High‐pressure melting of MgO from (Mg,Fe)O solid solutions

Du, Zhuofei; Lee, Kanani K. M.

doi:10.1002/2014gl061954

Cited by 51 publications

(71 citation statements)

References 47 publications

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“…A melt denser than the crystal will sink, facilitating the birth of a basal magma ocean [5], with important consequences for the geochemistry of the planet. From our ideal solution analysis, we find x ≈ 0.05 in crystalline (Mg,Fe)O along the liquidus, in excellent agreement with recent experimental data [50]. By assuming the mean atomic volume to be unchanged upon altering the Fe fraction, we estimate the density of (Mg,Fe)O along the liquidus.…”

Section: Spin Crossover and The Solid-liquid Transitionsupporting

confidence: 87%

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Spin crossover in liquid (Mg,Fe)O at extreme conditions

Holmström

Stixrude

2016

Phys. Rev. B

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We use first-principles free-energy calculations to predict a pressure-induced spin crossover in the liquid planetary material (Mg,Fe)O, whereby the magnetic moments of Fe ions vanish gradually over a range of hundreds of GPa. Because electronic entropy strongly favors the nonmagnetic low-spin state of Fe, the crossover has a negative effective Clapeyron slope, in stark contrast to the crystalline counterpart of this transition-metal oxide. Diffusivity of liquid (Mg,Fe)O is similar to that of MgO, displaying a weak dependence on element and spin state. Fe-O and Mg-O coordination increases from approximately 4 to 7 as pressure goes from 0 to 200 GPa. We find partitioning of Fe to induce a density inversion between the crystal and melt, implying separation of a basal magma ocean from a surficial one in the early Earth. The spin crossover induces an anomaly into the density contrast, and the oppositely signed Clapeyron slopes for the crossover in the liquid and crystalline phases imply that the solid-liquid transition induces a spin transition in (Mg,Fe)O.

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Section: Spin Crossover and The Solid-liquid Transitionsupporting

confidence: 87%

“…The spin crossover has a small but noticeable effect on the density contrast. In comparison [50] and gray symbols from measurements of Zhang and Fei [51].…”

Section: Spin Crossover and The Solid-liquid Transitionmentioning

confidence: 99%

Spin crossover in liquid (Mg,Fe)O at extreme conditions

Holmström

Stixrude

2016

Phys. Rev. B

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“…We take the pyrolite solidus to linearly increase and decrease from 3300 °C at z = 1740 km to 4000 °C at the CMB and 1740 °C at the surface, respectively. This bilinear fit to experimental constraints is a crude simplification (Andrault et al, 2011;Du and Lee, 2014) Feliquid/(Mgliquid + Feliquid). Accordingly, the minimum solidus temperature that can occur for maximal Fe#MO at the surface is 1000 °C.…”

Section: Methodsmentioning

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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“…The black line represents the melting temperatures calculated in this study, and the dashed gray line represents those by de Koker and Stixrude (2009). The melting temperatures determined by high-pressure experiments and ab initio calculations are also plotted: orange squares, Zerr and Boehler (1994); green triangles, Alfe (2005); blue circles, Zhang and Fei (2008); purple squares, Du and Lee (2014); and red squares, Kimura et al (2017). Figure S4: Melting phase diagram in the MgO-MgSiO 3 system at 24 GPa.…”

Section: Additional Filementioning

confidence: 98%

Melting phase relations in the MgSiO3–CaSiO3 system at 24 GPa

Nomura

Zhou

Irifune

2017

Prog Earth Planet Sci

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The Earth's lower mantle is composed of bridgmanite, ferropericlase, and CaSiO 3 -rich perovskite. The melting phase relations between each component are key to understanding the melting of the Earth's lower mantle and the crystallization of the deep magma ocean. In this study, melting phase relations in the MgSiO 3 -CaSiO 3 system were investigated at 24 GPa using a multi-anvil apparatus. The eutectic composition is (Mg,Ca)SiO 3 with 81-86 mol% MgSiO 3 . The solidus temperature is 2600-2620 K. The solubility of CaSiO 3 component into bridgmanite increases with temperature, reaching a maximum of 3-6 mol% at the solidus, and then decreases with temperature. The same trend was observed for the solubility of MgSiO 3 component into CaSiO 3 -rich perovskite, with a maximum of 14-16 mol% at the solidus. The asymmetric regular solutions between bridgmanite and CaSiO 3 -rich perovskite and between MgSiO 3 and CaSiO 3 liquid components well reproduce the melting phase relations constrained experimentally.

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High‐pressure melting of MgO from (Mg,Fe)O solid solutions

Cited by 51 publications

References 47 publications

Spin crossover in liquid (Mg,Fe)O at extreme conditions

Spin crossover in liquid (Mg,Fe)O at extreme conditions

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

Melting phase relations in the MgSiO3–CaSiO3 system at 24 GPa

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