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Neodymium stable isotope fractionation in minerals: Implications for Earth's differentiation, and planetary formation.

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Title: Neodymium stable isotope fractionation in minerals: Implications for Earth's differentiation, and planetary formation.
Authors: Nestmeyer, Mark1,2 (AUTHOR) mark.nestmeyer@my.jcu.edu.au, McCoy-West, Alex J.1,3 (AUTHOR)
Source: Geochimica et Cosmochimica Acta. May2026, Vol. 421, p342-355. 14p.
Subjects: Neodymium isotopes, Stable isotopes, Nebular hypothesis, Rare earth metals, Isotope geology, Internal structure of the Earth, Origin of planets
Abstract: The application of rare Earth element stable isotope compositions has become of increasing interest in geochemistry. Recently, studies have begun exploring variations in the stable 146Nd/144Nd isotope ratio in geological samples, with limited isotope fractionation observed in igneous rocks but significantly larger fractionations seen in low temperature systems. Experimental and theoretical studies on the equilibrium isotope fractionation of Nd are widely missing which can support understanding the fractionation of Nd isotopes among Earth's major reservoirs. Here, we have modelled the isotope fractionation factors for 15 common rock forming and accessory minerals to help understand equilibrium stable isotope fractionation during medium to high temperature processes. We estimate that mantle melting will produce minimal isotope fractionation while the residual peridotite ought to retain heavier Nd isotopes which could explain a potentially superchondritic composition of the depleted mantle. This can be predicted because in mantle minerals with Mg sites (e.g. olivine, orthopyroxene) substitution of isotopically heavier Nd is preferred compared to minerals with Ca sites (e.g. clinopyroxene), with the latter being the major contributor to basaltic melts. The Earth's outer core (i.e. sulfide matte) is a potential host of lighter Nd isotopes which we demonstrate favours sulfides over silicates. However, the low partition coefficients of rare Earth elements into the core leads to a composition of the bulk silicate Earth that is indistinguishable from chondrites. A better understanding of the δ 146/144Nd composition of the mantle is warranted to elucidate the isotope fractionation of Nd between Earth's major geochemical reservoirs. As Nd condenses from the solar nebular gas into primitive material, the mass-independent nuclear field shift effect dominates equilibrium isotope fractionation and produces significant fractionation in δ 146/144Nd even at high temperatures (>1000 °C) with the condensed material enriched in lighter Nd isotopes. However, the isotopic compositions reported for refractory inclusions (–1.86 to 2.20 ‰; Hu et al. (2021)) cannot be solely explained by equilibrium isotope fractionation and other mechanisms are required. [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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  Data: Neodymium stable isotope fractionation in minerals: Implications for Earth's differentiation, and planetary formation.
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  Data: <searchLink fieldCode="AR" term="%22Nestmeyer%2C+Mark%22">Nestmeyer, Mark</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<i> mark.nestmeyer@my.jcu.edu.au</i><br /><searchLink fieldCode="AR" term="%22McCoy-West%2C+Alex+J%2E%22">McCoy-West, Alex J.</searchLink><relatesTo>1,3</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. May2026, Vol. 421, p342-355. 14p.
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  Data: <searchLink fieldCode="DE" term="%22Neodymium+isotopes%22">Neodymium isotopes</searchLink><br /><searchLink fieldCode="DE" term="%22Stable+isotopes%22">Stable isotopes</searchLink><br /><searchLink fieldCode="DE" term="%22Nebular+hypothesis%22">Nebular hypothesis</searchLink><br /><searchLink fieldCode="DE" term="%22Rare+earth+metals%22">Rare earth metals</searchLink><br /><searchLink fieldCode="DE" term="%22Isotope+geology%22">Isotope geology</searchLink><br /><searchLink fieldCode="DE" term="%22Internal+structure+of+the+Earth%22">Internal structure of the Earth</searchLink><br /><searchLink fieldCode="DE" term="%22Origin+of+planets%22">Origin of planets</searchLink>
– Name: Abstract
  Label: Abstract
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  Data: The application of rare Earth element stable isotope compositions has become of increasing interest in geochemistry. Recently, studies have begun exploring variations in the stable 146Nd/144Nd isotope ratio in geological samples, with limited isotope fractionation observed in igneous rocks but significantly larger fractionations seen in low temperature systems. Experimental and theoretical studies on the equilibrium isotope fractionation of Nd are widely missing which can support understanding the fractionation of Nd isotopes among Earth's major reservoirs. Here, we have modelled the isotope fractionation factors for 15 common rock forming and accessory minerals to help understand equilibrium stable isotope fractionation during medium to high temperature processes. We estimate that mantle melting will produce minimal isotope fractionation while the residual peridotite ought to retain heavier Nd isotopes which could explain a potentially superchondritic composition of the depleted mantle. This can be predicted because in mantle minerals with Mg sites (e.g. olivine, orthopyroxene) substitution of isotopically heavier Nd is preferred compared to minerals with Ca sites (e.g. clinopyroxene), with the latter being the major contributor to basaltic melts. The Earth's outer core (i.e. sulfide matte) is a potential host of lighter Nd isotopes which we demonstrate favours sulfides over silicates. However, the low partition coefficients of rare Earth elements into the core leads to a composition of the bulk silicate Earth that is indistinguishable from chondrites. A better understanding of the δ 146/144Nd composition of the mantle is warranted to elucidate the isotope fractionation of Nd between Earth's major geochemical reservoirs. As Nd condenses from the solar nebular gas into primitive material, the mass-independent nuclear field shift effect dominates equilibrium isotope fractionation and produces significant fractionation in δ 146/144Nd even at high temperatures (>1000 °C) with the condensed material enriched in lighter Nd isotopes. However, the isotopic compositions reported for refractory inclusions (–1.86 to 2.20 ‰; Hu et al. (2021)) cannot be solely explained by equilibrium isotope fractionation and other mechanisms are required. [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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      – Type: doi
        Value: 10.1016/j.gca.2026.03.022
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      – Code: eng
        Text: English
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        PageCount: 14
        StartPage: 342
    Subjects:
      – SubjectFull: Neodymium isotopes
        Type: general
      – SubjectFull: Stable isotopes
        Type: general
      – SubjectFull: Nebular hypothesis
        Type: general
      – SubjectFull: Rare earth metals
        Type: general
      – SubjectFull: Isotope geology
        Type: general
      – SubjectFull: Internal structure of the Earth
        Type: general
      – SubjectFull: Origin of planets
        Type: general
    Titles:
      – TitleFull: Neodymium stable isotope fractionation in minerals: Implications for Earth's differentiation, and planetary formation.
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            NameFull: Nestmeyer, Mark
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            NameFull: McCoy-West, Alex J.
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            – D: 15
              M: 05
              Text: May2026
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              Y: 2026
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