Alpine tectonics north of the Alps
Klaus Reicherter, Nikolaus Froitzheim, Marek Jarosiński, Janusz Badura, Hans-Joachim Franzke, Martin Hansen, Christian Hübscher, Rainer Müller, Paweł Poprawa, John Reinecker, Werner Stackebrandt, Thomas Voigt, Hilmar Von Eynatten, Witold Zuchiewicz, 2008. "Alpine tectonics north of the Alps", The Geology of Central Europe Volume 2: Mesozoic and Cenozoic, T. McCann
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The Cenozoic tectonic evolution of Central Europe was governed over long periods of time by far-field stresses resulting from continent collision in the Alps (which is still ongoing) ridge push in the Atlantic Ocean, and other sources. Such far-field stresses interfered with more local stresses related to processes such as the rise of mantle plumes, leading to the Cenozoic volcanism of Central Europe, and glaciation. Alpine tectonics north of the Alps began with the effects, of Late Cretaceous_Early Palaeogene continent collision in the Pyrenees, on the European crust. During Tertiary times, the stress field was unstable and repeatedly changed both in terms of magnitude and orientation. Notably, an episode of ESE-WNW to east-west directed extension during the late Eocene to Oligocene created the European Cenozoic Rift System (Rhône-Bresse Graben, Upper Rhine Graben, Lower Rhine Basin, and others) which up to the present is tectonically the most active zone of Central Europe. Flexural basins formed in the southernmost part of the Alpine-Carpathian foreland. The Jura Mountains also form part of the Alpine foreland, although they could, from a tectonic point of view, also be regarded as part of the Alps. They represent the most external foreland fold-and-thrust belt of the Alps. Folding and thrusting in the Jura Mountains took place during the Middle Miocene to Pliocene, and the thrust front presently propagates northward into the Upper Rhine Graben. The Alpine tectonics of southern Germany may best be described in terms of reactivation of older inherited, mainly Variscan, basement structures. This is also the case for the central Leine Graben, the Harz Mountains and parts of the North German Basin. Because of the frequent reactivation of faults, the following sections include some remarks on pre-Alpine deformation and sedimentation history.
The general episodes of Alpine deformation north of the Alps can be subdivided into three main phases: (1) the period of Late Cretaceous-Early Palaeogene inversion tectonics, when far-field effects of continent collision and the formation of the Pyrenees resulted in deformation extending as far north as the Danish North Sea, including the large-scale uplift of the Harz Mountains; (2) Eocene to Miocene extensional tectonics with the formation of large graben systems, for example the Upper Rhine Graben; and (3) the phase of tectonics related to the reorganization of the stress field during the Late Miocene, which coincides with the initiation of the ‘neotectonic period’ and the present-day stress field in Central Europe, which is characterized by SE-NW compression and NE-SW extension.
The Neogene to recent evolution of northern Central Europe, including the North German Basin and the Polish Basin, which are parts of the Central European Basin System, was partly affected by glacial loading and unloading during the Pleistocene. Presently, these regions are areas of low seismicity (macroseis mic intensities III-IV EMS; Grünthal & Mayer-Rosa 1998). Major stresses acting within the North German Basin and the Polish Basin were induced by the North Atlantic ridge push forces (east-west, or NW-SE directed), the ongoing Alpine collision (north-south directed), and, from the late Pleistocene onwards, the post-glacial rebound of Fennoscandia (mainly vertical, but also with a horizontal, west-east directed component). Present-day maximum horizontal stresses within the North German Basin are generally directed NW-SE (Rockel & Lempp 2003), but fan and bend towards the NNE, north of 52°N and east of 11°E, especially in the Polish Basin. The present-day stress field in the Central European Basin System is influenced by the decoupling of two crustal units (Roth & Fleckenstein 2001), which are separated by Zechstein evaporites (the Pre Zechstein formations together with the older units are decoupled from the overlying Mesozoic and Cenozoic sediments). The general stress orientation, with NE-SW maximum horizontal stress, was regionally modified or disturbed (Rockel & Lempp 2003). In areas of salt movement and the formation of salt pillows, salt walls and diapirs, the resultant local increase or decrease in salt thickness had a marked effect on stresses and tectonic structures (e.g. in the western Baltic Sea (Hansen et al. 2005) and in the Gliickstadt Graben area (Maystrenko et al. 2005).
Major basement faults within the intracratonic Central European Basin System are orientated NW-SE, while minor faults trend NE-SW and NNE-SSW, and are clearly visible in shaded relief and satellite images (Reicherter et al. 2005). The northern rim of the Central European Basin System is bounded by the Tornquist Zone, which consists of the Teisseyre-Tornquist Zone from Poland to Bornholm Island, and the Sorgenfrei-Tornquist Zone from southern Sweden to Denmark (Fig. 19.1). Additionally, the drainage pattern and the distribution of lakes in northern Germany parallel the block boundaries and, hence, mark zones of present-day subsidence (Mörner 1979; Stackebrandt 2004; Reicherter et al. 2005). A broad zone of subsidence extends from Hamburg to Berlin and onto Wroclaw (Poland) and is delineated by the depth to the base of the Rupelian Clay (Oligocene; Garetzky et al. 2001). This zone shows relatively minor faulting in the near-surface layers. The depocentre axes also had a NW-SE trend during the Mesozoic.
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This two-volume set provides the first comprehensive account in English of the geology of Central Europe. Written by more than 200 scientists from universities and research centres spread across Europe and North America, the 21 chapters are based on the main stratigraphic periods. Individual chapters outline the evolution of the region divided into a variety of sections which include overviews of the stratigraphic framework, climate, sea-level variations, palaeogeography and magmatic activity. These are followed by more detailed descriptions of the Central European succession, covering the main basins and magmatic provinces. Each chapter is thoroughly referenced, providing a unique and valuable information source.
Volume 1 focuses on the evolution of Central Europe from the Precambrian to the Permian, a dynamic period which traces the formation of Central Europe from a series of microcontinents that separated from Gondwana through to the creation of Pangaea. Separate summary chapters on the Cadomian, Caledonian and Variscan orogenic events as well as on Palaeozoic magmatism provide an overview of the tectonic and magmatic evolution of the region. These descriptions sometimes extend beyond the borders of Central Europe to take in the Scottish and Irish Caledonides as well as the Palaeozoic successions in the Baltic region.
Volume 2 provides an overview of the Mesozoic and Cenozoic evolution of Central Europe. This period commenced with the destruction of Pangaea and ended with the formation of the Alps and Carpathians and the subsequent Ice Ages. Separate summary chapters on the Permian to Cretaceous tectonics and the Alpine evolution are also included. The final chapter provides an overview of the fossil fuels, ore and industrial minerals in the region.
The Geology of Central Europe is a key reference work suitable not only for libraries across the world, but of interest to all researchers, teachers and students of European Geology.