Results from two deep seismic reflection lines are presented. When combined, these lines span the rifted continental margin off Nova Scotia, from crust unaltered by rifting to the ocean basin. These data provide crustal and upper mantle reflection geometry to depths of over 50 km and elucidate the rifting process on this margin which occurred during the Mesozoic breakup of Pangaea. The continental crust below the continental shelf and slope becomes progressively thinner toward the ocean–continent boundary. In the upper crust, normal faults accommodated Mesozoic extension, and these flatten and terminate at 5–6 s (two-way time). In the lower crust and upper mantle Mesozoic rifting may be reflected in dipping events, which are interpreted to be normal faults. All Mesozoic extensional faulting could be controlled by the preexisting fabric of the crust, which in this region would be related to Appalachian compression within the Meguma Terrane. Below the continental rise, there is some evidence for magmatic underplating of the thinned continental crust, but the presence of synrift diapiric salt prevents clear definition of deeper structure. The extreme seaward end of the profile lies in a region interpreted in most other, earlier studies to be oceanic in nature. However, the seismic profile described here shows that relief on basement is associated with listric normal faults, which flatten in decollement, and that linear, landward-dipping intrabasement reflections characterize the area. These features can be explained in either a continental or an oceanic context.
Deep seismic reflection evidence for the role of extension in the evolution of continental crust
