Caledonian orogeny facts for kids
The Caledonian orogeny was a huge series of events that built mountains in parts of Europe and North America a very long time ago. Imagine giant landmasses slowly crashing into each other! This mountain-building happened from about 490 to 390 million years ago, during the Ordovician to Early Devonian periods.
It all started when a big ancient ocean, called the Iapetus Ocean, began to close. This ocean was between three major land blocks: Laurentia (which included parts of North America and Greenland), Baltica (parts of Scandinavia and Eastern Europe), and a smaller land block called Avalonia (parts of England, Wales, and eastern North America). When these land blocks collided, they pushed up the Earth's crust, forming mountain ranges.
The name "Caledonian" comes from Caledonia, the old Latin name for Scotland. Geologists first used this term in 1885 to describe these ancient mountain-building events in northern Europe. Today, we know that the Caledonian orogeny wasn't just one single event, but many different collisions and changes that happened over millions of years in various places.
Contents
How the Continents Moved Before the Mountains Formed
Long, long ago, most of Earth's land was joined together in a "supercontinent" called Rodinia. Think of it as one giant puzzle made of all the continents. Around 600 million years ago, Rodinia started to break apart.
Two large pieces, Laurentia and Baltica, began to drift away from a much larger landmass called Gondwana. As they moved, new oceans opened up between them. The Iapetus Ocean formed between Laurentia, Baltica, and Gondwana.
Later, a smaller land block called Avalonia also broke away from Gondwana. Avalonia then started moving northwest, heading towards Laurentia and Baltica. This movement caused the Iapetus Ocean to shrink as these land blocks got closer and closer. It was like three slow-moving ships heading for a collision!
Early Mountain-Building Events
Before the biggest collisions, there were some earlier, smaller mountain-building events. These events show that the Earth's crust was already active and changing.
For example, in northern Norway, there was an early event called the Finnmarkian Orogeny around 500 million years ago. Another event, the Jämtlandian Orogeny, happened in central Sweden about 455 million years ago. These were like early rumblings before the main earthquake.
In parts of Wales and England, the Shelveian Orogeny occurred in the Late Ordovician period. This event caused the land to fold and uplift, creating hills and valleys. It also led to some volcanic activity. These early phases were important steps in the long process of forming the Caledonian mountains.
The Main Mountain-Building Collisions
The biggest and most important parts of the Caledonian mountain-building cycle happened when the Iapetus Ocean finally closed. This involved a series of major collisions between Laurentia, Baltica, and Avalonia. These collisions created the impressive mountain ranges we see today (or their ancient roots).
The main phases were: the Grampian phase, the joining of Eastern Avalonia with Baltica, the Scandian phase, and the Acadian phase. These events happened from the middle of the Silurian period to the early Devonian period, roughly 420 to 405 million years ago.
Grampian Mountain Building
The Grampian orogeny involved collisions between parts of Laurentia (which included Scotland and northern and western Ireland) and a chain of volcanoes in the Iapetus Ocean. These volcanoes were like islands in the ocean. The other parts of the British Isles (England, Wales, and eastern Ireland) were part of the Avalonia land block at this time.
Avalonia's Two Parts
The Avalonia land block was actually made of two main parts:
- Western Avalonia joined with the eastern coast of what is now North America.
- Eastern Avalonia joined with Baltica and later with Scotland and northern Ireland.
Eastern Avalonia Joins Baltica
The eastern part of Avalonia gently joined with Baltica around 440 million years ago, near the end of the Ordovician period. This was more like a soft, sideways bump than a head-on crash. Because of this, it didn't create huge, dramatic mountains in places like southern Denmark, Poland, northern Germany, and Belgium.
The London–Brabant Massif is a large block of ancient rock found under central and southern England and Belgium. It shows evidence of the ocean closing beneath Avalonia.
The Trans-European Suture Zone
The Trans-European Suture Zone is like a long "seam" in the Earth's crust. It marks where Baltica and Eastern Avalonia finally joined together. This zone stretches from the North Sea, through southern Denmark, Poland, and into Ukraine. It's a very important geological boundary!
Scandian Mountain Building
The Scandian phase was a major collision between eastern Greenland (part of Laurentia) and the Fennoscandian peninsula (part of Baltica). This event created the Scandinavian Caledonides mountains in what is now Norway and Sweden. It happened from about 430 to 380 million years ago.
This collision also formed mountains in Greenland, like those in Queen Louise Land. The forces involved were immense, causing the land to fold, break, and slide over itself.
In Scotland and the outer Hebrides islands, this phase caused huge blocks of rock to be pushed over others, forming features like the Moine Thrust Belt. It also led to volcanic activity and the formation of large underground rock bodies called batholiths in places like Galloway and the Lake District in northern England. This activity crossed the Iapetus Suture zone, which is the line where the ancient ocean closed.
Acadian Mountain Building in the British Isles
The British Isles were once split between two different land blocks: Scotland and northern/western Ireland were part of Laurentia, while England, Wales, and the rest of Ireland were part of Avalonia. The Acadian event, which happened in the Early Devonian period, saw these parts finally join together to form the British Isles as we know them today.
This was another "soft docking" or gentle collision, where the land blocks came together with a lot of sideways movement rather than a direct head-on crash. This event caused folding and faulting across the region.
Northern England and the Lake District
The Lake District in northwestern England was at the edge of the Avalonia land block when it collided with Scotland. This collision caused the rocks in the Lake District to be squeezed and changed.
For example, soft mudrocks were turned into hard slates, which are still quarried today for roofing and other uses. Older rock groups like the Skiddaw Group and the Borrowdale Volcanic Group were folded and uplifted. The Windermere Supergroup, which formed in a basin, also experienced intense folding and squeezing during this time.
Isle of Man
The Isle of Man, located in the Irish Sea, sits very close to the Iapetus Suture line. The island is made of rocks like the Manx Group and Dalby Group. These rocks were strongly affected by the sideways squeezing and collision of the land blocks. This caused the rocks to fold and break, creating many faults.
Ireland
In Ireland, the Acadian orogeny affected all four main land blocks: Grampian, Midland Valley, Longford-Down, and Leinster. The collision here was mostly a sideways squeeze, so it didn't create extremely tall mountains. However, it did cause a lot of folding, faulting, and the formation of large underground rock bodies called plutons and batholiths.
For example, the Donegal batholith in the Irish Grampian area and the Leinster granite in the Leinster area are huge masses of igneous rock that formed during this period. The land was pushed, folded, and broken, shaping the landscape of Ireland.
The Iapetus Suture: An Ancient Seam
The Iapetus Suture is a very important geological line. It's like the "scar" or "seam" left behind where the ancient Iapetus Ocean finally closed up during the Caledonian orogeny.
In Ireland, this suture runs from the estuary of the River Shannon on the Atlantic coast, across the Irish Sea, and through the Isle of Man. In Britain, it runs roughly parallel to the border between England and Scotland. This suture also extends along the edge of Scandinavia and Greenland, marking where those landmasses collided. It's a powerful reminder of how much our planet has changed over millions of years!
See also
In Spanish: Orogenia caledoniana para niños
- Scandinavian Mountains
- Świętokrzyskie Mountains
- Geological structure of Great Britain
- Central Pangean Mountains
