Phyllosilicate fabric characterization by Low-Temperature Anisotropy of Magnetic Susceptibility (LT-AMS)

Abstract

This paper examines the use and applicability of anisotropy of magnetic susceptibility at Low-Temperature (77°K), called LT-AMS. Paramagnetic susceptibility increases significantly with low temperature, which permits high precision determination of the anisotropy of paramagnetic susceptibility of a rock from measurements at liquid nitrogen temperature. We describe a new procedure that measures directional susceptibility in an oriented rock specimen while immersed in liquid nitrogen. Our procedure overcomes the problem of temperature heterogeneity within a rock sample while its susceptibility is being measured, offering the opportunity to measure low-temperature susceptibility in multiple orientations. This non-destructive method provides a way of characterizing the principal paramagnetic minerals present in a rock, based on temperature-induced changes of the anisotropy degree. Moreover, the method offers a better-resolved relationship between anisotropy degree and grain alignment, which is used to quantify rock fabrics.