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

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.

Review of Nd isotopic data and xenocrystic and detrital zircon ages from the pre-Variscan basement in the eastern Bohemian Massif: speculations on palinspastic reconstructions

“…The amount o f juvenile material added during the young magmatic events must have been subordinate. Our interpretation of the Nd model ages may also be relevant to the western part of the Variscan Belt, where 1.4-1.7 Ga Nd model ages characterize large crustal segments (Michard et al 1985;Liew & Hofmann, 1988;D'Lemos & Brown 1993).…”

The Carolina Terrane in northwestern South Carolina: Insights into the development of an evolving island arc

“…4) places Carolina between Cadomia and Spain, adjacent to Morocco, with Bohemia filling in the puzzle between Carolina, Cadomia and the Trans-Amazonian-Eburian and Central Amazonian-Liberian craton. The position of Cadomia next to the Proterozoic craton is controlled by the mostly negative ε Nd data of Cadomia interpreted by D'Lemos and Brown (1993) and Nance and Murphy (1994) to indicate the ca. 600 Ma mixing of mantle material with Icartian (i.e., 2 Ga)-like basement.…”

Basement isotopic signatures and Neoproterozoic paleogeography of Avalonian-Cadomian and related terranes in the Circum-North Atlantic

“…Because U-Pb detrital zircon ages are not available for Cadomia, a direct comparison with West Avalonia is not possible. However, the proximity to the West African craton suggested for the Cadomian terranes by the Eburnian age of exposed Icartian basement (Auvray et al, 1980) is supported by the Nd isotopic signature of the basement gneisses (D'Lemos and Brown, 1993).…”