Rocks from a lost continent that broke up around 150 million years have been discovered deep beneath Baffin Island in northern Canada, providing new insights into the size and location of this ancient landmass.
The remarkable discovery was made entirely by accident when a team of scientists rummaged through a bunch of kimberlite rock samples that had been collected from the Chidliak Kimberlite Province by a diamond exploration company. Kimberlites are igneous rocks that formed millions of years ago at depths of hundreds of kilometers, and which are sometimes forced up to the surface by geological forces. They are of particular interest to diamond exploration companies as they occasionally bring these precious stones with them as they rise from the deep.
Writing in the Journal of Petrology, a team of researchers reveal how the samples they examined displayed a mineral structure that is only seen in rocks belonging to an ancient part of Earth’s continental crust called the North Atlantic craton (NAC).
Cratons are highly stable sections of the lithosphere that are billions of years old, and which modern continental plates formed around. While some cratons remain intact at the center of existing continents, the NAC has long since split into fragments. Portions of this craton have been found across a vast area stretching from Scotland to eastern Canada, via southern Greenland. Until now, however, no remnants of the NAC had been discovered as far north as Baffin Island.
The study authors were therefore extremely surprised to find such striking similarities between their kimberlite samples and the NAC. A particular giveaway was the composition of a magnesium iron silicate called olivine, which is a distinctive feature of the NAC that sets it apart from adjacent cratons in northern Canada.
“The mineral composition of other portions of the North Atlantic craton is so unique there was no mistaking it,” explained study author Maya Kopylova in a statement.
The discovery of fragments of the NAC in Baffin Island has major implications for our understanding of this ancient landmass, indicating it was some 10 percent larger than previously believed. Significantly, this is the first time that fragments of the planet’s continental plates have been retrieved from such immense depth, with previous reconstructions of these plates being based on rocks that formed at depths of 10 kilometers (6 miles) or less.
"With these samples, we’re able to reconstruct the shapes of ancient continents based on deeper, mantle rocks,” said Kopylova. “We can now understand and map not only the uppermost skinny layer of Earth that makes up 1 percent of the planet’s volume, but our knowledge is literally and symbolically deeper. We can put together 200-kilometer deep fragments and contrast them based on the details of the deep mineralogy.”