Variscan orogenesis

Arathem	system	Beginning ( mya )	Orogenesis
Cenozoic Modern Earth Duration: 66 Ma	quaternary	2,588	Alpid orogeny
	Neogene	23.03
	Paleogene	66
Mesozoic Middle Ages Duration: 186.2 Ma	chalk	145
	law	201.3
	Triad	251.9	Variscan orogeny
Paleozoic Earthen Period Duration: 288.8 Ma	Perm	298.9
	Carbon	358.9
	Devon	419.2
	Silurian	443.4	Caledonian orogeny
	Ordovician	485.4
	Cambrian	541	Cadomic orogeny
Neoproterozoic Jungproterozoikum Duration: 459 Ma	Ediacarium	635
	Cryogenium	720	various Precambrian rock formations
	Tonium	1000
Mesoproterozoic Mittelproterozoikum Duration: 600 Ma	Stenium	1200
	Ectasium	1400
	Calymmium	1600
Paleoproterozoic Altproterozoikum Duration: 900 Ma	Statherium	1800
	Orosirium	2050
	Rhyacium	2300
	Siderium	2500
Neo-Archaic Duration: 300 Ma		2800
Mesoarchean Duration: 400 Ma		3200
Paleoarchean Duration: 400 Ma		3600
Eoarchic Duration: 400 Ma		4000
Hadaikum Duration: 600 Ma		4600
Please note that this table is only intended to provide a rough overview. Information in the specialist literature at the beginning and end of a particular orogenesis may differ from the information in the table. a. because there are different concepts and definitions depending on the region and author .

The Variscan , Variscan or Variscan orogeny is a phase of mountain formation ( orogeny ) in the younger half of the Paleozoic Era , which was caused by the collision of Gondwana and Laurussia as well as several microplates ( terranes ) derived from Gondwana . This was probably accompanied by the subduction of entire ocean basins . Variscan orogeny was one of the most important steps in the formation of the supercontinent Pangea , which lasted until the end of the Paleozoic.

Concept history

The term was first introduced into literature by Eduard Suess in 1888. He writes:

“But nowhere do the outlines of individual old mountain cores emerge so clearly as in front of this main line, in the Münchberg gneiss mass at Hof and in the Saxon granulite mountains. It is therefore appropriate that in the country of the Varisker, the Vogtlande, the name of the mountain range comprising most of the German eyrie will be chosen, and the same will be called the Variscian mountains after the Curia Variscorum (Hof in Bavaria). "

- Eduard Suess: The face of the earth. Volume II, 1888, p. 131.

The Germanic tribe of the Varisker or Narisker is mentioned several times in Roman and late Roman sources in alternating spellings, but the residence of the Varisker cannot be precisely located. It is not certain that they were actually ever resident in what is now Vogtland.

Curia Variscorum is the neo-Latin name for court , as it was assumed that the main town or prince's seat of the Varisker was there. The name Curia Variscorum was not known in Roman times, it was not used by any of the classical writers. The name of the town of Hof is of medieval origin, the name of the original settlement before the town was founded was Rekkenitze . Therefore there is also the neo-Latin formation Curia Rekkenitze for the city of Hof or the form Curia Regnitz used in medieval documents . The name Variscia for the Vogtland is also of neo-Latin origin .

As early as 1889, Fritz Frech stated that the spelling should be more correctly varistic. He also represented this opinion and spelling in the following works (e.g. the Lethaea Geognostica ).

Since 1904, the Variscan spelling has also been used in the Handbook of Regional Geology . Also from 1904 is the first evidence of the Variscan spelling. This prompted Ernst Zimmermann in 1906 to write an article on the spelling of the words "Varistic" and "Rät" in the journal of the German Geological Society. He came to the conclusion that the "correct" spelling was Varist. However, none of the four spellings has finally established itself to this day. In German-language specialist publications (magazine articles and books) the spelling varis z isch is currently used the most.

The structure of the European variscides, which is still almost unchanged today, was developed in 1927 by geology professor Franz Kossmat , who works in Leipzig .

