October 17, 2024
3 min read
Ancient Seafloor Discovered Slowly Sinking into Earth’s Mantle
A vast, ancient slab of seafloor plunged beneath the Pacific Ocean and has hovered in Earth’s mantle for more than 120 million years, a new study suggests
The Nazca plate is located to the west of South America’s Pacific coast. On the western edge of the Nazca plate is the East Pacific Rise, while the Nazca subduction zone runs along the eastern edge.
Naeblys/Alamy Stock Photo
An ancient slab of seafloor that was around when Earth’s earliest known dinosaurs emerged, has been discovered beneath the Pacific Ocean, where it has seemingly hovered in a sort of mid-dive for more than 120 million years.
In addition to illuminating geological processes deep inside Earth, the cold, descending slab of dense rock, located some 410 to 660 kilometers below the planet’s surface, could explain a mysterious gap between two sections of a giant blob in the mantle layer.
“This study provides a first present-day example of how a cold downwelling from above is breaking up a deep mantle blob,” says Sanne Cottaar, a professor of global seismology at the University of Cambridge, who wasn’t involved in the discovery. The paper was published online on September 27 in Science Advances.
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Deep beneath our planet, two gargantuan, continent-size blobs of sizzling material rise from Earth’s hot, liquid outer core into its rock-filled mantle layer. Scientists can’t directly see these megastructures, which are hundreds of kilometers tall and thousands of kilometers wide. Instead researchers infer their existence from imaging techniques that rely on the way seismic waves travel through them. Within the blobs, seismic waves slow down, leading to their more technical name, large low-shear-velocity provinces (LLSVPs). The larger and better understood LLSVP, called the African blob, sits beneath the East African Rift Valley, which runs from the Red Sea to Mozambique. There two tectonic plates are slowly moving apart and may eventually split the continent.
“At the East African rift zone, we have a present-day example of how a large hot upwelling mantle plume that originates at these deep mantle blobs (so…
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