Description: New marine geophysical data acquired across the partly ice‐covered northern East Greenland continental margin highlight a complex interaction between tectonic and magmatic events. Breakup‐related lava flows are imaged in reflection seismic data as seaward dipping reflectors (SDRs), which are found to decrease in size both northwards and southwards from a central point at 75° N. We provide evidence that the magnetic anomaly pattern in the shelf area is related to volcanic phases and not to the presence of oceanic crust. The remnant magnetization of the individual lava flows is used to deduce a relative timing of the emplacement of the volcanic wedges. We find that the SDRs have been emplaced over a period of 2‐4 Ma progressively from north to south and from landward to seaward. The new data indicate a major post‐middle Eocene magmatic phase around the landward termination of the West Jan Mayen Fracture Zone. This post‐40 Ma volcanism likely was associated with the progressive separation of the Jan Mayen microcontinent from East Greenland. The break‐up of the Greenland Sea started at several isolated seafloor spreading cells whose location was controlled by rift structures and led to the present‐day segmentation of the margin. The original rift basins were subsequently connected by steady‐state seafloor spreading that propagated southwards, from the Greenland Fracture Zone to the Jan Mayen Fracture Zone. Key Points Polyphase Cenozoic volcanic rifting and consecutive emplacement of breakup‐related lava flows units along the northern East Greenland margin Breakup along restricted margin segments is followed by north to south directed progressive opening of the Greenland Sea Widespread post‐middle Eocene (〈 40 Ma) offshore magmatism, associated with the breakup of the Jan Mayen microcontinent from East Greenland

Description: 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.

Description: The Davis Strait is a bathymetric high that separates the southern Baffin Bay and the northern Labrador Sea. These basins are the result of Cretaceous and Paleogene rifting and seafloor spreading between the North American plate and Greenland. Being one of the main tectonic features of the Davis Strait, the Ungava Fault Zone is associated with transform motion related to a northward movement of Greenland relative to North America during rifting and seafloor spreading in Baffin Bay and Labrador Sea. The plate tectonic reconstruction of the Davis Strait contributes significantly to the understanding of the geodynamic history of the North-American - Greenland plates, not only the Davis Strait area but also the area of Lancaster Sound and Nares Strait, where it could shed light into the so-called Nares Strait Conflict. It is still under debate whether the spreading between Greenland and Baffin Island was compensated by sinistral transform motion along the proposed Wegener-Fault. Thus Nares Strait (trace of the Wegener Fault) and Lancaster Sound (failed arm rift) are relicts of this scenario. The lack of evidence for transform motion between Greenland and Ellesmere Island contradicts this model and provokes the conflict. As major compression along the Eurekan Fold Belt overprinted the proposed transform motion along the Wegener Fault, the Ungava Fault Zone in the Davis Strait could give the missing information for the plate tectonic reconstruction. The onshore-offshore geology and structural setting of Baffin Island is analysed by recent publications that show an essentially non-volcanic continental margin at Baffin Island that is interrupted by a volcanic-style margin around Cape Dyer. Intensive magmatic activity during the initial opening phase is indicated by widespread seaward-dipping-reflector sequences (SDRS) north of Cape Dyer. On the other hand, the structural setting of the Greenland margin side is unclear. The identification of the corresponding conjugate pattern on Greenland side provides fundamental information for the historic motion along the Ungava Fault Zone. The geophysical data of the DAVIS GATE cruise in 2008 provide new data to determine structure and type of conjugate margin segments of Greenland and Baffin Island. As part of the DAVIS GATE project, a set of multichannel seismic, refraction seismic, magnetic and gravity profiles across the Davis Strait was acquired with RV Maria S. Merian in 2008. In detail, three crossing refraction lines with up to 25 ocean-bottom seismographs, and 1500 nm multichannel seismic lines (3000 m streamer length, 240 channels and 50 litres airgun-array) build the framework of the DAVIS GATE project. This presentation illustrates first results from the multichannel seismic survey in addition with first results from magnetic and gravity profiling.