HR: 1340h
AN: T33A-0521    [Abstracts]
TI: Fluid-sediment Interaction and Formation of Mn oxi-hydroxide related to a Ridge Flank Hydrothermal System
AU: * Buatier, M D
EM: martine.buatier@univ-fcomte.fr
AF: Geosciences-EA 2642, Universite de Franche-Comte , 16 Route de Gray, Besancon, 25030 France
AU: Bodei, S
EM: sabine.bodei@univ-fcomte.fr
AF: Geosciences-EA 2642, Universite de Franche-Comte , 16 Route de Gray, Besancon, 25030 France
AU: Steinmann, M
EM: marc.steinmann@univ-fcomte.fr
AF: Geosciences-EA 2642, Universite de Franche-Comte , 16 Route de Gray, Besancon, 25030 France
AU: Manceau, A
EM: manceau@ujf-grenoble.fr
AF: Maison des Geosciences - LGIT, Universite J. Fourier, BP 53, Grenoble, 38041 France
AU: Karpoff, A
EM: amk@illite.u-strasbg.fr
AF: EOST-Centre de Geochimie de la Surface, CNRS UMR 7517 1 rue Blessig , Strasbourg, 67084 France
AU: Guillaume, D
EM: damien.guillaume@lmtg.obs-mip.fr
AF: LMTG, UMR 5563 CNRS-UPS-IRD, Observatoire Midi-Pyrenees,14 avenue Edouard Belin, Toulouse, 31400 France
AU: Wheat, C G
EM: wheat@mbari.org
AF: Undersea Research Unit, University of Alaska, Fairbanks, P. O. Box 475, Moss Landing, CA 95039 United States
AB: Fluid-sediment interaction at ridge flank permits the formation of metalliferous deposits that play a role in the scavenging of Fe, Mn and other trace elements. Several sites of active hydrothermal flow have been found on the eastern flank of Juan de Fuca Ridge (Retroflux) and along the Costa Rica margin (Ticoflux). These sites are typically located along edges of basaltic outcrops and seamounts where the sediment layers are thin. Mn and Fe oxides can be formed at such interfaces. These oxides form soft micro-concretions or slightly indurated black crusts. Detailed investigations combining geochemical (major, trace elements and REEY) and mineralogical (SEM, TEM, EELS EXAFS) analyses of these Mn and Fe-oxides allow formation mechanisms to be proposed. On the eastern flank of the Juan de Fuca Ridge above the 3.5 Ma-old seafloor, amorphous and poorly crystallized Mn-oxides are dispersed in altered sediments whereas pure birnessite is observed as crust layers. Hydrothermal birnessite and well-crystallized todorokite are found in sediments from the Costa Rica margin, on an 18-24 Ma seafloor. Our data suggest that the formation of hydrothermal Mn concretions occurs in several steps. The initial step is the adsorption or precipitation of Mn, Si and Fe around siliceous remains of fossils and around cell wall of bacteria and extracellular polymers. These poorly crystallized phyllomanganates give rise to the formation of better crystallized birnessite and todorokite, which progressively increase in size and crystallinity. This study shows that biogenic and amorphous components of sediments provide reactive sites for precipitation of metallic elements and the formation of hydrothermal oxi-hydroxides in ridge flank environments. These minerals, which are good scavengers of metallic elements, must be taken into account when considering the water-rocks reactions controlling oceanic chemical budgets.
DE: 0471 Oxidation/reduction reactions (4851)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1039 Alteration and weathering processes (3617)
DE: 1042 Mineral and crystal chemistry (3620)
SC: Tectonophysics [T]
MN: Fall Meeting 2005