A French research team has just set up a short-term seismic observatory around Narsaq (Greenland) to study an ancient rift. The region’s billion-year-old magma intrusions have intrigued geologists for centuries. A high concentration of rare minerals also makes this a unique site.
When Erik the Red arrived in Greenland at the dawn of the second millennium, he found “mountains beneath the glaciers” and settled in the verdant Gardar region. Using red sandstone to build a church in honor of his Christian wife, he had no idea that this rock came from a great rift active over a billion years ago. Nor did he have any idea of the mineral wealth that lies beneath Eriksfjord. Gardar is home to a wealth of rare minerals, known since the late 18th century. While these deposits are well identified, the mechanisms by which this (now ancient) collapse rift came into being are still incomplete in the eyes of scientists. Laurent Geoffroy, a geologist at the University of Brest, is interested in the history of rift formation. He has just returned from a three-week expedition during which he set up 15 seismic stations to measure the thickness of the earth’s crust and mantle, with logistical support from the French Polar Institute and the sailing boat Vagabond led by Éric Brossier and France Pinczon du Sel.
“The village of Narsaq is at the center of the region of interest,” explains Éric Brossier, referring to a maze of fjords over 100 kilometers long, where summer navigation is relatively peaceful. This year, its access from the Labrador Sea was blocked by patches of pack ice, which broke up in large quantities in north-east Greenland before drifting southwards. “Coming from Hopedale [province of Newfoundland and Labrador, Canada, ed. note], we had to head northwest up the coast before finding a passage,” he recalls. “As we entered the fjords, the temperature of the surface waters rose to around 10°C, and they were dark and full of sediment. The charts are inaccurate; there are a few sandbars and lots of icebergs.”
Vagabond has a flat bottom and shallow draught, and its crew knows the area well. With Laurent Geoffroy and fellow geophysicist Christian Schiffer, they found the 20-foot container sent by the French Polar Institute to Narsaq, loaded with seismic equipment, 35 batteries weighing 45 kilograms each and concrete blocks. “One ton of cargo doesn’t affect our 30-ton sailboat,” says the captain. “Especially not when we’re sheltered from heavy weather.” In this way, Éric Brossier and his acolytes cross from small bays to coves before deploying the seismographs on foot. “It was an intense physical effort to get to the spots,” explains Laurent Geoffroy, back in Brest. The team carried the equipment several hundred meters to reach the dykes on Tuttutooq Island.
Lava intrusion
“Originally, dyke is an English word that describes a wall. They are long, vertical magmatic rock formations about a metre thick on which walls could be built,” explains Adrian Finch, a geologist at the University of St Andrews in Scotland, who has been working in the area for 35 years. “But at Gardar, these dykes are up to 800 metres wide; they’re gigantic, which is quite rare.”
“When I went to Tuttutooq, it was to study the ancient rift that must have resembled today’s East African active rift – long, flat valleys lined with active volcanoes, with quite specific chemistry and rock types,” explains Lot Koopmans, an Oxford University geologist who worked on the island of Tuttutooq during his early scientific work with Adrian Finch.
Over a billion years ago, above the Earth’s core, the solid matter of the Earth’s surface stretched across this rift. Lava from pressurized magma chambers probably rushed into breccias and rectilinear fractures. “The width of the giant dykes is perhaps the result of a succession of breaks and lava intrusions in the same place”, says Adrian Finch, not ruling out other hypotheses.
Mineral outcrop
Brian Upton, emeritus researcher at the University of Edinburgh, explained (two years ago) to Geology Bites that the lava in the Gardar intrusions is rich in fluoride, an element that makes the magma more liquid. Under these conditions, elements such as gold, sodium and uranium could concentrate more easily in the magma not far from the surface. The origin of this rich fluoride content remains an open question. It is probably linked to granites in the Earth’s crust that were remelted during magmatic activity…
Concrete witnesses to tumultuous geological events, a few precious stones and mineral crystals sparkle in the rift remnants. At Ivittuut, for example, Inuit used the cryolite outcrops to make washing soda. On this Gardar site, a major deposit was discovered in the 18th century and mined in the 19th and 20th centuries. “Cryolite is essential for melting aluminum. It was thanks to this mine that Allied aircraft in the Second World War were lighter than those of the Nazis,” explains Adrian Finch. “The Nazis didn’t have access to this critical mineral, and their planes were built in steel.”
The Ivittuut deposit is said to contain a dozen rare minerals, while according to Brian Upton, near Narsaq, the Ilimaussaq magmatic intrusion contains over 220. “I would suspect very strongly that Mr. Trump’s bid to buy Greenland from Denmark was first and foremost concentrated on Ilimaussaq and one or two others in the Gardar province,” he explained.
Gardar’s magmatic intrusions have brought to the surface rare minerals indispensable for the manufacture of magnets, wind turbines, batteries… today sought after by the renewable energy sector.
A geological laboratory
“In 2021, there was a misalignment between the interests of the companies and the wishes of the locals”, recalls Adrian Finch, particularly concerning uranium-rich rocks near Narsaq. The company responsible for exploring the resources went against the wishes of the local population, leading to an outcry and the halting of the mining project. Unlike the industrialists, university scientists work in the region with a completely different objective and the approval of the local authorities. “We maintain good relations with the populations whose rocks we study”, says Adrian Finch.
“I’m not interested in rare earths or uranium-rich rocks, my research concerns the history of the ancient rift and I’d like to compare it with the ancient North American rift in the Great Lakes region,” explains Laurent Geoffroy. Studying the Gardar rift could be useful for understanding other parts of the world. “The advantage of Greenland is its exposure: there are a lot of rocks. If you go to the west of France, for example, there are fields, but not many rocks, so it’s harder to see what’s going on underground,” explains Lot Koopmans.
The seismic stations have been installed perpendicular to the giant Tuttutooq dykes in the Narsaq region. For one year, they will record the seismic waves generated in Japan, for example, which cross the globe and pass through the lithosphere. This will enable Laurent Geoffroy to deduce the thickness of the earth’s crust and part of the mantle of this ancient rift. A magnitude 4.5 earthquake shook the southern tip of Greenland just after the equipment was installed. “We felt it on board Vagabond moored in Narsaq”, Éric Brossier tells us. “A godsend for our mission, we’ll have some interesting data to study once we’ve recovered the stations.”
Next summer, the expedition will resume, to dismantle the seismographs and perhaps continue with the analysis of the surrounding rocks.
Camille Lin, Polar Journal AG
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