A Dynamic Model of the Iceland Plume Based on Tomography

Iceland is the surface expression of a large thermal anomaly in the North Atlantic. Following the tomography model of Bijwaard and Spakman (1999) one finds clear indications for a deep reaching structure of low seismic velocity, stretching down to the CMB. Based on this tomography data and using a 3D Cartesian convection code we modelled the gravity field and dynamic topography in the North Atlantic. We determined the density anomaly by using a constant conversion factor and estimated the temperature anomaly by accounting for a pressure and temperature dependent thermal expansivity. We found a maximum excess temperature of about 250 C in the proposed plume, not decreasing significantly from the lower to the upper mantle. The fitting of the observed geoid anomalies in the North Atlantic by the dynamic model demands a viscosity increase from the upper to the lower mantle of not more than 1 order of magnitude. Temperature dependent viscosity improves the fit, but does not change the general finding. The best fit is obtained in the area North of Iceland, which is characterized by shallow ocean depth and high temperature anomalies at the lithosphere base. The origin of this anomaly is explained in conjunction with a thermal anomaly below the eastern part of the Greenland Shield, which may represent the ancient plume head.