The Atlantic Ocean widens thanks to the rise of magma

In March 2016, a research team dropped 39 seismometers to the bottom of the Atlantic Ocean off the western tip of Africa, to listen to the rumbles of earthquakes near and far. A year later, they uncovered a hidden story of how the continents move apart – not pulled to one side or the other by subduction zones, as previously believed, but can – being pushed aside by the swelling magma in the center of the ocean.

The probes were placed in parallel lines stretching over 600 miles, across the submarine ridge that branches off the Atlantic. The instruments were part of the PI-LAB and EURO-LAB projects, efforts to better understand a transition zone in the Earth’s mantle, the limit where the rigid lithosphere, making up the crust and upper mantle of the planet, hosts the underlying, weaker asthenosphere. To collect the data, a research team from the University of Southampton and the University of Oxford planted sensors on the ocean floor. The data they collected spanned nearly 400 miles around the planet. Data analysis by the team is published today in the journal Nature.

“The transition zone itself was thinner than expected,” Kate Rychert, a seismologist at the University of Southampton and chief cruise scientist to drop off and retrieve sensors on the high seas, said during a video call. “What this suggests is that we have upwelling from the lower mantle. It is unusually hot; generally, we believe that this does not happen under mid-ocean ridges. “

Rychert said such upwelling from the lower mantle is usually associated with Hawaii or Iceland, volcanic islands known to repeatedly gush out. At the Mid-Atlantic Ridge, however, the material ascends from the lower mantle to the upper mantle, but it is obviously not erupting. Just press firmly upward, suggesting to researchers that convection throughout the planet’s mantle may have a significant role in the tectonics of the plates that rest on it.

“The incredible results shed new light on our understanding of how the Earth’s interior relates to plate tectonics, with observations never seen before,” said Matthew Aguis, seismologist at Università degli studi Roma Tre and main author of the article, at a university. of the Southampton press release.

Initially, the plan was to better understand the definition and thickness of the tectonic plates of the Mid-Atlantic Ridge. The seismometers and magnetocaloric instruments on the ocean floor were going to image the plate, and the team expected the transition zone to be “very boring,” Rychert said.

Conventional wisdom has held that places like the Mid-Atlantic Ridge are relatively calm with respect to plate tectonics, and the true geopolitical theater of the plates was the subduction zones, where two plates converge and one is pushed back into the coat by the other. These changes are responsible for the imperceptible drift of the continents from each other. Under the Pacific, tectonic plates move faster, resulting in the dramatic “ring of fire” that produces seismic and volcanic activity around the perimeter of the ocean. The same cannot be said for the gradual march of the Atlantic plates, which are moving apart about 1.6 inches per year.

“Why this work is interesting for understanding plate tectonics is that if the material rises in the transition zone, it means that there is an ascending convection cell that pushes upward on the plates and pushes them. outward, ”said co-author Nick Harmon, also a seismologist at the University of Southampton, during a video call.

If you are considering pizza dough, this is the difference between making the pie by pulling on the edges rather than pushing in the center. Of course, the difference is that you are pushing on a planetary scale rather than pushing down on the culinary scale.

Until better seismic technology is developed, it can be difficult to get a better understanding of what is going on so deep in the mantle. Even the best data today reads like a “fuzzy CAT scan,” Harmon said. But downstream – and under the sea – they hope to learn more about the dynamics elsewhere along the ridge, as well as the situation within the tectonic limits below the Pacific.