Zircon growth experiments reveal limited equilibrium Zr isotope fractionation in magmas
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1.
University of Arizona
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2.
California Institute of Technology
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3.
University of Lausanne
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4.
University of Rochester
Abstract
Recent studies of zirconium isotopes in igneous systems have revealed significant mass dependent variability, the origin of which remains intensely debated. While magmatic zircon crystallisation could potentially drive equilibrium isotope fractionation, given that Zr4+ undergoes a shift in coordination as zircon precipitates from a silicic melt, ab initio calculations predict only limited equilibrium fractionation between zircon and melt at magmatic temperatures. To resolve this debate, we determined the isotopic fractionation between co-existing zircon and silicic melt using controlled zircon growth experiments. Our experimental results indicate that zircon has a lower δ94/90Zr relative to co-existing melt by ∼0.045 ‰ at magmatic conditions, which is in excellent agreement with ab initio predictions. Our results imply that, for most natural systems studied to date, the observed variability is predominantly a result of non-equilibrium rather than equilibrium isotope fractionation during zircon crystallisation.
Copyright and License
© 2023 The Authors. Published by the European Association of Geochemistry under Creative Commons License CC BY-NC-ND 4.0.
Acknowledgement
The authors thank editor Anat Shahar, James Van Orman, and an anonymous reviewer, for constructive reviews that improved the clarity of this article.
Funding
This project was supported by NSF Graduate Research Fellowship award DGE-1746060, an MSA Student Research Grant, and a GSA Student Research Grant (to HGDT), as well as NSF-EAR grants 2131632 and 2143168 (to MIM), 1824002 (to FLHT), 1650033 (to DT), and SNSF Ambizione grant PZ00P2_173988 (to EB). FLHT acknowledges additional support from NSF grant MGG-2054892, a Packard Fellowship, a research award from the Heritage Medical Research Institute, and startup funds from Caltech
Supplemental Material
The Supplementary Information includes (PDF):
- Methods
- Zircon Isotope Data Processing and Modelling Approach
- Supplementary Tables S-1 to S-5
- Figures S-1 to S-6
- Supplementary Information References
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Additional details
Related works
- Is supplemented by
- Supplemental Material: https://www.geochemicalperspectivesletters.org/documents/GPL2310_SIonly.pdf (URL)
Funding
- National Science Foundation
- DGE-1746060
- Mineralogical Society of America
- Geological Society of America
- National Science Foundation
- EAR-2131632
- National Science Foundation
- EAR-2143168
- National Science Foundation
- EAR-1824002
- National Science Foundation
- EAR-1650033
- Swiss National Science Foundation
- PZ00P2_173988
- National Science Foundation
- MGG-2054892
- David and Lucile Packard Foundation
- California Institute of Technology
Dates
- Accepted
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2023-03-01Accepted
- Available
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2023-03-28Published