Drilling in the Newfoundland-Iberia rift has been tremendously successful in advancing our understanding of the evolution of nonvolcanic rifted margins, but major questions remain to be answered. In the Newfoundland Basin, the nature of the basement below the bottom of Site 1276 remains unknown. Seismic velocity models from refraction data (Van Avendonk et al., 2006) suggest that the drill site is very close to a boundary between highly thinned continental crust and exhumed upper mantle. Deepening this hole into basement will provide significant new insights into the nature of these rocks; their tectonic, igneous and metamorphic evolution; and the potential that they may have had for generating synrift melts and/or postrift magmatism that formed the overlying diabase sills.
The nature of basement near the continental margins and its lateral variability remain very poorly understood, particularly in the outer transition zone (TE2), where rifting of apparently subcontinental mantle lithosphere eventually gave way to seafloor spreading. A suite of drill sites along the transect of ODP Legs 149, 173, and 210 and extending seaward onto Albian oceanic crust (i.e., beyond the time of the Aptian event), would much more clearly define how the transition from nonvolcanic rifting to seafloor spreading occurs, as well as the role that mantle composition (e.g., subcontinental or asthenospheric) and heterogeneity may play in this evolution.
Finally, this rift should also be studied and drilled along another transect, ideally one between Flemish Cap and the Galicia margin where ODP Leg 103 drilled. The timing of breakup and the extent of TE2 (TE1 is not present there) are much different in this location than in the central to southern part of the rift. The phases of rifting along this corridor are well defined by basement structure and sedimentary stratigraphy in seismic reflection records, and the continental crust is highly thinned. Furthermore, the spatial relations between continental crust and the subcontinental mantle are constrained both vertically (as defined by the "S reflection") and horizontally (between the seaward-most continental blocks and the adjacent peridotite ridge).
With a few exceptions (e.g., Sites 398, 638, and 1276) the stratigraphic record associated with opening of the Newfoundland-Iberia rift is poorly sampled. Future drilling along either of the above transects should sample the most complete pre-, syn-, and postrift sedimentary sections that are technically feasible. Drilling should also include judicious sampling of basement highs to study the transition from exhumed mantle to oceanic crust.