Non-Tensorial Anhysteretic Remanent Anisotropy and the Detection of Composite Fabrics

Abstract

The anisotropy of anhysteretic remanent magnetization (AARM) provides a powerful, nondestructive means of assessing magnetic fabrics. It is widely applied to infer strain and emplacement conditions in sedimentary, volcanic, and intrusive rocks. AARM is generally represented by a symmetric second-rank tensor describing its orientation, strength, and shape. AARM, however, departs from a tensorial shape when the number of grains carrying each directionally imparted anhysteretic remanence (ARM) varies with ARM orientation – a condition that arises when the alternating field (AF) over which the ARM is imparted does not fully activate the sample. Experimental data from a highly anisotropic ignimbrite sample, together with multiparticle modeling, show that such partial activation produces non-tensorial AARMs. Although this behavior complicates tensor analysis, non-tensorial AARM can reveal superimposed fabrics, provided that users can apply AF and ARM in a broad range of orientations. This article presents theoretical models that demonstrate non-tensorial behavior and explains how to utilize these properties to discern superimposed fabrics in natural samples.

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