Tectonic evolution and subsidence history of the Rio Grande Rise.

Abstract

Drilling at Site 516 on the N 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. The anomalous elevation of the Rise is attributed to an eastward ridge crest jump to the W end of the Rise, 91 Ma. A model for the Rio Grande-Walvis system involving a slow westward component of drift of the ridge crest off a hot- spot swell is suggested. Data from the site suggest that a single short off-axis event affected the entire crestal region of the Rise. Perhaps the same midplate hot spot that produced an 80-50Ma volcanic episode in the Serra Geral of Brazil was responsible, but that was not the present Tristan hot spot. The data from Site 516 have been incorporated into a detailed model for the subsidence history of the main body of the Rise. -from Author