http://www.sciencenews.org | February 27, 2021 11EARTH & ENVIRONMENTUpwellings may push continents apart
Mid-ocean ridges may play an unexpected role in plate tectonicsBY MARIA TEMMING
An upsurge of hot rock from deep
beneath the Atlantic Ocean may be driv-
ing 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 underly-
ing those continents drift apart. Scientists
typically think tectonic plates separate
as the distant edges of those plates sink
down into Earth’s mantle, creating a gap
(SN: 1/16/21, p. 16). Material from the
upper mantle seeps up through the rift
between the plates to fill in the seafloor.
But new seismic data 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 platessliding apart. Rather, deep rock push-
ing toward the surface may be driving a
wedge between the plates, researchers
report in the Jan. 28 Nature.
A better understanding of plate tec-
tonics, which causes earthquakes and
volcanic eruptions, could help people bet-
ter prepare for these natural disasters.
Matthew Agius, a seismologist at Roma
Tre University in Rome, and colleagues
glimpsed what’s happening beneath the
Mid-Atlantic Ridge using 39 seismome-
ters on the seafloor near a spot along the
ridge between South America and Africa.
Those sensors monitored rumbles from
quakes 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 seismom-
eters, the recorded tremors contained
clues about the location and movementof 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 observa-
tion,” says Jeroen Ritsema, a seismologist
at the University of Michigan in Ann
Arbor. 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 try-
ing 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 at other
mid-ocean ridges, could help determine
whether deep mantle material surging up
beneath these rifts really plays a major
role in seafloor spreading. s11_atlantic-ridge.indd 1111_atlantic-ridge.indd 11 2/10/21 9:56 AM2/10/21 9:56 AM