• Login
    About WHOAS
    View Item 
    •   WHOAS Home
    • Woods Hole Oceanographic Institution
    • Marine Chemistry and Geochemistry (MC&G)
    • View Item
    •   WHOAS Home
    • Woods Hole Oceanographic Institution
    • Marine Chemistry and Geochemistry (MC&G)
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of WHOASCommunities & CollectionsBy Issue DateAuthorsTitlesKeywordsThis CollectionBy Issue DateAuthorsTitlesKeywords

    My Account

    LoginRegister

    Statistics

    View Usage Statistics

    Seawater-peridotite interactions : first insights from ODP Leg 209, MAR 15°N

    Thumbnail
    View/Open
    Bach 2004GC000744.pdf (815.0Kb)
    Date
    2004-09-10
    Author
    Bach, Wolfgang  Concept link
    Garrido, Carlos J.  Concept link
    Paulick, Holger  Concept link
    Harvey, Jason  Concept link
    Rosner, Martin  Concept link
    Metadata
    Show full item record
    Citable URI
    https://hdl.handle.net/1912/452
    As published
    https://doi.org/10.1029/2004GC000744
    DOI
    10.1029/2004GC000744
    Keyword
     Hydrothermal system; Ocean Drilling Program; Oceanic crust; Serpentinite; Water-rock interaction 
    Abstract
    We present first results of a petrographic study of hydrothermally altered peridotites drilled during Ocean Drilling Program (ODP) Leg 209 in the 15°20′N fracture Zone area on the Mid-Atlantic Ridge (MAR). We find that serpentinization is extensive at all drill sites. Where serpentinization is incomplete, phase relations indicate two major reaction pathways. One is reaction of pyroxene to talc and tremolite, and the other is reaction of olivine to serpentine, magnetite, and brucite. We interpret these reactions in the light of recent peridotite-seawater reaction experiments and compositions of fluids venting from peridotite massifs at a range of temperatures. We suggest that the replacement of pyroxene by talc and tremolite takes place at temperatures >350°–400°C, where olivine is stable. The breakdown of olivine to serpentine, magnetite, and brucite is favored at temperatures below 250°C, where olivine reacts faster then pyroxene. High-temperature hydrothermal fluids venting at the Logatchev and Rainbow sites are consistent with rapid reaction of pyroxene and little or no reaction of olivine. Moderate-temperature fluids venting at the Lost City site are consistent with ongoing reaction of olivine to serpentine and brucite. Many completely serpentinized peridotites lack brucite and talc because once the more rapidly reacting phase is exhausted, interaction with the residual phase will change fluid pH and silica activity such that brucite or talc react to serpentine. At two sites we see strong evidence for continued fluid flow and fluid-rock interaction after serpentinization was complete. At Site 1268, serpentinites underwent massive replacement by talc under static conditions. This reaction requires either removal of Mg from or addition of Si to the system. We propose that the talc-altered rocks are Si-metasomatized and that the source of Si is likely gabbro-seawater reaction or breakdown of pyroxene deeper in the basement. The basement at Site 1268 is heavily veined, with talc and talc-oxide-sulfide veins being the most common vein types. It appears that the systems evolved from reducing (oxygen fugacity buffered by magnetite-pyrrhotite-pyrite and lower) to oxidizing (dominantly hematite). We propose that this transition is indicative of high fluid flux under retrograde conditions and that the abundance of hematite may relate to the Ca-depleted nature of the basement that prevents near-quantitative removal of seawater sulfate by anhydrite precipitation. At site 1272 we find abundant iowaite partly replacing brucite. While this is the first report of iowaite from a mid-ocean ridge setting, its presence indicates, again, fairly oxidizing conditions. Our preliminary results indicate that peridotite-seawater and serpentinite-seawater interactions can take place under a wider range of temperature and redox conditions than previously appreciated.
    Description
    Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 5 (2004): Q09F26, doi:10.1029/2004GC000744.
    Collections
    • Marine Chemistry and Geochemistry (MC&G)
    Suggested Citation
    Geochemistry Geophysics Geosystems 5 (2004): Q09F26
     

    Related items

    Showing items related by title, author, creator and subject.

    • Thumbnail

      Coupled atmosphere-ocean-wave simulations of a storm event over the Gulf of Lion and Balearic Sea 

      Renault, Lionel; Chiggiato, Jacopo; Warner, John C.; Gomez, Marta; Vizoso, Guillermo; Tintore, Joaquin (American Geophysical Union, 2012-09-15)
      The coastal areas of the North-Western Mediterranean Sea are one of the most challenging places for ocean forecasting. This region is exposed to severe storms events that are of short duration. During these events, significant ...
    • Thumbnail

      Sea-ice production and air/ice/ocean/biogeochemistry interactions in the Ross Sea during the PIPERS 2017 autumn field campaign 

      Ackley, Stephen; Stammerjohn, Sharon E.; Maksym, Ted; Smith, Madison; Cassano, John; Guest, Peter; Tison, Jean-Louis; Delille, Bruno; Loose, Brice; Sedwick, Peter N.; De Pace, Lisa; Roach, Lettie; Parno, Julie (Cambridge University Press, 2020-06-11)
      The Ross Sea is known for showing the greatest sea-ice increase, as observed globally, particularly from 1979 to 2015. However, corresponding changes in sea-ice thickness and production in the Ross Sea are not known, nor ...
    • Thumbnail

      Constraining Southern Ocean air-sea-ice fluxes through enhanced observations 

      Swart, Sebastiaan; Gille, Sarah T.; Delille, Bruno; Josey, Simon A.; Mazloff, Matthew R.; Newman, Louise; Thompson, Andrew F.; Thomson, James M.; Ward, Brian; du Plessis, Marcel; Kent, Elizabeth; Girton, James B.; Gregor, Luke; Heil, Petra; Hyder, Patrick; Pezzi, Luciano Ponzi; de Souza, Ronald Buss; Tamsitt, Veronica; Weller, Robert A.; Zappa, Christopher J. (Frontiers Media, 2019-07-31)
      Air-sea and air-sea-ice fluxes in the Southern Ocean play a critical role in global climate through their impact on the overturning circulation and oceanic heat and carbon uptake. The challenging conditions in the Southern ...
    All Items in WHOAS are protected by original copyright, with all rights reserved, unless otherwise indicated. WHOAS also supports the use of the Creative Commons licenses for original content.
    A service of the MBLWHOI Library | About WHOAS
    Contact Us | Send Feedback | Privacy Policy
    Core Trust Logo