Shear strain in the St. Malo migmatite dome (N Brittany)

The Cadomian migmatite dome of St. Malo is affected by centimetric to metric shear bands. The shear bands bear a stretching lineation underlined by alignments of fibrous sillimanite crystals at Dinard and St. Briac outcrops. These shear bands were analysed by means of the Right Dihedra method. They indicate a NNE-SSW stretching direction and a subvertical shortening direction. They are consistent with foliation and stretching lineation orientations. This study suggests that the St. Malo migmatite dome was affected by a post-orogenic extensional tectonic regim