Continent-Ocean Transition Across the Northeastern Nova Scotian Margin From a Dense Wide-Angle Seismic Profile

To improve constraints on rifting processes resulting in the formation of the southeastern Canadian margin, we interpret the most detailed regional 2-D velocity model from offshore Nova Scotia constructed using wide-angle OETR-2009 data. This 405-km-long profile was collected with 78 ocean bottom seismometers. The presented data analysis and interpretation are supported by a reflection image from the coincident long streamer GXT-2000 profile. We identify a continental zone where the full-thickness (similar to 30 km), three-layered continental crust beneath the inner shelf thins sharply seaward by a listric fault that forms a 12-km-deep Huron Subbasin beneath a high-velocity carbonate bank (similar to 5.8 km/s), creating a shadow zone above tilted crustal blocks. Depth-dependent and variable initial thinning is evidenced in all three modeled crustal layers, which, nevertheless, pinch out together at their seaward ends. More gradual and regional thinning and a local amagmatic thickening are modeled seaward beneath the slope until 70 km from the shelf break, beyond which a deepwater amagmatic continent-ocean transition shows velocity characteristics not typical of either continental or oceanic crust. The 100-km-wide continent-ocean transition is characterized by a low-velocity (5.3-5.4 km/s), low gradient, <2-km thick upper crust, above a high-velocity (6.3-7.5 km/s), high gradient, <5-km-thick lower crust, which can be interpreted as moderately serpentinized mantle. Underneath this layer is a <5-km-thick low-velocity (7.1-8.0 km/s) partially serpentinized mantle layer. A similar to 5-km-thick oceanic crust is modeled seaward. Our results suggest that amagmatic processes dominated the continental breakup in this area.