Caledonian orogeny

The Caledonian orogeny was a mountain-building event 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.

This event helped shape the landscape of parts of Europe and shows how the Earth’s surface can change over very long periods. It is important for 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 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 moved 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 changed the landscape during the Late Ordovician period.

Main orogenic phases

The Caledonian orogeny was a time when mountains were built. This happened when many pieces of land came together. These events occurred between about 490 and 390 million years ago. They mainly happened because the Iapetus Ocean closed up.

The main parts of this event include the Grampian phase, the time when Eastern Avalonia joined with Baltica, the Scandian phase, and the Acadian phase.

During these times, different parts of what are now Europe and North America bumped into each other. For example, parts of what is now Scotland and Ireland moved toward and joined areas that are now part of England, Wales, and other places. These bumps caused the land to push upward, making mountains and changing the Earth’s surface. Big pieces of the Earth’s crust, called tectonic plates, moved and created new landforms and features we see today.

Controversies

Some scientists think that during the Caledonian orogeny, a small landmass called Armorica was also involved. Armorica included parts of southern Portugal, northern France, and parts of southern Germany and the Czech Republic. Armorica was not one single piece but a group of fragments. The Armorican and Bohemian Massifs are the most important pieces 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. 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.