POLYPHASE DUCTILE DEFORMATIONS IN THE ST-CLEMENT-DE-LA-PLACE ORTHOGNEISS ANTIFORM (LANVAUX UNIT, ARMORICAN MASSIF)

In the Armorican Massif the St-Clement-de-la-Place antiform results fr om two distinct but homoaxial deformations. The younger one correspond s to the emplacement of a granodiorite dated here at 312 Ma (Ar-40/Ar- 39 on biotite). Although coeval to the dextral motion of the South Arm orican shear zone, this pluton does not present the specific features of a synkinematic granite, the early deformation is responsible for th e mylonitisation of an orthogneiss with a subhorizontal foliation and NW-SE trending lineation. Top-to-the-NW shearing, incompatible with th e Carboniferous wrench tectonics, is the kinematic peculiarity of this orthogneiss. (C) Academie des sciences/Elsevier, Paris.