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1 Ifremer Centre de Brest, Département des Géosciences Marine, B.P. 70, F29280 Plouzané (jcsibuet{at}ifremer.fr)
2 Geological Survey of Canada, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, N.S., Canada, B2Y 4A2
Abstract
The new bathymetric map of the Bay of Biscay and Northeast Atlantic Ocean is based on available conventional and swath bathymetric data. It extends from the European coast to the mid-Atlantic ridge in longitude and from the Azores-Gibraltar fracture zone to 50°N in latitude. Grid spacing is 1 km. The map is in Mercator projection at a 1/2,400,000 scale (41°N latitude). With respect to previously published maps, the detailed morphology of the Eurasian and Iberian continental margins is now well established. In addition, we have mapped the two fossil trajectories of the Bay of Biscay triple junction, which limit the western extension of the Bay of Biscay sensu stricto.
The Bay of Biscay and Northeast Atlantic Ocean opened simultaneously, between chrons M0 (118 Ma) and 33o (80 Ma). A triple junction existed during that period. Fossil triple junctions trajectories on each of the three Eurasia (EU), Iberia (IB) and North America (NA) plates separate oceanic domains which were formed between the three plate pairs : IB/EU for the Bay of Biscay, EU/NA and IB/NA for the northern and southern portions of the Northeast Atlantic respectively. On each side of the fossil trajectories, rift directions formed between different plate pairs display different azimuths. The three triple junction branches have been identified on the basis of magnetic, seismic and bathymetric data. They are generally associated with a basement ridge which generally appears in the youngest parts of triple junction branches. The intersections of fossil trajectories with the base of the continental margins correspond to conjugate points before the opening of the Bay of Biscay, giving an additional independent constraint for plate reconstructions at M0 time. In addition, rotations of Iberia as deduced from plate kinematic reconstructions at chrons A33o (80 Ma), M0 (118 Ma) and M25 (156.5 Ma), fit with those derived from paleomagnetic declination data of the stable Iberia with respect to EU. The identification of chrons M0 and M3 (125 Ma) in the Bay of Biscay implies that the northern Bay of Biscay margin rifting episode ended in lowermost Cretaceous instead of late Aptian as currently admitted in the litterature. The duration of the rifting episode is reduced to about 20 Ma, as it has been already suggested for the Iberian Abyssal Plain margin [Wilson et al., 2001].
Key Words: Bathymetric map • Northeast Atlantic • Bay of Biscay • Plate kinematics • Triple junction
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