3He abundance, mantle and core heat fluxes, and our ingassed 3He abundances in a convective degassing model. According to this model, the mantle 3He abundance is evolving toward a statistical steady state, in which surface losses are compensated by enrichments from the core.

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Section: Discussionmentioning

confidence: 99%

Primordial Helium‐3 Exchange Between Earth's Core and Mantle

Olson

Sharp

2022

Geochem Geophys Geosyst

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“…The core of the impactor is sheared into multiple smaller components during the first stage of the collision and these smaller metal blobs subsequently undergo efficient emulsification while sedimenting to the core of the combined planet (Deguen et al 2014;Genda et al 2017). Laboratory experiments show that taking into account the inertia of the impactor dramatically increases the degree of mixing (Landeau et al 2021). Maas et al (2021) utilized convective magma ocean models and concluded that the convection and rotation of the planet leads to much larger fractions of equilibrated volume than previously estimated and that the equilibrated volume fraction increases with increasing impactor mass.…”

Section: Mixing Degree In the Giant Impactmentioning

confidence: 99%

Anatomy of rocky planets formed by rapid pebble accretion

Johansen

Ronnet

Schiller

et al. 2023

A&A

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We explore the heating and differentiation of rocky planets that grow by rapid pebble accretion. Our terrestrial planets grow outside of the ice line and initially accrete 28% water ice by mass. The accretion of water stops after the protoplanet reaches a mass of 0.01 ME where the gas envelope becomes hot enough to sublimate the ice and transport the vapour back to the protoplanetary disc by recycling flows. The energy released by the decay of 26Al melts the accreted ice to form clay (phyllosilicates), oxidized iron (FeO), and a water surface layer with ten times the mass of Earth’s modern oceans. The ocean–atmosphere system undergoes a run-away greenhouse effect after the effective accretion temperature crosses a threshold of around 300 K. The run-away greenhouse process vaporizes the water layer, thereby trapping the accretion heat and heating the surface to more than 6000 K. This causes the upper part of the mantle to melt and form a global magma ocean. Metal melt separates from silicate melt and sediments towards the bottom of the magma ocean; the gravitational energy released by the sedimentation leads to positive feedback where the beginning differentiation of the planet causes the whole mantle to melt and differentiate. All rocky planets thus naturally experience a magma ocean stage. We demonstrate that Earth’s small excess of 182W (the decay product of 182Hf) relative to the chondrites is consistent with such rapid core formation within 5 Myr followed by equilibration of the W reservoir in Earth’s mantle with 182W-poor material from the core of a planetary-mass impactor, provided that the equilibration degree is at least 25–50%, depending on the initial Hf/W ratio. The planetary collision must have occurred at least 35 Myr after the main accretion phase of the terrestrial planets.

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“…Embryo cores were also assumed to sink and merge with the proto-Earth's existing core before the next embryo impact and remained isolated from further equilibration. Even though the actual physics of metal-silicate mixing and equilibration during Earth's accretion are more complex (Deguen et al, 2014(Deguen et al, , 2011Landeau et al, 2021), these simplifying assumptions allow us to relate impact energies to the conditions of core formation. Smaller bodies <0.01 Earth masses (planetesimals) were below the threshold of masses compatible with the melt-scaling law of Nakajima et al (2021) and were small enough that they may have been stranded in the proto-Earth's mantle following an impact (de Vries et al, 2016).…”

Section: Metal-silicate Equilibrationmentioning

confidence: 99%