Orogeny which developed in continental detachment systems at converged plate margins. Orogeny An orogeny is an event that leads to both structural deformation and compositional differentiation of the Earth's lithosphere (crust and uppermost mantle) at convergent plate margins. An orogen or orogenic belt develops when a continental plate crumples and is pushed upwards to form one or more mountain ranges; this involves a series of geological processes collectively called orogenesis. Orogeny is the primary mechanism by which mountains are built on continents. The word "orogeny" comes from Ancient Greek (, , + , , ). Although it was used before him,
Cadomian Orogeny de Tréguier" and "Ignimbrites de Lézardrieux". The southern edge of the Gulf of Saint-Malo between Tregor and Cancale shows the deformational structures of the Cadomian Orogeny. These are East-west to North East trending upright folding. Schistosity is developed parallel to the axial plane of the folds. Prehnite-pumpellyite facies to mid-amphibolite facies have been produced by metamorphism. Movement was concentrated in shear belts such as at St Cast. The movement on the belts was sinistral and horizontal. During the orogeny the migmatite belts of north east Brittany were formed. Baie de St Brieuc and St Malo migmatites were deformed with the