In March 2016, a research team dropped 39 seismometers to the bottom of the Atlantic Ocean from the western tip of Africa to listen to the roar of earthquakes near and far. A year later, they’ve got a hidden story of how the continents are growing further apart – not pulled from either side by subduction zones, as previously believed, but perhaps pushed apart by magma bulging in the middle of the ocean.
The probes were placed in parallel lines that stretched for 600 miles, over the diving line that twisted the Atlantic Ocean. The instruments were part of the PI-LAB and EURO-LAB projects, attempts to better understand a transition zone in the mantle, the boundary where the rigid lithosphere, which composes the earth’s crust and the upper mantle, greets the underlying, weaker ashenosphere. To collect the data, a research team from the University of Southampton and the University of Oxford planted sensors on the bottom of the sea. The data they collected stretched nearly 400 kilometers to the planet. The team’s analysis of the data is published today in the journal Nature.
“The transition zone was thinner than we expected,” said Kate Rychert, a seismologist at the University of Southampton and a chief scientist on the voyage to deposit and recycle the deep-sea sensors, in a video call. ‘What this indicates is that we have material from the lower mantle. It is abnormally hot; We usually think this does not happen under mid-ocean ridges. ”
Rychert said such lower mantle subspecies are usually associated with Hawaii or Iceland – volcanic islands known to erupt time and time again. On the Mid-Atlantic Ridge, however, material rises from the lower to the upper mantle, but it does not break out, of course. Just push firmly upwards, and the researchers suggest that convection in the entire mantle of the planet may play a significant 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 related to plate tectonics, with observations not seen before,” said Matthew Aguis, a seismologist at the Università degli studi Roma Tre and lead author of the article, explained in a University. of press release from Southampton.
Initially, the plan was to better understand the definition and thickness of the tectonic plates at the Mid-Atlantic Ridge. The seismometers and magnetocellular instruments on the seabed would image the picture, and the team expected the transition zone to be ‘very boring’, ‘Rychert said.
Conventional wisdom has said that 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 one is pushed into the mantle by the other. These shifts are responsible for the imperceptible creep of the continents apart. Under the Pacific Ocean, tectonic plates move faster, hence the dramatic “Ring of Fire” that delivers seismic and volcanic activity on the ocean’s perimeter. The same cannot be said for the gradual rise of the Atlantic plates, which move about 1.6 centimeters apart per year.
“Why this work is interesting to understand plate tectonics is that as material surges through the transition zone, it means that there is an upward convection cell that pushes up and out on the plates,” co-author Nick Harmon, also a seismologist, told the University of Southampton, in a video call.
If you are considering a pizza dough, it is the difference between making the pie by pulling the edges rather than pressing in the middle. Of course, the difference is that one ascends on a planetary scale, rather than imprinting on a culinary one.
Until better seismological technology is developed, it can be difficult to get a better understanding of what is happening so deep in the mantle. Today, even the best data reads like a “vague CAT scan,” Harmon said. But along the line – and below the sea – they hope to learn more about dynamics elsewhere along the reef, as well as the situation in the tectonic boundaries under the Pacific Ocean.