Most Earth-surface calcites precipitate out of isotopic equilibrium

Abstract : Oxygen-isotope thermometry played a critical role in the rise of modern geochemistry and remains extensively used in (bio-)geoscience. Its theoretical foundations rest on the assumption that 18O/16O partitioning among water and carbonate minerals primarily reflects thermodynamic equilibrium. However, after decades of research, there is no consensus on the true equilibrium 18O/16O fractionation between calcite and water (18alphacc/w). Here, we constrain the equilibrium relations linking temperature, 18alphacc/w, and clumped isotopes (Delta47) based on the composition of extremely slow-growing calcites from Devils Hole and Laghetto Basso (Corchia Cave). Equilibrium 18alphacc/w values are systematically ~1.5 greater than those in biogenic and synthetic calcite traditionally considered to approach oxygen-isotope equilibrium. We further demonstrate that subtle disequilibria also affect Delta47 in biogenic calcite. These observations provide evidence that most Earth-surface calcites fail to achieve isotopic equilibrium, highlighting the need to improve our quantitative understanding of non-equilibrium isotope fractionation effects instead of relying on phenomenological calibrations.
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https://hal.archives-ouvertes.fr/hal-02011797
Contributor : Christine Maury Referent Hal Edytem <>
Submitted on : Friday, February 8, 2019 - 11:10:06 AM
Last modification on : Saturday, April 20, 2019 - 2:01:30 AM

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  • HAL Id : hal-02011797, version 1

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M. Daëron, R. Drysdale, M. Peral, D. Huyghe, D. Blamart, et al.. Most Earth-surface calcites precipitate out of isotopic equilibrium. Nature Communications, Nature Publishing Group, 2019, 10 (1). ⟨hal-02011797⟩

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