Here lies one of the thickest sections of Earth’s crust
The thick crust in this area may be close to two billion years old.
The Varanger Peninsula in northeastern Norway may be an almost untouched remnant from Earth's early history. Normally, it is beneath high mountains that we find very thick crust. But on the Varanger Peninsula, the landscape is relatively flat.(Photo: Raimo Bergroth / Shutterstock / NTB)
The Earth's crust beneath the Varanger Peninsula in northeastern Norway is about 65 kilometres thick.
That is nearly as thick as the crust beneath the Himalayas and the Andes. Both are enormous mountain ranges with deep ‘roots’ extending down into the Earth's magma.
The crust beneath the Varanger Peninsula is therefore thicker than the crust beneath the Alps.
Almost two billion years old
Normally, a very thick crust is associated with high mountains.
Annonse
But the Varanger Peninsula, like most of Finnmark, has a relatively flat landscape.
Researchers have now proposed a possible explanation: The remains of a mountain-building event that took place almost two billion years ago may lie beneath Finnmark.
In other words, the mountain range is incredibly old.
Also beneath Finland
Similarly thick crust can be found beneath central Finland, which is also a fairly flat landscape.
These two areas of unusually thick and dense crust are not necessarily connected.
But they may have been created by fairly similar geological processes.
Thickness of the Earth's crust
The thickness of the Earth's crust varies greatly depending on whether it lies beneath oceans or continents.
Average for the entire Earth: around 17–18 kilometres.
Beneath the world's oceans (oceanic crust): on average only 6–7 kilometres thick.
Beneath the continents (continental crust): on average 35–40 kilometres thick.
Sources: U.S. Geological Survey and Encyclopaedia Britannica
A remnant of something very ancient
The extraordinary age of the crust beneath the Varanger Peninsula is just as remarkable as its thickness.
It is probably more than 1.8 billion years, according to the research group, which includes researchers from Sweden, Finland, Poland, and Norway.
The researchers have considered three possible explanations for why the crust beneath the Varanger Peninsula is so unusually thick.
One possibility is that large amounts of magma accumulated at the bottom of the crust in more recent geological time. But there are few traces of volcanic activity in Finnmark.
The second possibility is that the crust was compressed and became thicker during a continental collision. This could have happened either around 600 million years ago (the Timanian mountain range) or during another such collision around 400 million years ago (the Caledonian mountain range, which shaped much of Norway's bedrock). But this explanation also appears inconsistent with the geology of the Varanger Peninsula, where the bedrock shows little evidence of severe deformation.
This leaves the researchers with a final hypothesis: The Varanger Peninsula rests on an extremely ancient crustal block. This block could have formed during a mountain-building event nearly two billion years ago.
Ancient crustal block
The researchers therefore consider the most likely explanation to be that the Varanger Peninsula sits on a very ancient crustal block.
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It may have formed during a peviously little-known mountain-building event, dating all the way back to a time when the Earth was almost only half as old as it is today.
If this is correct, the Varanger Peninsula in Finnmark is an almost untouched remnant from Earth’s early history.
Geologists believe that remnants of an incredibly ancient mountain range may lie beneath the Varanger Peninsula. Pictured here is Nesseby Church by the Varangerfjord.(Photo: Trond Olav Holmen / Shutterstock / NTB)
Preliminary results
If the researchers’ interpretation is correct, it means that the northernmost part of Fennoscandia – Norway, Sweden, and Finland – is more geologically complex than previously thought.
The suspected ancient continental block and unusually thick crust beneath the Varanger Peninsula may also extend farther north beneath parts of the Barents Sea.
But the researchers emphasise that what they are presenting remain preliminary hypotheses.
The study is funded by research councils, research funds, and research centres in Sweden and Poland. Further research may give us greater insight into how the ancient crust beneath Norway was formed.
