Tectonothermal Evolution of the Cadomian Orogen in the North Armorican Massif and Circum-Atlantic Correlations

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The North Armorican Massif is part of the Armorican Plate that separated from N. America, Baltica and Gondwana in the early Paleozoic. Large segments of Armorica were affected by the late Precambrian Cadomian orogeny, and the massif is one of very few areas where there is no apparent overprinting of Cadomian aged rocks during the late Paleozoic Variscan orogeny. This area is thus critical for resolution of tectonic linkages with correlative Avalonian and/or Pan-African sequences. Existing models for the Cadomian orogeny have a limited geochemical data base, although recent field work has shown that complex polyphase Precambrian metamorphic/structural events occurred. This study will make systematic determination of 40Ar/39Ar mineral ages and selected U-Pb zircon ages from representative lithological units within the massif, and will be conducted in collaboration with British field geologists working in the area. Co-operation with local French geologists has been arranged. The results of this research will permit detailed evaluation of Precambrian tectonothermal events and will help constrain tectonic models for the region.