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Article Dans Une Revue Nature Communications Année : 2019

Most Earth-surface calcites precipitate out of isotopic equilibrium

Résumé

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 18 O/ 16 O partitioning among water and carbonate minerals primarily reflects thermodynamic equilibrium. However, after decades of research, there is no consensus on the true equilibrium 18 O/ 16 O fractionation between calcite and water (18 α cc/w). Here, we constrain the equilibrium relations linking temperature, 18 α cc/w , and clumped isotopes (Δ 47) based on the composition of extremely slow-growing calcites from Devils Hole and Laghetto Basso (Corchia Cave). Equilibrium 18 α cc/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 Δ 47 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.

Domaines

Géochimie
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Dates et versions

hal-02396547 , version 1 (17-09-2020)

Identifiants

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M. Daëron, R. Drysdale, M. Peral, Damien Huyghe, D. Blamart, et al.. Most Earth-surface calcites precipitate out of isotopic equilibrium. Nature Communications, 2019, 10 (1), pp.409. ⟨10.1038/s41467-019-08336-5⟩. ⟨hal-02396547⟩
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