HR: 10:35h
AN: OS22A-02    [Abstracts]
TI: Hydrothermal Alteration in the Logatchev Hydrothermal Field: Implications From Secondary Mineral Assemblages and Mineral Chemistry
AU: * Lackschewitz, K S
EM: klackschewitz@ifm-geomar.de
AF: IFM-GEOMAR, Leibniz Institut fuer Meereswissenschaften, Wischhofstr. 1-3, Kiel, 24124 Germany
AU: Augustin, N
EM: naugustin@ifm-geomar.de
AF: IFM-GEOMAR, Leibniz Institut fuer Meereswissenschaften, Wischhofstr. 1-3, Kiel, 24124 Germany
AU: Devey, C W
EM: cdevey@ifm-geomar.de
AF: IFM-GEOMAR, Leibniz Institut fuer Meereswissenschaften, Wischhofstr. 1-3, Kiel, 24124 Germany
AU: Eisenhauer, A
EM: aeisenhauer@ifm-geomar.de
AF: IFM-GEOMAR, Leibniz Institut fuer Meereswissenschaften, Wischhofstr. 1-3, Kiel, 24124 Germany
AU: Garbe-Schoenberg, D
EM: dgs@gpi.uni-kiel.de
AF: Institut fuer Geowissenschaften, Universitaet, Olshausenstr. 40, Kiel, 24118 Germany
AU: James, R
EM: R.H.James@open.ac.uk
AF: Department of Earth Sciences, Open University, Walton Hall, Milton Keynes, MK7 6AA United Kingdom
AB: We present new data on secondary mineral assemblages, clay and whole rock chemistry and clay mineral strontium and lithium isotopic compositions of altered rocks and sediments from the active, ultramafic-hosted Logatchev hydrothermal field reflecting various alteration conditions (e.g. fluid mixing, water-rock interaction). The altered ultramafic rocks are mainly consist of lizardite, chrysotile whereas magnetite and pyrite are minor minerals. Chlorite, chlorite-smectite mixed-layer (e.g., corrensite), smectite and talc are additional common phases in the clay fraction of most of these samples.Iron-hydroxides and iron sulfides are the main components of the hydrothermal crusts, with some amounts of pyroxene, chlorite, illite and pyrite. The hydrothermal sediments beneath the crusts are characterized by quartz, smectite and chlorite as main minerals. Analyses of clay separates representing a variety of alteration styles demonstrates that significant and characteristic changes in the bulk rock chemical composition are associated with various alteration conditions. The elements Cr, Cu, Pb and U appears to have a general enrichment in the lizardite and chlorite concentrates in comparison to a depleted mantle. ⁸⁷Sr/⁸⁶Sr ratios of clay concentrates vary between 0.7083 and 0.7096 suggesting that the clays either formed as a result of seawater alteration or hydrothermal alteration with various portions of seawater. The strontium isotopic ratio of a chlorite sample from hydrothermal sediments beneath the hydrothermal crust is much lower than the isotopic data reported for the lizardites suggesting precipitation from fluid with lower seawater content. The Li isotopic composition (δ⁷Li) of the clay separates varies between -5.4 and +6.4‰. Thus, the clays are enriched in ⁶Li relative to both seawater (~31‰) and hydrothermal vent fluids from the Logatchev field (~6‰) suggesting that ⁶Li is preferentially retained in alteration products. When considered together with the Sr isotope data, these Li isotope data may be used to estimate the temperature of formation of the clay concentrates.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3616 Hydrothermal systems (0450, 1034, 3017, 4832, 8135, 8424)
DE: 3617 Alteration and weathering processes (1039)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005