Nature of Magnetic Anomalies in the Equatorial Ninetyeast Ridge

According to a set of geophysical methods, the equatorial Ninetyeast Ridge and neighboring areas of the Central (to the west) and Wharton (to the east) Basins have been studied. A detailed map of the magnetic anomalies (∆Ta) for this segment of the Ninetyeast Ridge was compiled for the first time following generalization of magnetic data from five cruises. The mapped area of 136 600 km2 is located near Site 216 DSDP. For the first time, it was found that linear magnetic anomalies C31r and C32n.1n do not terminate in front of the Ninetyeast Ridge, but continue here from the basins. The calculated spreading rate interval for the ridge is about 45 mm/year. In the Wharton Basin, the N-S Fracture Zone 90° E, along which linear magnetic anomalies ruptured and shifted, has been refined. Magnetic modeling for the seamount on the eastern slope of the Ninetyeast Ridge allowed the suggestion that this volcanic structure has deep roots. It could have formed as a result of repeated younger (secondary) magmatism after formation of the main volcanic massif of the ridge itself. Interpretation of magnetic survey data, heat flow measurements, and earthquake mechanisms indicate modern tectonic activity within the studied section of the ridge.