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

Our 2-D-layered velocity model along strike northeastern Nova Scotian margin, constrained by wide-angle seismic Profile OCTOPUS and coincident 9-km streamer Profile GXT-5100, displays highly variable basement structures interpreted to define four distinct zones within the continent-ocean transition: Zone I, with thin (1-2km) and laterally uniform upper crust (5.2-5.5km/s) and high-velocity lower crust (6.5-7.7 km/s); Zone II, with velocities of 5.5-7.5km/s and a high vertical velocity gradient (approximate to 1.1/s) characteristic of exhumed serpentinized (up to 90%) mantle (ESM) above approximate to 3.5-km-thick slightly (<30%) serpentinized mantle layer of reduced mantle velocities (7.5-8.0km/s); Zone III, with 1- to 2-km-thick upper crust and velocity of approximate to 5.2km/s above a approximate to 6-km-thick, moderately (<60%) serpentinized mantle layer (velocity approximate to 6.4-7.9km/s); and Zone IV, with lower crust (approximate to 0.7-3.0km thick and with velocity of 6.1-6.6km/s) between upper crust (velocity approximate to 5.0-5.4km/s) and a slightly serpentinized mantle layer (<40%; velocity approximate to 7.3-8.0km/s). These continent-ocean transition structures represent embryonic oceanic or rifted continental crust, and ESM. By combining our results with those from two dip-oriented crossing profiles, we map a regional track of non-ESM landward of Profile OCTOPUS with mostly uniform along-dip width, but a limited extent and variable width section of ESM seaward. Our results indicate that there can be a remarkable amount of short-wavelength (e.g., 50 km) lateral structural variability within individual rifted margin segments but that mapping it requires a grid of modern wide-angle profiles.