Seismic structure of the Iceland mantle plume

Oceanic hotspots are generally accepted to be the manifestations of plumes of hot, upwelling mantle material^1,2, but the nature of such flows remains enigmatic. Iceland, for example, is one of the most thoroughly investigated hotspots, yet previous seismological^3-5 and geodynamic^6-12 studies have been unable to constrain the width or temperature of the plume. Here we report the results of a regional broadband seismic experiment undertaken to determine the three-dimensional velocity structure of the upper mantle beneath Iceland using relative travel times of body waves from teleseismic earthquakes. Inversion solutions of the data show a cylindrical zone of low P- and S-wave velocities that extends from 100km to at least 400km depth beneath central Iceland. The radius of the low-velocity anomaly is about 150km, and its magnitude is approximately 2% for P waves and 4% for S waves, indicating that Iceland is underlain by a hot, narrow plume of upwelling mantle.