The southwestern Pacific-Antarctica ridge and the Pacific- Antarctica-Australia (Macquarie) triple junction region are now some of the tectonicly least well known areas of the world's oceans. Published plate reconstructions of the eastern Southeast Indian Ridge and the Pacific-Antarctica ridge span time intervals 5 to 10 million years in length. In some cases these lack an accurate assessment of the uncertainties in the reconstructions, or were based on sparse bathymetric coverage. Recently, detailed features of the seafloor have been revealed by observations of geoid anomalies (Geosat data). More detailed reconstructions, spanning time intervals of 1 or 2 m.y. can be obtained from the magnetic anomaly record adjacent to the Pacific-Antarctic Ridge and the Southeast Indian Ridge, and the uncertainties in these reconstructions will be dramatically decreased with the inclusion of bathymetric control from Geosat data. The PI will reanalyze existing marine magnetic, bathymetric, and Geosat data form magnetic and fracture zone data point, to complement existing results from both of these areas, in order to produce a more detailed set of poles and stage poles of reconstruction for times since about anomaly 13 (36 Ma). These reconstructions can be used to decipher in more detail the complex history of the seafloor near the Macquarie triple junction and along the southernmost Pacific-Antarctica ridge in regions that have not been well surveyed by ship.
