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 less than or equal to 500 km, rising from a broad root zone (>1000 km) and culminating in a plume top with a diameter of similar to 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 similar to 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. (C) 1999 Elsevier Science B.V. All rights reserved.