We have used recently collected magnetic profiles and high resolution multibeam bathymetry data near the southern Austral Islands in French Polynesia to constrain the relative motion of the Pacific and Farallon plates between chron 25 and chron 18 (42--59 Ma). A change in plate motion at about chron 21 (50 Ma), which reoriented spreading direction in the area by 10--12¿ clockwise was apparently accommodated by a southward propagating rift which transferred 160 km of Pacific crust to the Farallon plate, the outer pseudofault of which is preserved as the Adventure Trough. These new constraints significantly revise previous estimates of Pacific-Farallon relative motion at the crucial time period encompassing the bend in the Hawaiian-Emperor chain, believed to represent an abrupt change in the absolute motion of the Pacific plate. Disrupted lithosphere at the Adventure Trough has apparently been a preferred site for later midplate volcanic activity. ¿ 1998 American Geophysical Union