HR: 10:20h
AN: OS22A-01    [Abstracts]
TI: Sulphur Cycling at the Mid-Atlantic Ridge: Isotopic Evidence From the Logatchev and Turtle Pits Hydrothermal Fields
AU: Eickmann, B
OS22A-01 AF: Geologisch-Palaeontologisches Institut, Westfaelische Wilhelms-Universitaet, Corrensstr. 24, Muenster, 48149 Germany
AU: * Strauss, H
EM: hstrauss@uni-muenster.de
AF: Geologisch-Palaeontologisches Institut, Westfaelische Wilhelms-Universitaet, Corrensstr. 24, Muenster, 48149 Germany
AU: Koschinsky, A
OS22A-01 AF: International University Bremen, Campus Ring 1, Bremen, 28759 Germany
AU: Kuhn, T
OS22A-01 AF: IFM-Geomar, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Petersen, S
OS22A-01 AF: IFM-Geomar, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Schmidt, K
OS22A-01 AF: International University Bremen, Campus Ring 1, Bremen, 28759 Germany
AB: Mid-ocean ridges and associated hydrothermal vent systems represent a unique scenario in which the interaction of hydrosphere, lithosphere and biosphere and the related element cycling can be studied. Sulphur participates in inorganic and microbially driven processes and plays, thus, an important role at these vent sites. The sulphur isotopic compositions of different sulphur-bearing minerals as well as dissolved sulphur compounds provide a tool for identifying the sulphur source and pertinent processes of sulphur cycling. Here, we present sulphur isotope data from an ongoing study of the Logatchev hydrothermal field at 14°45^' N and the Turtle Pits hydrothermal field at 4°48^' S. The former is located in 2900 to 3060 m water depth, hosted by ultramafic rocks, while the latter is situated in 2990 m water depth, hosted by basaltic rocks. Different metal sulphides (chalcopyrite, pyrite, pyrrhotite, various copper sulphides), either particles from the emanating hot fluid itself or pieces of active and inactive black smokers, display δ³⁴S values between +2 and +9 ‰. So far, no significant difference is discernible between mineral precipitates from both hydrothermal fields. However, differences exist between different generations of sulphide precipitates. Based on respective data from other sites of hydrothermal activity at mid-ocean ridges, this sulphur isotope range suggests that sulphur in the hydrothermal fluid and mineral precipitates represents a mixture between mantle sulphur and reduced seawater sulphate. Anhydrite precipitates from hydrothermal chimneys, located inside sulphide conduits, and obvious late stage gypsum needles from voids, yielded sulphur isotope values between +17.5 and +20.0 ‰. This clearly identifies seawater sulphate as the principal sulphur source. Variable, but generally low abundances of sulphide and sulphate in differently altered mafic and ultramafic rocks point to a complex fluid-rock interaction. Sulphur isotope values for total sulphur range between 0.6 and +18.7 ‰, again reflecting a mixing between two principal end-members: seawater sulphate and mantle sulphur.
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005