Magnetic Anomalies off Eastern North America

Numerous magnetic profiles have been made across the continental margin of eastern North America by the U. S. Geological Survey, the U. S. Navy Hydrographic Office, and the Lamont Geological Observatory. These data, supplemented by areal studies in parts of the region, reveal an anomaly pattern which is essentially parallel to the margin and to the major structural features on shore. Calculations show that, while basement topography may contribute, the principal causes of the anomalies are compositional changes within the basement. Two exceptions to the pattern are noted; one is southern Florida, suggested by E. R. King to be an extension of the Ouachita system, and the other is a major feature normal to the coast at latitude 40°N interpreted as being associated with a transcurrent fault. Other geophysical and geological observations indicate a right lateral displacement of the fault of about 100 miles and a total length in excess of 600 miles. The implications of this and the possibility of other transcurrent movements along the Atlantic margin are examined.