Experimental constraints on the fate of H and C during planetary core-mantle differentiation. Implications for the Earth

Malavergne, Valérie; Bureau, Hélène; Raepsaet, Caroline; Gaillard, Fabrice; Poncet, Mélissa; Surblé, Suzy; Sebag, David; Shcheka, Svyatoslav; Fourdrin, Chloé; Deldicque, Damien; Khodja, H.

doi:10.1016/j.icarus.2018.11.027

Cited by 50 publications

(63 citation statements)

References 75 publications

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“…5, we plot our partitioning coefficients of H and H2O to compare with the literature. Our results agree with the findings of Kuramoto 5 and Malavergne et al 6 , hydrogen was introduced into the system by adding Al(OH)3 and brucite, and the H2O/MgSiO3 molar ratio is far less than that in Okuchi's experiments 2 . It is speculated that " # is low in experiments of Clesi et al 5 and Malavergne et al 6 , and the actual condition could be more like our oxidising case " # $ / " # &" # $ = 1.…”

Section: Pressure and Temperature Dependence Of Water Partitioningsupporting

confidence: 93%

“…Our H2O partitioning coefficient strongly increases from 20 GPa to 50 GPa. The data of Clesi et al 5 and Malavergne et al 6 at more oxidising conditions also show a similar trend from low pressures to ~20 GPa. Unfortunately, their data do not extend to 50 GPa and so cannot be used to confirm our high-pressure results, but the overlap at 20 GPa between our results and the experimental results is reassuring.…”

Section: Pressure and Temperature Dependence Of Water Partitioningsupporting

confidence: 58%

“…The contradiction to previous results was attributed to fugacity and possibly also the presence of carbon in samples. Malavergne et al 6 coupled the use of ERDA and Secondary Ion Mass Spectrometry (SIMS) to measure the hydrogen partition coefficient. Their study confirmed the pressure effect on hydrogen partitioning observed before, and also suggest that hydrogen could change from lithophile to siderophile above ~15 GPa.…”

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confidence: 99%

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The Earth’s core as a reservoir of water

Vočadlo

Sun

et al. 2020

Nat. Geosci.

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Current estimates of the budget and distribution of water in the Earth have large uncertainties, most of which come from the lack of information about the deep Earth. Recent studies suggest that the Earth could have gained a considerable amount of water during the early stages of Earth's evolution from the hydrogen-rich solar nebula, and that a large amount of the water in the Earth may have partitioned into the core. Here, we calculate the partitioning of water between iron and silicate melts at 20-135 gigapascals and 2800-5000 kelvin, using ab initio molecular dynamics and thermodynamic integration techniques. Our results indicate a siderophile nature of water at core-mantle differentiation and core-mantle boundary conditions, which can be weakened with increasing temperature; nevertheless, we find that water always partitions strongly into the iron liquid at both reducing and oxidising conditions. The siderophile nature of water is also verified by an empirical-counting method showing the distribution of hydrogen in an equilibrated iron and silicate melt. We therefore conclude that the Earth's core may act as a large reservoir containing most of the Earth's water. In addition to constraining accretion models and water distribution, the findings may partially account for the mismatch between mineral physics and seismic observations in the Earth's core.

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Section: Pressure and Temperature Dependence Of Water Partitioningsupporting

confidence: 93%

Section: Pressure and Temperature Dependence Of Water Partitioningsupporting

confidence: 58%

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confidence: 99%

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The Earth’s core as a reservoir of water

Vočadlo

Sun

et al. 2020

Nat. Geosci.

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“…The predicted K D value at 20 GPa (2,500 K) agrees with partition experiments of Okuchi (1997) at 7.5 GPa, and is in reasonable agreement with the experiments of Clesi et al (2018) at P ~ 20 GPa (SI, Table S6), although our results suggest a slightly stronger siderophile behavior. Differences in partitioning of hydrogen between the experiments by Okuchi (1997), on the one hand, and Clesi et al (2018) and Malavergne et al (2019), on the other hand, stem from the fact that Okuchi (1997) accounts for bubble volume in the recovered metal that reflects exsolved hydrogen during quench due to its low solubility in solid Fe at ambient conditions (Antonov et al, 1998, 2019; Fukai & Suzuki, 1986). Hirose et al (2019) and Umemoto and Hirose (2020) similarly arrive at the conclusion that the experiments by Clesi et al (2018) and Malavergne et al (2019) underestimate the hydrogen content in the metal.…”

Section: Resultsmentioning

confidence: 96%

Strong Sequestration of Hydrogen Into the Earth's Core During Planetary Differentiation

Yuan

Steinle‐Neumann

2020

Geophysical Research Letters

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We explore the partitioning behavior of hydrogen between coexisting metal and silicate melts at conditions of the magma ocean and the current core–mantle boundary with the help of density functional theory molecular dynamics. We perform simulations with the two‐phase and thermodynamic integration methods. We find that hydrogen is weakly siderophile at low pressure (20 GPa and 2,500 K), and becomes much more strongly so with pressure, suggesting that hydrogen is transported to the core in a significant amount during core segregation and is stable there. Based on our results, the core likely contains ~1 wt% H, assuming single‐stage formation and equilibration at 40 GPa. Our two‐phase simulations further suggest that silicon is entrained in the core‐forming metal, while magnesium remains in the silicate phase. This preferred incorporation of silicon hints at an explanation for the elevated Mg/Si ratio of the bulk silicate Earth relative to chondritic compositions.

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“…The previous metal-silicate partitioning experiments by Clesi et al (2018) and Malavergne et al (2019) argued that hydrogen is least partitioned into molten iron. However, they found at most only~500 ppm H in quenched molten Fe, because the vast majority of hydrogen had been lost during decompression.…”

Section: Introductionmentioning

confidence: 96%

Hydrogen Limits Carbon in Liquid Iron

Hirose

Tagawa

Kuwayama

et al. 2019

Geophysical Research Letters

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Melting experiments were performed on the Fe‐C‐H system to 127 GPa in a laser‐heated diamond anvil cell. On the basis of in situ and ex situ sample characterizations, we found that the solubility of carbon in liquid Fe correlates inversely with hydrogen concentration at ~60 GPa and ~3500 K, indicating that liquid Fe preferentially incorporates hydrogen rather than carbon under conditions with abundant C and H. While large amounts of both C and H may have been delivered to the growing Earth, C‐poor/H‐rich metals were likely added to the protocore in the late stages of core formation. We also obtained a melting curve of FeHx (x > 1) far beyond the pressure range in earlier determinations. Its liquidus temperature was found to be 2380 K at 135 GPa, lower than those of Fe alloyed with the other possible core light elements. Relatively low core temperature is thus supported by the presence of hydrogen.

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Experimental constraints on the fate of H and C during planetary core-mantle differentiation. Implications for the Earth

Cited by 50 publications

References 75 publications

The Earth’s core as a reservoir of water

The Earth’s core as a reservoir of water

Strong Sequestration of Hydrogen Into the Earth's Core During Planetary Differentiation

Hydrogen Limits Carbon in Liquid Iron

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