An upwelling of rock beneath the Atlantic may drive continents apart

An upsurge of hot rock from deep beneath the Atlantic Ocean may be driving the continents on either side apart.

The Americas are moving away from Europe and Africa by a few centimeters each year, as the tectonic plates underlying those continents drift apart. Researchers typically think tectonic plates separate as the distant edges of those plates sink down into Earth’s mantle, creating a gap (SN: 1/13/21). Material from the upper mantle then seeps up through the rift between the plates to fill in the seafloor.

But new seismic data from the Atlantic Ocean floor show that hot rock is welling up beneath a seafloor rift called the Mid-Atlantic Ridge from hundreds of kilometers deep in Earth’s mantle. This suggests that material rising up under the ridge is not just a passive response to tectonic plates sliding apart. Rather, deep rock pushing toward Earth’s surface may be driving a wedge between the plates that helps separate them, researchers report online January 27 in Nature.

A better understanding of plate tectonics — which causes earthquakes and volcanic eruptions — could help people better prepare for these natural disasters (SN: 9/3/17).

Matthew Agius, a seismologist at Roma Tre University in Rome, and colleagues glimpsed what’s happening beneath the Mid-Atlantic Ridge using 39 seismometers on the seafloor near a spot along the ridge between South America and Africa. Those sensors monitored rumbles from earthquakes around the world for about a year. Because the seismic waves from those quakes traveled deep through Earth’s mantle on their way to the seismometers, the recorded tremors contained clues about the location and movement of material far below the seafloor.

In those signals, Agius’ team saw hints of material from Earth’s lower mantle, more than 600 kilometers below the seafloor, welling up toward the Mid-Atlantic Ridge. “This was completely unexpected,” Agius says, and it could be a powerful force for pushing apart the tectonic plates on either side of the rift.

“It’s certainly an interesting observation,” says Jeroen Ritsema, a seismologist at the University of Michigan in Ann Arbor who was not involved in the work. But it’s hard to tell how much deep mantle upwelling contributes to Atlantic seafloor spreading, based on observations from only one group of seismometers near the equator, he says. It’s like “you’re looking through a keyhole, and you’re trying to see what’s in the living room and the bedroom and the kitchen.”

Observations at other locations along the Mid-Atlantic Ridge, as well as other mid-ocean ridges around the world, could help determine whether deep mantle material surging up beneath these rifts really plays a major role in seafloor spreading.