Seismic Refraction Studies in Baffin Bay: An Example of a Developing Ocean Basin

Abstract

Summary Sonobuoy and tape recording buoy seismic refraction measurements were carried out in Baffin Bay and Davis Strait to study the extent and tectonic development of the oceanic region and the structure of some of the major features of the surrounding continental shelves. Both the oceanic and continental shelf areas are occupied by thick sequences of sediment, 3–7 km, the sediment pile being thicker in the north. A refraction profile in Davis Strait shows that it is underlain by a crust similar to that beneath Iceland, with a total crustal thickness of over 20 km. The main difference is that a normal mantle velocity is measured beneath the Davis Strait. The results, supported by a seismic reflection profile in the region, suggest that Davis Strait may once have been the site of a hot spot or upwelling mantle plume. The main oceanic crustal layers, layers 2 and 3, under the central basin are thin. A total main crustal thickness of 4 km was measured (omitting the sediment, that is) compared with a mean thickness of 7 km for the major ocean basins. The crust is underlain by mantle rocks exhibiting normal mantle velocities, the mean being 8.0km s−1. Seven refraction lines distributed over the east-west extent of oceanic crust show no detectable median ridge. This accords well with models of the decrease of ridge topography after spreading has ceased as the thermal anomaly beneath decays and supports the hypothesis that the area has not been spreading for about 50 My. The anomalously thin crust can also be related to its age. Thin crust is found near the active mid-ocean ridges at distances corresponding to ages between 50 and 80 My. We postulate that the crust in Baffin Bay is not fully developed and in time a thicker crust will form. These results support the hypothesis that at least the lower part of layer 3 of the ocean basins is composed of altered mantle material.