Evolution of the Walvis Ridge-Rio Grande Rise Hot Spot system: implications for African and South American plate motions over plumes

Abstract

Crystallization ages of volcanic rocks, dredged or drilled from the Walvis Ridge (10 sites) and the Rio Grande Rise (1 site), have been determined by the 40Ar/39Ar incremental heating technique. The fundamentally age-progressive distribution of these basement ages suggests a common hot spot source for volcanism on the island of Tristan da Cunha, along the Walvis Ridge and Rio Grande Rise, and for the formation of the continental flood basalts located in Namibia and Brazil. The Walvis Ridge-Rio Grande Rise volcanic system evolved along a section of the S Atlantic spreading-axis, as the African and South American plates migrated apart, astride, or in close proximity to, an upwelling plume, Reconstructions of the spatial relationship between the spreading-axis, the Tristan hot spot, and the evolving Walvis Ridge-Rio Grande Rise volcanic feature show that, at about 70Ma, the spreading-axis began to migrate W, away from the hot spot. The resulting transition to intraplate hot spot volcanism along the Walvis Ridge also involved a N migration of previously formed African seafloor over the hot spot. Rotation parameters for African motion over fixed hot spots have been recalculated. -from Authors