Evolution of Labrador Sea–Baffin Bay: Plate or Plume Processes?

Breakup between Greenland and Canada resulted in oceanic spreading in the Labrador Sea and Baffin Bay. These ocean basins are connected through the Davis Strait, a bathymetric high comprising primarily continental lithosphere, and the focus of the West Greenland Tertiary volcanic province. It has been suggested that a mantle plume facilitated this breakup and generated the associated magmatism. Plume-driven breakup predicts that the earliest, most extensive rifting, magmatism and initial seafloor spreading starts in the same locality, where the postulated plume impinged. Observations from the Labrador Sea–Baffin Bay area do not accord with these predictions. Thus, the plume hypothesis is not confirmed at this locality unless major ad hoc variants are accepted. A model that fits the observations better involves a thick continental lithospheric keel of orogenic origin beneath the Davis Strait that blocked the northward-propagating Labrador Sea rift resulting in locally enhanced magmatism. The Davis Strait lithosphere was thicker and more resilient to rifting because the adjacent Paleoproterozoic Nagssugtoqidian and Torngat orogenic belts contain structures unfavourably orientated with respect to the extensional stress field at the time.RESUMELa cassure entre le Groenland et le Canada a entraine une expansion oceanique de la mer du Labrador et de la baie de Baffin. Ces bassins oceaniques sont relies par le detroit de Davis, un haut bathymetrique constitue principalement de lithosphere continentale et de la province volcanique tertiaire de l'ouest du Groenland. Il a ete suggere qu'un panache du manteau a facilite cette cassure et genere le magmatisme associe. L’hypothese d’une cassure produite par panache du manteau predit que la premiere distension oceanique, la plus importante, le magmatisme et l'expansion oceanique initial se produisent la ou le panache mantelique touche la croute continentale. Or les observations dans la region de la mer du Labrador–baie de Baffin ne correspondent pas a ces predictions. Et donc l'hypothese du panache ne fonctionne pas dans cette region a moins que des facteurs ad hoc determinants ne soient presents. Un modele qui correspond mieux aux observations presuppose la presence d’une epaisse quille lithospherique continentale d'origine orogenique sous le detroit de Davis qui aurait bloque l’expansion oceanique de la mer du Labrador vers le nord, ce qui aurait provoque une augmentation du magmatisme localement. La lithosphere du detroit de Davis etait plus epaisse et plus resistante a l’expansion oceanique parce que les bandes orogeniques paleoproterozoiques du Nagssugtoqidian et de Torngat renferment des structures defavorablement orientees par rapport au champ de contraintes d’extensions de l'epoque.