New constraints on the timing of late Carboniferous–early Permian volcanism in the central North Sea
Michel Heeremans, Martin J. Timmerman, Linda A. Kirstein, Jan Inge Faleide, 2004. "New constraints on the timing of late Carboniferous–early Permian volcanism in the central North Sea", 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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The Permo-Carboniferous evolution of the central North Sea is characterized by three main geological events: (1) the development of the West European Carboniferous Basin; (2) a period of basaltic volcanism during the Lower Rotliegend (latest Carboniferous–early Permian); and (3) the development of the Northern and Southern Permian Basins in late Permian times. The timing of the late Carboniferous–Permian basaltic volcanism in the North Sea is poorly constrained, as is the timing of extensional tectonic activity following the main phase of inversion during the Westphalian, due to the diachronous propagation of the Variscan deformation front. Results of high precision Ar-Ar dating on basalt samples taken from a core from exploration well 39/2–4 (Amerada Hess) in the UK sector of the central North Sea suggests that basaltic volcanism was active in the late Carboniferous, at c. 299 Ma. The presence of volcanics below the dated horizon suggests that the onset of Permo-Carboniferous volcanism in the central North Sea commenced earlier, probably at c. 310 Ma (Westphalian C). This is contemporaneous with other observations of tholeiitic volcanism in other parts of NW Europe, including the Oslo Graben, the NE German Basin, southern Sweden and Scotland. Interpretations of available seismic data show that main extensional faulting occurred after the volcanic activity, but the exact age of the fault activity is difficult to constrain with the data available.
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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.