Observations of anomalous oceanic crust in the Canada Basin, Arctic Ocean

We present a seismic reflection frofile and coincident refraction data in deep water north of the Northwind Ridge, in the Canada Basin. The reflection profile shows a package of bright events, which are locally nonparallel and discontinuous, about 2.5 s below the seafloor. These bright reflectors are of interest because previous reflection profiles in the Canada Basin have not penetrated the coherent flat-lying events, which are typical of bedded sedimentary rocks. These prominent reflections are recorded on the refraction profile as wide-angle reflections, and the locally nonparallel and discontinuous event as a refraction. On the refraction profile the nonparallel and discontinuous event exhibits lower frequencies and has an associated refraction with a velocity of 4.5 km/s and a high gradient. This event is interpreted as representing the top of oceanic layer 2, which is observed for the first time in the Canada Basin. Three kilometres beneath layer 2 a velocity of 7.2–7.5 km/s is measured. This layer could represent either a high-velocity layer 3 or serpentinized mantle. Based on comparison with the eastern Grand Banks and the west Iberian and Labrador Sea margins the interpretation of serpentinized mantle is preferred.