Induced susceptibility anisotropy of igneous rocks caused by uniaxial compression

Abstract

The effect of uniaxial compression on the initial susceptibility of a variety of igneous rocks has been studied to determine the dominant factors controlling their response. Hysteresis properties, Curie temperatures, and grain size distributions of the magnetic phases of the rocks have been determined to provide control data. The dominant characteristic influencing the stress response is the domain state, which is itself strongly dependent upon the grain size. Three types of response are defined. The single domain response consists of an increase in susceptibility in the direction perpendicular to stress and an equal decrease in the direction parallel to stress. In the pseudo-single domain range, wall nucleation appears to produce an isotropic increase in susceptibility. In multidomain material, the principal effects seems to be due to loss of wall area parallel to stress, accompanied by some gains in walls perpendicular to stress. -from Authors