Scientists Uncover a Hidden Ancient Connection Between Britain and France

For centuries, scientists have thought the British mainland was created by the coming together of two landmasses more than 400 million years ago. These two continental blocks are known as Avalonia (in the south) and Laurentia (in the north).

But now, a study published in the journal Nature Communications proposes the idea that a third landmass, known as Armorica, may have played a significant role in its formation, revealing an ancient connection between Britain and France.

"The results showed that a large part of southwest Britain has geological roots that are identical to those of France," lead author of the study Arjan Dijkstra, from the University of Plymouth, told Newsweek. "Geologically speaking we refer to the fragment that makes up France, Spain, and other parts of southern and central Europe as Armorica."

"So, we have a bit of Armorica in Britain, which we didn't know about," he said. "That means that Britain is not made of just two continental fragments as we always thought, but that there is a sliver of Armorica too in the very south [Cornwall and South Devon]."

The findings are unexpected given that Britain is one of the best-studied regions in the world in terms of geology. "It is a surprise that we have missed this so far," Dijkstra said.

The team came to their conclusions after examining mineral properties and exposed rock features in the southwest of the British mainland, specifically the counties of Devon and Cornwall.

"We have some unusual 300-million-year-old volcanic rocks—lamprophyres—in southwest Britain that are generally ignored because they are quite unusual and complicated," Dijkstra said. "Geologists still don't fully understand how they form exactly, and they don't fit in most of our rock classification schemes."

In an attempt to shine a light on these mysterious rocks, he asked his Master's student, co-author of the study Callum Hatch, to start investigating them with him a few years ago.

"One thing we worked out quickly is that the magma from which these rocks formed must have come from quite deep, 100 kilometers [62 miles] or so—much deeper than magmas that form ordinary volcanic rocks," Dijkstra said. "This is a level in the Earth that we cannot access directly—drilling only gets us to 10-14 kilometers max."

Intrigued, they proceeded to visit a number of sites in the southwest, taking rock samples they later chemically analyzed in the lab to understand what was going on deep below the surface.

"Much to our surprise, when we looked in detail at their chemical compositions, they formed two clear groups," he said. "One group had all the chemical properties that we expected based on what we know about British geology. However, the other group was compositionally very different, and we found that they were a perfect match for similar volcanic rocks with the same age in France, which also came from these depths."

These results, in combination with previous research, indicated to the scientists that there is a clear boundary, or "suture", running across Devon and Cornwall: areas north of it appear to share their geological roots with the rest of England and Wales, while everything south seems to be geologically linked to France and mainland Europe.

This is a completely new way of thinking about how Britain was formed, according to Dijkstra. It has always been presumed that the border of Avalonia and Armorica was further south, beneath the natural boundary of the English Channel.

The findings may also explain the immense abundance of minerals, particularly tin and tungsten, in the southwest of Britain—something that has long baffled geologists.

"Interestingly, the mineral wealth that the region is so famous for—think Poldark—only occurs on the Armorican geological fragment that we mapped," Dijkstra said. "It has always been a bit of a puzzle why this mining region stopped so abruptly on a map and isn't really duplicated elsewhere in Britain."

"We suggest that this fragment of Armorica had the right ingredients to make the tin-tungsten mineral deposits, but Avalonia probably didn't."

Godfrey Fitton, a Professor of Igneous Petrology from the School of GeoSciences at the University of Edinburgh who was not involved in the study described the latest study as "interesting" but warns that we should be cautious about interpreting the results.

"The existence of this suture has long been recognised and was thought to run about 40 kilometers (25 miles) south of the new location proposed here," he told Newsweek.

"So, the present paper represents a possible adjustment to our understanding of the geological history of southwest England. It's been known since the early 1970s that the continental mass of the U.K. and Ireland has been assembled through repeated continental collisions, the most obvious of which happened about 400 million years ago when what is now Scotland was united with England."

"Later, at about 290 million years ago, Armorica, which now forms large parts of continental Europe, collided with the southern part of the U.K., he said. "The exact location of the join is difficult to locate precisely, but the present authors think they've done this and relocated the suture about 40 km north of its previously assumed location. They may be correct in this, but as with all such studies, the data are subject to alternative explanations."

Britain and France are not the only regions that have ancient geological connections to one other. Around 600 million years ago, the northwest of what is now the British Isles lay at the edge of a vast continent called Larentia, which forms the ancient geological core of the North American continent.

At other periods in its history Laurentia has itself been part of larger continents and super-continents. These changes in the make-up of the Earth occur due to the gradual movements of tectonic plates—vast slabs of the planet's crust—and changes in global sea levels over millions and millions of years.

This article has been updated to include additional comments from Godfrey Fitton.