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Mineralogical and geochemical hydrothermal evidences on sediments from the serpentinite-hosted Saldanha hydrothermal field

  • Ágata S. C. M. A. Dias
  • Fernando J. A. S. Barriga
Conference paper

Abstract

Mineralogical and geochemical data of hydrothermal sediments collected from the Saldanha site are presented. The Saldanha hydrothermal field is located at the top of a serpentinized massif Mount Saldanha (MS), at a non-transform offset (NTOS) along the Mid-Atlantic Ridge (MAR), south of the Azores. It is one of the rare known sites where direct evidence of low-temperature hydrothermal activity has been provided by direct observtion of hydrothermal fluid venting through small orifices in the ocean floor sedimentary cover. This study reveals that these hydrothermal sediments are highly “diluted” within dominant foraminiferal nanofossiliferous ooze and that the mineral assemblage of the hydrothermal component is characterized by sulphides, poorly crystallized Mn oxihydroxides, Mn brucite and hydrothermal clays. Sediments with a stronger hydrothermal component are located at the top of the mount, where hydrothermal activity was observed. Here the sediments are enriched in Cu, Zn and Fe sulphides, Mn-Mg oxy-hydroxides and putative manganobrucite. Total geochemical analyses show that all sediments are enriched in elements such as Mn, Fe, Cu and Zn, derived from hydrothermal fluids, Mg, P and V, scavenged from seawater, and Ni, Cr and Co derived from ultramafic rocks. Sediments collected next to the vents are particularly enriched in Mn. The geochemical data together with the observed mineral assemblage and the geological setting suggest that the hydrothermal fluids have much higher temperature than those measured at the escape orifices (max. 9°C), and a strong enrichment in Mg, mainly at the top of the mount, agrees with extensive mixing of the hydrothermal fluid with unmodified seawater.

Keywords

Hydrothermal sediments low temperature vents ultramafic-hosted hydrothermal field Mount Saldanha 

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References

  1. Barriga F, Almeida A, Biscoito M, Colaço A, Company R, Costa R, Costa V, Cruz V, Dias Á, Ferreira P, Gadanho M, Iyer S, Kadar E, Lopes C, Lourenço N, Marques A, Martins V, Pinto Á, Relvas J, Rohais S, Segonzac M, and Serafim M (2003) Seahma-1 Cruise Report. In Creminer (ed. FCT). Faculty of Sciences University of LisbonGoogle Scholar
  2. Barriga F, Fouquet Y, Almeida A., Biscoito M, Charlou J-L, Costa R, Dias A, Marques A, Miranda M, Olu K, Porteiro F, and Queiroz P. (1998) Discovery of the Saldanha Hydrothermal Field on the FAMOUS Segment of the MAR (36° 30’N). AGU — Fall Meeting, Eos Transaction 79(45):F67Google Scholar
  3. Charlou J-L, Donval J-P, Douville E, Knoery J, Fouquet Y, Bougault H, Baptiste P, Stievenard M, and German C (1997) High methane flux between 15°N and the Azores Triple Junction, Mid-Atlantic ridge, hydrothermal and serpentinization processes. Eos trans. AGU 78(F831)Google Scholar
  4. German C, Parson L, and Team H (1996) Hydrothermal exploration near the Azores Triple Junction: Tectonic control of venting at slow-spreading ridges. Earth and Planetary Science Letters 138:93–104CrossRefGoogle Scholar
  5. Gràcia E, Charlou J-L, Radford-Knoery J, and Parson L (2000) Nontransform offset along the Mid-Atlantic ridge south of the Azores (38°N–34°N): ultramafic exposures and hosting of hydrothermal vents. Earth and Planetary Science Letters 177:89–103CrossRefGoogle Scholar
  6. Lowell R, Rona P (2002) Seafloor hydrothermal systems driven by the serpentinization of peridotite. Geophysical Research Letters 29(11):1–4CrossRefGoogle Scholar
  7. Michard A (1989) Geochimica et Cosmochimica Acta 53:745–750CrossRefGoogle Scholar
  8. Sinha M, Dzhatieva Z, Santos F, Silva N, Dias A, Marques A, Dean S, Morris E, Maxey A, Ellis M, Team C (2005) Active electromagnetic survey of hydrothermal venting area at Saldanha Massif, Mid-Atlantic Ridge. Geophysical Research Abstracts 7:07706, 2005Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2005

Authors and Affiliations

  • Ágata S. C. M. A. Dias
    • 1
  • Fernando J. A. S. Barriga
    • 1
    • 2
  1. 1.CREMINER, Faculdade de CiênciasUniversidade de LisboaPortugal
  2. 2.Dep. Geologia, Faculdade de CiênciasUniversidade de LisboaPortugal

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