HR: 1340h
AN: T33B-1357    [Abstracts]
TI: Structure and segmentation of the eastern Gulf of Aden basin and the Sheba ridge from gravity, bathymetric and magnetic anomalies: implications for accretion processes
AU: * d'Acremont, E
EM: elia.dacremont@upmc.fr
AF: University of Pierre et Marie Curie CNRS-UMR7072 Laboratoire de Tectonique, 4 Place Jussieu Case 129, Paris, 75252, France
AU: Leroy, S
EM: sylvie.leroy@lgs.jussieu.fr
AF: University of Pierre et Marie Curie CNRS-UMR7072 Laboratoire de Tectonique, 4 Place Jussieu Case 129, Paris, 75252, France
AU: Maia, M
EM: marcia@univ-brest.fr
AF: IUEM UBO Domaines Océaniques CNRS-UMR6538, Place Nicolas Copernic, Plouzane, 29280, France
AU: Gente, P
EM: pascal.gente@univ-brest.fr
AF: IUEM UBO Domaines Océaniques CNRS-UMR6538, Place Nicolas Copernic, Plouzane, 29280, France
AU: Autin, J
EM: julia.autin@lgs.jussieu.fr
AF: University of Pierre et Marie Curie CNRS-UMR7072 Laboratoire de Tectonique, 4 Place Jussieu Case 129, Paris, 75252, France
AB: The eastern Gulf of Aden is a key place for investigating seafloor spreading processes and the evolution in space and time of the margin and ridge segmentation. The rifting of the Gulf that separated Arabia from Somalia started around 35 Ma ago followed by oceanic accretion from at least17.6 Ma. Bathymetric, gravity and magnetic data from the Encens-Sheba cruise are used to study the structure and segmentation of the eastern part of the basin and ridge, which have strong implications for accretion processes. The segmentation of the first oceanic spreading centre, which is dated at least 17.6 Ma by the magnetic anomaly (A5d) identification, seems to be directly related to the structural geometry of the margins. Then, magmatic processes governed the evolution of the segmentation. The segmentation of the oceanic crust evolved, by eastward propagation of the western segment, from three segments (from an5d to an5) to two segments (from an5). At 6 Ma (an3a) a third segment appeared by duplication of the Socotra transform fault, maybe due to a regional kinematics change. The Encens-Sheba oceanic domain is divided in two distinct areas trending NE-SW perpendicular to the Sheba ridge. (1) The Eastern area is characterized by a shorter wavelength variation of the axial segmentation with two spreading segments 30 to 40 km long, and by a thin crust particularly on the northern and southern ends of its flanks. (2) The Western zone, whose axial segment is more than 120 km long, is characterized by a thick crust and/or a hot mantle and no axial rift valley. This abnormal volcanic activity for a slow spreading ridge is emphasized by bathymetric highs with 5-10 km wide volcanic edifices, and by a negative anomaly of the MBA. These different results support the presence of an off-axis thermal anomaly located below the southern flank of the Sheba ridge. The magnetic anomalies and spreading asymmetry reveal that the location of this thermal anomaly might be relatively recent (~ 10 Ma). We propose that at 10 Ma the ridge jumped southwards as attracted by this thermal anomaly, which explains the asymmetry observed between the 5c and 5 anomalies (16 to 10 Ma).
DE: 3035 Midocean ridge processes
DE: 3039 Oceanic transform and fracture zone processes
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8109 Continental tectonics: extensional (0905)
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting