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Lithium isotope fractionation in LCT pegmatite systems: a density functional theory study.

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Title: Lithium isotope fractionation in LCT pegmatite systems: a density functional theory study.
Authors: Lin, He-Feng1 (AUTHOR), Zhu, Wen-Bin1 (AUTHOR) zwb@nju.edu.cn, Wei, Hai-Zhen1 (AUTHOR) haizhenwei@nju.edu.cn, Xu, Xi-Sheng1 (AUTHOR), Xu, Zhi-Qin1 (AUTHOR), Palmer, M.R.2 (AUTHOR), Chen, Shuang3 (AUTHOR), Ma, Jing4 (AUTHOR), Li, Yin-Chuan5 (AUTHOR), Zuo, Da-Sheng1 (AUTHOR), Yang, Ke1 (AUTHOR)
Source: Geochimica et Cosmochimica Acta. May2026, Vol. 421, p157-178. 22p.
Subjects: Lithium isotopes, Density functional theory, Fluids, Crystallization, Pegmatites, Kinetic isotope effects, Molecular dynamics
Abstract: Lithium is a fluid-mobile and incompatible element, that is enriched in highly differentiated felsic systems, particularly in lithium-cesium-tantalum (LCT) pegmatites. While Li isotope fractionation has often been considered negligible at magmatic temperatures, recent studies reveal variations of Li isotope (δ7Li) exceeding 10‰ in pegmatites, highlighting the need for a quantitative understanding of the controlling mechanisms. A key limitation lies in the absence of reliable fractionation factors for silicate melts, likely due to the complexities in melt structures, composition, and dynamics. To address this knowledge gap, ab initio molecular dynamics and density functional theory calculation were used to compute equilibrium lithium isotope fractionation factors among Li-bearing minerals, hydrothermal fluids, and felsic melts. The results show that the composition, water content, and halogen (F/Cl) significantly influence Li isotope partitioning by modifying Li‒O bond length, coordination environments, and polyhedral structure. At the deposit scale, compilation of δ7Li data from LCT pegmatites and granites worldwide shows that the largest isotope fractionation occurs prior to lithium mineralization. To investigate the underlying mechanisms, we developed numerical models incorporating fractional crystallization, fluid exsolution, melt-melt immiscibility, and further kinetic isotope effects associated with rapid crystal growth and diffusion. The results demonstrate that fractional crystallization and melt-melt immiscibility induce δ7Li variations of up to ∼ 3‰, whereas fluid exsolution can drive δ7Li shifts exceeding 10‰ in residual melts at magmatic temperatures. Additionally, kinetic induced isotope fractionation further contributes to shifts in δ7Li up to 15‰. These findings suggest that the pronounced Li isotope variations (>10‰) observed in pegmatite deposits, such as Jiajika, Tin Mountain, and Qinghe, are dominantly controlled by fluid exsolution and kinetic effects, providing new insights into the lithium isotopic evolution during petrogenesis and mineralization of pegmatite systems. [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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  Data: Lithium isotope fractionation in LCT pegmatite systems: a density functional theory study.
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  Data: <searchLink fieldCode="AR" term="%22Lin%2C+He-Feng%22">Lin, He-Feng</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Zhu%2C+Wen-Bin%22">Zhu, Wen-Bin</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> zwb@nju.edu.cn</i><br /><searchLink fieldCode="AR" term="%22Wei%2C+Hai-Zhen%22">Wei, Hai-Zhen</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> haizhenwei@nju.edu.cn</i><br /><searchLink fieldCode="AR" term="%22Xu%2C+Xi-Sheng%22">Xu, Xi-Sheng</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Xu%2C+Zhi-Qin%22">Xu, Zhi-Qin</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Palmer%2C+M%2ER%2E%22">Palmer, M.R.</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Chen%2C+Shuang%22">Chen, Shuang</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Ma%2C+Jing%22">Ma, Jing</searchLink><relatesTo>4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Li%2C+Yin-Chuan%22">Li, Yin-Chuan</searchLink><relatesTo>5</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Zuo%2C+Da-Sheng%22">Zuo, Da-Sheng</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Yang%2C+Ke%22">Yang, Ke</searchLink><relatesTo>1</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. May2026, Vol. 421, p157-178. 22p.
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  Data: <searchLink fieldCode="DE" term="%22Lithium+isotopes%22">Lithium isotopes</searchLink><br /><searchLink fieldCode="DE" term="%22Density+functional+theory%22">Density functional theory</searchLink><br /><searchLink fieldCode="DE" term="%22Fluids%22">Fluids</searchLink><br /><searchLink fieldCode="DE" term="%22Crystallization%22">Crystallization</searchLink><br /><searchLink fieldCode="DE" term="%22Pegmatites%22">Pegmatites</searchLink><br /><searchLink fieldCode="DE" term="%22Kinetic+isotope+effects%22">Kinetic isotope effects</searchLink><br /><searchLink fieldCode="DE" term="%22Molecular+dynamics%22">Molecular dynamics</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Lithium is a fluid-mobile and incompatible element, that is enriched in highly differentiated felsic systems, particularly in lithium-cesium-tantalum (LCT) pegmatites. While Li isotope fractionation has often been considered negligible at magmatic temperatures, recent studies reveal variations of Li isotope (δ7Li) exceeding 10‰ in pegmatites, highlighting the need for a quantitative understanding of the controlling mechanisms. A key limitation lies in the absence of reliable fractionation factors for silicate melts, likely due to the complexities in melt structures, composition, and dynamics. To address this knowledge gap, ab initio molecular dynamics and density functional theory calculation were used to compute equilibrium lithium isotope fractionation factors among Li-bearing minerals, hydrothermal fluids, and felsic melts. The results show that the composition, water content, and halogen (F/Cl) significantly influence Li isotope partitioning by modifying Li‒O bond length, coordination environments, and polyhedral structure. At the deposit scale, compilation of δ7Li data from LCT pegmatites and granites worldwide shows that the largest isotope fractionation occurs prior to lithium mineralization. To investigate the underlying mechanisms, we developed numerical models incorporating fractional crystallization, fluid exsolution, melt-melt immiscibility, and further kinetic isotope effects associated with rapid crystal growth and diffusion. The results demonstrate that fractional crystallization and melt-melt immiscibility induce δ7Li variations of up to ∼ 3‰, whereas fluid exsolution can drive δ7Li shifts exceeding 10‰ in residual melts at magmatic temperatures. Additionally, kinetic induced isotope fractionation further contributes to shifts in δ7Li up to 15‰. These findings suggest that the pronounced Li isotope variations (>10‰) observed in pegmatite deposits, such as Jiajika, Tin Mountain, and Qinghe, are dominantly controlled by fluid exsolution and kinetic effects, providing new insights into the lithium isotopic evolution during petrogenesis and mineralization of pegmatite systems. [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.2026.02.035
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 22
        StartPage: 157
    Subjects:
      – SubjectFull: Lithium isotopes
        Type: general
      – SubjectFull: Density functional theory
        Type: general
      – SubjectFull: Fluids
        Type: general
      – SubjectFull: Crystallization
        Type: general
      – SubjectFull: Pegmatites
        Type: general
      – SubjectFull: Kinetic isotope effects
        Type: general
      – SubjectFull: Molecular dynamics
        Type: general
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      – TitleFull: Lithium isotope fractionation in LCT pegmatite systems: a density functional theory study.
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              M: 05
              Text: May2026
              Type: published
              Y: 2026
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