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For centuries, scientists have thought that the British mainland was the result of the meeting of two land masses, known as Avalonia and Laurentia, more than 400 million years ago.
Now, a study published in the journal Nature Communications proposes that a third land mass, known as Armorica, could also have played a role in its formation, revealing an old connection between Britain and France.
"The results showed that much of southwestern Britain has geological roots identical to those of France," said lead author of the study, Arjan Dijkstra. , from Plymouth University. Newsweek. "Geologically speaking, we are referring to the fragment that makes up France, Spain and other parts of southern and central Europe such as Armorica."
"So we have a bit of Armorica in Britain, which we do not know," he said. "This means that Britain is not composed of two continental fragments as we have always thought. [Laurentia in the North, Avalonia in the south], but that there is a ribbon of Armorica also in the south [Cornwall and South Devon]. "
The results are unexpected given that Britain is one of the best studied regions in the world in terms of geology. "It's a surprise to find that we've missed that so far," Dijkstra said.
The team came to its conclusions after examining the mineral properties and exposed rock elements in the southwestern British continent, particularly the counties of Devon and Cornwall.
"We have unusual volcanic rocks dating back 300 million years – lamprophyres – in southwestern Britain that are generally ignored because they are quite unusual and complicated," said Dijkstra. "Geologists still do not understand exactly how they are formed and they do not fit in most of our rock classification systems."
To try to illuminate these mysterious rocks, he asked the student of his master, co-author of the study Callum Hatch, to begin studying with him a few years ago.
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"One thing we quickly developed is that the magma from which these rocks are formed must be 100 kilometers deep. [62 miles] or so – much deeper than the magmas that form ordinary volcanic rocks, "said Dijkstra. "It's a level on the Earth that we can not access directly – drilling only allows us to reach 10-14 kilometers maximum."
Intrigued, they visited a number of sites in the southwest, taking samples of rocks that they then chemically analyzed in the laboratory to understand what was happening beneath the surface.
"To our surprise, when we looked at their chemical compositions in detail, they formed two clear groups," he said. "A group had all the expected chemical properties based on what we knew of British geology. However, the other group was very different in terms of composition, and we found that they perfectly matched similar volcanic rocks of the same age in France, which also came from these depths.
These results, combined with previous research, have shown scientists that there is a clear border crossing Devon and Cornwall: the northern regions seem to share their geological roots with the rest of England and Wales, then that the whole south seems geological. linked to France and continental Europe.
According to Dijkstra, this way of thinking is totally new as to how Britain was created. It has always been presumed that the frontier of Avalonia and Armorica was under the natural boundary of the English Channel.
The discoveries could also explain the immense abundance of minerals, particularly tin and tungsten, in southwestern Britain – a situation that has long puzzled geologists.
"Interestingly, the mineral wealth for which the region is so famous – think Poldark"Only occurs on the Armorican geological fragment that we have mapped," Dijkstra said. "It has always been difficult to understand why this mining region stopped so abruptly on a map and is not really duplicated elsewhere in Britain."
"We suggest that this Armoric fragment contains the right ingredients to make the tin and tungsten deposits, but that's probably not the case with Avalonia.
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