Abstract
Stress stability of the remanent magnetization of basalt under compression was experimentally tested. It was also examined, using a thick lava of basalt, whether the effect of compressive stress on remanent magnetization depends upon grain size of rock-forming ferromagnetic minerals. Intensity of IRM of the rocks shows an irreversible and remarkable reduction under axial compression. TRM and NRM decrease gradually as axial force is increased. Change of remanent magnetizations with respect to pressure is well expressed in a hyperbolic form: M(P)=M0/(1+βr·P), in the same manner as that of the initial magnetic susceptibility of volcanic rocks. TRM is more stable than IRM against pressure. For IRM, the stronger the applied magnetic field, the more stable the intensity and direction of remanent magnetization become with respect to pressure. It was found that the magnetically effective grain size of ferromagnetic minerals controls the stress stability of NRM as well as the intensities of TRM, the coercive force and the initial magnetic susceptibility.
