Variscan orogeny: Difference between revisions
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In the [[Ordovician]] Period, a land mass, which has been named [[Gondwana]], straddled the space between the [[South Pole]] and the [[Equator]] on one side of the globe. Off to the west were three other masses: [[Laurentia]], [[Siberia]] and [[Baltica]], located as if on the vertices of a triangle. To the south of them was a large archipelago, [[Avalonia]]. |
In the [[Ordovician]] Period, a land mass, which has been named [[Gondwana]], straddled the space between the [[South Pole]] and the [[Equator]] on one side of the globe. Off to the west were three other masses: [[Laurentia]], [[Siberia]] and [[Baltica]], located as if on the vertices of a triangle. To the south of them was a large archipelago, [[Avalonia]]. |
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By the end of the [[Silurian]], a rift to the south of Avalonia had pushed the latter into north Laurentia, creating the Caledonide mountains. In the succeeding [[Devonian]], the rift entirely closed [[Iapetus Ocean]] between Avalonia and Laurentia, joining the two masses and thrusting up the northern [[Appalachians]] in the [[Acadian orogeny]]. Contemporaneously, the archipelago of southern Europe, which had been between Avalonia and Gondwana, was now pushed into Avalonia, creating a second range, the Variscan, to the east of the Caledonide/Appalachian. Both ran in a NW-SE direction |
By the end of the [[Silurian]], a rift to the south of Avalonia had pushed the latter into north Laurentia, creating the Caledonide mountains. In the succeeding [[Devonian]], the rift entirely closed [[Iapetus Ocean]] between Avalonia and Laurentia, joining the two masses and thrusting up the northern [[Appalachians]] in the [[Acadian orogeny]]. Contemporaneously, the archipelago of southern Europe, which had been between Avalonia and Gondwana, was now pushed into Avalonia, creating a second range, the Variscan, to the east of the Caledonide/Appalachian. Both ran in a NW-SE direction. |
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The Variscan belt was in place by the early Carboniferous. By the end of the Carboniferous, Gondwana had united with Laurentia. Siberia was approaching from the northeast, separated from Laurentia only by shallow waters. The [[Triassic]] Period of the [[Mesozoic]] Eon, animals could move without oceanic impediment from Siberia over the North Pole to Antarctica over the South Pole. This traversability especially assisted the spead of the mobile [[Dinosaurs]]. In the [[Cenozoic]] Eon, [[Laurasia]] divided from Gondwana, while Siberia with Baltica split from Laurentia. As a consequence, the Variscan Belt around the then periphery of Baltica ended up many hundreds of miles from the Appalachians. |
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==External Links== |
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*[http://www.scotese.com/newpage3.htm Early Devonian Map] |
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*[http://www.scotese.com/newpage4.htm Early Carboniferous Map] |
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*[http://www.scotese.com/late.htm Late Carboniferous Map] |
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*[http://www.scotese.com/newpage8.htm Triassic Map] |
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Revision as of 18:46, 10 August 2005
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The Variscan or Hercynian orogeny is a hypothetical sequence of events in geologic history that account for a group of highlands similar in age, stratigraphy, composition and fossils, called the Variscan Belt. It includes the mountains of Portugal and western Spain, southwestern Ireland and England, in France the Ardennes, Massif Central and Vosges, Corsica, Sardinia, in Germany the Black Forest and Harz Mountains, and in Czechoslovakia the Bohemian Massif. In the United States, the Variscan was contemporaneous with the Acadian orogeny, which raised the Appalachian Mountains, then continuous with the Caledonides, the mountains raised by the Caledonian orogeny.
The name, Variscan, comes from Variscite, a rare green mineral produced by the orogeny, first discovered in the Vogtland district of Saxony in Germany, which is in the Variscan belt. Variscite was named from the mediaeval Latin name for the district, Variscia, which undoubtedly comes from the name of a Germanic tribe, the Varisci. Hercynian, on the other hand, derives from the ancient name for the Black Forest, which then stretched across all southern Germany and parts of Czechoslovakia. The orogenic belt is the same, though it may not have all been raised in the same period.
The same plate movements that caused the Caledonian orogeny in the Silurian also were responsible for the Variscan orogeny in the succeeding Devonian Period (ca. 416-359 MYBP) and the Carboniferous Period (ca. 359-299 MYBP). Both resulted from the assembly of a supercontinent, Pangaea, which was essentially complete by the end of the Carboniferous.
In the Ordovician Period, a land mass, which has been named Gondwana, straddled the space between the South Pole and the Equator on one side of the globe. Off to the west were three other masses: Laurentia, Siberia and Baltica, located as if on the vertices of a triangle. To the south of them was a large archipelago, Avalonia.
By the end of the Silurian, a rift to the south of Avalonia had pushed the latter into north Laurentia, creating the Caledonide mountains. In the succeeding Devonian, the rift entirely closed Iapetus Ocean between Avalonia and Laurentia, joining the two masses and thrusting up the northern Appalachians in the Acadian orogeny. Contemporaneously, the archipelago of southern Europe, which had been between Avalonia and Gondwana, was now pushed into Avalonia, creating a second range, the Variscan, to the east of the Caledonide/Appalachian. Both ran in a NW-SE direction.
The Variscan belt was in place by the early Carboniferous. By the end of the Carboniferous, Gondwana had united with Laurentia. Siberia was approaching from the northeast, separated from Laurentia only by shallow waters. The Triassic Period of the Mesozoic Eon, animals could move without oceanic impediment from Siberia over the North Pole to Antarctica over the South Pole. This traversability especially assisted the spead of the mobile Dinosaurs. In the Cenozoic Eon, Laurasia divided from Gondwana, while Siberia with Baltica split from Laurentia. As a consequence, the Variscan Belt around the then periphery of Baltica ended up many hundreds of miles from the Appalachians.