Early Palaeozoic rift-related magmatism in Variscan Europe: fragmentation of the Armorican Terrane Assemblage |
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| Authors: | QG Crowley PA Floyd JA Winchester W Franke & JG Holland |
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| Institution: | School of Earth Sciences and Geography, Keele University, Staffordshire ST5 5BG, UK; Institut für Geowissenschaften, Justus Liebig Universitait, Senckenbergstr. 3, D-35390 Giessen, Germany; Department of Geological Sciences, University of Durham, Durham DH1 3LE, UK |
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| Abstract: | Early Palaeozoic bimodal rift-related magmatism is widespread throughout much 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 plutonism was generated by partial melting of Cadomian basement, whereas contemporaneous 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 plume convection assisted the early Palaeozoic dispersal of terranes from the N Gondwana margin. Continued fragmentation resulted in development of an archipelago of related terranes separated by a network of seaways and formation of oceanic crust. |
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