Investigating the tectonic evolution of Baffin Bay, northern Canada, using a combination of constrained 3-D gravity inversion and deformable plate tectonic models

At the northwestern limit of the North Atlantic Realm lies Baffin Bay, an underexplored extinct rift and spreading system between North America and Greenland. Baffin Bay formed from the northward propagation of the rifting that created the Labrador Sea to the south. From the tectonic evolution of the Labrador Sea, we know that the rift history of Baffin Bay likely began during the Mesozoic. Rifting, breakup, and seafloor spreading persisted into the Cenozoic for Baffin Bay where extinct spreading axes and fracture zones are clearly observed from potential field data. The deep crustal structure of Baffin Bay has been probed by approximately ten seismic refraction/wide-angle reflection surveys but the broad 3-D crustal structure has remained largely unknown. In order to infill existing sparse seismic constraints from within and around the margins of Baffin Bay, constrained 3-D gravity inversions were performed using two independent inversion methodologies. By combining the inversion results with seismic constraints, a regional view of the crustal architecture of Baffin Bay is obtained and used to test the validity of deformable plate tectonic reconstructions derived using GPlates, while assessing the influence of pre-existing structures. These complementary datasets reveal significant asymmetry in crustal thickness beneath Baffin Bay with thicker crust (25-30 km) over a wider zone on the Greenland margin. Higher density lower crust is needed along the Greenland margin in order to reproduce the observed gravity anomalies while also ensuring that the 3-D density model is consistent with available deep seismic constraints. The thinnest resolved crust (5-13 km) predictably aligns with Eocene spreading centres. From the deformable models, an initial unstretched crustal thickness of 34-36 km is required in order for the models to evolve toward present-day crustal thicknesses. Such thicknesses agree with the onshore crustal thicknesses obtained from teleseismic studies beyond the limits of the deformation zone. For Baffin Bay, pre-existing structures do not appear to have played a significant role in rifting at the regional scale as the overall present-day crustal architecture can be reproduced with a simple, uniform pre-rift model.