Seismic study of the transform-rifted margin in Davis Strait between Baffin Island (Canada) and Greenland: What happens when a plume meets a transform

摘要

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.