Timing, geodynamic setting and character of Permo-Carboniferous magmatism in the foreland of the Variscan Orogen, NW Europe

Abstract In the early Carboniferous, final subduction of the Rhenohercynian Ocean, accretion of a magmatic arc and docking of microcontinents caused fault reactivation, extension and fault-controlled basin formation in the foreland of the Variscan Orogen. Lithospheric stretching resulted in generally mildly alkaline basaltic volcanism that peaked in the Visean. In the internal Variscides, rapid uplift and granitoid plutonism shortly followed collision and was probably due to slab detachment(s) or removal of orogenic root material. A regional-scale, E-W-oriented stress field was superimposed on a collapsing orogen and its foreland from the Westphalian onwards. In the Stephanian-Early Permian, a combination of outward-propagating collapse, mantle or slab detachment and the regional stress field resulted in widespread formation of fault-controlled basins and extensive magmatism dated at 290-305 Ma. In the foreland, large amounts of felsic volcanic rocks erupted in northern Germany, accompanied by mafic-felsic volcanics and intrusions in the Oslo Rift, and dolerite sills and dyke swarms in Britain and Sweden. In the internal Variscides, mafic rocks are rare and felsic-intermediate compositions predominate. Their apparent subduction-related signature may have been inherited from metasomatized mantle sources or caused by extensive assimilation of continental crust.