The western intersection of Oceanographer fracture zone with the mid-Atlantic ridge

A survey across the western intersection of the mid-Atlantic ridge with Oceanographer fracture zone near 35 degree N shows this intersection to be different in character from its more typical eastern counterpart. At the western junction the transform valley broadens into a parallelogram shaped deep some 46 by 24 km, which extends well across the trace of the active transform. Within 30 km south of the fracture zone the median valley becomes oblique forming a NE trending ridge which is the SE edge of the deep. Magnetic mapping shows the current spreading centre to be adjacent to this ridge. A sequence of evolution for this intersection over the past 0.7 Ma is proposed to explain the features mapped. The authors suggest that the oblique ridge crest trends extended across the transform trace to form the elongated graben-like deep with its associated faults and sediment slumps. Such complex patterns may occur as plate-wide changes in spreading direction become modified by localised shear stress fields at ridge crest-transform intersections, as have been observed in a number of other cases. The absence of significant tranverse ridges across from the spreading centre at this particular fracture zone intersection, may have temporarily allowed these stess patterns to propagate across the fracture zone.