Variscan orogeny

The Variscan, Variscan orogeny Variscan or is a phase of mountain building ( orogeny ) in the middle Paleozoic ( Palaeozoic ), which was caused by the collision of Gondwana and Laurussia and several of Gondwana -derived microplates ( terranes ). This probably was accompanied by the subduction of entire ocean basins.

• 2.1 Outline of the Variscides in Central Europe
• 2.2 Outline of the Variscides in North America

Conceptual history

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

"Nowhere but enter the outlines of individual old mountain cores forth as clearly as before this main line, in the Münchberger gneiss mass at court and in the Saxon Granulitgebirge. It is therefore in accordance with that am selected in the land of the Varisker, the Vogt land, the name of the most comprehensive German clumps Mountains, and it is the same after the Curia Variscorum (Hof in Bavaria), the Variscan mountains are called. "

The Germanic tribe of the Varisker is called at several times in Roman and late Roman sources in alternate spellings ( " Narisker " ), but the residences of the Varisker not precisely localized. It is not certain that they were ever actually resident in today's Vogtland.

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

1889 performs Fritz Frech that the spelling would have real hot varistisch. This opinion and spelling, he represented in the following work (eg the Lethaea Geognostica ).

Since 1904 the spelling is variskisch occupied in the "Handbook of the regional geology ." Also from 1904 comes a first evidence of the Variscan spelling. This prompted Ernst Zimmermann 1906 an article " About the spelling of the words " varistisch "and" Advises " " in the Journal of the Geological Society. He came to the conclusion that the varistisch was " correct" spelling. However, none of the four spellings has finally prevailed until today. In German-language publications ( journal articles and books), the notation currently used Variscan most.

The still almost unchanged valid classification of the European Variscides was developed in 1927 by acting in Leipzig Geology Professor Franz Kossmat.

Distinction between

In English-speaking, in addition to Variscan Variscan instead the term Hercynian used, which is manned hercynian already coined by the geographical extent of the resin towards geological term in Germany. In the U.S., the term is not used for the orogenies in the Appalachian Mountains, here are the local names of mountain building in the Appalachian Mountains in use.,

As the tectonic deformation of numerous rock formations in many parts of the world, partly accompanied by intense metamorphism, a common orogeny in middle Palaeozoic can be traced back ( Devonian to Carboniferous) is Variscan understood not only as structural, but, informally, as a temporal specification. It stands for a period prior to about 400-300 Ma ago. In publications dealing with the geology of East Asia, are also slightly younger orogenies - up until about 230 Ma - calculated for Variscan orogeny. The delineation of a Variscan mountain belt is based on the scientific literature neither in space nor in time clearly.

The term Variscan refers more broadly to the mountain building phase in the younger half of the Paleozoic. In a narrow sense refers to the Variscan orogenic processes in the collision of Gondwana and Laurussia in today's central, western and south-western Europe, eastern North America and western North Africa.

Position of the Variscan Mountains

The Variszikum in the narrower sense extends over large parts of Central Europe and has been researched here first. The above ground open-minded Variscan rocks occur in two strands. The northern strand leading from western Poland and Bohemia and northern Austria across Germany and southern Belgium through Brittany and Devon / Cornwall in southern England to Wales and Southern Ireland, to then across the Atlantic to the Paleozoic mountains of the Canadian and U.S. East Coast continue. From Corsica, Sardinia, the French Massif Central and the Montagne Noire, the second mountain arch over the Pyrenees, the Cantabrian - Asturian and zentraliberischen chains in Spain and the Balearic Islands via the Mediterranean to Morocco in the Moroccan Meseta and the Anti-Atlas.

Because of the strong overprinting by the folding of the Alps the exact continuation of the Variscides is not clear to the southeast in detail. To them, the Alpine Variscan massifs ( Mercantour, Pelvoux, Belle Donne, Mont Blanc, the Aar Massif, a large part of the Central Eastern Alps ), the Dinaric Mountains and Greek as well as mountain ranges in Turkey are counted. To the west, the Central European Variscides find their direct continuation of the North American east coast in Newfoundland, Nova Scotia, New England and in further distribution in the Appalachian Mountains. In the Ouachita Mountains in Arkansas and Oklahoma remains of much further to the west ranging mountain chain of the Ouachita orogen are obtained, which originated in the collision of North America with South. This mountain range is almost completely covered by younger rocks.

Mountain ranges of the Spätpaläozoikums ( Perm ), which are expected only in a broad sense to the Variscides, can be found beyond the Urals, the Pamir, Tianshan and other mountains of Asia. For an independent orogeny system and thus not to the Variscides is likewise one of that time coming, situated on the North American West Coast Antler Orogen and the formerly associated with him mountain ranges on the west side of South America, Antarctica, at the southern tip of Africa and in ostaustralischen Tasman Mountains in Victoria and New South Wales.,

Outline of the Variscides in Central Europe

From north to south a pre-zone and three Variscan mountain arcs can be distinguished, which differ greatly in their geological structure. Today, tremendous fault zones separating these regions from each other.

