Brucite formation and dissolution in oceanic serpentinite

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2020-10-27
Authors
Klein, Frieder
Humphris, Susan E.
Bach, Wolfgang
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10.7185/geochemlet.2035
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Keywords
Serpentinisation
Serpentinite
Peridotite
Brucite
Seafloor weathering
Seawater
Water
Magnesium
Alkalinity
Abstract
Brucite is an important, albeit elusive, hydrous mineral formed during serpentinisation, a vector of Mg from the mantle to seawater, and possibly a significant host of water in oceanic serpentinite. However, the abundance of brucite has not been quantified in oceanic serpentinite and its fate and related chemical fluxes remain uncertain. We used thermal analysis and confocal Raman spectroscopy to determine the abundance and distribution of brucite in serpentinite recovered by seafloor drilling (n = 48) and dredging (n = 22). Almost all (90 %) of the drilled serpentinite samples contained brucite. The brucite contents increased with increasing extent of serpentinisation and constituted up to 15.6 wt. % of the altered rock. In contrast, dredged serpentinites were devoid of brucite and lost 4.0 wt. % MgO on average, which translates to an estimated average annual flux of 1.3 × 1010 mole Mg and about 2 × 1010 mole alkalinity during seafloor weathering of serpentinite globally. Our data suggest that, on average, brucite stores ∼20 % of the water in unweathered serpentinite, making brucite one of the largest water carriers in slow and ultra-slow spreading oceanic lithosphere.
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© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Klein, F., Humphris, S. E., & Bach, W. Brucite formation and dissolution in oceanic serpentinite. Geochemical Perspectives Letters, 16, (2020): 1-5, doi:10.7185/geochemlet.2035.
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Klein, F., Humphris, S. E., & Bach, W. (2020). Brucite formation and dissolution in oceanic serpentinite. Geochemical Perspectives Letters, 16, 1-5.
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