Resolution of tomographic models of the mantle beneath Iceland

The locations of volcanic islands may be controlled by thin or extending pa rts of the lithosphere over a partially molten asthenosphere [Anderson and Bass, 1984; Favela and Anderson, 2000], by edge effects near the boundaries of thick cratonic lithosphere [Anderson, 1998], or by narrow jets of hot m antle rising from deep within the mantle [Campbell and Griffiths, 1992; Mor gan, 1971; Wilson, 1986]. Many hotspots are found on or near ridges, at lit hospheric discontinuities, or in extensional environments, so high resoluti on seismic images are required to determine whether it is lithospheric stru cture, stresses in the lithosphere, or the deep mantle that is the controll ing factor for the location of these volcanoes. In this study, we perform a simple experiment in which we use basic geometrical arguments to better un derstand the resolution of tomographic images of the upper 400 km of the ma ntle under Iceland. Our results indicate that a narrow, deep seated mantle plume is not required in order to explain the observed travel time delays i n this region. Results of tomographic inversions are often viewed as unique ; however, recent seismic studies of the Icelandic Hotspot have illustrated the non-unique nature of these models.