Hydrogen incorporation and retention in metamorphic olivine during subduction: Implications for the deep water cycle

Kempf, Elias Dominik; Hermann, Jörg (2018). Hydrogen incorporation and retention in metamorphic olivine during subduction: Implications for the deep water cycle. Geology, 46(6), pp. 571-574. Geological Society of America 10.1130/G40120.1

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Incorporation of hydrogen into metamorphic olivine during dehydration reactions in the subducting oceanic lithosphere provides a mechanism to replenish the deep mantle with water. Fourier transform infrared spectroscopy of metamorphic olivines formed at 2.5 GPa and 550 °C through the reaction antigorite + brucite = olivine + chlorite + water shows water contents between 100 and 140 ppm H2O associated exclusively with silicon vacancies, similar to the highest values found in peridotite xenoliths. Brucite involvement in the olivine-forming reaction ensures H2O saturation and a low Si activity, favoring hydrogen incorporation into Si vacancies. The mapped water distribution in olivine is consistent with growth zoning and there is no evidence of water gain or loss. Thus, even for metamorphic timescales of several million years at 550 °C, no ionic diffusion modification is observed, in agreement with recent experimental findings. Metamorphic olivines formed by this dehydration reaction may contribute considerable amounts of water to the deep water cycle. Additionally, olivine with abundant H in Si vacancies are expected to be rheologically weaker than anyhdrous mantle olivine, and might provide a weak interface between slabs and mantle wedges in subduction zones at conditions beyond the stability of hydrous phases.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences > Petrology
08 Faculty of Science > Institute of Geological Sciences

UniBE Contributor:

Kempf, Elias Dominik and Hermann, Jörg

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0091-7613

Publisher:

Geological Society of America

Language:

English

Submitter:

Jörg Hermann

Date Deposited:

23 Nov 2018 14:35

Last Modified:

23 Nov 2018 14:38

Publisher DOI:

10.1130/G40120.1

BORIS DOI:

10.7892/boris.121238

URI:

https://boris.unibe.ch/id/eprint/121238

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