The Search for Concealed Continental Basement Beneath the Margins and Coastal Basins of the North Atlantic: Methods and Motives

Abstract

The continental basement marginal to the Atlantic Ocean basin is never directly observed in outcrop. This concealed border zone is sometimes only about 50 km wide, as on the W. African or Iberian margins; elsewhere, off the Canadian Coast, the continental margin is nearly 700 km wide. Apart from these extreme cases, it appears there is a gap of about 500 km, between known basement areas in both sides of the North Atlantic, when account is made for ocean floor spreading. The missing information must be found if correlations (other than pure speculation) are to be established between basement terrains in Europe, Africa and America. The term “basement” in this study, is, above all, taken to mean rocks of Pre-Cambrian and Palaeozoic age — the oldest basement terrains found in the studied area are Lewisian or equivalent in age (max: 2900 Ma). Triassic events affecting the basement are well marked during the early stages of opening of the North Atlantic; this aspect of basement history is not treated in the present study because such effects often obscure the structural relationships of pre- Mesozoic basement terrains.