THE OCEAN CONTINENT TRANSITION ALONG A PROFILE THROUGH THE LOFOTEN BASIN, NORTHERN NORWAY

The Cenozoic margins of the Norwegian-Greenland Sea offer ideal condit ions for passive margin studies. A series of structural elements, firs t observed on these margins, led to the concept of volcanic passive ma rgins. Questions still remain about the development of such features a nd the location of the boundary between oceanic and continental crust. Despite the thin sediment cover of the margins, seismic reflection da ta are not able to image the deeper structures due to the occurrence o f igneous rocks at shallow depth. This paper presents a 320-km long pr ofile perpendicular to the strike of the main structural units of the Lofoten Margin in Northern Norway. A geological model is proposed, bas ed on observations made with ocean bottom seismographs, which recorded seismic refraction data and wide angle reflections, along with a seis mic reflection profile covering the same area. Ray-tracing was used to calculate a geophysical model from the shelf area into the Lofoten ba sin. The structures typical of a volcanic passive margin were found, s howing that the Lofoten Margin was influenced by increased volcanic ac tivity during its evolution. The ocean/continent transition is located in a 30-km wide zone landwards of the Voring Plateau escarpment. The whole margin is underlain by a possibly underplated, high velocity lay er. Evidence for a pre-rift sediment basin landwards of the escarpment , overlain by basalt flows, was seen. These structural features, relat ed to extensive volcanism on the Lofoten Margin, are not as distinct a s further south along the Norwegian Margin. Viewed in the light of the hot-spot theory of White and McKenzie (I 989) the Lofoten Margin can be interpreted as a transitional type between volcanic and non-volcani c passive margin.