[1] The Nova Scotia continental margin off eastern Canada marks a transition from a volcanic to a nonvolcanic style of rifting. The northern (nonvolcanic) segment of the margin was studied by a 490-km-long refraction seismic line with dense air gun shots, coincident with previous deep reflection profiles. A P wave velocity model was developed from forward and inverse modeling of the wide-angle data from 19 ocean bottom seismometers and coincident normal incidence reflection profiles. The continental crust has a maximum thickness of 36 km and is divided into three layers with velocities of 5.7-6.9 km/s. Crustal thinning down to 3 km occurs in a 180-km-wide zone and the sediment cover in this area is up to 15 km thick. Farther seaward, a 150-km-wide transition zone is observed with a 5-km-thick lower layer (7.2-7.6 km/s) interpreted as partially serpentinized mantle. At the landward end, this layer is overlain by highly altered continental crust (5.4 km/s) extending up to the seaward limit of the Jurassic salt province. Farther seaward, the upper layer is interpreted as exhumed and highly serpentinized mantle (5.1 km/s) separated from the lower layer by subhorizontal reflectivity, which probably represents a serpentinization front. Oceanic crustal thickness is 4 km with layer 2 velocities of 4.6-5.0 km/s. Layer 3 velocities of 6.4-6.55 km/s are lower than typical lower oceanic crust velocities but consistent with a low magma supply and increased tectonism as observed on the reflection profile. This reduced magma production might be related to the proximity of the Newfoundland transform margin.

The Davis Strait transform margin was studied using a 630‐km‐long wide‐angle reflection/refraction seismic transect extending from SE Baffin Island to Greenland. Dense airgun shots were recorded by 28 ocean bottom seismometers deployed along the line. A P wave velocity model was developed from forward and inverse modeling of the wide‐angle data and incorporation of coincident deep multichannel reflection seismic data. Off Baffin Island in the Saglek Basin, 7 to 11‐km‐thick two‐layered continental crust (5.8–6.6 km/s) is observed. Off Greenland, continental crust is divided into three layers (5.4–6.8 km/s) with a maximum thickness of 20 km. Farther offshore Greenland the crust thins to 7–12 km and the lower crust disappears. Between the continental blocks a 140‐km‐wide zone with oceanic crust (layer 2 is 5.4–6.2 km/s and layer 3 is 6.7–7.0 km/s) is located. The western half of this zone is interpreted to be part of a volcanic margin with seaward dipping reflectors; the eastern part is associated with the Ungava fault zone (UFZ), the major transform fault in Davis Strait. The UFZ thus acted as leaky transform fault during phases of transtension. Southward flow of material from the Iceland plume created a 4 to 8‐km‐thick underplated layer (7.4 km/s) beneath the thinned portions of the continental crust and beneath previously emplaced oceanic crust. Plume related Paleogene volcanism is indicated by an up to 4‐km thick layer (4.3–5.8 km/s) with basalts and interbedded sediments that can be traced from SE Baffin Island 400 km toward the east.

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