The structure of Fe–Si alloy in Earth's inner core

Tateno, Shigehiko; Kuwayama, Yasuhiro; Hirose, Kei; Ohishi, Yasuo

doi:10.1016/j.epsl.2015.02.008

Cited by 84 publications

(141 citation statements)

References 56 publications

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“…Here we only compared with the data measured by Tateno et al (). So far, the EOS for hcp Fe‐9Si has been measured by Hirao et al (), Fischer et al (), and Tateno et al (), respectively. All the parameters were list in Table .…”

Section: Results and Geophysical Implicationmentioning

confidence: 99%

Equation of State for Shocked Fe‐8.6 wt% Si up to 240 GPa and 4,670 K

et al. 2019

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Using dynamic compression technique, the equation of state for Fe‐8.6 wt% Si was measured up to 240 GPa and 4,670 K. A least squares fit to the experimental data yields the Hugoniot parameters C0 = 4.603±0.101 km/s and λ = 1.505±0.037 with initial density ρ0=7.386±0.021 g/cm3. Based on the Hugoniot data, the calculated isothermal equation of state is consistent with static compression data when the lattice Grüneisen parameter γl =1.65(7.578/ρ) and electronic Grüneisen parameter γe=1.83. The calculated pressure‐density data at 300 K were fitted to a third‐order Birch‐Murnaghan equation of state with zero pressure the parameters K0=192.1±6.3 GPa, K0'=4.71±0.27 with fixed ρ0ε =7.578±0.050 g/cm3. Under the conditions of Earth's core, the densities of Fe‐8.6±2.0 wt% Si and Fe‐3.8±2.9 wt% Si agree with preliminary reference Earth mode (PREM) data of the outer and the inner core, respectively. These are the upper limits for Si in the core assuming Si is the only light element. Simultaneously considering the geophysical and geochemical constraints for a Si‐S‐bearing core, the outer core may contain 3.8±2.9 wt% Si and 5.6±3.0 wt% S.

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Section: Results and Geophysical Implicationmentioning

confidence: 99%

Equation of State for Shocked Fe‐8.6 wt% Si up to 240 GPa and 4,670 K

et al. 2019

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“…For example, the Earth's core is known to contain several percent of some element(s) lighter than iron, based on its seismologically inferred density (Birch, 1952). Approximately 7-10 wt% oxygen (Fischer et al, 2011;Jeanloz and Ahrens, 1980) or 8-13 wt% silicon Lin et al, 2003;Mao et al, 2012;Sata et al, 2010;Tateno et al, 2015;Zhang et al, 2014) in an iron-nickel alloy could match the outer core's density and sound velocity (though some studies disagree on this number; cf., Morard et al, 2013), but the partitioning behaviors of these elements that could account for their presence in the core need to be better understood to help discriminate between these endmember cases.…”

Section: Introductionmentioning

confidence: 95%

High pressure metal–silicate partitioning of Ni, Co, V, Cr, Si, and O

Fischer

Nakajima

Campbell

et al. 2015

Geochimica et Cosmochimica Acta

210

263

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High pressure metal-silicate partitioning of Ni, Co, V, Cr, Si, and O, Geochimica et Cosmochimica Acta (2015), doi: http://dx.High pressure metal-silicate partitioning of Ni, Co, V, Cr, Si, and O AbstractThe distributions of major and minor elements in Earth's core and mantle were primarily established by high pressure, high temperature metal-silicate partitioning during core segregation. The partitioning behaviors of moderately siderophile elements can be used to constrain the pressure-temperature conditions of core formation and the 2 core's composition. We performed experiments to study the partitioning of Ni, Co, V, Cr, Si, and O between silicate melt and Fe-rich metallic melt in a multianvil press and diamond anvil cell, up to 100 GPa and 5700 K. Combining our new results with data from 18 previous studies, we parameterized the effects of pressure, temperature, and metallic melt composition on partitioning. Ni and Co partitioning are insensitive to composition. At low pressures, these elements become less siderophile with increasing temperature, with this trend reversing above ~45 GPa. V and Cr partitioning are much more sensitive to metallic melt composition and less sensitive to pressure. Partitioning of Si and O are insensitive to pressure, but with strong and moderate temperature dependences, respectively. Our new parameterizations of Ni and Co partitioning suggest that the Earth's distributions of these elements can be matched by single-stage coremantle equilibration at 54 ± 5 GPa and 3300-3400 K. These conditions would result in 8.5 ± 1.4 wt% Si and 1.6 ± 0.3 wt% O in the core, compatible with the core's measured density. However, this single-stage model matches the Earth's V and Cr distributions less well. We also incorporated our parameterizations into models of multi-stage core formation over evolving pressure-temperature-oxygen fugacity conditions, reproducing the Earth's Ni and Co distributions while simultaneously producing a core whose light element composition is consistent with its density.

