Variscan orogeny

The Variscan or Hercynian orogeny is a geologic mountain-building event recorded in the European mountains and hills called the Variscan Belt. This occurred in Paleozoic times (from ~390 to ~310 mya) and reflects continental collision between Laurasia and Gondwana to form Pangea. This early collision was a precursor to the collision that caused the Variscan-Allegheny-Ouachita orogeny in Pennsylvanian times. The Variscan orogeny is sometimes also known as the Amorican orogeny.

The European Variscan Belt (also called Variscides) includes the mountains of Portugal and western Spain, south-western Ireland (i.e Munster), Cornwall, North Devon, Pembrokeshire, the Gower peninsula and the Vale of Glamorgan. Its effects are present in France from Brittany, below the Paris Basin to the Ardennes, the Massif Central, the Vosges and Corsica. It shows in Sardinia in Italy and in Germany where the Hunsrück, the Black Forest and Harz Mountains remain as testimony. Also, in the Czech Republic the Bohemian Massif is the eastern end of the Variscan belt of crustal deformation in Europe. The Variscan was contemporaneous with the Acadian orogeny in the United States, which raised the Appalachian Mountains; then continuous with the Caledonides, the mountains raised by the Caledonian orogeny.

The name, Variscan, comes from the Medieval Latin name for the district, Variscia, which undoubtedly comes from the name of a Germanic tribe, the Varisci. Variscite, a rare green mineral found in the region and first discovered in the Vogtland district of Saxony in Germany, which is in the Variscan belt, has the same etymology. Hercynian, on the other hand, derives from the Harz Mountains, in northern Germany.

Plate convergence that caused the Caledonian orogeny in the Silurian continued to from the Variscan orogeny in the succeeding Devonian (ca. 416-359 Ma) and Carboniferous (ca. 359-299 Ma) Periods. Both resulted in the assembly of a super-continent, 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, the terrane, Avalonia.

By the end of the Silurian, seafloor spreading to the south of Avalonia had pushed the latter into north Laurentia, creating the Caledonide mountains. In the succeeding Devonian, the Iapetus Ocean between Avalonia and Laurentia entirely closed, 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 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. Collision with Siberia produced the Ural Mountains in the latest Paleozoic. In the Triassic Period of the Mesozoic Era, animals could move without oceanic impediment from Siberia over the North Pole to Antarctica over the South Pole. This traversability especially assisted the spread of the mobile Dinosaurs. In the Cenozoic Era, 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.

External links

• Early Devonian Map
• Early Carboniferous Map
• Late Carboniferous Map
• Triassic Map