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Diffusion-driven zircon Zr isotopic fractionation during ultramafic–mafic magmatic differentiation.

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Title: Diffusion-driven zircon Zr isotopic fractionation during ultramafic–mafic magmatic differentiation.
Authors: Ma, Li-Tao1 (AUTHOR), Dai, Li-Qun1,2 (AUTHOR) lqdai@ustc.edu.cn, Zhang, Shao-Bing1,2 (AUTHOR), Chen, Ren-Xu1,2 (AUTHOR), Xia, Qiong-Xia1,2 (AUTHOR), Zhao, Zi-Fu1,2 (AUTHOR)
Source: Geochimica et Cosmochimica Acta. Jul2025, Vol. 400, p129-141. 13p.
Subjects: Isotopic fractionation, Igneous intrusions, Mafic rocks, Stable isotopes, Isotopic analysis, Supersaturation
Abstract: Previous studies of natural samples have documented marked variations in zircon Zr stable isotopes. However, the petrological mechanisms responsible for Zr stable isotopic fractionation during magmatic differentiation remain unclear. To address this, in situ Zr stable isotopic analyses of magmatic zircons were carried out on a suite of mafic plutonic rocks from the southwestern Tianshan, west China. Our results suggest that diffusion-driven Zr stable isotopic fractionation during zircon growth produces per mil-level, mass-dependent isotopic fractionation. Zircon Zr stable isotopic compositions range from –4.50 ‰ to +1.48 ‰, spanning a variation of 5.98 ‰. Some zircon grains exhibit internal Zr stable isotopic zoning, with lighter Zr isotopes in the core and heavier Zr isotope toward the rim, with intra-grain variations of up to 2.82 ‰. In addition, these zircons exhibit significant intra-grain variations in Zr/Hf ratios and Ti contents, which generally decrease with increasing δ 94/90Zr values. While the Zr/Hf and Ti variations likely record fractional crystallization processes, the Zr stable isotopic variations cannot be attributed to mass-dependent, stable isotopic equilibrium fractionation, which would produce only ∼0.08 ‰ fractionation at 800 °C. As the temperature decreases and Zr supersaturation in the magma increases, the Zr stable isotopic fractionation becomes more pronounced. The δ 94/90Zr values exhibit increasing variability toward both higher and lower values, rather than trending in a single direction. These variable Zr stable isotopic compositions can be explained by the diffusion-limited crystallization (DLC), which is primarily controlled by the zircon crystallization temperature and Zr supersaturation in the melt. As temperature decreases during magmatic differentiation, the diffusion-driven zircon Zr isotopic fractionation is enhanced. Therefore, diffusion during crystal accumulation provides a plausible explanation for the large Zr stable isotopic variability observed in zircons. [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: Diffusion-driven zircon Zr isotopic fractionation during ultramafic–mafic magmatic differentiation.
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  Data: <searchLink fieldCode="AR" term="%22Ma%2C+Li-Tao%22">Ma, Li-Tao</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Dai%2C+Li-Qun%22">Dai, Li-Qun</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<i> lqdai@ustc.edu.cn</i><br /><searchLink fieldCode="AR" term="%22Zhang%2C+Shao-Bing%22">Zhang, Shao-Bing</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Chen%2C+Ren-Xu%22">Chen, Ren-Xu</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Xia%2C+Qiong-Xia%22">Xia, Qiong-Xia</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Zhao%2C+Zi-Fu%22">Zhao, Zi-Fu</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. Jul2025, Vol. 400, p129-141. 13p.
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  Data: <searchLink fieldCode="DE" term="%22Isotopic+fractionation%22">Isotopic fractionation</searchLink><br /><searchLink fieldCode="DE" term="%22Igneous+intrusions%22">Igneous intrusions</searchLink><br /><searchLink fieldCode="DE" term="%22Mafic+rocks%22">Mafic rocks</searchLink><br /><searchLink fieldCode="DE" term="%22Stable+isotopes%22">Stable isotopes</searchLink><br /><searchLink fieldCode="DE" term="%22Isotopic+analysis%22">Isotopic analysis</searchLink><br /><searchLink fieldCode="DE" term="%22Supersaturation%22">Supersaturation</searchLink>
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  Data: Previous studies of natural samples have documented marked variations in zircon Zr stable isotopes. However, the petrological mechanisms responsible for Zr stable isotopic fractionation during magmatic differentiation remain unclear. To address this, in situ Zr stable isotopic analyses of magmatic zircons were carried out on a suite of mafic plutonic rocks from the southwestern Tianshan, west China. Our results suggest that diffusion-driven Zr stable isotopic fractionation during zircon growth produces per mil-level, mass-dependent isotopic fractionation. Zircon Zr stable isotopic compositions range from –4.50 ‰ to +1.48 ‰, spanning a variation of 5.98 ‰. Some zircon grains exhibit internal Zr stable isotopic zoning, with lighter Zr isotopes in the core and heavier Zr isotope toward the rim, with intra-grain variations of up to 2.82 ‰. In addition, these zircons exhibit significant intra-grain variations in Zr/Hf ratios and Ti contents, which generally decrease with increasing δ 94/90Zr values. While the Zr/Hf and Ti variations likely record fractional crystallization processes, the Zr stable isotopic variations cannot be attributed to mass-dependent, stable isotopic equilibrium fractionation, which would produce only ∼0.08 ‰ fractionation at 800 °C. As the temperature decreases and Zr supersaturation in the magma increases, the Zr stable isotopic fractionation becomes more pronounced. The δ 94/90Zr values exhibit increasing variability toward both higher and lower values, rather than trending in a single direction. These variable Zr stable isotopic compositions can be explained by the diffusion-limited crystallization (DLC), which is primarily controlled by the zircon crystallization temperature and Zr supersaturation in the melt. As temperature decreases during magmatic differentiation, the diffusion-driven zircon Zr isotopic fractionation is enhanced. Therefore, diffusion during crystal accumulation provides a plausible explanation for the large Zr stable isotopic variability observed in zircons. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
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  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.2025.04.020
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 13
        StartPage: 129
    Subjects:
      – SubjectFull: Isotopic fractionation
        Type: general
      – SubjectFull: Igneous intrusions
        Type: general
      – SubjectFull: Mafic rocks
        Type: general
      – SubjectFull: Stable isotopes
        Type: general
      – SubjectFull: Isotopic analysis
        Type: general
      – SubjectFull: Supersaturation
        Type: general
    Titles:
      – TitleFull: Diffusion-driven zircon Zr isotopic fractionation during ultramafic–mafic magmatic differentiation.
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            NameFull: Ma, Li-Tao
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            NameFull: Dai, Li-Qun
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            NameFull: Zhang, Shao-Bing
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            NameFull: Chen, Ren-Xu
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            NameFull: Xia, Qiong-Xia
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            NameFull: Zhao, Zi-Fu
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            – D: 01
              M: 07
              Text: Jul2025
              Type: published
              Y: 2025
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              Value: 400
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