Flemish Cap-Goban Spur conjugate margins: New evidence of asymmetry

We present the combined results of deep multichannel refl ection and refraction seismic surveys across the Flemish Cap-Goban Spur conjugate margin pair (North Atlantic), which we use to infer rifting style and breakup. Profi les on both margins cross magnetic anomaly 34 and extend into oceanic crust, making it possible to observe the complete history from continental rifting through to the formation of initial oceanic crust. The deep multichannel seismic (MCS) refl ection data have previously been used to support a model of symmetric pure shear extension followed by asymmetric breakup and a sharp continent-ocean boundary. Using both types of seismic data, our results indicate instead that asymmetric structures are formed during all stages of rifting, breakup, and complex transition to oceanic spreading. The differing nature of the two oceancontinent transition zones is particularly striking. For Flemish Cap, our reprocessed image of the MCS profi le clearly shows tilted fault blocks beneath back-tilted sediment packages, consistent with a wide region of highly thinned continental crust inferred from wideangle seismic data. In contrast, normal incidence and wide-angle seismic data for the Goban Spur transition zone indicate the presence of exhumed serpentinized mantle.