Caledonian orogeny

The Caledonian orogeny was a mountain-building cycle that happened a very long time ago, about 490 to 390 million years ago. It took place in parts of the British Isles, Scandinavian Caledonides, Svalbard, eastern Greenland, and north-central Europe. This big change in the Earth's surface was caused when several land pieces, called continents and a small land piece called a microcontinent, moved together and crashed into each other.

The name "Caledonian" comes from Caledonia, the old Latin name for Scotland. A scientist named Eduard Suess first used this name in 1885 to describe the mountain building that happened in northern Europe before a time called the Devonian period. Since then, scientists have learned that the Caledonian orogeny happened in several steps over millions of years, and different parts of the mountains formed at different times.

This event helped shape the landscape of parts of Europe and shows how the Earth’s surface can change dramatically over very long periods. It is an important part of understanding how mountains are made and how continents move.

Palaeogeographic evolution prior to the orogeny

In the Neoproterozoic, most of Earth's land was part of a huge landmass called Rodinia supercontinent. As Rodinia broke apart, two important land pieces, Laurentia and Baltica, moved away from another large landmass, Gondwana. This movement created a new ocean called the Iapetus Ocean between them.

Later, another small land piece called Avalonia microcontinent began to move northward from near Gondwana. As Avalonia moved, it helped close the Iapetus Ocean and brought Laurentia, Baltica, and itself closer together. These movements set the stage for the mountain-building events known as the Caledonian orogeny.

Early orogenic phases

The Caledonian orogeny includes many tectonic events from the Cambrian to the Devonian periods, about 490 to 390 million years ago. These events happened as the Iapetus Ocean closed and continents like Laurentia, Baltica, and Avalonia came together.

Some early phases of mountain building happened in places like Norway, Sweden, and parts of the United Kingdom. For example, the Finnmarkian Orogeny in northern Norway began around 500 million years ago. Another event, the Jämtlandian Orogeny in Sweden, happened around 455 million years ago. In the Shelve area of England and Wales, the Shelveian Orogeny created folds and led to important changes in the landscape during the Late Ordovician period.

Main orogenic phases

The Caledonian orogeny was a series of mountain-building events that happened when several landmasses came together. These events happened between about 490 and 390 million years ago, mainly due to the closure of the Iapetus Ocean. The main phases include the Grampian phase, the docking of Eastern Avalonia with Baltica, the Scandian phase, and the Acadian phase.

During these phases, different parts of what are now Europe and North America collided. For example, parts of what is now Scotland and Ireland moved towards and joined with areas that are now part of England, Wales, and other regions. These collisions caused the land to push upward, forming mountains and changing the shape of the Earth's surface. The processes involved movements of large pieces of the Earth's crust, known as tectonic plates, and resulted in the formation of new landforms and geological features we see today.

Controversies

Some scientists believe that during the Caledonian orogeny, another small landmass called Armorica was also involved. This landmass included parts of southern Portugal, northern France, and sections of southern Germany and the Czech Republic. Armorica was not one single piece but a group of fragments, with the Armorican and Bohemian Massifs being the most significant today.

The exact position of these Armorica fragments between the Ordovician and Carboniferous periods is still debated. Some think the Bohemian Massif moved northward starting in the Ordovician, while others believe these fragments joined the southern edge of the combined landmass of Laurentia, Baltica, and Avalonia (called Euramerica, Laurussia or Old Red Continent) during a later event known as the Variscan orogeny around 340 million years ago. After the Caledonian orogeny, a basin called the Rhenohercynian basin formed at the southern edge of Euramerica.