Experimental deformation of synthetic magnetite-bearing calcite sandstones: effects on remanence, bulk magnetic properties, and magnetic anisotropy

Abstract

This paper quantifies effects of experimental deformation on the magnetic properties of a set of synthetic "calcite sandstone' samples containing magnetite. Macroscopically ductile shortening strains of up to 25% produced the following irreversible changes in magnetic properties: 1) increased bulk coercivity, remanence coercivity, and mean anhysteretic remanence susceptibility; 2) decreased mean low-field susceptibility; 3) decreases in the component of remanence parallel to shortening; 4) smaller decreases for most samples in the component normal to shortening; 5) large decreases in the normal component in a few samples; 6) increased magnetic anisotropy; and 7) increased "deformation' of initial magnetic ellipsoids. A comparison of data for samples deformed under dry and wet conditions indicates that remanence reorientation and susceptibility anisotropy are controlled primarily by bulk strain, whereas coercivity and anhysteretic anisotropy are controlled dominantly by microstrain or intragranular stress. -from Authors