• Subvariszische foredeep or Subvariszische foredeep with strong paralischer coal formation ( cyclic change between swamp forests and sea ( burial and coalification ) ): from Ardennes via the Ruhr region to Upper Silesia.
• Rhenoherzynikum (named after the Rhine and resin ) resin, Rhenish Massif, Ardennes, southern England (particularly Cornwall), Southern Portugal.
• Saxothuringian (named after Saxony and Thuringia ): Sudetes, Ore Mountains, Franconian Forest, Thuringian Slate Mountains, Thuringian Forest, Spessart, Odenwald, Northern Black Forest, Vosges du Nord.
• Moldanubicum (named after Moldova and Danube ): Bohemian Massif, Black Forest, the Vosges, the Massif Central, Armorican Massif, Zentraliberische zone. In this geologically oldest part of the mountain most of the magmatism took place (mostly granites, as well as smaller amounts of mafic rocks ) held during the orogeny.

The geological interpretation of these units as well as you associated fault zones, as for example former subduction zones and thus be the former present a Saxothuringian or Moldanubian Ocean is partly still subject of current research discussions.

Outline of the Variscides in North America

The Südappalachen be divided from west to east in several runs approximately from north to south belt.

• Appalachian Plateau ( foreshore )
• Valley -and- Ridge Province, foreland thrust belt, east of the Blue Ridge Province in subsequent flat overthrust web far beyond postponed ( Grandfather Mountain Window )
• Blue Ridge Province, Piedmont ( metamorphic core of the Südappalachen ), Interior Piedmont ( annexation to America about 500-450 Ma, taconische phase)
• Piedmont ( metamorphic core of the Südappalachen ): Charlotte belt and Carolina slate belt ( annexation to America about 380 Ma, Acadian phase)
• Coastal Plain (passive Riftrand of the Atlantic since 200 Ma), younger rocks over remains of the Charlotte belt and Carolina slate belt

Across the Atlantic form the so-called Mauritanides to the North African west coast since 200 Ma passive Riftrand of the Atlantic. Before the opening of the Atlantic, they were among today's Appalachian Mountains. Here looking thrusts are preserved to the east, where metamorphic layers, which are the rocks of the Carolina slate belt similar, were not stacked on top of metamorphic foreland, which belongs to Africa. These rocks are considered as the suture zone alleghenischen orogeny (collision of Africa as part of Gondwana with North America in Laurussia before 270 Ma).

Formation

During the Variscan orogeny the collision occurred several micro- continents (see also: Armorica ) with the existing northern continent. This led in Europe after partial shallow marine flooding the unfolding of a system of high mountains, which lasted in several phases from the Devonian to the end of the Paleozoic. The remains of these orogens can be found as the tail and low mountain range in western and central Europe again.

This mountain system was preceded by the formation of a northern continent of the continental blocks of Laurentia and Fennosarmatia, merged in the Ordovician ( 490-440 Ma) as a result of the Caledonian orogeny. Remnants of older Precambrian metamorphic basement are detected in the subsurface of Bohemia, Thuringia and by the Upper Rhine. About the starting material relatively little is known datings of individual mineral inclusions in these rocks were age, which probably date back to far older, sometimes even archaic (about 3.2 billion years ) orogenic phases.

The existing old land mass sank to the Variscan trough. Mighty sediments were deposited here, which led to high pressure and high temperatures of the underlying rock strata and subsequently at their metamorphic transformation. By plate tectonic processes, especially by the approach of the African plate to the Eurasian plate, worked during the pressure from the southeast. This resulted in zones with large-scale bulges and hollows. It followed the unfolding of the Variscan high mountains. The resulting by the orogeny Hochgebirgszug Central Europe, which is also called Carboniferous Alps was about 600 km long and had an average height of probably about 5 km, which corresponds roughly to the present-day Tibetan plateau.

Simultaneously with this orogeny put a severe erosion, which increases with increasing distance from the sea level (increased relief energy ). In the warm climate, the coal seams of the Ruhr caused by covering of organic layers with the eroded sediments. At fault lines magma could ascend and led to volcanic activity or the formation of underground plutons.

As early as the Permian Variscan high mountains to the so-called Permian peneplain was eroded and was overlain by sedimentary layers. This hull Mountains have been preserved after a new tectonic uplift by the formation of the Alps as Variscan Islands ( plateaus ) between the younger rocks of the Mesozoic era. These are partially cut by fluvial erosion processes and are also known as Riedel. In the course of another geologic faulting, which shaped the still existing highlands followed.

Just before the beginning of the Variscan orogeny originated in Devon by the submarine weathering of volcanic rocks with numerous deposits Roteisenerzen that were mined in iron ore mines. In the Lower Carboniferous greywackes were deposited in many places, which ( million years ago, 322-290 ) show a main phase of mountain building in the time of the Upper Carboniferous. The originally flat- deposited rock units were folded, broken and geschiefert. From argillaceous rocks today's slate, which were won long as roofing slate emerged.