Baffin Bay is a small ocean basin. This has been shown by seismic refraction studies. The depth to mantle beneath the central part of the basin is approximately 10 km, consisting of 2 km of water, 4 km of sediment and 4 km of oceanic crust, with the oceanic crust thickening toward Greenland. Sediments thicken northward and beneath the northern margin, east of Lancaster Sound, and are 6-7 km thick. The margin of the ocean basin can be delineated by gravity measurements, and the change in gravity is accompanied by change in magnetic-field-anomaly characteristics and change in structural style in sediments. Sediment-filled grabenlike structures occupy Melville Bay and Lancaster Sound, and smaller sedimentary basins are present in the southern part of Nares Straits and in Jon s Sound. Extensions of the Tertiary igneous rocks of West Greenland and eastern Baffin Island are found offshore. Oceanic "basement" at the southern end of Baffin Bay rises to the surface on the northern side of Davis Strait. This sill is Icelandic in character, and may have been a site of a mantle plume which was at least in part responsible for the opening of the Bay.

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