Notes on Piezo-remanent Magnetization of Igneous Rocks

Abstract

Various observed characteristics of the six types of stress-affected remanent magnetization of igneous rocks are theoretically derived for a model rock in which a large number of ferrimagnetic minerals having an isotropic magnetostriction are distributed at random.For small magnetic fields (H) and small uniaxial compressions (P) irreversible displacements of 90° domain walls alone are subjected to a uniaxial compression in the acquisition process of remanent magnetization. Hence Rayleigh's law of the magnetic hysteresis loop is adopted in examining the effect of H and P on the displacement of 90° walls.Results of calculations based on these assumptions give theoretical curves of JR(P+P0H+H0) vs P/H, JR(H+H0P+P0) vs P/H, JR(H+P+P0H0) vs H/P, JR(P+H+P0H0) vs H/P, JR(H+P+P0H0) vs H/P and JR(P+H+H0P0) vs H/P. These theoretical curves reasonably well fit the observed curves, having all observed characteristics of respective types of stress-affected remanent magnetization. The effect of P on the remanent magnetization is a little smaller in the case of P⊥H than in the case of P//H in both the experiment and the theory. However, numerical disagreement between experimental and theoretical results are still noticed in regard to details of the phenomena.