Definition of terms

In English-speaking countries, the term hercynian is used in addition to variscan . In the German-speaking countries, the term Hercynian orogeny or Hercynian folding is less common because the term Hercynian is already occupied by the term derived from the longitudinal extent of the Harz for a general strike in Central Europe. The names Acadian Orogeny , Alleghenian Orogeny and Ouachita Orogeny are also used for the Devonian to Early Permian orogeny phases in the east and south-east of North America, for which a close to immediate connection with the Variscan Orogeny in Europe is assumed, but for either temporal or spatial one another There are distinct individual deformation events, whereby the assignment of Acadian orogenesis to Variscan orogenesis is controversial. In the Francophone area, the term Orogenèse Hercynienne is still used today, especially in connection with the geology of the Alps , based on the work of Marcel Bertrand and Émile Haug .

Since the tectonic deformation of numerous rock formations in large parts of the earth, sometimes accompanied by intense metamorphosis, can be traced back to a common orogeny in the Middle Ages ( Devonian to Carboniferous ), Variscan becomes not only structural and regional geological, but, informally, also temporal Indication understood. It stands for a period before about 400 to 300 Ma before today. In publications dealing with the geology of East Asia, somewhat more recent mountain formations - up to about 230 Ma - are counted as part of the Variscan orogeny. The delimitation of a Variscan mountain range is neither spatially nor temporally clear on the basis of the scientific literature.

The term Variscan refers in a broader sense to the orogeny phase in the younger half of the Paleozoic Era. In a narrower sense, Variscan describes the mountain-forming processes during the collision between Gondwana and Laurussia in what is now Central, West and Southwestern Europe, in eastern North America and in western North Africa.

Location of the Variscan Mountains

Current location ( outcrop ) of middle and late Paleozoic orogen complexes (hatched). It should be noted that these are partly contained in the Young Mesozoic-Tertiary mountain belts (e.g. the Pyrenees ). In addition, the Urals and the East Asian complexes are rarely subsumed under the term “Variscan”.

Paleogeographic map of North America and Europe in “Variscan” times showing the extent of the Ouachita-Alleghenian-Mauritanian-Hercynian fold belt

The variscicon in the narrower sense extends over large parts of Central Europe and was first researched here. The Variscan rocks that have been exposed for days occur in two strands. The northern strand leads from western Poland and Bohemia or northern Austria across Germany and southern Belgium via Brittany and Devon / Cornwall in southern England to Wales and southern Ireland , and then across the Atlantic to the Palaeozoic mountains of the Canadian and American east coast continue. From Corsica , Sardinia , the French Massif Central and the Montagne Noire , the second mountain arch leads over the Pyrenees , the Cantabrian - Asturian and Central Iberian chains in Spain and the Balearic Islands across the Mediterranean to Morocco into the Moroccan Meseta and the Anti-Atlas .

Because of the strong overprinting by the folding of the Alps, the exact continuation of the Variscides to the southeast has not been clarified in detail. These include the alpine Variscan massifs ( Mercantour , Pelvoux , Belledonne , Mont Blanc , Aarmassiv , large parts of the Central Eastern Alps ), the Dinaric and Greek mountains and mountain ranges in Turkey . To the west, the Central European Variscides find their direct continuation on the North American east coast in Newfoundland , Nova Scotia , New England and, more widely, in the Appalachians . In the Ouachita Mountains in Arkansas and Oklahoma , remnants of the Ouachita Orogens mountain range, which extends much further to the west and formed when South America collided with North America, have been preserved. This mountain range is almost completely covered by younger rocks.

Mountain ranges of the Late Paleozoic ( Permian ), which are only counted as Variscides in a broader sense, can also be found in the Urals , Pamir , Tianshan and other mountains in Asia . The Antler-Orogen, which is also from this time and is located on the North American west coast, and the mountain ranges that were formerly connected with it on the west side of South America, in Antarctica, on the southern tip of Africa and in the east Australian Tasman, belong to an independent mountain formation system and thus not to the Variscides. Mountain range in Victoria and New South Wales .

Classification of the variscids in Central Europe

Classification of the Variscides in Germany and the surrounding area according to Kossmat 1927 (changed)

A pre-zone and three Variscan mountain arches are distinguished from north-west to south-east, which differ significantly in their geological structure and are separated from one another by extensive and very deep fault zones.

