Late Precambrian thrust and wrench zones in northern Brittany (France)

Brioverian units of northern Brittany (Armorican massif, France) were deformed and metamorphosed during a late Precambrian tectonic episode: the Cadomian orogeny. Kinematic study (strain and displacement) in the St Cast-St Brieuc area shows that this tectonic episode was characterized by the obduction of a back-arc basin over a continental margin around 580-590 Ma ago. Strain-pattern analysis reveals a constant interaction between SSW-directed imbricated thrust zones and ductile sinistral wrench zones trending N 50°E. The arcuate pattern of Cadomian structures in this area results from such an interaction. Thickening as a result of the thrusts induced migmatization and the development of a high temperature belt around 540 Ma in the St Malo-Guingamp area.