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.

SUMMARY The crustal structure in the southern Davis Strait and the adjacent ocean–continent transition zone in NE Labrador Sea was determined along a 185‐km‐long refraction/wide‐angle reflection seismic transect to study the impact of the Iceland mantle plume to this region. A P‐wave velocity model was developed from forward and inverse modelling of dense airgun shots recorded by ocean bottom seismographs. A coincident industry multichannel reflection seismic profile was used to guide the modelling as reflectivity could be identified down to Moho. The model displays a marked lateral change of velocity structure. The sedimentary cover (velocities 1.8–3.9 km s−1) is up to 4 km thick in the north and thins to 1 km in the south. The segment of the line within southern Davis Strait is interpreted to be of continental character with a two‐layered 13‐km‐thick crust with P‐wave velocities of 5.6–5.8 and 6.4–6.7 km s−1 in the upper and lower crust, respectively. The crust is underlain by a 2‐ to 4‐km‐thick high‐velocity layer (7.5 km s−1). This layer we interpret as underplated material related to the Iceland plume. The southern segment of the line in Labrador Sea displays a 2‐km‐thick layer with a velocity of 4.5 km s−1. This layer can be correlated to a well about 100 km to the west of the line, where Palaeocene basalts and interbedded sediments were drilled. Underneath is a 12‐km‐thick crust with a 2‐km‐thick upper layer (5.8–6.6 km s−1) and a 10‐km‐thick lower layer (6.8–7.2 km s−1). This crust is interpreted to be of oceanic character. S‐wave modelling yields a Poisson's ratio of 0.28 for the lower crust, compatible with a gabbroic composition. The igneous crust is 5 km thicker than normal oceanic crust. We suggest that the increased magma production was created by buoyancy‐driving flow. We propose a model in which initial seafloor spreading occurred between Labrador and West Greenland, when the Iceland plume arrived in the area at ∼62 Ma and caused enhanced magma production. Shortly afterwards (chron 27–26), plume material was channelled southward underplating part of Davis Strait and forming basaltic flows interbedded with sediment.

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.

S U M M A R YThe crustal structure of the NE Flemish Cap margin was determined along a 460-km-long refraction/wide-angle reflection seismic transect (FLAME Line) to define the thickness, structure and composition of the crust and uppermost mantle along the line. A P-wave velocity model was developed from forward and inverse modelling of dense airgun shots recorded by 19 ocean bottom seismometers. A coincident multichannel seismic profile was used to guide the modelling as reflections could be identified down to Moho. The model displays a sediment cover of up to 3.6-km-thick, subdivided into three layers with velocities of 1.8-1.9 km s −1 , 2.8-3.1 km s −1 and 4.7-4.8 km s −1 . For the western part of the FLAME Line over Flemish Cap, the P-wave velocity model displays an up to 32-km-thick, three-layer continental crust. The continental crust has velocities of 5.8-6.1 km s −1 , 6.3-6.45 km s −1 and 6.65-6.85 km s −1 and thicknesses of about 5 km, 7 km and 20 km in the upper, middle and lower layers, respectively. The thick continental crust thins to a two-layer, 6-km-thick crust (upper layer is 5.55-6.0 km s −1 and the layer below is 6.65-6.8 km s −1 ) over a distance of 45 km. S-wave velocities are determined in the upper layer of the thick continental crust over Flemish Cap and the transition zone by assigning Poisson's ratios in the P-wave velocity model. Comparison of calculated to observed arrival times gives a Poisson's ratio of 0.27 in the upper layer and 0.28 in the layer below, which suggests that the composition of the crust is primarily continental in both the thick crust and the thin crust of the transition zone. The thin continental crust is stretched over a width of 80 km and is underlain by a layer with velocities of 7.5-7.9 km s −1 . We interpret this layer as partially serpentinized mantle, which is consistent with observations from the Newfoundland margin to the south. The serpentinized mantle terminates 30 km seaward of the thick continental crust. At the seaward-most end of the thin continental crust, a prominent ridge feature is observed. The seismic refraction and multichannel seismic data results indicate a mixed character between serpentinized mantle with volcanic extrusions or continental crust. The reflection seismic data show a high relief basement from the ridge feature and seaward. The FLAME Line crosses magnetic anomaly 34 and extends another ∼50 km seaward well into oceanic crust. The ridge is flanked seaward by a two-layer oceanic crust. The upper layer (Layer 2) has velocities of 4.8-5.0 km s −1 for the landward-most 35 km of oceanic crust and 4.8-6.2 km s −1 for the seaward 60 km. The average thickness of Layer 2 is ∼2 km. The lower layer (Layer 3) has velocities of 6.7-7.2 km s −1 and a thickness of ∼3.5 km. The velocity model is consistent with a sharp onset of seafloor spreading seaward of the ridge feature.

