Molecular hydrogen in minerals as a clue to interpret ∂D variations in the mantle

• Published in: Nature communications Vol. 11; no. 1; p. 3604
• Main Authors: Moine, B. N., Bolfan-Casanova, N., Radu, I. B., Ionov, D. A., Costin, G., Korsakov, A. V., Golovin, A. V., Oleinikov, O. B., Deloule, E., Cottin, J. Y.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 17-07-2020; Nature Publishing Group; Nature Portfolio
• Subjects: 140/125; 140/58; 704/2151/209; 704/2151/210; 704/2151/330; Cratons; Dehydration; Density; Earth mantle; Earth Sciences; Fractionation; Geochemistry; Humanities and Social Sciences; Hydrogen; Hydrogen isotopes; Isotope fractionation; Isotopes; Melting; Minerals; multidisciplinary; Plate tectonics; Science; Science (multidisciplinary); Sciences of the Universe; Storage capacity; Tectonics; Terrestrial environments; Viscosity
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-020-17442-8

Trace amounts of water dissolved in minerals affect density, viscosity and melting behaviour of the Earth’s mantle and play an important role in global tectonics, magmatism and volatile cycle. Water concentrations and the ratios of hydrogen isotopes in the mantle give insight into these processes, as well as into the origin of terrestrial water. Here we show the presence of molecular H
2
in minerals (omphacites) from eclogites from the Kaapvaal and Siberian cratons. These omphacites contain both high amounts of H
2
(70 to 460 wt. ppm) and OH. Furthermore, their ∂D values increase with dehydration, suggesting a positive H isotope fractionation factor between minerals and H
2
–bearing fluid, contrary to what is expected in case of isotopic exchange between minerals and H
2
O-fluids. The possibility of incorporation of large quantities of H as H
2
in nominally anhydrous minerals implies that the storage capacity of H in the mantle may have been underestimated, and sheds new light on H isotope variations in mantle magmas and minerals.
Trace amounts of water dissolved in minerals play an important role in global tectonics through changing the density, viscosity and melting behaviour of the Earth’s mantle. Here, the authors identify the presence of molecular hydrogen in nominally anhydrous ecolgite minerals from the Kaapvaal and Siberian cratons, indicating that the storage capacity of H in the mantle may have been underestimated.