Sm–Nd isotope characteristics of late Cadomian granite magmatism in northern France and the Channel Islands

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Abstract
Sm–Nd isotopic studies of granites within the late Precambrian, Cadomian, orogenic belt of the North Armorican Massif (northwestern France) and Channel Islands reveal differences between arc-related granite magmatism in outboard terranes and intracrustal granite magmatism in inboard terranes. Late Cadomian (c. 570 Ma), arc-related granitoids exhibit a range of εnd( - 2 to - 6) and Nd model ages (TDM1.0–1.3 Ga) reflecting variable contamination between late Precambrian mantle derived magmas and ancient (c. 2.0 Ga?) continental crust. The contamination did not involve exposed granitic Icartian basement to anygreat degree, a more likely contaminant being unexposed lower crust of intermediate to acidic granulitic composition, or early Cadomian plutons which were themselves contaminated by lower crust. Voluminous granites of the Mancellian region (c. 550–540 Ma) share common isotopic characteristics (εNd-4 to -7, TDM1.5–1.7 Ga) with migmatites and anatectic granites produced by partial melting of metasedimentary sequences within the St Malo region consistent with a common source.