Crustal structure of the mid-ocean ridges: 3. Magnetic anomalies over the mid-Atlantic ridge

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Fifty-eight magnetic profiles, of varying length, were used in a study of the magnetic anomaly pattern over the mid-Atlantic ridge between 60°N and 42°S. It was found that there is a basic pattern to the magnetic anomalies. A large anomaly is everywhere associated with the axis of the ridge. This anomaly is continuous over all latitudes except for offsets at fracture zones. This anomaly is caused by a volcanic body of limited width and depth which has an upper surface at, or very near to, the sea floor. This large axial magnetic anomaly is located in a zone of otherwise small anomalies. The axial magnetic zone is of the order of 1000 km wide and is centered on the ridge axis. The limits of this axial zone are marked by anomalies of larger amplitude and longer wavelength on the lower flanks of the ridge. The axial anomaly and the axial zone are apparently characteristics of the entire mid-ocean ridge system. It is shown that the high heat flow over the mid-Atlantic ridge elevates the Curie-point isotherm to such an extent that an observable magnetic effect is produced.