HR: 1340h
AN: OS43A-0996    [Abstracts]
TI: Low-Temperature Hydrothermal Deposits at the 71„aN Vent Fields at the Arctic Mid-Ocean Ridge: Architecture, Microtextures, and Geochemistry
AU: * Thorseth, I H
EM: Ingunn.Thorseth@geo.uib.no
AF: Centre for Geobiology, University of Bergen, Allegaten 41, Bergen, 5007, Norway
AU: * Thorseth, I H
EM: Ingunn.Thorseth@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, 5007, Norway
AU: Pedersen, R B
EM: Rolf.Pedersen@geo.uib.no
AF: Centre for Geobiology, University of Bergen, Allegaten 41, Bergen, 5007, Norway
AU: Pedersen, R B
EM: Rolf.Pedersen@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, 5007, Norway
AU: Kruber, C
EM: Claudia.Kruber@geo.uib.no
AF: Centre for Geobiology, University of Bergen, Allegaten 41, Bergen, 5007, Norway
AU: Kruber, C
EM: Claudia.Kruber@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, 5007, Norway
AU: Kosler, J
EM: Jan.Kosler@geo.uib.no
AF: Centre for Geobiology, University of Bergen, Allegaten 41, Bergen, 5007, Norway
AU: Kosler, J
EM: Jan.Kosler@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, 5007, Norway
AB: Vast amounts of low-temperature siliceous Fe-deposits are formed distal to a high-temperature hydrothermal venting areas at the southwestern part of the Mohns Ridge. The low-temperature deposits occur as small yellow to rust coloured mounds and chimney-like structures along faults and fissures in the rift valley floor, for distances up to several kilometres. The mounds and chimneys have a stratified structure of millimetres to centimetres thick laminated layers that are alternating with centimetre sized hollow spaces. The individual layers have in general a highly porous microtexture of most frequently branching, twisted filaments resembling stalks of the iron-oxidising Gallionella sp, which have different thickness and colour of the mineral coating in the separate lamina. Other filamentous structures of apparently biogenic as well as abiotic origin are also present, and dominate in some lamina. The deposited material is loosely consolidated due to infilling of the interspaces between the filaments in a number of thin, discrete lamina. The filaments and the interstitial material have a similar composition of mainly FeO and silica, and electron diffraction reveal 2-line ferrihydrite. The REE composition of the siliceous ferrihydrite show a similar pattern to that of the basaltic crust, indicating that they formed from low-temperature hydrothermal fluids, derived from interactions between the basaltic crust and circulating seawater. Mn-accumulation is observed within lamina most commonly at the surface of deposits. Sediment particles of basaltic glass, high- temperature vent minerals like baryte, and diatoms within lamina that are present in discrete layers show that they sequentially formed at the surface of the deposits at the different stages of growth. This together with the architecture of alternating layers of biogenic filaments and hollow spaces suggest that the formation of these deposits were controlled by biofilms of Fe-oxidising microorganisms that developed at the interface between the reduced vent fluid and the surrounding oxidized seawater. Successive nucleation and precipitation of ferrihydrite and amorphous silica on the microbial stalks results in the formation of the mounds and chimneys.
DE: 0419 Biomineralization
DE: 0448 Geomicrobiology
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1065 Major and trace element geochemistry
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting