Since the North Atlantic continental breakup in the early Tertiary, the process of rifting above a mantle plume has produced large thicknesses of igneous crust. We report results of an integrated offshore-onshore seismic study of the crust and upper mantle along a transect of the aseismic Faroe-Iceland Ridge, between the continental fragment beneath the Faroe Islands and the present-day spreading center in northeast Iceland. Normal-incidence seismic data provide an image of the uppermost crust, which is complemented by a velocity model from streamer refraction analyses. These data together image four sedimentary basins, up to 400 m deep, along the crest of the ridge. The streamer refraction velocity model in turn forms the uppermost section of a full crustal velocity model derived from travel time modeling of air gun and explosive data. The compressional to shear wave velocity ratio in the crust of the Faroe-Iceland Ridge is 1.77¿0.02, similar to that of eastern Iceland. The Moho beneath the Faroe-Iceland Ridge lies at a depth of 25--30 km. Crust of 25--30 km thickness requires an upper mantle potential temperature elevated 200--250 ¿C above normal if formed by passive adiabatic decompression melting of the mantle or a somewhat less elevated temperature if, as is likely, there is a component of active convection in the underlying mantle plume core. ¿ 1999 American Geophysical Union