HR: 0800h
AN: T41E-1258    [Abstracts]
TI: Joint analysis of seismic, gravity, magnetism and seismological data for passive margin structure imaging
AU: * D'Acremont, E
EM: dacremont@obs-vlfr.fr
AF: Laboratoire de tectonique CNRS UMR7072 UPMC, 4 place jussieu, Paris cedex 05, 75252 France
AU: Leroy, S
EM: sylvie.leroy@lgs.jussieu.fr
AF: Laboratoire de tectonique CNRS UMR7072 UPMC, 4 place jussieu, Paris cedex 05, 75252 France
AU: Tiberi, C
EM: christel.tiberi@lgs.jussieu.fr
AF: Laboratoire de tectonique CNRS UMR7072 UPMC, 4 place jussieu, Paris cedex 05, 75252 France
AU: Pointu, A
EM: agnes.pointu@lgs.jussieu.fr
AF: Laboratoire de tectonique CNRS UMR7072 UPMC, 4 place jussieu, Paris cedex 05, 75252 France
AU: Ebinger, C
EM: c.ebinger@gl.rhul.ac.uk
AF: Royal Holloway university of London, Geology dept., Queen's building, Egham, TW20 0EX United Kingdom
AB: The eastern Gulf of Aden is a key place for investigating seafloor spreading processes and strain localisation, given its thin post-rift sedimentary strata, the good exposure of onshore and nearshore rift structures, the lack of salt deformation structures and its large distance away from the Afar plume. Further, exploratory well data exist for stratigraphic ties, and the two conjugate passive margins can be reconstructed within lateral errors smaller than 10 km. First, the 2000 ENCENS-SHEBA cruise has revealed the structural and geophysical framework using bathymetric swath mapping and underway geophysics (Leroy et al. 2004; d'Acremont et al. submitted). Second, the Dhofar Seismic network in 2004, on the onshore Northern margin (11 BB stations for receiver function and tomography studies) has improved our understanding of the rifting and the oceanic spreading processes in this area, as well as the transitional phase between them. A smaller deformation wavelength prevails on the northern margin, which is also steeper and narrower than the southern one. The southern-rifted domain is about twice as large as the northern one, while the crust is thinner in the northern margin. Besides the influence of rifting obliquity, this asymmetry of the structural pattern could be a consequence of inherited basins and faults associated with the Jurassic rifting episode that affected the southern domain. The transition between the thinned continental crust and the onset of oceanic seafloor spreading is characterized by an ocean-continent transition (OCT). Although its precise nature remains unknown, two possible origins can be proposed with respect to our data; either an exhumed mantle, or an ultra-thinned continental crust intruded by partial melt products from the underlying mantle. Between the Alula-Fartak and Socotra transform faults, the non-volcanic margins and the OCT are segmented by two transfer fault zones trending N027řE. These zones define three N110řE trending segments which evolve with time. 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.
DE: 8105 Continental margins and sedimentary basins
DE: 8122 Dynamics, gravity and tectonics
DE: 7218 Lithosphere and upper mantle
DE: 3010 Gravity
DE: 3025 Marine seismics (0935)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting