CALEDONIAN OROGENIC EPISODES IN BRITISH ISLES AND NORTHWESTERN FRANCE AND THEIR TECTONIC AND CHRONOLOGICAL INTERPRETATION

The paper is an attempt at the interpretation of recent structural, stratigraphical and geochronological work on younger Precambrian and Lower Palaeozoic rocks of the British Isles and northwest France. A correlation of Late Precambrian strata is proposed and is made the basis of the definition of the Caledonian orogenic and sedimentation cycles. Within the Caledonian tectonic cycle four orogenic episodes are defined - the Cadomian, the Grampian, the Lakelandian and the Cymrian. Each episode involves a spatially restricted region of the orogenic belt, produces interpenetrative deformation (cleavage, schistosity), and is accompanied by an episode of dynamothermal metamorphism and intrusion of granite. The Caledonian sedimentary cycle is defined so as to end before the onset of Old Red Sandstone Devonian sedimentation. The interpretation of isotope dates allows a fairly accurate assessment of the chronology of orogenic episodes and of the nature of tectonic uplift involved. These interpretations are used in deciphering the tectonic and thermal history of the Caledonian orogenic belt. © 1969.