Constraining the rate and extent of mantle serpentization from seismic and petrological data: Implications for chemosynthesis and tectonic processes.
2005 (English)In: Geofluids, ISSN 1468-8115, E-ISSN 1468-8123, Vol. 5, no 3, 153-164 p.Article in journal (Refereed) Published
We used seismic velocity as a proxy for serpentinization of the mantle, which occurred beneath thinned but laterally continuous continental crust during continental break up, prior to opening of the Atlantic Ocean. The serpentinized sub-continental mantle is now exhumed, beneath the Iberia Abyssal Plain and was accessed by scientific drilling on Ocean Drilling Program legs 149 and 173. Chromatographic modelling of kinetically limited transport of the serpentinization front yields a front displacement of 2197 ± 89 m, a time-integrated fluid flux of 1098 ± 45 m<sup>3</sup> m<sup>−2</sup> and a Damköhler number of 6.0 ± 0.2. Whether either surface reaction or chemical transport limit the rate of reaction, we calculate timescales for serpentinization of approximately 10<sup>5</sup>–10<sup>6</sup> years. This yields time-average fluid flux rates for H<sub>2</sub>O, entering and reacting with the mantle, of 60–600 mol m<sup>−2</sup> a<sup>−1</sup> and for CH<sub>4</sub>, produced as a by-product of oxidation of Fe<sup>++</sup> to magnetite and exiting the mantle, of 0.55–5.5 mol m<sup>−2</sup> a<sup>−1</sup>. This equates to a CH<sub>4</sub>-flux of 0.18–1.8 Tg a<sup>−1</sup> for coeval serpentinization of the mantle that was exhumed west of Iberia. This represents 0.03–0.3% of the present-day annual CH<sub>4</sub>-flux from all sources and a higher fraction of pre-anthropogenic (lower) CH<sub>4</sub> levels. CH<sub>4</sub> released by serpentinization at or beneath the seafloor could provide substrate for biological chemosynthesis and/or promote gas-hydrate formation. Finally, noting its volumetric extent and rapidity (<10<sup>6</sup> years), we interpret serpentinization to be a reckonable component of tectonic processes, contributing both diapiric and expansional forces and helping to ‘lubricate’ extensional processes. Given its anisotropic permeability, actively deforming serpentinite might impede melt migration which may be of interest, given the apparent lack of melt in some rifted margins.
Place, publisher, year, edition, pages
2005. Vol. 5, no 3, 153-164 p.
Earth and Related Environmental Sciences
IdentifiersURN: urn:nbn:se:su:diva-33989DOI: 10.1111/j.1468-8123.2005.00111.xOAI: oai:DiVA.org:su-33989DiVA: diva2:283928