Acknowledgements

This synthesis is the result of several years of field and laboratory work conducted in the Massif Central and Massif Armoricain throughout various Ph. D. and Master thesis and partly supported by the French National program GéoFrance 3D. Our reflection benefited from discussions with P. Matte, P. Ledru, JM. Lardeaux, JY. Roig and O. Monod.