Early Palaeozoic rift-related magmatism in Variscan Europe: fragmentation of the Armorican Terrane Assemblage

Early Palaeozoic bimodal rift-related magmatism is widespread throughout mu ch of the Variscides of Europe. It is traceable from the Polish Sudetes to NW Iberia. Granitic plutonism generally predates Cambro-Ordovician bimodal magmatism. In the N Bohemian Massif this early Palaeozoic granitic plutonis m was generated by partial melting of Cadomian basement, whereas contempora neous alkali granites with a mantle component are typical of the NW Iberian Massif. Silurian-Devonian mafic magmatism in the N Bohemian Massif, Massif Central and NW Iberian Massif is partly preserved as obducted ophiolites. Compositional diversity displayed by Cambro-Ordovician mafic magmatism can be accounted for by interaction between a spreading centre and an upwelling mantle plume. This indicates that combined tensional forces and mantle plu me convection assisted the early Palaeozoic dispersal of terranes from the N Gondwana margin. Continued fragmentation resulted in development of an ar chipelago of related terranes separated by a network of seaways and formati on of oceanic crust.