Diversity of Ultramafic Hosted Hydrothermal Deposits on the Mid Atlantic Ridge: First Submersible Studies on Ashadze, Logatchev 2 and Krasnov Vent Fields During the Serpentine Cruise.

HR: 08:30h
AN: T51F-03 [Abstracts]
TI: Diversity of Ultramafic Hosted Hydrothermal Deposits on the Mid Atlantic Ridge: First Submersible Studies on Ashadze, Logatchev 2 and Krasnov Vent Fields During the Serpentine Cruise.
AU: * Fouquet, Y
EM: fouquet@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29280, France
AU: Cherkashov, G
AF: VNIIOkeangeologia, Angliysky Avenue, St.Petersburg, 190121, Russian Federation
AU: Charlou, J
AF: IFREMER, BP 70, Plouzane, 29280, France
AU: Ondreas, H
AF: IFREMER, BP 70, Plouzane, 29280, France
AU: Cannat, M
AF: IPGP, CNRS UMR 7154, 4 place Jussieu, Cedex 05, Paris, 75252, France
AU: Bortnikov, N
AF: IGEM, Staromonetny per., 35, Moscow, 119017, Russian Federation
AU: Silantiev, S
AF: Vernadsky Institute, 10 Kosigin Street, Moscow, 119991, Russian Federation
AU: Etoubleau, J
AF: IFREMER, BP 70, Plouzane, 29280, France
AU: Scientific Party of the SERPENTINE cruise
AB: During the Serpentine cruise (March 2007) we have explored and sampled, using the ROV Victor, new ultramafic hydrothermal fields between 13°N and 17°N on the Mid Atlantic Ridge (MAR). The Serpentine cruise was part of a 4 years cooperation agreement between France and Russia. Targets were Ashadze1 and 2 (12°58"N), Logatchev 1 (14°45"N) and 2 (14°43"N) and Krasnov (16°38"N) fields localized after several surface cruises of the R/V professor Logatchev. A significant portion of the dives was dedicated to detailed microbathymetry, 50 m and 20 m above the seafloor, and simultaneous physical and chemical plume studies and magnetic surveys. High resolution (30cm) maps were further used for geological, biological, microbiological and fluid sampling operations. The cruise identified three new very active black smoker fields (Ashadze 1 and 2, Logatchev 2) on serpentinized peridotites. One extensive low temperature inactive deposit (dominantly birnessite) was discovered 1 km east of the Logatchev 1 field. The basaltic hosted Krasnov field was inactive. The Ashadze 1 site at 4080m of water depth is the deepest active black smoker field so far known in the ocean. Inactive and basalt hosted sulfide chimneys (Ashadze 4) were found at the base of the rift valley at 4530 m. Extensive gravity sliding related to the emplacement of the ultramafic rocks is evident at all ultramafic sites (see abstract by Ondreas et al.). Fluids, enriched in H2 and hydrocarbon, confirm the originality of ultramafic environments (see abstract by Charlou et al.). Logatchev 2 is venting low salinity black smoker fluids indicating phase separation. In addition, its position 12 km off axis, moves from 8 (Logatchev 1) to 12 km the possibility to have off axis black smokers long the MAR. Basaltic hosted deposits are dominated by pyrite and silica at Krasnov (Fe:39%, Si:11%, Cu:2.2%, Zn:0.14%) and by sphalerite and pyrite at Ashadze 4 (Fe:24%, Si:1.5%, Cu:0.15%, Zn:32%). Ultramafic deposits are characterized by high copper concentration dominated by chalcopyrite and isocubanite. Ashadze 1 (Fe:33%, Si:1.3%, Cu:14%, Zn:14%) and Logatchev 2 (Fe:20%, Si:3%, Cu:14%, Zn:23%) are enriched in sphalerite. New samples at Logatchev 1 confirm that copper is largely dominant at this site (Fe:29%, Si:3%, Cu:28%, Zn:4%). The Ashadze 2 field is unusual. A small active crater can be interpreted as a hydrothermal volcano built up with a mixture of carbonates and secondary copper sulfides and chlorides. Massive sulfide chimneys are associated with the active smokers at the center of the crater. Many inactive carbonates/sulfides mounds are also aligned along a N-S depression. Two types of hydrothermal deposits are observed: massive copper-rich sulfides associated with the black smokers and carbonate/sulfides chimneys. Average composition of hydrothermal deposits for the field is Fe:26%, Si:11%, Cu:11%, Zn:5%, Ca:8%. The dominant carbonate is aragonite, Mg-Calcite is rare, and talc is common. Comparisons with other ultramafic sites along the MAR will also bee presented.
UR: http://www.ifremer.fr/serpentine
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3035 Midocean ridge processes
DE: 3621 Mantle processes (1038)
DE: 3665 Mineral occurrences and deposits
SC: Tectonophysics [T]
MN: 2007 Fall Meeting