Unusual sea-floor fabric near the Bullard fracture zone imaged by GLORIA sidescan sonar
THE tectonic fabric of the sea floor created at spreading ridges generally curves in the direction of ridge offset near transform faults, owing to the influence of shearing stress on transform faults. Here we present new GLORIA sidescan sonar images from the South American–Antarctic Ridge, showing fabric to the north of the Bullard transform with a reversed sense of curvature. This curvature, and that observed in an area of older sea floor near the eastern ridge–transform intersection, appears to result from post-emplacement deformation, caused by the transmission of shear stresses across transforms. The deformation was probably related to a major Early Miocene change in spreading direction, which would have imposed a component of compression on the transforms. Such a sense of curvature has not, to our knowledge, been observed elsewhere on the deep ocean floor, although apparently similar patterns have been reported in ophiolites.