• Subvariszische foredeep or Subvariszische foredeep : carbonic Gebirgsvortiefe with extensive paralic coal formation (cyclic change between swamp forests and sea → formation of an alternation of coal-bearing non-marine and carbonless marine layers); extends from the Ardennes over the Ruhr area to Upper Silesia , with the Central and East German parts all lying deep underground.
• Rhenohercynian (named after the Rhine and Harz): the folded, largely unmetamorphic filling of the Rhenohercynian basin, consisting of marine, predominantly siliciclastic sediments and basic submarine volcanic rocks; hardly interspersed with late and post-orogenic granites; open today in the Ardennes , in the Rhenish Slate Mountains and in the Harz Mountains .
• Saxothuringian (named after Saxony and Thuringia): folded filling of the Saxothuringian basin, partly unmetamorphic and then facially quite similar to the layers of the Rhenohercynian, partly present in different metamorphic facies, on Cadomian basement; relatively heavily interspersed with late and post-orogenic granites; today open-minded in the Thuringian Slate Mountains , Franconian Forest , Vogtland , Fichtel Mountains , Ore Mountains , Upper Lusatia and the Sudetes
  • On the northwest edge of the Saxothuringian along a by pulling crystalline embossed, as a former island arc interpreted rock belt as a means German crystallizer threshold is called (FMD) and in the northern part of the Vosges - and Black Forest crystallin, as well as in the western Spessart ( "Vorspessart"), in western Odenwald , in the northern Thuringian Forest (Ruhlaer Kristallin) and in the Kyffhäuser Mountains.
• Moldanubic (named after the Moldau and Danube): in fact, a rock complex consisting exclusively of crystalline; interspersed with large granitoids; today open in the southern part of the Vosges and the Black Forest and especially in the Bohemian Massif south of the Fichtelgebirge and the Egergraben .

The geological development of these units and the nature of the fault zones that separate them from one another, for example whether they are evidence of former subduction zones and thus relics of a Saxothuringian or Moldanubian ocean, is in part still the subject of intensive scientific research.

Outline of the variscides in North America

The southern Appalachians are divided from west to east into several belts running roughly from north to south.

• Appalachian Plateau (foreland)
• Valley-And-Ridge-Province, foreland thrust belt, from the adjoining Blue-Ridge Province to the east, far thrust on a flat thrust orbit (Grandfather Mountain Window)
• Blue Ridge Province, Piedmont (metamorphic core of the Southern Appalachians), Inner Piedmont (affiliation with America approx. 500-450 Ma, Taconic phase)
• Piedmont (metamorphic core of the Southern Appalachians): Charlotte belt, Carolina slate belt (affiliation to America approx. 380 Ma, Acadian phase)
• Coastal Plain (passive reef edge of the Atlantic since 200 Ma), younger rocks above remnants of the Charlotte Belt and the Carolina Shale Belt

Across the Atlantic, the so-called Mauritanids on the African north-west coast have been the passive reef edge of the Atlantic for 200 Ma. Before the opening of the Atlantic, they were part of today's Appalachian Mountains. East-facing thrusts have been preserved here, where metamorphic layers, which are comparable to the rocks of the Carolina slate belt, were stacked over non-metamorphic foreland, which belongs to Africa. These rocks are considered to be the suture zone of the Alleghenian orogeny (collision of Africa as part of Gondwana with North America in Laurussia 270 Ma ago).

Emergence

During the Variscan orogeny, several microcontinents (see also: Armorica ) collided with the already existing northern continent. In Europe, this led to the unfolding of a system of high mountains after partial shallow sea ​​flooding , which lasted in several phases from the Devonian to the end of the Paleozoic Era. The remnants of this orogen can be found as rump and low mountain ranges in Western and Central Europe.

