SUMMARY Baffin Bay represents the northern extension of the extinct rift system in the Labrador Sea. While the extent of oceanic crust and magnetic spreading anomalies are well constrained in the Labrador Sea, no magnetic spreading anomalies have yet been identified in Baffin Bay. Thus, the nature and evolution of the Baffin Bay crust remain uncertain. To clearly characterize the crust in southern Baffin Bay, 42 ocean bottom seismographs were deployed along a 710‐km‐long seismic refraction line, from Baffin Island to Greenland. Multichannel seismic reflection, gravity and magnetic anomaly data were recorded along the same transect. Using forward modelling and inversion of observed traveltimes from dense airgun shots, a P‐wave velocity model was obtained. The detailed morphology of the basement was constrained using the seismic reflection data. A 2‐D density model supports and complements the P‐wave modelling. Sediments of up to 6 km in thickness with P‐wave velocities of 1.8–4.0 km s−1 are imaged in the centre of Baffin Bay. Oceanic crust underlies at least 305 km of the profile. The oceanic crust is 7.5 km thick on average and is modelled as three layers. Oceanic layer 2 ranges in P‐wave velocity from 4.8 to 6.4 km s−1 and is divided into basalts and dykes. Oceanic layer 3 displays P‐wave velocities of 6.4–7.2 km s−1. The Greenland continental crust is up to 25 km thick along the line and divided into an upper, middle and lower crust with P‐wave velocities from 5.3 to 7.0 km s−1. The upper and middle continental crust thin over a 120‐km‐wide continent–ocean transition zone. We classify this margin as a volcanic continental margin as seaward dipping reflectors are imaged from the seismic reflection data and mafic intrusions in the lower crust can be inferred from the seismic refraction data. The profile did not reach continental crust on the Baffin Island margin, which implies a transition zone of 150 km length at most. The new information on the extent of oceanic crust is used with published poles of rotation to develop a new kinematic model of the evolution of oceanic crust in southern Baffin Bay.

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Wide‐angle reflection/refraction seismic data were acquired on a 450‐km‐long transect in southern Baffin Bay extending from Baffin Island to Greenland. Dense air gun shots were recorded on 22 ocean bottom seismometers. APwave velocity model was developed from forward and inverse modeling of the observed travel times. Beneath the Baffin Island shelf, a three‐layered continental crust is observed with velocities of 5.5 to 6.9 km/s. Typical for transform margins, there is a sharp transition between continental and oceanic crust. Off Baffin Island, 7‐km‐thick oceanic crust is interpreted to lie in a major transform fault identified on the gravity map. Beneath the deep Baffin Bay basin, 9‐km‐thick oceanic crust is encountered but thins to 6 km within an assumed fracture zone. The thicker than normal oceanic crust indicates an ample magma supply, possibly related to melt extracted from a mantle plume. Seaward of the Greenland continental crust, 20‐km‐thick igneous crust (6.3 to 7.3 km/s) is encountered in a 25‐km‐wide zone interpreted as a leaky transform fault that can be correlated southward through Davis Strait. The igneous crust is bounded by a 20‐km wide basin to the west, underlain by 4‐km‐thick crust of unknown affinity. This structure is probably associated with transform movements. A high‐velocity lower crustal layer (7.1 km/s) of 8 km thickness is indicated beneath the Greenland crust and can be correlated into the adjacent thick igneous crust. Both the thick igneous and Greenland crust are covered by up to 4 km of Paleogene volcanics (5.2 to 5.7 km/s).

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The Davis Strait is located between Canada and Greenland and connects the Labrador Sea and the Baffin Bay basins. Both basins formed in Cretaceous to Eocene time and were connected by a transform fault system in the Davis Strait. Whether the crust in the central Davis Strait is oceanic or continental has been disputed. This information is needed to understand the evolution of this transform margin during the separation of the North American plate and Greenland. We here present a 315-km-long east-west-oriented profile that crosses the Davis Strait and two major transform fault systems-the Ungava Fault Complex and the Hudson Fracture Zone. By forward modelling of data from 12 ocean bottom seismographs, we develop a P-wave velocity model. We compare this model with a density model from ship-borne gravity data. Seismic reflection and magnetic anomaly data support and complement the interpretation. Most of the crust is covered by basalt flows that indicate extensive volcanism in the Davis Strait. While the upper crust is uniform, the middle and lower crust are characterized by higher P-wave velocities and densities at the location of the Ungava Fault Complex. Here, P-wave velocities of the middle crust are 6.6 km s −1 and of the lower crust are 7.1 km s −1 compared to 6.3 and 6.8 km s −1 outside this area; densities are 2850 and 3050 kg m −3 compared to 2800 and 2900 kg m −3. We here interpret a 45-km-long section as stretched and intruded crust or as new igneous crust that correlates with oceanic crust in the southern Davis Strait. A high-velocity lower crust (6.9-7.3 km s −1) indicates a high content of mafic material. This mantle-derived material gradually intruded the lower crust of the adjacent continental crust and can be related to the Iceland mantle plume. With plate kinematic modelling, we can demonstrate the importance of two transform fault systems in the Davis Strait: the Ungava Fault Complex with transpression and the Hudson Fracture Zone with pure strike-slip motion. We show that with recent poles of rotation, most of the relative motion between the North American plate and Greenland took place along the Hudson Fracture Zone.