Intensity of Magnetization of Subaerial and Submarine Basalts and its Possible Change with Time

• Published in: Geophysical Journal International
• Main Authors: Prévot, Michel, Grommé, Sherman
• Format: Text
• Language: English
• Published: Oxford University Press 1975
• Subjects: Original Article; North Atlantic
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/40/2/207; https://doi.org/10.1111/j.1365-246X.1975.tb07047.x

Intensities of natural remanent magnetization compiled for 177 subaerial basaltic flows ranging from historical time to 10 My and for 204 submarine basalt samples from the North Atlantic basement show that subaerial basalts have a mean intensity, reduced to an equatorial equivalent value, of 36 × 10−4 emu cm−3, about 2·5 times weaker than for submarine basalts (89·6 × 10−4 emu cm−3). Normally magnetized flows have significantly greater NRM than reversed flows owing to a viscous component that represents about one-fifth of the stable remanence. No significant difference appears in the mean intensity between the Brunhes basalts and the older normal basalts or between the intensity, after partial demagnetization, of historic basalts and those ranging from 0·01 to 1, 1 to 2, 2 to 3, or 3 to 4 My. This seems to indicate (i) that no important decrease of the intensity of magnetization of subaerial basalts takes place for periods of several million years, and (ii) that a possible increase of the intensity of the geomagnetic field during the Brunhes epoch is not responsible for the larger amplitude of the axial magnetic anomaly over mid-ocean ridges. For the oceanic basement, the mean intensity decreases by about two-thirds from the basalts of the bottom of the median valley to the basalts from the crests and flanks of the ridge. This diminution, probably produced by intensive low-temperature oxidation of titanomagnetite, is comparable to the decrease of the magnetic anomalies observed in the North Atlantic when going away from the ridge axis.