Saxon clod tectonics

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The saxonic floe tectonics (also called saxonic fracture tectonics or incorrectly called saxonic orogeny and saxonic mountain formation ) is a tectonic phase in Central Europe north of the Alps that is characterized by fracture floe tectonics . It began in the Santonian ( Upper Cretaceous ) around 85 million years ago and lasted until the late Pliocene around 2 million years ago. It was caused by the north drift of the African plate and its upstream small plates against the Eurasian plate ( Alpid mountain formation ), which increased the pressure on the earth's crust in today's Central Europe. In contrast to the alpine mountain ranges further south, where cover thrusts with fold formation predominated, in Central Europe crust clods were lowered or raised along faults without any folds occurring.

Earth historical background

Many European low mountain ranges have been lifted out by the Saxon clod tectonics and are therefore also referred to as clod mountains. Although the rocks of these mountains show folds, the folds go back to a significantly older mountain formation, the so-called Variscan orogeny in the Upper Carboniferous (approx. 340-320 mya ). During this mountain formation, not only did folds develop, but the tectonic forces also led to the formation of a regular network of faults, which still pervades the entire mountain range today.

After the Variscan high mountains had been largely eroded in the Permian , it was overlaid by mighty sea and mainland sediments as large areas of Europe sank in the subsequent geological ages ( Triassic , Jura ) - henceforth one speaks of the Variscan basement (in contrast the overlying layers are called overburden ).

From the Upper Cretaceous the tectonic situation changed fundamentally. Due to the north drift of the African plate, pressure was exerted on the European crust from the south, initially from the south-west due to the beginning collision of the Iberian plate with Europe, from the early Tertiary ( Paleocene or Eocene ) directly from the south from the Alpine region. This pressure was relieved by more or less vertical evasive movements taking place in the basement at the already Variscan faults, which of course also affected the overburden above. As a result, the Variscan fault network broke through to the surface of the earth. A distinction is made between three main directions of disturbance : NE-SW (referred to as Variscan or Erzgebirge), NW-SE (Hercynian / Harz) and NNE-SSW (Rhenish). Many mountain ranges and river valleys in Central Europe follow these directions.

Effects

The vertical evasive movements of the Central European crust are expressed in the small chambers of the German low mountain range with eyrie and ditch structures. Tectonic structures such as shed clods are conspicuous , although they were clumpy but were preferentially pushed out at one of the main limiting disturbances. Today's German low mountain ranges such as Harz , Thuringian Forest or Black Forest are broken clods that were raised so far that the entire overburden was removed and the Variscan basement is now exposed there again. In contrast, some of the clods were significantly lowered and filled with additional sediment. The largest such area in Central Europe is the Upper Rhine Graben .

The reactivated Variscan faults also resulted in volcanic activity in some cases. The best-known examples of this in Germany are the Vulkaneifel , the Westerwald , the Vogelsberg and the Rhön .

The last significant Saxon movements took place with the uplift of the Rhenish Slate Mountains and the sinking of the Lower Rhine Rift in the Pliocene. But strictly speaking, the Saxon phase is not yet over. The pressure from the Alpine region today leads to noticeable, very rarely stronger earthquakes, which mostly occur in southwest and western Germany, especially along the Rhine, but also further east, in the Vogtland .

literature

  • J. Kley, T. Voigt: Late Cretaceous intraplate thrusting in central Europe: Effect of Africa-Iberia-Europe convergence, not Alpine collision . In: Geology . tape 36 , no. 11 , 2008, p. 839-842 , doi : 10.1130 / G24930A.1 .
  • Hans Murawski: Geological Dictionary . 8th edition. Enke, Stuttgart 1983, ISBN 3-432-84108-6 , pp. 280 .
  • Roland Walter et al .: Geology of Central Europe . 5th edition. Schweizerbart'sche Verlagbuchhandlung, Stuttgart 1992, ISBN 3-510-65149-9 .
  • PA Ziegler, S. Cloetingh, J.-D. van Wees: Dynamics of intra-plate compressional deformation: the Alpine foreland and other examples . In: Tectonophysics . tape 252 , no. 1 , 1995, p. 7-59 , doi : 10.1016 / 0040-1951 (95) 00102-6 .

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Remarks

  1. ↑ There were already subsidence areas in the Permian, although they were spatially relatively narrow. At the former position of these Permian sedimentary basins , the greatest regional thicknesses occur today in the overburden.
  2. ↑ Essentially today's Iberian Peninsula . It broke away from Africa and Europe in the Mesozoic Era , then led a brief life of its own and was "squeezed in" between Western Europe and Africa by Africa's northern drift.
  3. ↑ If there is movement again in an old disorder, one speaks of a reactivation of the disorder.