Toward a coherent model for the melting behavior of the deep Earth’s mantle

Andrault, Denis; Bolfan-Casanova, Nathalie; Bouhifd, Mohamed Ali; Boujibar, A.; Garbarino, Gastón; Manthilake, Geeth; Mézouar, M.; Monteux, J.; Parisiades, Paraskevas; Pesce, G.

doi:10.1016/j.pepi.2017.02.009

Cited by 37 publications

(40 citation statements)

References 98 publications

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“…This suggests that the core cooling in the magma ocean stage is likely to be insignificant, and an initial core temperature will characterize the thermal state of the core at the beginning of subsolidus convection stage. The core temperature suggested here is similar to that in Andrault et al (), although our result changes with the choice of the initial core temperature.…”

Section: Discussionsupporting

confidence: 88%

On the Timescale of Magma Ocean Solidification and Its Chemical Consequences: 2. Compositional Differentiation Under Crystal Accumulation and Matrix Compaction

Miyazaki

Korenaga

2019

JGR Solid Earth

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The solidification of a putative magma ocean sets the stage for subsequent subsolidus mantle convection. Whereas it may have resulted in a compositionally stratified mantle, the efficiency of relevant processes to cause chemical differentiation, such as crystal accumulation and matrix compaction, remains uncertain. The purpose of this study is to present the thermochemical structure of end-member cases where potential differentiation mechanisms are taking full effect. We employ a self-consistent thermodynamic model to make our model consistent in both thermal and chemical aspects. The accumulation of crystals at the base of magma ocean can enrich the upper mantle with iron, but such a global-scale compositional stratification is likely to be quickly eliminated by gravitational instability, leaving small-scale heterogeneities only. On the other hand, the compaction of solid matrix in the deep mantle creates a long-lasting molten layer above the core-mantle boundary. Our results suggest that the efficiency of compaction is the key factor to generate compositional stratification during solidification.

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Section: Discussionsupporting

confidence: 88%

On the Timescale of Magma Ocean Solidification and Its Chemical Consequences: 2. Compositional Differentiation Under Crystal Accumulation and Matrix Compaction

Miyazaki

Korenaga

2019

JGR Solid Earth

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“…A recent study showed that only highly Fe-rich melts (e.g., ~0.35 of Fe/(Mg+Fe)) could be denser than the surrounding mantle (Karki et al 2018). However, to generate such a Fe-rich melt, very low partition coefficients (D Fe mineral/melt ) and low degree of partial melting are required (e.g., Andrault et al 2017), while these parameters at ultrahigh pressure and high temperature conditions of the deep lower mantle are still under debate (e.g., Andrault et al 2017). On the other hand, Fe-free CaAl 2 Si 2 O 8 glass has markedly higher density than SiO 2 and MgSiO 3 glasses above 100 GPa (Fig.…”

Section: Discussionmentioning

confidence: 99%

Ultrahigh pressure structural changes in a 60 mol. % Al2O3–40 mol. % SiO2 glass

Ohira¹,

Kono²,

Shibazaki³

et al. 2019

Geochem. Persp. Let.

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Structure of an Al-containing silicate glass (60 mol. % Al 2 O 3-40 mol. % SiO 2 , A40S) is investigated up to 131 GPa, a pressure close to that of the Earth's coremantle boundary, by using our recently developed double stage large volume cell. The first peak (r1) of the pair distribution function, which corresponds to TO distance (T = Al, Si), rapidly increases below 16 GPa, indicating an increase of average coordination number (CN) of TO from ~4 to 6. The r1 linearly decreases in the pressure range of 25-110 GPa, but it displays a slope change and becomes nearly constant above 110 GPa. The slope change may imply a structural change in the A40S glass around 110 GPa, and may be explained by the change in Al-O distance associated with the Al-O CN increase from 6 to >6 as predicted by molecular dynamics simulations (Ghosh and Karki, 2018). Our observations suggest an important role for aluminum in densification of aluminosilicate at the deep lower mantle, which might imply a dense aluminosilicate magma with negative buoyancy.

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“…In case the initial depth extent of the MO was indeed significantly smaller than that of the CMB, the classical scenario for the formation of a ''primary'' basal magma ocean (BMO) is called into question. In this scenario, a BMO is separated from the ''surficial'' MO due to an isochemical density crossover between solids and Geochemistry, Geophysics, Geosystems 10.1002/2017GC006917 liquids and/or a crossover in the slopes of the mantle solidus and adiabat [Andrault et al, 2017;Thomas et al, 2012]. As any potential crossovers are inferred to occur at very high pressures, if at all [Andrault et al, 2012;de Koker et al, 2013;Ghosh and Karki, 2016;Nomura et al, 2011;Stixrude et al, 2009], they may only be relevant for (near-)complete melting of the early Earth's mantle, e.g., in a giant-impact scenario.…”

Section: Discussionmentioning

confidence: 99%

Reconciling magma‐ocean crystallization models with the present‐day structure of the Earth's mantle

Ballmer

Lourenço

Hirose

et al. 2017

Geochem Geophys Geosyst

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Terrestrial planets are thought to experience episode(s) of large‐scale melting early in their history. Fractionation during magma‐ocean freezing leads to unstable stratification within the related cumulate layers due to progressive iron enrichment upward, but the effects of incremental cumulate overturns during MO crystallization remain to be explored. Here, we use geodynamic models with a moving‐boundary approach to study convection and mixing within the growing cumulate layer, and thereafter within the fully crystallized mantle. For fractional crystallization, cumulates are efficiently stirred due to subsequent incremental overturns, except for strongly iron‐enriched late‐stage cumulates, which persist as a stably stratified layer at the base of the mantle for billions of years. Less extreme crystallization scenarios can lead to somewhat more subtle stratification. In any case, the long‐term preservation of at least a thin layer of extremely enriched cumulates with Fe# > 0.4, as predicted by all our models, is inconsistent with seismic constraints. Based on scaling relationships, however, we infer that final‐stage Fe‐rich magma‐ocean cumulates originally formed near the surface should have overturned as small diapirs, and hence undergone melting and reaction with the host rock during sinking. The resulting moderately iron‐enriched metasomatized/hybrid rock assemblages should have accumulated at the base of the mantle, potentially fed an intermittent basal magma ocean, and be preserved through the present‐day. Such moderately iron‐enriched rock assemblages can reconcile the physical properties of the large low shear‐wave velocity provinces in the present‐day lower mantle. Thus, we reveal Hadean melting and rock‐reaction processes by integrating magma‐ocean crystallization models with the seismic‐tomography snapshot.

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Toward a coherent model for the melting behavior of the deep Earth’s mantle

Cited by 37 publications

References 98 publications

On the Timescale of Magma Ocean Solidification and Its Chemical Consequences: 2. Compositional Differentiation Under Crystal Accumulation and Matrix Compaction

On the Timescale of Magma Ocean Solidification and Its Chemical Consequences: 2. Compositional Differentiation Under Crystal Accumulation and Matrix Compaction

Ultrahigh pressure structural changes in a 60 mol. % Al2O3–40 mol. % SiO2 glass

Reconciling magma‐ocean crystallization models with the present‐day structure of the Earth's mantle

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