A theoretical and experimental comparison of the anisotropies of magnetic susceptibility and remanence in rocks and minerals

Abstract

Susceptibility, thermo-remanent magnetization (TRM) and isothermal remanent magnetization (IRM) anisotropy ellipsoids have been determined for several rock samples. The results indicate that the ellipsoid of initial susceptibility is less anisotropic than the TRM and low field IRM ellipsoids which are found experimentally t o be of identical shape. This suggests that palaeomagnetic data for anisotropic rocks may be corrected by using the anisotropy ellipsoid determined from magnetically non-destructive low field IRM measurements. Such IRM measurements can also be used t o obtain anisotropy axes of samples which are inherently anisotropic but which have a susceptibility which is too weak to be accurately measured. The results for a series of artificial anisotropic samples containing magnetite particles of different skes (in the range 0.2-90pm) were very similar to those for the rocks. In contrast, a comparison of the susceptibility and IRM ellipsoids for anisotropic samples containing particles from a magnetic tape gave very different results in accordance with theory. Such results imply that susceptibility and IRM ellipsoids could be used to determine whether anisotropic rocks contain uniaxial single-domain particles (magnetization confined to the easy axis) or whether the particles are essentially multidomain.

An Archaeometric and Archaeological Approach to Hellenistic-Early Roman Ceramic Workshops in Greece: Contribution to Dating

“…The anisotropy of magnetic susceptibility (AMS) and the one of remanence have been extensively studied in archaeological ceramic materials (Veitch et al 1984;Stephenson et al 1986) and their impact to the possible deflection of the remanence direction has been monitored. AMS was measured for the whole collection of samples; in general, the samples were not particularly anisotropic.…”

An integrated paleomagnetic and magnetic anisotropy study of the Oligocene flysch from the Dukla nappe, Outer Western Carpathians, Poland

“…The degree of the anisotropy of remanence, which is the expression of the fabric of the ferromagnetic minerals, can be used to decide if the paleomagnetic inclination could have been flattened. According to Stephenson et al (1986) inclination flattening can be ruled out if the degree of AARM aniso tropy (P) is lower than 5 percent. The P parameters we measured exceed this limit (Table 2).…”

Magnetic fabric and emplacement of dykes of lamprophyres and related rocks of the Central Bohemian Dyke Swarm (Central European Variscides)

“…1). This magnetic fabric is attributed to secondary processes such as hydrothermal alteration (Rochette et al 1991) or to single domain effect if very small magnetic grains carry the AMS (Stephenson et al 1986). There is also a fourth type showing almost random orientations of magnetic foliations and lineations, which may result from very complex flow patterns or from severe post-magmatic changes of magnetic minerals (Hrouda 1985;Raposo 2011).…”