The Rio Grande Rise (RGR) in the South Atlantic has been debated as either an oceanic plateau linked to the Tristan-Gough mantle plume or a detached continental fragment. New major and trace element data from volcanic rocks across the RGR and the adjacent Jean Charcot Seamount Chain reveal that the eastern RGR and older western RGR consist of tholeiitic basalt, suggesting formation above the Tristan-Gough plume near the Mid-Atlantic Ridge. Younger alkaline lavas from the western RGR and the Jean Charcot Seamount Chain formed from lower degrees of melting beneath thicker lithosphere during intraplate rifting. No geochemical evidence supports the presence of underlying continental crust.

Patrick A. Hoyer, Karsten M. Haase, Marcel Regelous, John M. O'Connor, Stephan Homrighausen, Wolfram H. Geissler, Wilfried Jokat