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GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 24, 2215, doi:10.1029/2002GL015459, 2002

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

Josep M. Parés

Dept. of Geological Sciences, University of Michigan, Ann Arbor, MI, USA


Ben A. van der Pluijm

Dept. of Geological Sciences, University of Michigan, Ann Arbor, MI, USA


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.

Published 27 December 2002.

Index Terms: 1518 Geomagnetism and Paleomagnetism: Magnetic fabrics and anisotropy; 1540 Geomagnetism and Paleomagnetism: Rock and mineral magnetism; 1594 Geomagnetism and Paleomagnetism: Instruments and techniques; 5109 Physical Properties of Rocks: Magnetic and electrical properties; 8030 Structural Geology: Microstructures.

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Citation: Parés, J. M., and B. A. van der Pluijm (2002), Phyllosilicate fabric characterization by Low-Temperature Anisotropy of Magnetic Susceptibility (LT-AMS), Geophys. Res. Lett., 29(24), 2215, doi:10.1029/2002GL015459.