A whole-rock Rb-Sr isochron age of 533±16Ma determined for the Jersey Andesite Formation is interpreted as the age of crystallization, and suggests that Upper Brioverian sedimentation continued into the Cambrian. It provides a maximum age limit of Middle Cambrian for the late Cadomian molasse-type Rozel Conglomerate, and supports the existence of a late orogenic (post 533±16Ma) phase of Cadomian deformation, which was followed by molasse sedimentation. There are, therefore, at least two separate phases of Cadomian deformation in the northern part of the Armoricain Massif, the previously recognized earlier event being late Precambrian in age.

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