Magnetic fabric and structural study of the Eaux-Chaudes intrusion: Understanding the Variscan deformation in the Western Axial Zone (Pyrenees)

The present study provides new magnetic and microstructural data for the Eaux-Chaudes granodioritic massif (Western Axial Zone, Pyrenees) and contributes to the understanding of its geometry, internal structure and emplacement mechanism. Moreover, the geological crosssections and field data allow to reconstruct the evolution of the whole area from Variscan to Alpine times and to integrate the emplacement of the igneous body in the context of the Variscan orogeny. The Eaux-Chaudes pluton (301 ± 9 Ma) is mainly composed by granodiorite, describing a normal compositional zoning and an approximately concentric arrangement that is consistent with the zonation of the low-field magnetic susceptibility. Magnetic foliation is subhorizontal in the inner part of the intrusion and becomes parallel to the petrographical contacts along pluton margins, roughly describing the geometry of the intrusion. Magnetic lineations are dominantly subhorizontal, with E–W to ENE–WSW directional maximum. The general parallelism between Variscan structures of the host rock and the geometry and magmatic fabric of the intrusion reveals a late syn-Variscan emplacement. The tectonic regime registered during magma emplacement is in agreement with an N–S shortening and an E–W stretching direction, consistent with the transpressive regime deduced for other Pyrenean intrusions. Alpine overprint produced a slight tilting in the southern part of the intrusion, but it can be considered that the original Variscan structure is basically unchanged.The authors thank M. Tricas for the preparation of thin sections and Rocı´o Navarrete, Pablo Calvı´n and Gelu Lo´pez, for their help during the collecting and lab drilling of the samples. This work forms part of the research projects CGL2009-08969 and CGL2006-05817 (Spanish Ministry of Education) and is included in the objectives of the pre-doctoral grant AP-2009—0554 (Esther Izquierdo) (Programa de formacio´n de profesorado universitario, Spanish Ministry of Education). The authors acknowledge the careful and constructive revisions from Jose´ Marı´a Tubı´a and Karel Schulmann.Peer Reviewe