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Book Chapter

Problems in interpreting AMS parameters in diamagnetic rocks

By
František Hrouda
František Hrouda
AGICO Inc., Ječná 29a, Box 90, CZ-621 00 Brno, Czech Republic (e-mail: fhrouda@agico.cz)Institute of Petrology and Structural Geology, Charles University, Albertov 6, CZ-128 43 Praha, Czech Republic
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Published:
January 01, 2004

Abstract

The AMS parameters widely used to characterize the magnetic fabric of rocks (L, F, P, T) are not directly applicable to diamagnetic rocks. Namely, there are two principal methods of their definition: (1) from the signed principal susceptibilities or (2) from the absolute values of the principal susceptibilities. The first method results in L, F and P values less than one in contrast to materials whose susceptibility arises from paramagnetism and/or ferromagnetism sensu lato, where they are greater than one by definition. The ratio parameters decrease with increasing intensity of alignment of the magnetic minerals; the calculated shape parameters are, however, correct. The second method gives L, F and P values greater than one; they increase with increasing preferred orientation, however the ellipsoid shape parameters are inverse. The development of AMS parameters with increasing preferred orientation is modelled mathematically for quartzite/evaporite (para- and/or ferromagnetic AMS superimposed on the isotropic diamagnetic matrix) and for marble/limestone (preferred orientation of calcite in a rock). A rational set of AMS parameters is then recommended.

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Contents

Geological Society, London, Special Publications

Magnetic Fabric: Methods and Applications

F. Martín-Hernández
F. Martín-Hernández
Faculty of Geosciences, Utrecht University, The Netherlands
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C. M. Lüneburg
C. M. Lüneburg
Department of Geology and Geophysics, University of New Orleans, USA
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C. Aubourg
C. Aubourg
Laboratoire de Tectonique, Université de Cergy-Pontoise, France
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M. Jackson
M. Jackson
Institute for Rock Magnetism, University of Minnesota, USA
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Geological Society of London
Volume
238
ISBN electronic:
9781862394865
Publication date:
January 01, 2004

GeoRef

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