A model for the plate tectonic evolution of the east-central Pacific based on SEASAT investigations

A complete SEASAT dataset is used to investigate the small-scale bathymetry of a 15° by 15° area of the east-central Pacific, northeast of Pitcairn Island, which was involved in the Miocene ridge jump and reorientation. Two fracture zones (FZ1 and FZ2) are mapped along 450 km, at an azimuth of N95°E, while the signature of the Austral Fracture Zone disappears east of 135°W. Several seamounts are discovered or confirmed along the Oeno-Henderson-Ducie lineament, and the degree of isostatic compensation of a number of islands at the eastern end of the Tuamotu group is studied: islands of the northern branch have practically no signatures in the geoid, while the southern ones must have formed on lithosphere at least 10 Ma old. On the basis of these constraints, we present a model of the evolution of spreading since 40 Ma B.P., in which the deactivation of the Austral Fracture Zone and the transfer of its offset to FZ1 in the Late Oligocene is interpreted as due to rift propagation, triggered by a northern Tuamotu hotspot; we propose that the Oeno-Ducie chain is the surface expression of a southern Tuamotu hotspot, deviated 15° in azimuth by the presence of a young and fresh fracture zone. Thus our model predicts that hotspots and ridge systems can have a moderate influence on each other's kinematics and surface expressions, which does not however extend to permanent trapping.