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“…The alloying effects of Si on the structural stability and elasticity of Fe at high P‐T relevant to the Earth's core are of particular interest in regard to the geophysical constraints on the light elements in the core. Theoretical and experimental results have shown that the incorporation of Si into Fe can enhance the stability field as well as the V P and V S anisotropy of Fe in the body‐centered cubic (bcc) structure [ Lin et al , ; Belonoshko et al , ; Lin et al , ; Liu et al , ], although Fe with approximately 4–5 wt % Si is likely to be stable in the hexagonal close packed (hcp) structure at relevant P‐T conditions of the inner core [ Lin et al , ; Asanuma et al , ; Tateno et al , ]. Furthermore, hcp‐Fe with up to approximately 8 wt % Si exhibits a similar compressional wave velocity and density ( V P ‐ρ ) behavior to that of the hcp‐Fe at high pressure, except that there is a decrease in density due to the light element Si substitution in the hcp‐Fe lattice [ Mao et al , ].…”

Section: Introductionmentioning

confidence: 99%

Seismic parameters of hcp‐Fe alloyed with Ni and Si in the Earth's inner core

et al. 2016

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Iron alloyed with Ni and Si has been suggested to be a major component of the Earth's inner core. High‐pressure results on the combined alloying effects of Ni and Si on seismic parameters of iron are thus essential for establishing satisfactory geophysical and geochemical models of the region. Here we have investigated the compressional (VP) and shear (Vs) wave velocity‐density (ρ) relations, Poisson's ratio (ν), and seismic heterogeneity ratios (dlnρ/dlnVP, dlnρ/dlnVS, and dlnVP/dlnVS) of hcp‐Fe and hcp‐Fe86.8Ni8.6Si4.6 alloy up to 206 GPa and 136 GPa, respectively, using multiple complementary techniques. Compared with the literature velocity values for hcp‐Fe and Fe‐Ni‐Si alloys, our results show that the combined addition of 9.0 wt % Ni and 2.3 wt % Si slightly increases the VP but significantly decreases the VS of hcp‐Fe at a given density relevant to the inner core. Such distinct alloying effects on velocities of hcp‐Fe produce a high ν of about 0.40 for the alloy at inner core densities, which is approximately 20% higher than that for hcp‐Fe. Analysis of the literature high P‐T results on VP and VS of Fe alloyed with light elements shows that high temperature can further enhance the ν of hcp‐Fe alloyed with Ni and Si. Most significantly, the derived seismic heterogeneity ratios of this hcp alloy present a better match with global seismic observations. Our results provide a multifactored geophysical constraint on the compositional model of the inner core which is consistent with silicon being a major light element alloyed with Fe and 5 wt % Ni.

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The structure of Fe–Si alloy in Earth's inner core

Cited by 84 publications

References 56 publications

Equation of State for Shocked Fe‐8.6 wt% Si up to 240 GPa and 4,670 K

Equation of State for Shocked Fe‐8.6 wt% Si up to 240 GPa and 4,670 K

High pressure metal–silicate partitioning of Ni, Co, V, Cr, Si, and O

Seismic parameters of hcp‐Fe alloyed with Ni and Si in the Earth's inner core

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