The crustal structure in the southern Davis Strait and the adjacent ocean-continent transition zone in NE Labrador Sea was determined along a 185-km-long refraction/wide-angle reflection seismic transect to study the impact of the Iceland mantle plume to this region. A P-wave velocity model was developed from forward and inverse modelling of dense airgun shots recorded by ocean bottom seismographs. A coincident industry multichannel reflection seismic profile was used to guide the modelling as reflectivity could be identified down to Moho. The model displays a marked lateral change of velocity structure. The sedimentary cover (velocities 1.8-3.9 km s(-1)) is up to 4 km thick in the north and thins to 1 km in the south. The segment of the line within southern Davis Strait is interpreted to be of continental character with a two-layered 13-km-thick crust with P-wave velocities of 5.6-5.8 and 6.4-6.7 km s(-1) in the upper and lower crust, respectively. The crust is underlain by a 2- to 4-km-thick high-velocity layer (7.5 km s(-1)). This layer we interpret as underplated material related to the Iceland plume. The southern segment of the line in Labrador Sea displays a 2-km-thick layer with a velocity of 4.5 km s(-1). This layer can be correlated to a well about 100 km to the west of the line, where Palaeocene basalts and interbedded sediments were drilled. Underneath is a 12-km-thick crust with a 2-km-thick upper layer (5.8-6.6 km s(-1)) and a 10-km-thick lower layer (6.8-7.2 km s(-1)). This crust is interpreted to be of oceanic character. S-wave modelling yields a Poisson's ratio of 0.28 for the lower crust, compatible with a gabbroic composition. The igneous crust is 5 km thicker than normal oceanic crust. We suggest that the increased magma production was created by buoyancy-driving flow. We propose a model in which initial seafloor spreading occurred between Labrador and West Greenland, when the Iceland plume arrived in the area at similar to 62 Ma and caused enhanced magma production. Shortly afterwards (chron 27-26), plume material was channelled southward underplating part of Davis Strait and forming basaltic flows interbedded with sediment.