Magnetic anomalies in the Pacific and sea floor spreading

Abstract

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.

Rises, Trenches, Great Faults and Crustal Blocks

“…The data on which this study is based are given in Pitman et al [1968] and also in Heirtzler [1968]. Le Pichon [1968] has also investigated this region and has found a pole position practically identical to that listed above.…”

“…Magnetic profiles of twelve crossings of this ridge have been presented by Heirtzler [1968] an'd Pitman et al [1968]. Ten of these profiles were analyzed in the following manner to obtain the spreading rates shown in Figure 16 No attempt was made to construct a diagram predicting the spreading rate perpendicular to the strike of the ridge as was done for the Atlantic.…”

Paleomagnetic and Rock Magnetic Properties of Jurassic Quiet Zone Basalts, Hole 801C . . .

“…Pitman et al (1968) suggested that the magnetic properties of rocks of the Cretaceous quiet zone may have changed owing to diagenetic processes, a scenario that can easily be extended to include the Jurassic Quiet Zone. Indeed, the process of hydrothermal alteration of source basalts has been implied by several authors as a possible cause for the Jurassic Quiet Zone (Vogt et al, 1971;Taylor et al, 1968).…”

Advances in New Zealand oceanography, 1967–91

“…Magnetometers towed across the east Pacific (Pitman et al 1968) revealed magnetic stripes that supported a controversial theory of "sea floor spreading", a theory that metamorphosed in 1968 into the all-embracing "theory of plate tectonics" (Morgan 1968). For the first time there was a concept that made sense of a multitude of disparate geological facts.…”