(Table 1) Lithology of DSDP Hole 72-516F sediments@en

Drilling at Site 516 on the northern shoulder of the main Rio Grande Rise has improved our understanding of the tectonic evolution and subsidence history of the Rise and of the entire Rio Grande-Walvis seamount and aseismic ridge system. Evidence from this site indicates that basalts at the bottom of Hole 516F were produced at the ridge crest and that the ridge crest was subaerial. I attribute the anomalous elevation of the Rise to an eastward ridge crest jump to the western end of the Rise, 91 Ma, and, recognizing a southward progression of such eastward jumps, I suggest a model for the Rio Grande-Walvis system involving a slow westward component of drift of the ridge crest off a hot-spot swell. This drift caused off-axis volcanism that in the Cretaceous succeeded but in the Cenozoic failed to capture the ridge crest. The probable mechanism of capture involved counteraction of the ridge push force within the lithosphere by a swell push force. This would make capture more likely in lithosphere produced by fast spreading, perhaps explaining the change of mode at the end of the Cretaceous. […]