Magnetic anomalies in the Pacific and sea floor spreading

The symmetric linear magnetic pattern found over the crest of the Pacific-Antarctic and Juan de Fuca ridges can now be traced across the flanks and into the basins in the North and the South Pacific Ocean. The bilateral symmetry is best shown in the South Pacific, where the western half of the pattern can be traced to the edge of the New Zealand plateau. The eastern half extends to at least 90°W at 62°S. Although sections of the pattern south of the ridge axis have not yet been mapped because of the difficulties of data collection in antarctic waters, sufficient marine data are available to compile a magnetic map of these linear anomalies in the South Pacific from 35° to 65°S and from 90°W to 175°E. In the North Pacific, the eastern half of the symmetric pattern is generally masked by the North American continent. The complete axial pattern can be observed only in the area north of the Mendocino fracture zone. The western half of the pattern is, however, identical to that observed in the South Pacific to the west of the ridge axis. The North Pacific pattern extends from 51° to 25°N and from the edge of the continental rise as far west as 165°W at 51°N. Previous work has shown that the axial magnetic anomaly pattern correlates with the known history of reversals of the, earth's magnetic field. It is now possible to correlate between contemporaneous regions in the North and South Pacific and to assign relative ages to over one-half the Pacific basin.