While looking for a destination for his camping vacation on Quebec’s Côte-Nord, Joël Lapointe spotted on Google Maps what appeared to be a crater created by the impact of a meteorite from space. He then alerted the Meteoritical Society, in the hope that scientists from this organization would look into his discovery. This is how French researcher Pierre Rochette set about confirming the meteoritic origin of this depression, about fifteen kilometers in diameter, which contains Lake Marsal in its center, which is located about a hundred kilometers north of the village of Magpie.
The circular shape of the depression discovered by Mr. Lapointe immediately attracted the interest of Pierre Rochette, a geophysicist at the European Center for Research and Education in Environmental Geosciences (CEREGE) at Aix-Marseille University. In his eyes, the particular topography of the area strongly suggests that it is an impact crater.
The Geological Survey of Canada sent him rock samples that had been collected in the 1990s at the crater site. In one of the samples, he found grains of zircon, a mineral that “records the shock effect” caused by the very high pressure reached when an asteroid from the sky impacts the ground on which it crashes. Rochette hopes that by analyzing all the zircons present in the samples, he will provide proof that these rocks were subjected to “a very high pressure that can only be caused by an extraterrestrial impact.” Such pressures do not normally exist on the surface of the Earth, except in diamond deposits, he says.
“Zircon is a mineral that is found in small quantities in granites. When it is subjected to very high pressure, it transforms into another mineral called reidite, a bit like carbon transforms into diamond,” he explains. “And when the pressure is released, the reidite becomes zircon again, but a trace remains inside it that tells us that it has undergone a transformation. It is not exactly the same mineral that we find. The zircon is separated into very small grains, and these grains have orientations relative to each other that are specific to this transformation.”
So Mr. Rochette found zircon in one of the samples, and it appears in the form of small grains, which suggests that they were shocked. “But we have to study the orientation of these grains to prove that they did indeed undergo a large shock.”
The researcher’s team will also try to collect evidence of impact in the field, called cone shocks. “When the extraterrestrial object hits the surface, there is a shock wave that propagates through the rock and fractures and breaks it, creating these cone shocks. These are very particular fractures, cone-shaped rather than flat, and on these cones, it looks like a hair, or striations that are not all parallel but diverge. These types of phenomena only form during impacts,” he emphasizes.
He also hopes to collect other rocks that may have been melted by the impact, which would show signs of shock, or even traces of extraterrestrial material. “The problem is that the rocks present in this region are already rich in nickel, chromium and cobalt, which are elements that are often used as evidence of extraterrestrial origin. So it will be more difficult to see an extraterrestrial addition in these rocks,” he warns.
Geologists who explored the depression 25 years ago found molten rocks, called impact melt breccias, in the center of the ring, which they identified as volcanic rocks, but “which are typical of a meteorite impact,” Rochette said. These rocks look a lot like those found in the middle of the Rochechouart-Chassenon crater in France, he said. “These are likely rocks that were under the asteroid, and which, under the effect of the impact, fragmented, melted, mixed and cooled rapidly, which gives them a glassy appearance, similar to that of volcanic rocks.”
Exploration in sight
Mr. Rochette, who has studied impact craters all over the world, including two in the Canadian Arctic — the Hsughton Crater and the Tunnunik Crater — plans to come to Quebec next year to properly document the site of the possible Côte-Nord crater, in particular “to see how the floor of the crater is organized and to collect other samples.”
Already, from the images he has, Mr. Rochette estimates that the piece of asteroid that dug this crater was about two kilometers in diameter. “This crater has visibly been eroded, the impact probably took place a very long time ago,” he says. “If the impact occurred 100 million years ago, erosion by glaciers and rivers may have removed one to two kilometers of rock. The current topography between the edges and the bottom of the crater tells us that there is a 200-meter difference in height. What we see today was therefore probably two kilometers deep below the surface just after the impact.”
To date the moment of impact, the researcher will use isotopic methods, which consist of counting the radioactive isotopes that have disintegrated in a mineral (zircon contains uranium that disintegrates into lead). “By measuring the lead isotopes, we can determine how long the uranium has been trapped in this zircon,” he explains.
Rochette plans to explore the Marsal Lake site with Gordon Osinski, a fellow geologist from the University of Western Ontario. But to do so, they need to find the necessary funding.
Mr. Rochette hopes to complete his expedition to Quebec as soon as possible, ideally in September 2025. “We don’t discover new craters every day and we don’t want to be overtaken by colleagues who are friends but competitors!” he says.