HR: 1340h
AN: T13C-1391    [Abstracts]
TI: Structure of Mesozoic Oceanic Crust in the Vicinity of the Cape Verde Islands From Seismic Reflection Profiles
AU: * Ali, M Y
EM: mali@pi.ac.ae
AF: The Petroleum Institute, P.O. Box 2533, Abu Dhabi, 2533 United Arab Emirates
AU: Watts, A B
EM: tony@earth.ox.ac.uk
AF: University of Oxford, Department of Earth Sciences Parks Road, Oxford, OX1 3PR United Kingdom
AB: Multichannel seismic reflection profile data have been used to determine the internal structure of Mesozoic oceanic crust in the vicinity of the Cape Verde islands. The data show the oceanic crust to be characterized by both dipping and sub-horizontal reflectors. Several lines of evidence argue against the reflectors being scattering artifacts arising, for example, from rough basement topography. Instead, the reflectors are attributed to tectonic and magmatic processes associated with the accretion of oceanic crust at the mid-Atlantic ridge. The upper crust shows variable reflectivity due to both dipping and sub-horizontal events. We interpret the dipping reflectors, which have been identified on both ridge-normal and ridge-parallel profiles, as sub-surface expressions of normal faults that formed at or near the mid-Atlantic ridge. There is no evidence that the faults are caused by loading of the oceanic crust by either the Cape Verde islands or their associated topographic swell. Some faults, however, can be traced into the overlying sediments suggesting they may have been re-activated since their formation at the ridge. The origin of the sub-horizontal reflectors is not as clear. We believe them to be boundaries of different igneous lithologies, such as that between basalts and gabbros. The lower crust is highly reflective in some areas, whereas in others only a few dipping and sub-horizontal reflectors are observed. Some of the dipping reflectors can be traced into the upper crust suggesting they are also normal faults. Others, however, appear to be confined to the lower crust. The sub-horizontal, discontinuous, reflectors about 2.0-2.5 two-way travel time below the top of oceanic basement are attributed to the Moho.
DE: 8159 Rheology--crust and lithosphere
DE: 3010 Gravity
DE: 3025 Marine seismics (0935)
DE: 3099 General or miscellaneous
DE: 0930 Oceanic structures
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting