C-Souque Thèse

Anisotropy of magnetic susceptibility (AMS) is commonly used to define shortening directions because AMS is efficient even if strain is to weak to be macroscopically visible. We focus here on the ASM answer to polyphased strain, either linked to two distinct and successive shortening directions, or to succession of layer parallel shortening (LPS) and folding. In this way, a sampling has been performed in the Pyrenean foreland in different structural positions of the Lagrasse fold (Corbières, France) and in the different sheets of the “La Cagalière” duplex, hectometric structure in the depths of the Lagrasse fold. All these structures were emplaced in two successive shortening directions.
While regionally recorded AMS is early tectonic anisotropy connected to LPS in the first direction, is not altered by the second one and is only sheared during folding, AMS is really different close to thrusts and without any simple meaning at first sight. The use of a thermic treatment on these sites allowed us to decipher the early tectonic anisotropy due to LPS and thus to rediscover informations about the first shortening direction underwent and rotations about vertical axis recorded since then. This early anisotropy is thus not erased but only masked by later crystallizations, and this technique turn out to be valid in different facies. By return, those data allowed us to interpret the duplex as a stopping structure of the lateral propagation of the Lagrasse fold thrust, and to chronogically place the duplex emplacement between this stopping and the sliping transfer on an out-of-sequence thrust.

STRUCTURAL MAGNETISM, TOOL OF TECTONIC ANALYSIS AT DIFFERENT SCALES (FROM OUTCROP TO REGIONAL) : EXAMPLES FROM CORBIERES, FRANCE.

defended on the 20th of September 2002 in front of a jury composed of :
MM.
Martin BURKHARD,	Professor at the University of Neuchâtel (Switzerland) President
Dominique FRIZON de LAMOTTE,	Professor at the UCP Supervisor
Philippe ROBION,	Maître de Conférence at the UCP Co-Supervisor
Jean-Luc BOUCHEZ,	Professor at the Univ. of Toulouse Rapporteur
Jean-Christophe MAURIN,	Professor at the Univ. of La Rochelle Rapporteur
Catherine KISSEL,	Research ingenior at the LSCE (CEA-CNRS) Gif-sur-Yvette Examiner
Bernard HENRY,	Research director, IPG Invited
Abstract :

Anisotropy of magnetic susceptibility (AMS) is commonly used to define shortening directions because AMS is efficient even if strain is to weak to be macroscopically visible. We focus here on the ASM answer to polyphased strain, either linked to two distinct and successive shortening directions, or to succession of layer parallel shortening (LPS) and folding. In this way, a sampling has been performed in the Pyrenean foreland in different structural positions of the Lagrasse fold (Corbières, France) and in the different sheets of the “La Cagalière” duplex, hectometric structure in the depths of the Lagrasse fold. All these structures were emplaced in two successive shortening directions. While regionally recorded AMS is early tectonic anisotropy connected to LPS in the first direction, is not altered by the second one and is only sheared during folding, AMS is really different close to thrusts and without any simple meaning at first sight. The use of a thermic treatment on these sites allowed us to decipher the early tectonic anisotropy due to LPS and thus to rediscover informations about the first shortening direction underwent and rotations about vertical axis recorded since then. This early anisotropy is thus not erased but only masked by later crystallizations, and this technique turn out to be valid in different facies. By return, those data allowed us to interpret the duplex as a stopping structure of the lateral propagation of the Lagrasse fold thrust, and to chronogically place the duplex emplacement between this stopping and the sliping transfer on an out-of-sequence thrust.