Self-reversal of remanent magnetization in some dredged submarine basalts

Abstract

Several cases of selfreversal of remanent magnetization in ferromagnetic minerals and rocks have been known [ 1-4] . However, occurrence of self-reversal in basalts is extremely rare in spite of numerous reports on their magnetic properties [5-71 . Lately, we had a chance to study several basalts dredged from deep sea mounts in the Pacific Ocean (table 1). We found that three of eight dredged basalts from various localities-showed self-reversal of remanent magnetization. Although very little has been studied about magnetic properties of dredged basalts [S, 91, a high percentage of occurrence of self-reversal of remanent magnetization in the dredged basalts would imply that ferromagnetic minerals in submarine basalts differ significantly from those in continental basalts. In this short note, we report results of some preliminary experiments on self-reversal of remanent magnetization in dredged basalts. Pig. 1 indicates an occurrence of self-reversal of thermo-remanent magnetization in WPDR-2, in which the ordinate represents an intensity of thermoremanent magnetization produced by cooling the sample to room temperature in the geomagnetic field in air of various temperatures. Thermoremanent magnetization produced below 3000C has a parallel direction to the ambient geomagnetic field, whereas those produced between 3000C and 33000 have a reversed direction indicating self-reversal of the thermoremanent magnetization, When the sample is cooled from above 33000, thermoremanent magnetization has again a parallel direction to the geomagnetic field .