Phase Diagrams and Thermodynamics of Lower Mantle Materials

Dorfman, Susannah M.

doi:10.1002/9781118992487.ch19

Cited by 7 publications

(4 citation statements)

References 83 publications

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“…Differences in partitioning behavior between Fe-rich and Fe-poor compositions may be due to differences in the conditions at which high-to-low spin transitions occur in Fe- [19]) and thermodynamic calculations in previous work (red: [46], green: [47]) and this study (bold black lines). Thermodynamic calculations using excess mixing volume term in this study successfully reproduce experimental observations of very high solubility of FeSiO 3 in bridgmanite at deep lower mantle pressures >80 GPa.…”

Section: Multivariable Effects On Partitioningmentioning

confidence: 68%

“…Figure 5. Phase diagram of MgSiO 3 -FeSiO 3 system at~2000 K based on experimental observations (blue:[19]) and thermodynamic calculations in previous work (red:[46], green:[47]) and this study (bold black lines). Thermodynamic calculations using excess mixing volume term in this study successfully reproduce experimental observations of very high solubility of FeSiO 3 in bridgmanite at deep lower mantle pressures >80 GPa.…”

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confidence: 83%

“…Thermodynamic parameters for Mws and Bdg phases have been constrained by previous studies, for example summarized in a database by [46]. The equation of state of iron-bearing Bdg and free energies consistent with observed phase equilibria in the MgSiO 3 -FeSiO 3 sytem were updated by [47]. However, an initial attempt to model iron partitioning between Mws and Bdg according to the above framework yielded K D inconsistent with experimental observations (Supplementary Figure S10).…”

Section: Thermodynamic Modelingmentioning

confidence: 99%

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Composition and Pressure Effects on Partitioning of Ferrous Iron in Iron-Rich Lower Mantle Heterogeneities

et al. 2021

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Both seismic observations of dense low shear velocity regions and models of magma ocean crystallization and mantle dynamics support enrichment of iron in Earth’s lowermost mantle. Physical properties of iron-rich lower mantle heterogeneities in the modern Earth depend on distribution of iron between coexisting lower mantle phases (Mg,Fe)O magnesiowüstite, (Mg,Fe)SiO3 bridgmanite, and (Mg,Fe)SiO3 post-perovskite. The partitioning of iron between these phases was investigated in synthetic ferrous-iron-rich olivine compositions (Mg0.55Fe0.45)2SiO4 and (Mg0.28Fe0.72)2SiO4 at lower mantle conditions ranging from 33–128 GPa and 1900–3000 K in the laser-heated diamond anvil cell. The resulting phase assemblages were characterized by a combination of in situ X-ray diffraction and ex situ transmission electron microscopy. The exchange coefficient between bridgmanite and magnesiowüstite decreases with pressure and bulk Fe# and increases with temperature. Thermodynamic modeling determines that incorporation and partitioning of iron in bridgmanite are explained well by excess volume associated with Mg-Fe exchange. Partitioning results are used to model compositions and densities of mantle phase assemblages as a function of pressure, FeO-content and SiO2-content. Unlike average mantle compositions, iron-rich compositions in the mantle exhibit negative dependence of density on SiO2-content at all mantle depths, an important finding for interpretation of deep lower mantle structures.

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Section: Multivariable Effects On Partitioningmentioning

confidence: 68%

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confidence: 83%

Section: Thermodynamic Modelingmentioning

confidence: 99%

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Composition and Pressure Effects on Partitioning of Ferrous Iron in Iron-Rich Lower Mantle Heterogeneities

et al. 2021

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“…Estimates of the composition of the average mantle agree that the phase fraction of ferropericlase exceeds this limit, although the precise amount remains a focus of ongoing study. The phase fraction of ferropericlase in the pyrolite model is estimated to be ∼16% (Dorfman, 2016). While some high‐pressure elasticity measurements support the pyrolite model for the composition of the lower mantle (Criniti et al., 2021), others suggest that a better match to average seismic wave speeds is obtained for a mantle composed of ∼7%–12% ferropericlase (Mashino et al., 2020; Murakami et al., 2012).…”

Section: Discussionmentioning

confidence: 99%

High Sodium Solubility in Magnesiowüstite in Iron‐Rich Deep Lower Mantle

Dorfman,

Hsu,

Nabiei

et al. 2024

Geochem Geophys Geosyst

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Abstract(Mg,Fe)O ferropericlase‐magnesiowüstite has been proposed to host the majority of Earth's sodium, but the mechanism and capacity for incorporating the alkali cation remain unclear. In this work, experiments in the laser‐heated diamond anvil cell and first‐principles calculations determine the solubility of sodium and favorability of sodium incorporation in iron‐rich magnesiowüstite relative to (Mg,Fe)SiO3 bridgmanite. Reaction of Mg/(Mg + Fe) (Mg#) 55 and 28 olivine with NaCl at 33–128 GPa and 1600–3000 K produces iron‐rich magnesiowüstite containing several percent sodium, while iron‐rich bridgmanite contains little to no detectable sodium. In sodium‐saturated magnesiowüstite, sodium number [Na/(Na + Mg + Fe)] is 2–5 atomic percent at pressures below 60 GPa and drastically increases to 10–20 atomic percent at deep lower mantle pressures. For these two compositions, there is no significant dependence of the results on Mg#. Our calculations not only show consistent results with experiments but further indicate that such an increase in solubility and partitioning of Na into magnesiowüstite is driven by the spin transition in iron. These results provide fundamental constraints on the crystal chemistry of sodium at lower‐mantle conditions. If the sodium capacity of (Mg,Fe)O is not strongly dependent on Mg#, (Mg,Fe)O in the lower mantle may have the capacity to store the entire sodium budget of the Earth.

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Lower-Mantle Mineral Associations

Kaminsky¹

2017

The Earth's Lower Mantle

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Phase Diagrams and Thermodynamics of Lower Mantle Materials

Cited by 7 publications

References 83 publications

Composition and Pressure Effects on Partitioning of Ferrous Iron in Iron-Rich Lower Mantle Heterogeneities

Composition and Pressure Effects on Partitioning of Ferrous Iron in Iron-Rich Lower Mantle Heterogeneities

High Sodium Solubility in Magnesiowüstite in Iron‐Rich Deep Lower Mantle

Lower-Mantle Mineral Associations

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