In March 2016, a research team dropped 39 seismometers to the bottom of the Atlantic Ocean off the west tip of Africa to hear rumors of near and far earthquakes. A year later, they have found a hidden history of how continents distance themselves; they are not dragged on either side or by the subduction zones, as previously believed, but were perhaps separated by magma coming out of the center of the ocean.
The probes were placed in parallel lines spanning more than 600 miles, across the submarine ridge that forks the Atlantic. The instruments were part of the PI-LAB i EURO-LAB projects, efforts to better understand a transition zone in the Earth’s mantle, the boundary where it greets the rigid lithosphere, which makes up the crust and upper mantle of the planet. the underlying and weaker asthenosphere. To collect the data, a research team from the University of Southampton and Oxford University planted sensors at the bottom of the ocean. The data they collected spread about 400 kilometers to the planet. The analysis of the data by the team is published today in the journal Nature.
“The transition zone itself was thinner than we expected,” Kate Rychert, a seismologist at the University of Southampton and chief scientist of the cruise ships for depositing and retrieving altitude sensors, said in a video call. “What this suggests is that we have bottom mantle outcrop material. It’s abnormally hot; we usually think this doesn’t happen under the mid-ocean ridges.”
Rychert said these lower mantle swells are often associated with Hawaii or Iceland, known volcanic islands that erupt over and over again. On the crest of the Mid-Atlantic, however, the material rises from the lower mantle to the upper, but obviously does not erupt. Simply pressing firmly upwards, suggesting to researchers that convection across the planet’s mantle may play a substantial role in the tectonics of the plates resting on it.
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“The incredible results shed new light on our understanding of how the Earth’s interior is connected to plate tectonics, with observations that had not been seen before,” explains Matthew Aguis, a seismologist at the Università degli studi Roma. Tre and main author of the document. of the Southampton press release.
Initially, the plan was to better understand the definition and thickness of tectonic plates on the mid-Atlantic ridge. Seismometers and magnetocaloric instruments from the ocean floor were going to imagine the plate and the team expected the transition zone to be “very boring,” Rychert said.
According to conventional wisdom, places like the Mid-Atlantic ridge are relatively quiet when it comes to plate tectonics, and the real geopolitical theater for plates was the subduction zones, where two plates converge and the other pushes back. towards the mantle. These changes are responsible for the imperceptible fluidity of continents far apart. Under the Pacific, tectonic plates move faster, hence the dramatic “Ring of Fire” that produces seismic and volcanic activity on the perimeter of the ocean. The same cannot be said for the gradual march of the Atlantic plates, which are spaced at about 1.6 centimeters per year.
“The reason this work is interesting for understanding plate tectonics is that if the material flows through the transition zone, it means that there is a convective cell flowing upwards on the plates and expelling them.” , co-author Nick Harmon, also a seismologist at the University of Southampton, said in a video call.
If you consider a pizza dough, it’s the difference between making the cake by pulling on the edges instead of pushing it in the center. Of course, the difference is that it’s being pushed up on a planetary scale, rather than pushing toward a culinary one.
Until better seismological technology is developed, it can be difficult to better understand what goes on so deeply in the mantle. Today, even the best data reads like a “blurry CAT scan,” Harmon said. But along the line – and under the sea – they hope to know the dynamics elsewhere in the ridge, as well as the situation at the tectonic borders under the Pacific.