Abstract
Recent accretion on the Cocos-Nazca spreading center has been asymmetric, with more material (along most of the rise) added to the Cocos than to the Nazca plate. There is evidence in the magnetic record that some of this asymmetric accretion has resulted from small discrete jumps of the rise axis to the south, forming and destroying transform faults.
Relative and absolute models of instantaneous plate motions derived here provide an accurate representation of recent motions in the east Pacific. The existence of a self-consistent model that fits all the relative-motion data provides strong support for the hypothesis that plates behave rigidly. In addition, the exceptional agreement between the relative-motion and absolute-motion models provides strong support that the Wilson-Morgan hotspot hypothesis holds for the recent past. In particular, the agreement of the predicted instantaneous azimuths of the Cocos and Carnegie Ridges with their observed azimuths strongly suggests that at least the young parts of both aseismic ridges were formed by the motion of the Cocos and Nazca plates over a Galapagos hotspot.
