A detailed geophysical study in the Canary Basin (eastern Atlantic): implications for the internal structure of 130 Ma oceanic crust

We report the results of a detailed geophysical survey sited on two previously imaged dipping reflectors, one dipping towards and the other away from the present-day Mid-Atlantic Ridge axis, within Mesozoic;aged crust of the east Atlantic. The new data include gravity, magnetic and seismic refraction and reflection profiles collected in a grid that constrain the crustal structure as well as the reflector geometry. A second-order axial discontinuity, which is associated with anomalous crustal structure, is located within the survey area. The westward-dipping reflector can be traced from the Moho to the top of the igneous crust, where it coincides with a step of 800 m in the basement. This reflector is approximately planar, with a dip of 28 degrees +/- 2 degrees W and occurs similar to 8 km north of the axial discontinuity. We interpret this reflector as being a whole-crustal normal fault that was generated within the median valley. The eastward-dipping reflector cannot be traced across seismic layer 2 and does not correlate with any feature of the basement. It penetrates 2-3 km into the upper mantle. Its reflection strength is about twice that of the Moho reflection. This reflector, which is approximately planar, strikes parallel to the isochrons, has a length of 18 +/- 2 km and a dip of 28 degrees +/- 2 degrees E. We speculate that this reflector is also a fault that was generated on the western wall of the median valley but was 'captured' from the North American Plate by a lateral shift in the axis of spreading, possibly associated with a major change in plate motion.