Sound Velocities in FeSi at Lower Mantle Conditions and the Origin of Ultralow‐Velocity Zones

Mergner, V.; Kupenko, Ilya; Spiekermann, Georg; Petitgirard, Sylvain; Libon, Lélia; Chariton, Stella; Krug, Matthias; Steinbrügge, René; Sergueev, Ilya; Sanchez-Valle, Carmen

doi:10.1029/2020gl092257

Cited by 9 publications

(14 citation statements)

References 87 publications

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“…The gray dashed vertical lines indicate pressures at the core‐mantle boundary (CMB) and inner‐core boundary (ICB). The circle, square, triangle, and diamond markers represent results from M2021 (Mergner et al., 2021), V2007 (Vočadlo, 2007), D2022 (Dominijanni et al., 2022), and O2013 (Ono, 2013), respectively. Horizontal red, green, and blue lines represent PREM values and velocity anomalies (−10% and −20% for V P and −15% and −30% for V S ) for density, V P , and V S , respectively.…”

Section: Resultsmentioning

confidence: 99%

“…Using X-ray powder diffraction and diamond anvil cells, the EOS of B2-FeSi has been determined up to 67 GPa by Ono et al (2007) and 180 GPa by Sata et al (2010) at room temperature, and up to 145 GPa and 3400 K by Fischer et al (2014) and 120 GPa and 3,000 K by Yokoo et al (2023). Using nuclear inelastic scattering, Mergner et al (2021) measured the elastic velocities of B2-FeSi up to 115 GPa and 1,600 K. However, all these experiments were performed at pressures of more than 150 GPa below the inner core pressures, thus making extrapolations to inner core pressures largely uncertain. Limitations in pressures and temperatures can also be found in results from first-principles studies based on the density functional theory (DFT).…”

Section: Introductionmentioning

confidence: 99%

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Thermoelastic Properties of B2‐Type FeSi Under Deep Earth Conditions: Implications for the Compositions of the Ultralow‐Velocity Zones and the Inner Core

Liu,

Jing

2024

JGR Solid Earth

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The CsCl‐type (B2) phase of FeSi (B2‐FeSi) has been proposed as a candidate phase in the ultralow‐velocity zones (ULVZs) at the base of the lower mantle and in the Earth's inner core. However, the elastic properties of B2‐FeSi under relevant conditions remain unclear. Here we determine the density, elastic constants, and velocities of B2‐FeSi at high pressures (90–390 GPa) and temperatures (3,000–6,000 K) relevant to the Earth's lower most mantle and the inner core, using first‐principles molecular dynamics simulations. At the base of the lower mantle, B2‐FeSi shows significantly lower velocities and a higher density than those of the ambient mantle. Mechanical mixing models suggest the presence of ∼27–39 vol% B2‐FeSi in the silicate mantle is consistent with the reduced velocities and the elevated density of ULVZs observed seismically. On the other hand, the hcp‐Fe and B2‐FeSi mixture exhibits higher bulk sound velocity compared to the PREM under inner core conditions. Adding superionic H in the interstitial sites of B2‐FeSi lowers its density but has little effect on the bulk sound velocity of B2‐FeSi, precluding H‐bearing B2‐FeSi as a major component in the Earth's inner core.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermoelastic Properties of B2‐Type FeSi Under Deep Earth Conditions: Implications for the Compositions of the Ultralow‐Velocity Zones and the Inner Core

Liu,

Jing

2024

JGR Solid Earth

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“…These compositions could serve as possible contributors to ULVZs. ULVZs have multiple proposed explanations, including FeSi formed through core‐mantle reactions (Mergner et al., 2021), hydrous phases such as (Al,Fe)OOH (Thompson et al., 2021), Fe‐rich post perovskite (Garnero & McNamara, 2008), Fe‐rich (Mg,Fe)O (Solomatova et al., 2016; Wicks et al., 2010), and patches of partial melt (Williams & Garnero, 1996). Partial melt is a likely explanation for ULVZs due to the 3:1 ratio of S‐to‐P wave velocity reduction (Garnero & McNamara, 2008; Williams & Garnero, 1996).…”

