Structural characteristics of the ocean-continent transition along the rifted continental margin, offshore central Labrador

Studies of the structural deformation and the nature of the ocean-continent transition zone at the rifted continental margin, offshore central Labrador, and its conjugate off West Greenland have been conducted over several decades and helped to define our understanding of the controlling factors in the development of magma-poor margins globally. New two-dimensional seismic reflection data are now available across the Labrador margin which can help to modify and refine this understanding. In this paper, we describe some of these new seismic data and the corresponding potential field data in relation to earlier studies, including an existing deep seismic crustal velocity profile. These data cross the three major structural and compositional zones below the sedimentary wedge defined in earlier deep seismic experiments as: 1) extended zone of continental crust, including the hyper-extended region, partly underlain by serpentinized mantle; 2) exhumed and serpentinized continental mantle zone; and 3) zone of oceanic crust. We are able to extend these zones laterally over 200 km along the margin. The rifted continental crust is hyper-extended over tens of kilometers landward of the breakup location, where many varieties of normal faults and possible low-angle detachment surfaces are present, some of which are near or at the base of the crust. Further seaward, mantle was serpentinized and likely exhumed, and possesses a seismic character very different from the continental crust. Basement in this zone may locally form prominent ridges. Within the oceanic zone we define a further sub-division into a 'proto-oceanic' domain with thin, variable oceanic crust of about 70-65 Ma in age (magnetic chrons 27 to 31) and a steady-state seafloor spreading region further seaward. Thus, seafloor spreading starts at about chron 31 time. Potential field data and models are broadly consistent with these zones. A strongly reflective, post-rift volcanic event is present across much of the region, especially over the exhumed mantle zone and parts of the oceanic crust. These results are discussed and compared to earlier studies of the West Greenland conjugate margin and to other well-studied magma-poor margins. Given that this rift occurred in thick, cold cratonic lithosphere, the results are remarkably similar to those off Iberia and Newfoundland, suggesting that a long rift history and/or mantle metasomatism may have weakened the lithosphere prior to the main rifting event.