Cadomian tectonics in northern Brittany

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Abstract
Major Cadomian structures of northern Brittany, France, are reviewed from the Léon region in the west to the Mancellian region in the east. The whole region is dominated by a NE trending structural grain. From the NW to the SE three main tectonic units have been distinguished: (a) the Trégor volcanic and plutonic belt; (b) the Baie de St Brieuc metamorphic-thrust belt and (c) the Guingamp-St Malo high temperature belt. Principal strain trajectories, finite strain measurements, shear criteria and geochronological data are used to establish a kinematic model of Cadomian deformation. The three units have been thrust over each other and towards the SW at 590–580 Ma. An extrapolation at a regional scale is made using available geophysical data (gravimetry, magnetism and SWAT seismic lines). A new model for oblique thrusting toward the SW along an ENE trending plate boundary is proposed.