Fragment of Ancient Lost Continent Off the Coast of Canada Revealed in Rocks From Deep Beneath the Surface

A previously unknown fragment of an ancient continent has been discovered by researchers studying rock samples on Baffin Island in the Canadian territory of Nunavut.

According to a study published in the Journal of Petrology, the team of scientists were investigating pieces of kimberlite—igneous rocks that sometimes contain diamonds—when they noticed that their mineral signature closely matched an ancient part of Earth's crust known as the North Atlantic craton (NAC.)

Cratons are large, stable blocks of the Earth's crust usually found in the middle of tectonic plates that form the basis of continents. For example, the North American craton, or Laurentia, sits at the geological core of North America.

However, the continental plate of the NAC, which stretches from Labrador in Canada, to the southern part of Greenland and northern Scotland, began fragmenting more than 150 million years ago,

"Cratons are the ancient heart of Earth's continents—they were formed and stabilized during the Archean Eon, 4,000-2,500 million years ago," Nicholas Gardiner, a researcher from the University of St. Andrews, U.K., who was not involved in the study, told Newsweek. "They are rigid, and resist the tectonic forces that form mountain belts. Since they contain Earth's oldest rocks, cratons are our record of how the Earth evolved through key points in its history, from a time when the planet was unrecognizable from today towards more recent tectonic processes.

"[The NAC] contains some of Earth's oldest rocks—up to 3,900 million years old in west Greenland. It was most recently part of the super continent Pangaea, which started to breakup about 175 million years ago with the southern rifting of Gondwana, and then more recently the opening of the North Atlantic about 50 million years ago split it further."

The authors of the latest study say mineral signatures in the rocks they found in southern Baffin Island indicate this region hides piece of the NAC, while suggesting the craton may have had a bigger geographic extent—around 10 percent larger—than previously thought.

"The mineral composition of other portions of the North Atlantic craton is so unique there was no mistaking it," Maya Kopylova, a geologist from the University of British Columbia, Canada, and lead author of the study, said in a statement. "It was easy to tie the pieces together. Adjacent ancient cratons in northern Canada—in northern Quebec, northern Ontario and in Nunavut—have completely different mineralogies."

Identifying where the fragments of the NAC are today can help researchers to understand how they evolved over time, casting light on the history of Earth's plate tectonics.

"Finding these 'lost' pieces is like finding a missing piece of a puzzle. The scientific puzzle of the ancient Earth can't be complete without all of the pieces," Kopylova said.

The key to the latest findings were the kimberlite rocks that formed deep below the Earth—between depths of around 90 and 250 miles—millions of years ago. Over time, these rocks are pushed to the surface by geological and chemical forces.

"Kimberlites are deep-sourced magmatic intrusions—they are what bring diamonds to the surface—and they can help us understand the geological history of the craton by sampling pieces of its interior as they ascend," Gardiner said. "The study looks at rocks—so-called xenoliths—entrained in kimberlites from Baffin Island. Cratons comprise both a crust and a rigid upper mantle part—the so-called lithosphere—and the scientists studied peridotite and pyroxenite xenoliths, which originate from the upper mantle.

Baffin Island, Canada
Stock photo: An image of Baffin Island, Canada. iStock

"Baffin Island is not universally believed to represent part of the North Atlantic Craton. However, geochemical analysis of the xenoliths provided distinctive geochemical fingerprints, which are a unique match for similar rocks found in West Greenland within the core of the North Atlantic Craton. The implications of the study is that the lithosphere underneath Baffin Island was once part of the North Atlantic Craton, which may have separated, or rifted, off during its breakup."

The authors of the latest study say this is the first time that geologists have been able to reconstruct the size and location of ancient continents based on rocks that lie deep down in the Earth's mantle.

"With these samples we're able to reconstruct the shapes of ancient continents based on deeper, mantle rocks," Kopylova said. "We can now understand and map not only the uppermost skinny layer of Earth that makes up one percent of the planet's volume, but our knowledge is literally and symbolically deeper.

"The study is fairly unique in using mantle-derived rocks to fingerprint cratonic roots."