Section: Discussionmentioning

confidence: 99%

Carbon Storage in Earth's Deep Interior Implied by Carbonate‐Silicate‐Iron Melt Miscibility

Davis,

Solomatova,

Caracas

et al. 2023

Geochem Geophys Geosyst

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Carbonate melts have been proposed to exist in the lower mantle, but their interaction with other lower mantle melt compositions is poorly understood. To understand miscibility in the carbonate‐silicate‐metal melt system, we simulate endmember, binary, and ternary melt mixtures and study how their Gibbs free energies of mixing evolve with pressure. We find that carbonate‐metal and carbonate‐silicate melts have miscibility gaps that close with increasing pressure, while silicate‐metal melts are immiscible at all lower‐mantle pressures. Extending this analysis to the core‐mantle boundary, we suggest three miscible melt fields near the endmember carbonate, silicate, and iron melt compositions. Analysis of the densities of these miscible melt compositions indicates that some carbonate‐rich and some silicate‐rich melt compositions are gravitationally stable at the core‐mantle boundary and could be candidate compositions to explain ultra‐low velocity zones. Additionally, we evaluate the speciation of an example immiscible melt composition at various pressures throughout the mantle and identify reduced carbon species that would be expected to form in the melt. Our analysis reveals that a majority of Earth's carbon could have been transported to the core during core‐mantle differentiation and that much of Earth's carbon may be stored in the deep interior today.

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“…ULVZs have multiple proposed explanations, including FeSi formed through core-mantle reactions (Mergner et al, 2021), hydrous phases such as (Al,Fe)OOH (Thompson et al, 2021), Fe-rich post perovskite (Garnero & McNamara, 2008), Fe-rich (Mg,Fe)O (Solomatova et al, 2016;Wicks et al, 2010), and patches of partial melt (Williams & Garnero, 1996). Partial melt is a likely explanation for ULVZs due to the 3:1 ratio of S-to-P wave velocity reduction (Garnero & McNamara, 2008;Williams & Garnero, 1996).…”

Section: Gibbs Free Energy Of Mixingmentioning

confidence: 99%

Carbon storage in Earth's deep interior implied by carbonate-silicate-iron melt miscibility

Davis

Solomatova

Caracas

et al. 2023

Preprint

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Carbonate melts have been proposed to exist in the lower mantle, but their interaction with other lower mantle melt compositions is poorly understood. To understand miscibility in the carbonate-silicate-metal melt system, we simulate endmember, binary, and ternary melt mixtures and study how their Gibbs free energies of mixing evolve with pressure. We find that carbonate-metal and carbonate-silicate melts have miscibility gaps that close with increasing pressure, while silicate-metal melts are immiscible at all lower-mantle pressures. Extending this analysis to the core-mantle boundary, we suggest three miscible melt fields near the endmember carbonate, silicate, and iron melt compositions. Analysis of the densities of these miscible melt compositions indicates that some carbonate-rich and some silicate-rich melt compositions are gravitationally stable at the core-mantle boundary and could be candidate compositions to explain ultra-low velocity zones. Additionally, we evaluate the speciation of an example immiscible melt composition at various pressures throughout the mantle and identify reduced carbon species that would be expected to form in the melt. Our analysis reveals that a majority of Earth’s carbon could have been transported to the core during core-mantle differentiation and that much of Earth’s carbon may be stored in the deep interior today.

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Sound Velocities in FeSi at Lower Mantle Conditions and the Origin of Ultralow‐Velocity Zones

Cited by 9 publications

References 87 publications

Thermoelastic Properties of B2‐Type FeSi Under Deep Earth Conditions: Implications for the Compositions of the Ultralow‐Velocity Zones and the Inner Core

Thermoelastic Properties of B2‐Type FeSi Under Deep Earth Conditions: Implications for the Compositions of the Ultralow‐Velocity Zones and the Inner Core

Carbon Storage in Earth's Deep Interior Implied by Carbonate‐Silicate‐Iron Melt Miscibility

Carbon storage in Earth's deep interior implied by carbonate-silicate-iron melt miscibility

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