Magmatism of the late Variscan intermontane Saar-Nahe Basin (Germany): A review
Volker Von Seckendorff, Christoph Arz, Volker Lorenz, 2004. "Magmatism of the late Variscan intermontane Saar-Nahe Basin (Germany): A review", 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 Saar–Nahe Basin is a late Variscan intermontane basin that developed on the site of an earlier island arc, the Mid-German Crystalline Rise. Within the c. 6500m-thick continental sedimentary fill of the basin, a large variety of igneous rocks was emplaced over a period of c. 4 Ma from 296 to 293 Ma as high-level intrusions and lava flows, extrusive domes, diatremes and pyroclastic deposits, ranging in composition from basalt and basaltic andesite to rhyodacite, rhyolite and trachyte. Composite intrusive–extrusive complexes consist of andesite, rhyodacite and alkali feldspar trachyte with up to 10 wt% K2O. The geochemical characteristics of the most primitive mafic magmas indicate a slightly enriched upper mantle source modified by subduction-related fluids. Nd–Sr–O isotope data indicate that crustal contamination was important in the petrogenesis of the more differentiated magmas.
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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.