Diamond-encrusted rock samples discovered on a Canadian island come from an ancient continent that was likely 10% larger than previously thought, geologists say in the Journal of Petrology , which publishes the study.
Fragments of the North Atlantic Craton, a large land mass that stretched from Europe to North America, were found on Baffin Island in northern Canada. Scientists stumbled upon them while searching for diamond samples in the area.
Baffin Island, located between the Canadian mainland and Greenland, is a vast Arctic expanse covering more than 500,000 square kilometers, making it the fifth largest island in the world.
Cratons are stable fragments of the continental crust
By analyzing igneous rock samples recovered from diamond exploration drilling in the Kimberlite province of Chidliak on the southern reaches of Baffin Island, the researchers identified a mineral signature in the rock that they did not expect to find, as it matches other parts of the North Atlantic Craton. They are about 150 million years old.
Kimberlite rock samples, formed millions of years ago at depths of 150 to 400 kilometers, are driven to the surface by geological and chemical forces. And sometimes these igneous rocks have diamonds embedded within them. In this case, the “passengers” were not diamonds but fragments of the Earth’s ancient continental crust that stretches from Scotland to Labrador.
” Finding these missing pieces is like finding a missing piece of a puzzle, ” said Maya Kopylova, a geologist at the University of British Columbia.
“The mineral composition of other parts of the North Atlantic craton is so unique that it cannot be mistaken,” continues Kopylova. “It was easy to put the pieces together. The adjacent ancient cratons in northern Canada, northern Quebec, northern Ontario, and Nunavut have completely different mineralogies.”
In geological terms, the emergence of these rocks below modern Baffin Island represents the end of a colossal dispersal that occurred approximately 150 million years ago, during the breakup of the North Atlantic Craton (NAC) continental plate. The NAC was present as a single continent before being divided into many fragments by the emerging seas and oceans.
The power of the kimberlites
To arrive at their findings, the team used a number of analytical techniques, including petrography, mineralogy, and thermobarometry, to study 120 rock samples, called xenolites, taken from the kimberlite province.
The results showed that the Chidliak mantle “remarkably resembles” the NAC rocks of West Greenland in terms of its bulk composition and mineral chemistry, while showing numerous contrasts with markers from other cratons. “We conclude that the Chidliak mantle demonstrates an affinity with only one adjacent block of cratonic mantle, the NAC,” the authors explain.
Because the new rock samples were found to a never-before-seen and unimagined depth in the earth, it suggests that this ancient land mass may have been even larger than previously believed.
“With these samples we can reconstruct the shapes of ancient continents based on deeper mantle rocks,” Kopylova said. “Now we can understand and map not only the highest thin layer on Earth that makes up 1% of the planet’s volume, but our knowledge is literally and symbolically deeper.”
Referencia: M G Kopylova et al. The metasomatized mantle beneath the North Atlantic Craton: Insights from peridotite xenoliths of the Chidliak kimberlite province (NE Canada), Journal of Petrology (2019). DOI: 10.1093/petrology/egz061
