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Mesozoic-Palaeozoic Europe |
Laboratoire de Dynamique de la Lithosphère, Université Montpellier 2, Place E. Bataillon, 34095 Montpellier, France (matte{at}dstu.univ-montp2.fr)
The Urals are a linear north-south-trending belt (2500 km in length, from Novaya Zemlya to the Aral Sea). Their apparent narrowness (100-150 km) in the polar and cispolar parts is mainly due to the Siberian Meso-Cenozoic post-tectonic cover. In the southern, broadest part that crops out, the width of the Urals is close to 500 km. The Urals are very different from the other European Palaeozoic belts, the Caledonides and Variscides: despite subduction that built volcanic arcs in Silurian-Devonian times and pushed continental crust to great depth, where it underwent UHP metamorphism, the global shortening is relatively small, without great nappes, and the level of erosion very high, mainly east of the oceanic suture, where high-grade Uralian metamorphism is scarce. Another unusual feature is the preservation of an orogenic root in the centre of the orogen. These characteristics are due to the plate tectonic history that led to the orogeny: eastward subduction of the European passive margin stopped quickly after the Devonian because it was difficult for a so large a continent to sink further. Orogeny continued by westward subduction, east of the volcanic arc, closure of oceanic basins and accretion of small continental blocks and arcs without large underthrusting, and thus with little metamorphism or erosion (soft collision) but with large strike-slip motion. Preservation of the root is thought to be due to the high density of the central volcanic arc at depth (mantle and probably mafic granulites), which precluded strong uplift and erosion.
