HR: 08:15h
AN: T51F-02 INVITED    [Abstracts]
TI: Geological Context of Ultramafic-Hosted Hydrothermal Vent Fields in the 13-15°N Region of the Mid Atlantic Ridge : Preliminary Results of the Serpentine Cruise.
AU: * Cannat, M
EM: cannat@ipgp.jussieu.fr
AF: Institut de Physique du Globe, CNRS, 4 place Jussieu, Paris, 75252, France, Metropolitan
AU: Ondreas, H
EM: hondreas@ifremer.fr
AF: Ifremer, BP 70, Plouzane, 29280, France, Metropolitan
AU: Fouquet, Y
EM: yves.fouquet@ifremer.fr
AF: Ifremer, BP 70, Plouzane, 29280, France, Metropolitan
AU: Silantiev, S
EM: silantyev@geokhi.ru
AF: Vernadsky Institute, Academy of Sciences, Kosygin av, Moscow, 119991, Russian Federation
AU: Hoise, E
EM: hoise@geologie.ens.fr
AF: Ecole Normale Superieure de Paris, 24 rue Lhomond, Paris, 75005, France, Metropolitan
AU: Fontaine, F
EM: fontaine@ipgp.jussieu.fr
AF: Institut de Physique du Globe, CNRS, 4 place Jussieu, Paris, 75252, France, Metropolitan
AU: Scientific Party, S
EM: yves.fouquet@ifremer.fr
AB: During the SERPENTINE cruise (feb. 25 to apr. 5, 2007) on board the new RV Pourquoi Pas?, we used the VICTOR 6000 ROV to conduct a multidiciplinary (geology, fluid studies, biology) exploration of the Ashadze 1 and 2 (12deg58N) and Logatchev 1 and 2 (14deg43N and 14deg45N) hydrothermal fields. ROV observations and sampling were complemented by a night program of dredging, water sampling and underway geophysics. The Ashadze and Logatchev fields are located respectively on the west and east flank of the Mid-Atlantic Ridge, on outcrops of mantle-derived peridotites and interspersed gabbroic rocks. We present our principal findings in terms of geology, focusing on the geological context of hydrothermal vents. Ashadze comprises two active vent fields located at different levels on the western wall of the axial valley near 13°N : Azhadze-1 at 4000 m depth, and Ashadze-2 at 3300 m. We also sampled extinct sulfide chimneys near the base of the axial valley wall at 4530 m depth. The top of the wall, at 2300 m, corresponds to the termination of a large fossil corrugated surface. The axial valley at this latitude is strongly asymmetric, with higher relief to the west. This asymmetry is reversed immediately to the south, where the axial magnetic anomaly appears offset by a few kilometers to the west. The active and extinct Ashadze vents are roughly aligned to the north of this minor axial discontinuity. We find similarities between this general context, and the setting of the two Logatchev active vent fields: Logatchev-1 on the east axial valley wall near 14deg45N, and the smaller Logatchev-2 in a seemingly off-axis position near 15deg43N. Both fields lie to the north of a small offset axial discontinuity, and in an inward position relative to fossil corrugated surfaces. Based on seafloor morphology, dive observations, and rock sampling, we develop a model whereby ultramafic-hosted hydrothermal venting in the 13-15N region of the MAR involves both large active normal faults, and an inside corner-type position relative to a small offset of the volcanic axis. We discuss the relevance of this model for the TAG hydrothermal field at 26N, and for the Rainbow field at 36deg10N.
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3035 Midocean ridge processes
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting