Rapid formation of the Shatsky Rise oceanic plateau inferred from its magnetic anomaly

SHATSKY Rise, in the northwest Pacific Ocean, is probably the oldest extant oceanic plateau, and as with most such features, its origin is uncertain. Both oceanic plateaus and continental flood basalts are thought to be formed by rapid, voluminous eruptions that occur when the 'head' of a newly born mantle plume ascends to the base of the lithosphere1–3. High eruption rates have been estimated for flood basalts (for example, 1.5km3 yr−1 for the Deccan Traps2) from dating of lava flows, but the inaccessibility of oceanic plateaus makes it necessary to extrapolate dating information from a small number of samples and sites4. Here we estimate the eruption rate of Shatsky Rise by a method that is indirect, but has the virtue of 'sampling' the entire volume of the plateau above the surrounding sea floor. The main, southern part of the plateau has a positive magnetic anomaly, corresponding to a reversed geomagnetic polarity at the time of eruption. Using age constraints to identify the longest period of reversed polarity during which the plateau could have formed, we estimate that 2 × 106 km3 of material erupted at a minimum rate of 1.7km3 yr−1. This issomewhat less than the rate of 8–22 km3 yr−1 estimated for the Ontong–Java Plateau4, but still represents a massive eruption, consistent with the plume-head hypothesis.