This mountain system was preceded by the formation of a northern continent from the mainland blocks Laurentia and Fennosarmatia , which merged in the Ordovician (490-440 Ma) as a result of the Caledonian mountain formation . Metamorphic remains of the older Precambrian basement have been found in the subsoil of Bohemia, Thuringia and up to the Upper Rhine. Relatively little is known about their source material; the dating of individual mineral inclusions in these rocks resulted in ages that probably go back to much older, in some cases even archaic (approx. 3.2 billion years), ore formation phases. The existing old land mass sank to the Variscan trough . Thick sediments were deposited here, which led to high pressure and high temperatures in the rock layers below and, as a result, to their metamorphic transformation. Through plate tectonic processes, above all through the approach of the African plate to the Eurasian plate, pressure from the southeast acted. This created zones with bulges and large hollows . This resulted in the unfolding of the Variscan high mountains . The high mountain range of Central Europe, which is also called the Carboniferous Alps , was about 600 km long and had an average height of probably about 5 km, which roughly corresponds to today's Tibetan high plateau.

At the same time as this ore formation began strong erosion, which increases with increasing distance from sea level (increased relief energy ). In the warm climate, the coal seams of the Ruhr area were created by covering organic layers with the eroded sediments. At fault lines could magma to rise and led to volcanic activity or the formation of underground plutons .

Already in the Permian the Variscan high mountains had eroded into the so-called Permian hull area and was covered by layers of sediment. These rump mountains are preserved today after a new tectonic uplift due to the formation of the Alps as Variscan islands (plateaus) between the younger rocks of the Mesozoic Era. These are partially cut up by fluvial erosion processes and are also known as riedel . In the course of the further history of the earth the fracture tectonics followed , which shaped the low mountain ranges that are still present today.

Shortly before the beginning of the Variscan ore formation, numerous deposits of red iron ore were created in the Devonian due to the submarine weathering of volcanic rocks , which were mined in iron ore mines . In many places in the Lower Carboniferous Grauwacken were deposited, which indicate a main phase of the mountain formation in the time of the Upper Carboniferous (322 to 290 million years ago). The originally flat rock units were folded , broken and shale. Today's slate , which has long been extracted as roofing slate , was made from clayey rock .

See also : Old crystalline

Web links

Commons : Variscan Orogeny  - collection of images, videos and audio files

• The Paleozoic . The Paleozoic at palaeos.com (English)
• The Paleomap Project by C. Scotese (English)

