Abstract The West Sudetes, NE Bohemian Massif, comprises several suspect terranes accreted to the margins of Laurussia during Variscan orogenesis. Whole rock REE and Sm-Nd isotope data for seven separate provinces (Izera, Kaczawa, Rudawy Janowickie and Kłodzko complexes; Fore-Sudetic and Góry Sowie Blocks; Slęża Ophiolite) suggest involvement of a variety of crustal and mantle sources. Felsic metasedimentary rocks (εNd(t) = −8.3 to −5.0) have two stage T DM ages of 1.9 to 1.5 Ga, whereas acidic metavolcanic rocks and granite gneisses (εNd(t) = −5.4 to +0.8) have two stage T DM ages of 1.5 to 1.0 Ga. A range of sources is implicated: predominantly Archaean and Palaeoproterozoic sources for the metasedimentary rocks, and Archaean. Palaeoproterozoic and Neoproterozoic to early Palaeozoic sources for the meta-igneous felsic lithologies. LREE depleted tholeiitic metabasites ((Ce/Yb) N = 0.8 to 3.4) generally have εNd(t) = +4.0 to +9.1, indicating derivation from depleted mantle asthenosphere. LREE enriched meta-alkali basalts ((Ce/Yb) N = 4.6 to 10.1) with εNd(t) between +3.1 and +7.0 implicate utilization of enriched mantle asthenosphere. Analogous lithologies from elsewhere in the Sudetes, North Bohemian Massif and the Armorican Terrane Assemblage have similar REE abundances, εNd values and T DM ages. Complexes previously considered to have had disparate Neoproterozoic to early Palaeozoic histories may be integrated into a unifying geodynamic model of derivation from the North Gondwanan (North African) margin during a widespread episode of continental margin break-up.

Abstract The potential use of radiogenic isotopes in the study of geological problems was recognized at an early stage in the investigation of nuclear science. At the turn of the century, F. Soddy and E. Rutherford first proposed the law of radioactive decay, and in 1905, Rutherford obtained the first age estimates of uraniferous minerals by measuring their helium content. The first U-Pb chemical dates for uraninites were published two years later byB.B. Boltwood (1907). F.W. Aston's development of the mass spectrometer shortly after the end of World War I led to the confirmation that many elements consist of isotopes having different atomic mass (Aston, But it was A.O. Nier's refinements of mass spectrometer design during and after World War II that provided the technological breakthrough required for routine geochronological measurements (Nier, 1940). Subsequent instrumental developments have principally involved improvements in precision and sensitivity, with the current generation of thermal ionization multi-collector mass spectrometers (TIMS) offering rapid simultaneous measurement of several isotopes from nanogram-sized samples.