Conceptual Model for the Block-Fault Origin of the North American Atlantic Continental Margin Geosyncline

Abstract

A new interpretation of the basement structure of the Atlantic continental margin is proposed. The basins of the geosyncline are believed to be isolated fault-bounded troughs with alignments more or less paralleling that of the continental slope. Fundamental basement faults can be inferred from linear magnetic anomalies and from linear hinge zones in the basement surface. Three distinguishable tectonic systems can be identified from the strike of the fundamental faults and the tension-type hinge zones forming the boundaries of the basins. One stress system is associated with the northwest-striking, right-lateral shear faults of the Atlantic Ocean fracture zones, and with north-striking tensional faults such as those of the Blake Plateau basin. Another stress system is associated with the nearly north-striking White Mountain magma series, taken to manifest a right-lateral fault zone, and with northeast-trending tensional faults of the Georges Bank basin. Finally, a third stress system is manifest in the northeast-striking, right-lateral shear faults of the Labrador Sea fracture zones and the nearly east-striking tensional faults of the Labrador shelf basin. Conceptually, such a stress pattern can be explained by the clockwise rotation of a unit structural block encompassing the entire North American continental margin from Labrador to the Bahamas. The differential opening of the Labrador Sea would result in clockwise rotational couple in the unit block; the differential opening of the Atlantic Ocean would further contribute to this clockwise rotational couple. East-west tension with north-south compression of the Atlantic stress system within the unit block and north-south extension with east-west compression of the Labrador system would be compatible with such a rotation. The White Mountain stress system is thought to be a result of the combination of the other two systems in the presence of possibly preexisting fundamental fractures.