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Experimental constraints on germanium diffusivity in metal and silicate phases during core formation of planetesimals and terrestrial planets.

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Title: Experimental constraints on germanium diffusivity in metal and silicate phases during core formation of planetesimals and terrestrial planets.
Authors: Le Bellego, Baptiste1 (AUTHOR) baptiste.le-bellego@univ-lorraine.fr, Dalou, Celia1 (AUTHOR) celia.dalou@univ-lorraine.fr, Luais, Béatrice1 (AUTHOR) beatrice.luais@univ-lorraine.fr, Condamine, Pierre2 (AUTHOR) pierre.condamine@uca.fr, Motto-Ros, Vincent3 (AUTHOR) vincent.motto-ros@univ-lyon1.fr, Tissandier, Laurent1 (AUTHOR) laurent.tissandier@univ-lorraine.fr
Source: Geochimica et Cosmochimica Acta. Jun2026, Vol. 422, p397-411. 15p.
Subjects: Diffusion coefficients, Oxidation-reduction potential, Planetesimals, Inner planets, Internal structure of the Earth, Analytical geochemistry, High pressure (Science)
Abstract: The segregation of metallic cores from silicate mantles during early planetary differentiation is a key process shaping the chemical evolution of terrestrial bodies. A critical factor controlling metal-silicate equilibration during this stage is the diffusive behavior of moderately siderophile elements, which governs chemical exchange timescales. As a moderately siderophile and moderately volatile element, Ge is particularly sensitive to redox conditions, pressure, temperature, and the presence of light elements in the metal phase, making it an ideal tracer of core formation processes. However, experimental constraints on Ge diffusion under relevant high-pressure, high-temperature, and low oxygen fugacity conditions are lacking. Here, we present new experimental measurements of Ge diffusion coefficients in Fe-Ni metal and silicate (CMAS) melt, analogous to planetary cores and mantles, under high-pressure (0.5 – 1 GPa), high-temperature (1350 °C) conditions and low oxygen fugacities (IW-5.4 to IW-1.5). Ge diffusion in liquid silicate and liquid metal was found to be significantly faster (∼10−11 m2/s) than in solid metal (∼10−13 m2/s), with transport further influenced by oxygen fugacity and Si content. Under highly reducing conditions, high Si concentrations inhibit Ge diffusion in solid metal by reducing vacancy availability and inducing partial melting, forming immiscible metal droplets that act as localized Ge sinks. Diffusion timescale calculations indicate that, for Earth-like planets, even at high temperatures (1800 °C), estimated equilibration times are too long for large metal fragments (>10 m) to fully equilibrate before descending to the core. Thus, additional processes such as turbulent convection or percolation are required for efficient metal–silicate exchange. In contrast, on Mars-like bodies with long-lived magma oceans, solely diffusion, even at low temperature (1350 °C), could be sufficient to equilibrate large metal fragments. [ABSTRACT FROM AUTHOR]
Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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DbLabel: Engineering Source
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  Label: Title
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  Data: Experimental constraints on germanium diffusivity in metal and silicate phases during core formation of planetesimals and terrestrial planets.
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  Data: <searchLink fieldCode="AR" term="%22Le+Bellego%2C+Baptiste%22">Le Bellego, Baptiste</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> baptiste.le-bellego@univ-lorraine.fr</i><br /><searchLink fieldCode="AR" term="%22Dalou%2C+Celia%22">Dalou, Celia</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> celia.dalou@univ-lorraine.fr</i><br /><searchLink fieldCode="AR" term="%22Luais%2C+Béatrice%22">Luais, Béatrice</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> beatrice.luais@univ-lorraine.fr</i><br /><searchLink fieldCode="AR" term="%22Condamine%2C+Pierre%22">Condamine, Pierre</searchLink><relatesTo>2</relatesTo> (AUTHOR)<i> pierre.condamine@uca.fr</i><br /><searchLink fieldCode="AR" term="%22Motto-Ros%2C+Vincent%22">Motto-Ros, Vincent</searchLink><relatesTo>3</relatesTo> (AUTHOR)<i> vincent.motto-ros@univ-lyon1.fr</i><br /><searchLink fieldCode="AR" term="%22Tissandier%2C+Laurent%22">Tissandier, Laurent</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> laurent.tissandier@univ-lorraine.fr</i>
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  Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. Jun2026, Vol. 422, p397-411. 15p.
