Magnetic Anisotropy

Anisotropy of magnetic susceptibility (AMS) is a fast and non-destructive way of investigating rock fabrics, which are too subtle to be seen or measured in the field. For this reason, it has been widely used to determine quantitative, three dimensional petrofabrics ( [MacDonald and Ellwood, 1987], [Borradaile, 1988], [Jackson and Tauxe, 1991], [Rochette et al., 1992] and [Tarling and Hrouda, 1993]). Its principle relies on a physical property of rocks that reflects the magnetic fabric of a geological material due to a preferred alignment of anisotropic magnetic mineral. The AMS of rocks depends on the intrinsic anisotropy of the individual grains, their shape preferred orientation and their distribution ( [Stacey, 1960], [Hargraves et al., 1991] and [Rochette et al., 1992]). The AMS is a second-rank tensor ellipsoid given by the length and orientation of the three principal susceptibility axes (k₁>k₂>k₃, maximum, intermediate and minimum, respectively). In general k₁, the maximum magnetic susceptibility direction, corresponds to the mineral lineation, and k₃, minimum magnetic susceptibility direction, is taken as the pole to the foliation.

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