Tomographic evidence for a whole mantle plume below Iceland

Iceland has long been known to be a centre of both hotspot and Mid-Atlantic Ridge activity. Hotspots are generally thought to be the surface expression of mantle plumes: relatively narrow channels of hot mantle upwellings. We will present the first images of a whole mantle plume below Iceland from recent global tomography research. In the mantle below Iceland we observe a wavy, plume-shaped, low wavespeed anomaly with a broad (1000 km wide) root zone, an approximately 500 km wide central part and a large (1200 km) 'plume head'. At several depths this anomaly appears to be connected to other low velocity features. For example, at approximately 1300 km depth it is part of a semi-circular ring of low velocities below Europe and northern Africa that connects several hotspot regions (Eifel, Massif Central, Hoggar, Canary Islands). Apart from that, the plume-shaped anomaly appears to be deflected with a root zone stretching west toward Greenland and a central part east from Iceland, approximately 1000 km below the Faeroe Islands. This wavy shape may contradict the concept of stationary hotspots. The vertical continuity of the (deflected) structure is well resolved (on the order of 120-200 km) which suggests a D" origin for the Iceland hotspot. The amplitude of the inferred seismic anomaly can be translated into an excess temperature of 200-300 K for the entire mantle which agrees well with previous and independent estimates.