Individual evidence

1. ^ DSK: German Stratigraphic Commission (ed.): Stratigraphie von Deutschland X, Rotliegend, Part I: Innervariscische Becken. (= Publication number Dt. Ges. Geowiss. 61). Hannover 2013, ISBN 978-3-510-49225-1 .
2. ↑ Eduard Suess: The face of the earth. Second volume, Temsky, Prague / Vienna; Freytag, Leipzig 1888, p. 131. (Online at archive.org)
3. ^ ^{A b} Rudolf Köster: Proper names in the German vocabulary: a lexicon. 2003, p. 183. (Online at Google Books)
4. ↑ Wilhelm Obermüller: German-Celtic, historical-geographical dictionary: to explain the river, mountain, village, Gau, people and person names in Europe, West Asia and North Africa in general, and especially Germany, along with the resulting conclusions for the prehistory of mankind. Volume 2, Denicke, Berlin 1872.
5. ↑ Johann Adolph Schultes: Diplomatic contributions to the history of the Counts of Andechs and subsequent dukes of Meran etc. In: Historical treatises of the Royal Bavarian Academy of Sciences. 4: 157- Munich. Online at Google Books .
6. ^ Fritz Frech: The French Central Plateau. A sketch of its development. In: Journal of the Society for Geography in Berlin. 24, Berlin 1889, pp. 132-165. (archive.org)
7. ↑ Ferdinand Roemer, Fritz Frech: Lethaea geognostica: Handbook of the history of the earth with illustrations of the most characteristic fossils for the formations. Part 1, Volume 2, E. Schweizerbart'schen Verlagsbuchhandlung (E. Nägele), 1902.
8. ^ Alfred Hettner: The German low mountain range. Attempt a comparative characteristic. In: Geographical Journal. 10 (1), Stuttgart 1904, pp. 13-25. (Online at JSTOR)
9. ^ Gustav Steinmann, Otto Wilckens: Handbook of regional geology. Volume 1, part 5, C. Winter's Universitätsbuchhandlung, Heidelberg 1904. (books.google.de)
10. ↑ Ernst Zimmermann: About the spelling of the words "Varistic" and "Rät". In: Journal of the German Geological Society. 58, Berlin 1906, pp. 50-51.
11. ↑ Search Variscan *
12. ↑ Search Variscan * on Google Books
13. ^ F. Kossmat: Structure of the Varist mountain building. In: Dep. Sächs. Geol. L.-A. 1, Leipzig 1927, pp. 1-39.
14. ^ Brian F. Windley: The Evolving Continents. 3. Edition. Wiley, Chichester et al. 1995, ISBN 0-471-91739-7 , p. 168.
15. ↑ David R. Oldroyd: The Biography of the Earth. 2nd Edition. Zweiausendeins, Frankfurt am Main 2007, pp. 474–475.
16. ^ Reed Wicander, James S. Monroe: Historical Geology. 6th edition. Cengage Learning, 2010, ISBN 978-0-495-56007-4 , p. 233 ff.
17. ^ H. Williams: Historical Geology. The Hercynian Orogeny. (No longer available online.) In: Historical Geology. University of North Texas, archived from the original on April 21, 2008 ; Retrieved August 1, 2013 . 
18. ^ Klaus KE Neuendorf, James P. Mehl, Julia A. Jackson: Glossary of Geology. 5th edition. American geological Institute, Alexandria, 2005, ISBN 0-922152-76-4 , p. 298.
19. ↑ Marcel Alexandre Bertrand: La chaîne des alpes et la formation du continent européen. In: Bull. De la Soc. géol. de France. 3rd series, Volume 15, 1887.
20. ↑ Hans Murawski : Geological Dictionary. 8th edition. DTV, Munich 1983, ISBN 3-423-03038-0 , p. 94.
21. ^ KY Lee: Geology of petroleum and coal deposits in the North China Basin, Eastern China. In: USGS Bulletin 1871. 1989, p. 3 , accessed August 1, 2013 (Table 1). 
22. ^ Tectonic Map of the western Tethysides. ( Memento of February 6, 2012 in the Internet Archive ) Institute of Geology and Paleontology at the University of Lausanne. (English)
23. ↑ R. Hohl (ed.): The history of the development of the earth . 6th edition. Werner Dausien, Hanau 1985, ISBN 3-7684-6526-8 , pp. 230 .
24. ↑ Paleo-Tethys Ocean. The Variscan development based on paleogeographic reconstructions. ( Memento of February 6, 2012 in the Internet Archive ) Tethyan Plate Tectonic working group at the University of Lausanne. (English)
25. ↑ C. Scotese: Paleogeographical Configuration Lower Carboniferous (English) Paleomap Project. Retrieved December 29, 2007.
26. ↑ Victoria's geology until Carboniferous. ( Memento of January 2, 2007 in the Internet Archive ) (English) Geology of the state of Victoria to the Carboniferous. Retrieved December 28, 2007.
27. ↑ as it is shown, for example, in the synopsis on the regional geology of the study area in: Yvonne Hofmann: Gravimetric and geodynamic modeling in the swarmquake region Vogtland / NW Bohemia. Dissertation to obtain the academic degree doctor rerum naturalium (Dr. rer. Nat.), Faculty of Chemical and Geosciences, Friedrich Schiller University Jena, 2003 ( PDF 12 MB), p. 5 ff.
28. ↑ FA Cook among other things: The growth of the continents. In: Oceans and Continents. Spectrum der Wissenschaft Verlag, Heidelberg 1987, ISBN 3-922508-24-3 , pp. 158-171.
29. ^ U. Linnemann: Pre-Mesozoic Geology of Saxo-Thuringia . From the Cadomian Active Margin to the Variscan Orogen. Ed .: RL Romer. Swiss beard, 2010, p. 485 (English).
30. ^ W. Dörr, G. Zulauf: Elevator tectonics and orogenic collapse of a Tibetan-style plateau in the European Variscides: the role of the Bohemian shear zone. In: International Journal of Earth Sciences. Volume 99, Issue 2, March 2010, pp. 299-325.