Thermodynamics of the MgO–SiO2 liquid system in Earth's lowermost mantle from first principles

Koker, Nico de; Karki, Bijaya B.; Stixrude, Lars

doi:10.1016/j.epsl.2012.11.026

Cited by 86 publications

(166 citation statements)

References 44 publications

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“…of de Koker et al (2013), the excess entropies are some 50% lower. However, they provide an excellent fit to the forsterite and orthoenstatite melting curves (see Supplementary Materials).…”

mentioning

confidence: 99%

“…Model fits to the data use the melt formulation of Silver and Stolper (1985), with r=1 and K=K(T) (see discussion in main text). Properties of the anhydrous solid and melt are taken from published literature (Stixrude and Lithgow-Bertelloni, 2011;de Koker et al, 2013). An additional subregular interaction term is required to match the composition and temperature of brucite dehydration.…”

Section: Ex-situ Observationsmentioning

confidence: 99%

“…The adjustments required here may not be a failing of the MD simulations; it is likely that the coordination changes in the SiO 2 melt require a higher order Birch Murnaghan EoS than that used by (de Koker et al, 2013). Our adjusted model is probably only accurate in a range of about ±5 GPa around the triple 220 point.…”

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confidence: 99%

“…Conveniently, we also have a way to test the volumes predicted by the model of de Koker et al (2013) at around 13 GPa. The experimentally-derived slope of the 210 coesite melting curve is essentially zero at the triple point with stishovite at 13.7…”

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confidence: 99%

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Hydrous melting and partitioning in and above the mantle transition zone: Insights from water-rich MgO–SiO2–H2O experiments

Myhill

Frost

Novella

2017

Geochimica et Cosmochimica Acta

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Abstract Hydrous melting at high pressures affects the physical properties, dynamics and chemical differentiation of the Earth. However, probing the compositions of hydrous melts at the conditions of the mantle transition zone has traditionally been challenging. In this study, we conducted high pressure multianvil experiments at 13 GPa between 1200 and 1900 • C to investigate the liquidus in the system MgO-SiO 2 -H 2 O. Water-rich starting compositions were created using platinic acid (H 2 Pt(OH) 6 ) as a novel water source. As MgO:SiO 2 ratios decrease, the T-X H2O liquidus curve develops an increasingly pronounced concave-up topology. The melting point reduction of enstatite and stishovite at low water contents exceeds that predicted by simple ideal models of hydrogen speciation. We discuss the implications of this work on the behaviour of melts in the deep upper mantle and transition zone, and present new models describing the partitioning of water between the olivine polymorphs and associated hydrous melts.

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confidence: 99%

Section: Ex-situ Observationsmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Hydrous melting and partitioning in and above the mantle transition zone: Insights from water-rich MgO–SiO2–H2O experiments

Myhill

Frost

Novella

2017

Geochimica et Cosmochimica Acta

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“…Experimental work utilizing shockwave experiments [6], and the laser-heated diamond anvil cell [7] has produced valuable results, but many properties of these liquids remain weakly constrained. Quantum-mechanical, finite-temperature density-functional theory (DFT) molecular dynamics (MD) [8,9] has proved to be a powerful and accurate theoretical method for predicting the properties of liquid silicates [10][11][12][13], oxides [14,15], and metals [16] at extreme conditions. In this approach, no assumptions are made on the shape of the electronic charge density, and the effects of temperature are included in both the electronic and ionic degrees of freedom.…”

Section: Introductionmentioning

confidence: 99%

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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Influence of combined primordial layering and recycled MORB on the coupled thermal evolution of Earth's mantle and core

Nakagawa

Tackley

2014

Geochem Geophys Geosyst

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A thermo‐chemical mantle convection model with both primordial compositional layering and recycling of mid‐ocean ridge basalt (MORB) coupled to a parameterized core heat balance model is used to investigate how the thermo‐chemical evolution of the mantle affects the thermal history of the core including primordial material proposed by early Earth hypotheses. The viscosity formulation has been improved from our previous works. The amount of MORB that accumulates above the CMB is strongly dependent on effective Rayleigh number, such that more accumulates at higher Ra (lower viscosity), but a continuous layer of MORB is not obtained here. With initial primordial layering, large‐scale thermo‐chemical anomalies are found in the deep mantle, which are generated mainly by the primordial material with small amount of segregated basaltic material on top of it, localized in the hot upwelling region. A successful core evolution can only be obtained when initial primordial layering is present. In conclusion, primordial material above the CMB originated from early mantle differentiation might be needed to construct a realistic model of a coupled mantle and core evolution. However, in the current study, the convective vigor is lower than realistic and we only consider the case that primordial material is denser than MORB.

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Thermodynamics of the MgO–SiO2 liquid system in Earth's lowermost mantle from first principles

Cited by 86 publications

References 44 publications

Hydrous melting and partitioning in and above the mantle transition zone: Insights from water-rich MgO–SiO2–H2O experiments

Hydrous melting and partitioning in and above the mantle transition zone: Insights from water-rich MgO–SiO2–H2O experiments

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

Influence of combined primordial layering and recycled MORB on the coupled thermal evolution of Earth's mantle and core

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