Magnetic Anisotropy

Abstract

Pioneering works on the magnetic anisotropy of rocks were carried out during the 1940s and 1950s (Ising, 1942; Graham, 1954). These authors first realized that magnetic methods may be used to characterize the preferred orientation of minerals within the rock samples. Ising studied varved clays in Sweden and noticed that the magnetic susceptibility was higher on the bedding plane than orthogonally to it. Graham recognized that the anisotropy of magnetic susceptibility (AMS) may be regarded as a petrofabric element; he later extended the analysis to various sedimentary rocks of the Appalachian Mountains and pointed out the existence of distinct and systematic relationships of the magnetic properties with structural setting (Graham, 1966). The studies progressively developed in the following decades and a first comprehensive review on magnetic anisotropy and its application in geology and geophysics was published by Hrouda (1982). Over the past 20–30 years, researches on magnetic anisotropy gained widespread use and were extended to examine the fabric in a variety of sedimentary, igneous, and metamorphic rocks (e.g., see reviews by Jackson, 1991; Jackson and Tauxe, 1991; Rochette et al., 1992; Tarling and Hrouda, 1993; Borradaile and Henry, 1997; Borradaile, 2001; Borradaile and Jackson, 2004; Tauxe, 2005; Lanza and Meloni, 2006; Hrouda, 2007). Presently, the study of the magnetic anisotropy of rocks is still one of the most promising research issues in the field of rock magnetism.