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  Data: <searchLink fieldCode="DE" term="%22Diffusion+coefficients%22">Diffusion coefficients</searchLink><br /><searchLink fieldCode="DE" term="%22Oxidation-reduction+potential%22">Oxidation-reduction potential</searchLink><br /><searchLink fieldCode="DE" term="%22Planetesimals%22">Planetesimals</searchLink><br /><searchLink fieldCode="DE" term="%22Inner+planets%22">Inner planets</searchLink><br /><searchLink fieldCode="DE" term="%22Internal+structure+of+the+Earth%22">Internal structure of the Earth</searchLink><br /><searchLink fieldCode="DE" term="%22Analytical+geochemistry%22">Analytical geochemistry</searchLink><br /><searchLink fieldCode="DE" term="%22High+pressure+%28Science%29%22">High pressure (Science)</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: The segregation of metallic cores from silicate mantles during early planetary differentiation is a key process shaping the chemical evolution of terrestrial bodies. A critical factor controlling metal-silicate equilibration during this stage is the diffusive behavior of moderately siderophile elements, which governs chemical exchange timescales. As a moderately siderophile and moderately volatile element, Ge is particularly sensitive to redox conditions, pressure, temperature, and the presence of light elements in the metal phase, making it an ideal tracer of core formation processes. However, experimental constraints on Ge diffusion under relevant high-pressure, high-temperature, and low oxygen fugacity conditions are lacking. Here, we present new experimental measurements of Ge diffusion coefficients in Fe-Ni metal and silicate (CMAS) melt, analogous to planetary cores and mantles, under high-pressure (0.5 – 1 GPa), high-temperature (1350 °C) conditions and low oxygen fugacities (IW-5.4 to IW-1.5). Ge diffusion in liquid silicate and liquid metal was found to be significantly faster (∼10−11 m2/s) than in solid metal (∼10−13 m2/s), with transport further influenced by oxygen fugacity and Si content. Under highly reducing conditions, high Si concentrations inhibit Ge diffusion in solid metal by reducing vacancy availability and inducing partial melting, forming immiscible metal droplets that act as localized Ge sinks. Diffusion timescale calculations indicate that, for Earth-like planets, even at high temperatures (1800 °C), estimated equilibration times are too long for large metal fragments (>10 m) to fully equilibrate before descending to the core. Thus, additional processes such as turbulent convection or percolation are required for efficient metal–silicate exchange. In contrast, on Mars-like bodies with long-lived magma oceans, solely diffusion, even at low temperature (1350 °C), could be sufficient to equilibrate large metal fragments. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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      – Type: doi
        Value: 10.1016/j.gca.2025.11.038
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 15
        StartPage: 397
    Subjects:
      – SubjectFull: Diffusion coefficients
        Type: general
      – SubjectFull: Oxidation-reduction potential
        Type: general
      – SubjectFull: Planetesimals
        Type: general
      – SubjectFull: Inner planets
        Type: general
      – SubjectFull: Internal structure of the Earth
        Type: general
      – SubjectFull: Analytical geochemistry
        Type: general
      – SubjectFull: High pressure (Science)
        Type: general
    Titles:
      – TitleFull: Experimental constraints on germanium diffusivity in metal and silicate phases during core formation of planetesimals and terrestrial planets.
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            NameFull: Le Bellego, Baptiste
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            NameFull: Dalou, Celia
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            NameFull: Luais, Béatrice
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            NameFull: Condamine, Pierre
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          Dates:
            – D: 01
              M: 06
              Text: Jun2026
              Type: published
              Y: 2026
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              Value: 422
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