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Keywords:

  • Continental Drift: Crustal Structure;
  • Crust: North America;
  • Fractures: Genesis;
  • Marine Geology: Structure;
  • North America: Structural Geology;
  • Sea-Floor Spreading: Atlantic Ocean;
  • Tectonics: Plate Tectonics

Several morphologic features associated with the continental margins of North America (Newfoundland fracture zone, Kelvin seamount chain, Cape Fear arch, Bahama platform) and Africa (Canary Islands, Cape Verde Islands, and Guinea fracture zone) are interpreted as structural lineaments delineating lines of crustal weakness which are related to fracture zones and the early opening of the Atlantic. The Newfoundland fracture zone, which is a prolongation of the largest offset in the continental margin, constrained the movement of the separating continents to a single rotation, making adjustments mechanically difficult until the continental edges were separated by a distance of about twice the length of the largest offset. Using the trend of the Newfoundland, Bahama, and Guinea fracture zones, a pole of early opening was computed that is located 25° away from the Newfoundland fracture zone at the northern limit of the basin and 50° from the Bahama fracture zone at the southern limit. The total opening about this pole is 46°. The other fracture zones approximately define concentric circles, and the magnetic discontinuities of Vogt et al. (1970) are isochron lines about this pole. About 80 m.y. ago, when the separated blocks no longer constrained movement, the early opening phase ended, and a complete reorganization occurred, resulting from a migration of the pole toward the north. The major physiographic differences between the mid-Atlantic ridge and the basin provinces can be explained by the rearrangement of the relative movements of the plates 80 m.y. ago.