Stress-induced magnetizations of some rocks with analyzed magnetic minerals

Abstract

Magnetostriction can be of major importance in interpreting measurements of the residual magnetism of rock samples. A description is given of the experimental procedures that were used to determine the influence of axial compression on the natural magnetizations of a variety of rock core samples whose magnetic minerals have been analyzed. Changing the stress from 350 to 2,650 psi caused a marked decrease in magnetic intensity of rocks containing magnetite or ilmenomagnetite, and a slight increase when the magnetic minerals are in the system FeTiO3-Fe2O3. Directions of magnetization also changed, in a non-systematic manner. Inasmuch as many rocks acquire magnetization while under directed stress and are relatively stress-free when their magnetizations are measured, these results are offered as support of the opinion that many conclusions that have been offered on the basis of rock-magnetism data, relating to polar wandering, continental drift, secular variation, and reversal of the earth's magnetic field, are subject to serious doubt.