Tectonic ceiling , Überschiebungs- or thrust ceiling are extended, flat or corrugated body of rock in folded mountains , as allochthonous , i.e. as transported stationary foreign material on which Autochthon , lie, that is, on the located at the original site of its formation rock mass. Several such ceilings can be stacked on top of each other and together form a ceiling system or a ceiling complex. When a fold mountains is mostly composed of such a ceiling or ceiling complexes, it is called in the geology and by a ceiling mountains .
The displaced rock bodies can have been moved many kilometers to several hundred kilometers from their area of origin, the ceiling root , to their front edge, the ceiling forehead . The stratigraphically deepest, i.e. H. The oldest rocks within a single ceiling are sometimes referred to as ceiling cores (especially if they consist of crystalline basement ). They are usually located on or near the underside, the base or sole , of a ceiling. Ceilings that are assumed to have slipped on gently sloping surfaces under the influence of gravity are referred to as sliding ceilings .
In folded mountains more in each case by flat often are incident distortions separated from one another ceiling stacked and form a ceiling system . Due to their nature as non-local rock bodies, ceilings are also referred to as allochthonous ("remote from the place of formation"), while underneath crustal areas that are not shifted are referred to as autochthonous ("on site"). Parautochthonous nappes are only shifted over short distances compared to their place of origin.
History of the ceiling theory
The role of thrusts in the Alps was discovered using the example of the conspicuous Glarus thrust (see there for a detailed history). Initially, Arnold Escher von der Linth and Albert Heim established an interpretation as a folding phenomenon ( Glarner double fold ), although Roderick Murchison had already advocated a thrust during a visit to Escher von Linth in 1848, drawing on observations in Scotland. Heim had a heated argument with the proponent of the ceiling theory August Rothpletz in the 1890s. Findings in support of the ceiling theory of Marcel Alexandre Bertrand (1884), which he gained in the Ardennes and which the alpine geologists regarded as purely theoretical ( "reverie" ) (since he had not researched on site in the Alps), played with the Alpine geologists were initially irrelevant, as was Archibald Geikie's in Scotland (1883). Although the great Austrian geologist of the 19th century, Eduard Suess , had reinterpreted the “Glarner double fold” as an overthrow as early as 1883, it was only investigations by Hans Schardt (1893) and especially Maurice Lugeon in western Switzerland that led Albert Heim to rethink (around 1902). One of the turning points for the recognition of the ceiling theory was the International Geological Congress in Vienna in 1903. The final breakthrough came at the Geological Association in Innsbruck in 1912, which was also attended by the now 81-year-old Eduard Suess. Previously, studies (among others by Otto Ampferer 1901, Karwendel thrust, Pierre-Marie Termier 1904: transfer to the Eastern Alps) had shown a far greater spread of the thrust phenomenon in the Alps, which was characteristic of even entire parts of the Alps. Associations with the movement of plates (North Africa) made in the Alps in 1915 Émile Argand , who in the 1920s also professed the theory of continental drift .
Causes of blanketing
The cause of a blanket formation is strong lateral pressure on already existing arches of the earth's crust , which is mostly due to large-scale plate tectonics . If a piece of the earth's crust (see lithosphere ) is affected by very strong tectonic constriction, it can lead to a horizontal thrust over other, neighboring rock or mountain bodies on a gently rising, firmer base .
The mechanism of blanket formation is not fully understood in detail . When the rock packs are pushed over, which are very thin in comparison to their size, increased pore water pressure plays a role, as it were, pushing the ceiling upwards and greatly reducing its resistance on the sliding surface. The presence of flexible layers such as salt deposits, marls or clay stones also supports the formation of cover sheets.
Like layers in an undisturbed sedimentary sequence, tectonic nappes also form rock piles, the structure of which has an impact on the local hydrogeology. For example, spring outflows can be found at outcrops from thrust areas if there is tectonic contact between a groundwater-retaining and a groundwater-conducting rock. An example of this is provided by the springs on the southeast side of the Engadine window near Scuol in the Swiss canton of Graubünden , where, while still within the Penninic , groundwater- conducting Bündnerschiefer (fissured aquifers) are run over by groundwater-retaining ceiling units (Ramosch zone, Roz-Champatsch zone and Tasna ceiling) are.
In the Alps , large parts of the mountain range consist of over-arched ceiling systems. The nappes of the Northern Limestone Alps , the Grauwackenzone and accompanying rocks were pushed over at least 150 km above their sub-stock, but the transport distance was probably more than 1000 km. The rocks of the Penninic and the Helvetic in Switzerland, France and Austria were also transported as blankets, but over shorter distances. Overhead transport also took place in the Apennines , the Carpathians and other mountains of the Alpid orogeny such as the Himalayas .
Ceilings are also known from older mountains (the so-called Rumpfgebirge ), for example from the Caledonian Mountains in Scotland and Norway, or the Variscan Mountains (example: the Moldanubic of the Bohemian Massif or the Giessener ceiling in the Rhenish Slate Mountains ).
- Gerhard H. Eisbacher: Introduction to Tectonics . 1st edition. Ferdinand Enke Verlag, Stuttgart 1991, ISBN 3-432-99251-3 , pp. 57 ff .
- Dieter Richter: General Geology . 3. Edition. de Gruyter Verlag, Berlin - New York 1985, ISBN 3-11-010416-4 , pp. 233 ff .
- Stefan Lienert (Red.): Geology and geotopes in the canton of Schwyz. Reports of the Schwyzerische Naturforschenden Gesellschaft. Vol. 14, 2003 ( online ), p. 119 (glossary)
- cf. Rudolf Staub: The construction of the Alps - attempt at a synthesis. A. Francke A.-G., Bern 1924 ( archive.org )
- Geikie himself only referred to Heim's theory in the 1893 edition of his geology textbook
- Alexander Tollmann: The importance of Eduard Suess for the ceiling theory. Communications from the Austrian Geological Society. Vol. 74/75, 1981, pp. 27-40 ( PDF 1.14 MB)
- Rudolf Trümpy: The Glarus Nappes: A Controversy of a Century Ago. In: DW Mueller, JA McKenzie, H. Weissert (Eds.): Controversies in Modern Geology. Academic Press, London 1991, pp. 385-404
- Helmut W. wing: Wegener-Ampferer-Schwinner: A contribution to the history of geology in Austria. Communications from the Austrian Geological Society. Vol. 73, 1980, pp. 237-254 ( PDF 1.34 MB)
- Bruce B. Hanshaw, E-An Zen: Osmotic equilibrium and overthrust faulting. Geological Society of America Bulletin, Vol. 76, No. 12, 1965, pp. 1379-1385, doi : 10.1130 / 0016-7606 (1965) 76 [1379: OEAOF] 2.0.CO; 2
- Pius Bissig: The CO 2 -rich mineral springs of Scuol-Tarasp (Lower Engadine, Kt. GR). Applied Geology Bulletin. Vol. 9, No. 2, 2004, pp. 39-47, doi : 10.5169 / seals-224995
- Reinhard Schönenberg, Joachim Neugebauer: Introduction to the geology of Europe . 4th edition. Verlag Rombach, Freiburg 1981, ISBN 3-7930-0914-9 , p. 194 .
- Stefan M. Schmid, Bernhard Fügenschuh, Eduard Kissling, Ralf Schuster: Tectonic map and overall architecture of the Alpine orogen. Eclogae geologicae Helvetiae. Vol. 97, 2004, pp. 93–117 ( PDF )