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

Abstract

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 (~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 (~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~5-km-thick oceanic crust is modeled seaward. Our results suggest that amagmatic processes dominated the continental breakup in this area.Subsequent to these previous studies, a dense wide-angle profile OETR-2009

Along‐Strike Variations in Structure of the Continent‐Ocean Transition at the Northeastern Nova Scotia Margin From Wide‐Angle Seismic Observations

“…Figure shows that the sedimentary layers are more‐or‐less laminated beddings over the whole profile except for Layer S3 where more internal dipping reflections can be observed. This is also true on the dip profile GXT‐2000 coincident with the OETR‐2009 profile (Lau et al, ), suggesting a regional flatness of these sediments in deep water (∼4‐km depth). Interface S3/S4 represents a major velocity contrast (Figures a and b) that coincides with the interpreted Reflector K94 for model distance <72 km but with Reflector K130 (Valanginian‐Hauterivian; 130 Ma) for the rest of the profile (Play Fairway Analysis Atlas, ).…”

“…COT studies of the Tantallon Subbasin and its vicinity along the northeastern Nova Scotia margin demonstrated this problem well (Figure ; Lau et al, ). Across the southwestern Tantallon Subbasin, Funck et al () interpreted hyperextended continental crust and exhumed, highly serpentinized mantle for the landward and seaward half of the COT, respectively.…”

“…No exhumed mantle is, however, observed on the conjugate Moroccan margin (Biari et al, ; Contrucci et al, ; Klingelhoefer et al, ). Farther seaward into the oceanic crustal zone, normal oceanic crust is modeled to be thinner on Profile SMART‐1 (∼4 km; Funck et al, ) than on Profile OETR‐2009 (∼4–6 km; Lau et al, ).…”

“…(main) Color bathymetry map showing the location of the OCTOPUS wide‐angle seismic profile (thick white line) together with other nearby OBS profiles (thin gray lines) OETR‐2009 (Lau et al, ) and the SMART‐1 and SMART‐2 (Funck et al, ; Wu et al, ). Multichannel seismic profiles GXT‐2000 and GXT‐5100, coincident with OBS profiles OCTOPUS and OETR‐2009, are shown with black dashed lines.…”

“…Interpreted rifted margin structure according to the seaward sections of wide‐angle seismic velocity models (a) OETR‐2009 (Lau et al, ) and (b) SMART‐1 (Funck et al, ). SM = serpentinized mantle; ESM = exhumed serpentinized mantle.…”