We present the combined results of deep multichannel refl ection and refraction seismic surveys across the Flemish Cap-Goban Spur conjugate margin pair (North Atlantic), which we use to infer rifting style and breakup. Profi les on both margins cross magnetic anomaly 34 and extend into oceanic crust, making it possible to observe the complete history from continental rifting through to the formation of initial oceanic crust. The deep multichannel seismic (MCS) refl ection data have previously been used to support a model of symmetric pure shear extension followed by asymmetric breakup and a sharp continent-ocean boundary. Using both types of seismic data, our results indicate instead that asymmetric structures are formed during all stages of rifting, breakup, and complex transition to oceanic spreading. The differing nature of the two oceancontinent transition zones is particularly striking. For Flemish Cap, our reprocessed image of the MCS profi le clearly shows tilted fault blocks beneath back-tilted sediment packages, consistent with a wide region of highly thinned continental crust inferred from wideangle seismic data. In contrast, normal incidence and wide-angle seismic data for the Goban Spur transition zone indicate the presence of exhumed serpentinized mantle.

Seismic reflection data and shallow cores from the SE Greenland margin show that rift basins formed by the mid- to Late Cretaceous in the offshore area near Ammassalik. Here termed the Ammassalik Basin, this contribution documents the area using reprocessed older shallow seismic reflection data together with a more recent, commercial deep seismic reflection profile. The data show that the basin is at least 4 km deep and may be regionally quite extensive. Interpretation of gravity anomaly data indicate that the basin potentially covers an area of nearly 100 000 km2. The sediments in the basins are at least of Cretaceous age, as indicated by a sample from just below the basalt cover that was dated as Albian. Dipping sediment layers in the basins indicate that older sediments are present. Comparison of the data to the conjugate Hatton margin where older basins are exposed beneath the volcanic cover shows similar stratigraphy of similar ages. Reconstructions of the position of the basin during the Permian–Triassic and Jurassic suggest that older sedimentary strata could also be possible. In contrast to the conjugate Hatton margin, possible older strata subcrop out below the seafloor along the shallow margin, providing a future opportunity to sample some of the oldest sediments to determine the onset of rifting between SE Greenland and the Hatton margin.

The Ammassalik Rifted Margin TSE comprises the Ammassalik and the Kangerlussuaq rift basins located on the southern East and South-East Greenland margin. The offshore Ammassalik Basin is one of the last virtually undescribed segments of the North Atlantic continental margins with a very sparse seismic coverage. The basin is compartmentalized into smaller sub-basins up to at least 4 km deep blanketed by Paleocene-Eocene basalt towards the east. Albian sediments cored in the basin suggest an at least partly Cretaceous age, making the Ammassalik Basin a likely analogue to basins on the conjugate outer British continental margin. However, the deeper, undated succession could include pre-Cretaceous strata. Located onshore southern East Greenland, the Kangerlussuaq Basin contains a Barremian/Aptian-Danian succession of estuarine-marine strata overlain by Paleocene fluvial sediments, basalts and thinner marine interludes. The sedimentary succession is less than 1 km thick. Cenozoic uplift and erosion affected both basins. Unlike the Kangerlussuaq Basin, the Ammassalik Basin may contain a working petroleum system. Together with the very large fault structures identified in the basin, this makes the Ammassalik Basin an interesting future exploration target, with the main challenge being to demonstrate a mature source rock, together with qualifying the effects of the Paleocene-Eocene magmatism and Cenozoic exhumation on the potential petroleum system.