Crust generated above the Iceland mantle plume: From continental rift to oceanic spreading center

Since the North Atlantic continental breakup in the early Tertiary, the pro cess of rifting above a mantle plume has produced large thicknesses of igne ous crust. We report results of an integrated offshore-onshore seismic stud y of the crust and upper mantle along a transect of the aseismic Faroe-Icel and Ridge, between the continental fragment beneath the Faroe Islands and t he present-day spreading center in northeast Iceland. Normal-incidence seis mic data provide an image of the uppermost crust, which is complemented by a velocity model from streamer refraction analyses. These data together ima ge four sedimentary basins, up to 400 m deep, along; the crest of the ridge . The streamer refraction velocity model in turn forms the uppermost sectio n of a full crustal velocity model derived from travel time modeling of air gun and explosive data. The compressional to shear m ave velocity ratio in the crust of the Faroe-Iceland Ridge is 1.71 +/- 0.02, similar to that of eastern Iceland. The Moho beneath the Faroe-Iceland Ridge Lies at a depth o f 25-30 km. Crust of 25-30 km thickness requires an upper mantle potential temperature elevated 200-250 degrees C above normal if formed by passive ad iabatic decompression melting of the mantle or a somewhat less elevated tem perature if, as is likely, there is a component of active convection in the underlying mantle plume core.