Geochemical evidence for a mid-Cretaceous superplume

Basalt lavas with a high Nb/Y ratio for a given Nb/Zr ratio occur in the Polynesian "superswell" region of the South Pacific, which probably formed by upwelling of a deep-mantle superplume. The distinctive geochemical characteristics of the Polynesian basalts may be attributed to melting of a mantle source that is more enriched in a basaltic (ancient mid-oceanic-ridge basalt) component, Basalts displaying such chemical signatures have been found on Shatsky Rise, the Ontong Java Plateau, and greenstones from subduction-zone complexes of Sakhalin Island, The occurrence of Polynesian-type basalts, together with an estimate of their ages, suggests that the South Pacific superplume was active as long ago as 90-150 Ma, The superplume activity preceded the onset of the superchron, supporting an idea that the superplume acted as a trigger for such a global event.