Tomographic evidence for a narrow whole mantle plume below Iceland

Iceland is known to be a centre of both hotspot and Mid-Atlantic Ridge activity. A plume origin for the hotspot has been suggested by observational, laboratory and numerical investigations as well as by several seismological studies. The latter have, however, not yielded a detailed image of the entire mantle volume below Iceland. We present tomographic images of a narrow low velocity anomaly below Iceland, extending from the core-mantle boundary to the surface. From these images we infer a bent plume with a diameter ≤500 km, rising from a broad root zone (>1000 km) and culminating in a plume top with a diameter of ∼1200 km. The anomaly amplitude can, if only controlled by temperature, be converted into excess temperatures in the upper and lower mantle of the order of 200–300 K and ∼200 K, respectively. The wavy shape of the anomaly together with its lateral branches, may indicate that the position of the Iceland hotspot is not stationary.