Some remarks on fabric overprints and constrictional AMS fabrics in igneous rocks |
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| Authors: | Karel Schulmann Josef Je?ek |
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| Institution: | 1.Institute de Physique de Globe, EOST,UMR 7516 Université de Strasbourg,Strasbourg cedex,France;2.Institute of Applications of Mathematics and Information Technologies, Faculty of Science,Charles University,Prague,Czech Republic |
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| Abstract: | During the ascent, emplacement and post-emplacement deformation of igneous rocks, two or more phases of deformation that overprint
each other are often depicted. These overprints, when magnetic minerals are present, are recorded in magnetic fabric. In this
contribution, overprints are studied by means of numerical modeling, following several basic scenarios common to igneous rocks.
Biotite and amphibole that occur often together in igneous rocks are considered as carriers of the anisotropy of magnetic
susceptibility. Modeling shows that (1) a constrictional fabric with a low degree of anisotropy as commonly recorded in magmatic
rocks may result from a deformation overprint and not necessarily from an extensional/transtensional regime, and (2) that
the constrictional AMS fabrics originates from orthogonal superimposition of a deformation event on an AMS fabric inherited
from earlier magma emplacement history. Therefore, the interpretation of a constrictional fabric must be performed with caution.
Numerical modeling may provide a suitable help in strengthening the interpretation of real magnetic fabric data. |
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