Variscan events: early Palaeozoic continental rift metamorphism and late Palaeozoic crustal shortening

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Abstract
Summary: Variscan events are interpreted in terms of a geodynamic process of long duration. It began in the early Palaeozoic, possibly in the late Precambrian in some regions, with widespread rifting of the continental lithosphere. Granulite facies metamorphism, widely in evidence in the Ordovician and Silurian, coincides in time with igneous activity and with continuous accumulation of sediment at the surface. That association is taken to indicate continental rift metamorphism above anomalous regions of the mantle. Folding and metamorphism of what is now regarded as the basement began early in the Devonian. By Upper Devonian at the latest wide areas of crystalline basement had been deeply exposed by erosion. The orogenic crustal shortening which began early in Devonian time induced intensive development of nappe tectonics involving the basement rocks. This resulted in deep-reaching crustal imbrications, especially well shown at the Moldanubian-Saxothuringian zone and Saxothuringian-Rhenohercynian zone boundaries, which evolved to carry crystalline basement rocks towards their foreland regions over distances greater than 100 km. During the course of these nappe developments folding of the adjacent sedimentary troughs proceeded. A geodynamic model of the northern flank of the central European Variscan orogen is presented. (Rb/Sr data are given using λRb 87 = 1.42 × 10 −11 y −1 . The error limits are taken from the original papers, original data are given in brackets.)