EVOLUTION OF THE PACIFIC-ANTARCTIC RIDGE SOUTH OF THE UDINTSEV FRACTURE-ZONE

Because of the proximity of the Euler poles of rotation of the Pacific and Antarctic plates, small variations in plate kinematics are fully recorded in the axial morphology and in the geometry of the Pacific-An tarctic Ridge south of the Udintsev fracture zone. Swath bathymetry an d magnetic data show that clockwise rotations of the relative motion b etween the Pacific and Antarctic plates over the last 6 million years resulted in rift propagation or in the linkage of ridge segments, with transitions from transform faults to giant overlapping spreading cent ers. This bimodal axial rearrangement has propagated southward for the last 30 to 35 million years, leaving trails on the sea floor along a 1000-kilometer-long V-shaped structure south of the Udintsev fracture zone.