Timing, geodynamic setting and character of Permo-Carboniferous magmatism in the foreland of the Variscan Orogen, NW Europe
Martin Jan Timmerman, 2004. "Timing, geodynamic setting and character of Permo-Carboniferous magmatism in the foreland of the Variscan Orogen, NW Europe", Permo-Carboniferous Magmatism and Rifting in Europe, M. Wilson, E.-R. Neumann, G. R. Davies, M. J. Timmerman, M. Heeremans, B. T. Larsen
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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.
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Widespread extension occurred within the Variscan orogen and its northern foreland during Late Carboniferous to Early Permian times. This was associated with magmatism and with a fundamental change, at the Westphalian-Stephanian boundary, in the regional stress field, coincident with the termination of orogenic activity and onset of dextral translation between North Africa and Europe. Rifting propagated across basement terranes with different ages and thermal histories. Most of the rift basins developed on relatively thin lithosphere; however, the highly magmatic Oslo Graben initiated within the edge of a craton. Early Stephanian regional uplift is contemporaneous with the onset of magmatism, inviting speculation that it might have been induced by a thermal anomaly within the upper mantle. The contributions to this volume suggest that the geodynamic setting in which magmatism occurred was complex, involving wrench tectonics, slab detachment, and delamination or thermal erosion of the base of the lithosphere.