GEOPHYSICS OF THE PITMAN FRACTURE-ZONE AND PACIFIC-ANTARCTIC PLATE MOTIONS DURING THE CENOZOIC

Multibeam bathymetry and magnetometer data from the Pitman fracture zo ne (FZ) permit construction of a plate motion history for the South Pa cific over the past 65 million years. Reconstructions show that motion between the Antarctic and Bellingshausen plates was smaller than prev iously hypothesized and ended earlier, at chron C27 (61 million years ago). The fixed hot-spot hypothesis and published paleomagnetic data r equire additional motion elsewhere during the early Tertiary, either b etween East Antarctica and West Antarctica or between the North and So uth Pacific. A plate reorganization at chron C27 initiated the Pitman FZ and may have been responsible for the other right-stepping fracture zones along the ridge. An abrupt (8 degrees) clockwise rotation in th e abyssal hill fabric along the Pitman flowline near the young end of chron C3a (5.9 million years ago) dates the major change in Pacific-An tarctic relative motion in the late Neogene.