Late seafloor carbonate precipitation in serpentinites from the Rainbow and Saldanha sites (Mid-Atlantic Ridge)

Ribeiro da Costa, Isabel, Barriga, Fernando J.A.S. and Taylor, Rex N. (2008) Late seafloor carbonate precipitation in serpentinites from the Rainbow and Saldanha sites (Mid-Atlantic Ridge). European Journal of Mineralogy, 20 (2), 173-181. (doi:10.1127/0935-1221/2008/0020-1803).

Abstract

Serpentinized ultramafic rocks recovered during several recent oceanographic missions (1997-2002) on the Rainbow hydrothermal field and on the Saldanha seamount (36°14'N and 36°34'N, Mid-Atlantic Ridge) often exhibit late-stage carbonatization associated to secondary oxidation effects. These carbonate occurrences, mostly vein-filling aragonite, occasionally form dense webs almost completely engulfing and replacing the serpentinite itself.

The 87Sr/86Sr (approx. 0.709) and stable isotope signatures (?13CPDB = 0.2-3.3 ‰; ?18OV-SMOW = 32.2-35.2 ‰) of the carbonate fraction in these serpentinites indicate carbonate precipitation from unmodified seawater, under abiotic conditions, and very low temperatures, close to bottom-water temperatures measured at the sampling stations. These analytical data imply that, unlike the serpentinite-hosted carbonate chimneys in the Lost City hydrothermal field (Ludwig et al., 2006), the vein-filling aragonite in the Rainbow and Saldanha serpentinites has a non-hydrothermal, low-temperature seawater origin.

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Contributors

Author: Rex N. Taylor

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