Researchers have found new evidence that a gigantic superplume of hot rock is rising beneath Africa, causing intense volcanic activity and splitting the continent in two.
Geologists have long known that Africa is slowly breaking apart in a region called the East African Rift System (EARS), but the driving force behind this massive geological process was up for debate. Now, a new study has presented geochemical evidence that a previously theorized superplume is pressing up against — and fracturing — the African crust.
Scientists found that gases at the Meengai geothermal field in central Kenya have a chemical signature that comes from deep inside Earth’s mantle, likely from between the bottom of the mantle and the core. The signature matches those of gases found in volcanic rocks to the north, in the Red Sea, and to the south, in Malawi, indicating all of these places are sitting on the same deep mantle rock, according to a statement from the University of Glasgow in Scotland.
“The deep mantle signatures observed in different segments of EARS are remarkably similar, suggesting that they all originate from a common deep source,” study first-author Biying Chen, a postdoctoral research associate in the School of Geosciences at the University of Edinburgh in Scotland, told Live Science in an email.
The researchers published their findings May 12 in the journal Geophysical Research Letters.
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EARS is the largest active continental rift system on Earth, ripping through around 2,175 miles (3,500 kilometers) of Africa. The lithosphere, Earth’s rocky outer shell of crust and upper mantle, has been gradually breaking apart across the rift for around 35 million years. This has left a network of valleys that carve through the top of the continent from the Red Sea off northeastern Africa to Mozambique in southern Africa.
Previous studies identified signs of a deep mantle plume beneath EARS in noble gas signatures. Noble gases, such as helium and neon, are rare and inert, which means they usually don’t chemically react with other substances. As a result, they stick around for a long time, so researchers can use them to trace long-term geological processes. However, Chen noted that these geochemical tracers have been sparse and often controversial beneath EARS.
To help clarify what’s going on beneath EARS, the team used high-precision instruments to look for neon (Ne) isotopes in Kenyan gases — and they detected a deep mantle signature. The signature in the gases is very similar to those of the most primordial (ancient) surface signatures in Hawaii, which is also thought to be sitting on a deep mantle plume.
“We were very excited to see the preliminary Ne isotope data showing the primordial deep mantle signature,” Chen said. “But the deep mantle signature is small and we had to work hard to disentangle it — truthfully there was no Eureka moment, we frequently questioned the result and spent many hours checking and re-checking the data.”
Once the team had rigorously assessed the data, they became confident that the signature was genuine and matched signatures found in other parts of the rift. Chen noted that the EARS plume likely originates from the core-mantle boundary, about 1,800 miles (2,900 km) deep inside the Earth.
While the EARS signatures are similar to those found in volcanic rocks on Hawaii, Chen noted that the Hawaii plume is proposed to be a discrete rising stream of hot mantle, a bit like a lava lamp, while the EARS plume is probably a different shape.
“More likely a large mass of upwelling of hot buoyant material from deep within the Earth has replaced the mantle that was originally beneath the EARS,” Chen said. “As it has risen and meets the solid colder lithosphere it spreads out generating enough force to fracture the thin lithosphere, leading to intense volcanic activity in the region.”
