Failure of plume theory to explain midplate volcanism in the southern Austral islands

It has long been recognized that the properties of the Cook–Austral chain (Fig. 1) of volcanoes in the South Pacific are difficult to reconcile with the theory that volcanic activity in plate interiors is produced by the drift of tectonic plates over narrow, stationary plumes1 of hot mantle material upwelling from depth. Radiometric dates2,3 from many island samples are younger or older than would be predicted if a single plume currently located at volcanically active Macdonald seamount4 was responsible for all of the volcanoes. Indeed, only the southernmost part of the Austral volcanic line has hitherto appeared to be consistent with plume activity, and then only within the past 6 million years (Myr)5,6. Here we report radiometric dates that demonstrate that these southern Austral volcanoes are actually composed of three distinct volcanic chains with a range of ages spanning 34 Myr and with inconsistent age progressions. Gravity anomalies and seafloor fabric suggest that the volume and location of volcanism in this region is controlled by stress in the lithosphere rather than the locus of narrow plumes rising from the deep Earth. Figure 1 Bathymetric map of the South Pacific seen from ship soundings and satellite altimetry24. The solid red line is the locus of present-day sea-floor spreading in the Pacific. The broken red line is the 30-Myr isochron25. The box shows the location of the region surveyed in the southern Austral islands. Open circles (Ngatemato), triangles (Taukina) and stars (Macdonald) indicate the location of dredge sites for dated volcanic rocks; filled counterparts show the reconstructed positions of the dated volcanic rocks when they erupted using Pacific-hotspot finite rotation poles7. The thick black line gives the location of the profile shown in Fig. 3.