HR: 1340h
AN: T53B-1310    [Abstracts]
TI: High Resolution Mapping of the Ashadze and Logachev Hydrothermal Fields, Mid Atlantic Ridge 13-15°N.
AU: * ONDREAS, H
EM: Helene.Ondreas@ifremer.fr
AF: IFREMER, BP 70, PLOUZANE, 29280, France
AU: CANNAT, M
AF: IPG CNRS UMR 7154, 4 place Jussieu, PARIS Cedex 05, 75252, France
AU: CHERKASHOV, G
AF: VNIIOkeangeologia, Angliysky Avenue, St PETERBURG, 190121, Russian Federation
AU: FOUQUET, Y
AF: IFREMER, BP 70, PLOUZANE, 29280, France
AU: NORMAND, A
AF: IFREMER, BP 70, PLOUZANE, 29280, France
AU: SERPENTINE scientific party, a
AB: During the SERPENTINE cruise (feb 25 to apr. 5, 2007) on board the french research vessel Pourquoi Pas? a new multibeam bathymetric system (RESON 7125 echo sounder) was used on the ROV Victor 6000 to gather real time fine-scale bathymetry. The resolution is 5% of the altitude above the seafloor (h), and the footprint at the seafloor is 0.2% of h. The Ashadze and Logachev hydrothermal fields are located in the 13-15°N region of the Mid-Atlantic Ridge, on outcrops of serpentinized mantle-derived peridotite with interspeded gabbroic bodies. Maps at 50 m above the seafloor were done to investigate the relationships between the vent fields and their tectonic/volcanic environnement. Higher resolution mapping, 20 m above the seafloor, was done at the scale of the vent fields. These maps, which have resolutions of a few tens of centimetres, are unique tools to understand the local geological control on the vents. Our observations also emphasize the role of slope failure, and spreading-parallel or oblique structural lineaments on the fine scale topography of MAR axial valley walls. Ashadze area comprises two active vent fields located at two different levels on the western wall of the axial valley near 13°N. The Ashadze1 and 2 sites, 5 km apart, are respectively 4 km and 9 km off-axis. Active vents at Azhadze1 (4100 m) are distributed over an area about 150 m-long, along an EW-trending south-facing scarp. High resolution mapping at 20 m (450x450 m area) reveals the fine structure of sulfide mounds, as well as complex fissure arrays near the vents. Away from the vents, topography appears dominated by slope failure, with prominent landslides. Black smokers at Ashadze 2 (3260 m) are located in a crater-shaped depression, about 25 m in diameter, which lies in a narrow (about 70 m), N-S trending trough. On the high resolution maps at Ashadze 2 (800x450 m) the N-S trending trough appears bounded to the east by a faulted gabbroic body. To the west, it is limited by a narrow N-S trending ridge, 20 to 50 m-high, that bears numerous extinct hydrothermal chimneys. Logachev comprises two active vent fields located east of the ridge near 14°45"N. Logachev 1 and 2 sites, 5 km apart, are located 8 km and 12 km off-axis. We only mapped Logatchev 1, which is a large and well studied vent field on the eastern axial valley wall. It comprises many vents in a NW-trending elongated area about 400 m-long. High resolution mapping at 20m (550X750 m) reveals the circular shape of the main sulfide mounds, as well as complex arrays of scarps and fissures, oriented predominantly E-W, and NE- SW. Numerous lens-shaped slump features are also revealed near the vents.
DE: 3035 Midocean ridge processes
DE: 8135 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8424)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting