Isotopic evidence for Late Cretaceous plume-ridge interaction at the Hawaiian hotspot

When a mantle plume interacts with a mid-ocean ridge, both are noticeably a ffected. The mid-ocean ridge can display anomalously shallow bathymetry, ex cess volcanism, thickened crust, asymmetric sea-floor spreading and a plume component in the composition of the ridge basalts(1-4). The hotspot-relate d volcanism can be drawn closer to the ridge, and its geochemical compositi on can also be affected(3,5-7). Here we present Sr-Nd-Pb isotopic analyses of samples from the next-to-oldest seamount in the Hawaiian hotspot track, the Detroit seamount at 51 degrees N, which show that, 81 Myr ago, the Hawa iian hotspot produced volcanism with an isotopic signature indistinguishabl e from mid-ocean ridge basalt. This composition is unprecedented in the kno wn volcanism from the Hawaiian hotspot, but is consistent with the interpre tation from plate reconstructions(8) that the hotspot was located close to a mid-ocean ridge about 80 Myr ago. As the rising mantle plume encountered the hot, low-viscosity asthenosphere and hot, thin lithosphere near the spr eading centre, it appears to have entrained enough of the isotopically depl eted upper mantle to overwhelm the chemical characteristics of the plume it self. The Hawaiian hotspot thus joins the growing list of hotspots that hav e interacted with a rift early in their history.