Sub-Saharan Africa may be breaking apart within millions of years, and scientists believe they may be witnessing the early stages of this geological process.
The rift will occur along the Kafue Rift, part of a roughly 1,500-mile (2,500-kilometer) rift line from Tanzania to Namibia. Rifts are cracks in the earth’s crust that disturb the surface and can cause land subsidence and earthquakes. Thousands of Rifts exist around the world, and while most Rifts are inactive or dead, they occasionally reactivate.
Geologists believe the Kafue Rift Valley is long dead. But some experts now say it has shown signs of activity over the past few decades. Mounting evidence raises suspicions that the feature could become a new continental rift and, ultimately, could serve as a new boundary between tectonic plates, creating entirely new oceans in the process.
Previous studies have gathered these clues. The quakes were too weak to be felt but strong enough to be picked up by instruments, and the rise in underground temperatures, along with small changes in ground elevation detected by satellites, suggested possible tectonic activity in the area.
Now, a new study published Monday in the journal Frontiers in Geoscience goes one step further. “We have the first geochemical data from this region,” said Rūta Karolytė, who led the study and was then a postdoctoral researcher at the University of Oxford in the United Kingdom. “This is a completely different line of evidence that really reinforces our view that there is rifting activity in the area.”
Studying new continental rifts will help answer one of the most fundamental questions in tectonics.
“How do new plate boundaries begin? Mature plate boundaries are easy to identify. The earliest stages are much more subtle,” said Estella Atekwana, distinguished professor of Earth and planetary sciences at UC Davis, who was not involved in the study.
“If the Kafue Rift is part of a nascent plate boundary, it provides us with a rare opportunity to study the birth of a plate boundary before volcanic activity, large earthquakes and significant surface deformation override the original conditions.”
Clues for new sections
To gather evidence, Carolit and her colleagues collected samples from hot springs and geothermal wells in Zambia that occur naturally above the suspected rift valley. “The hot water bubbled to the surface and we sampled the gas produced from it,” says Karolytė, who is currently chief product scientist at Snowfox Discovery, a British natural hydrogen exploration company.
The researchers focused on studying the ratio between two types of helium – helium 3 and helium 4. The team looked for a telltale sign that the springs and wells were connected to the Earth’s mantle, the layer sandwiched between the Earth’s crust and the Earth’s hundreds of miles thick core. “We found more helium-3 than is usually found in the Earth’s crust, which is usually a sign of mantle fluids entering the water,” Karolytė added.
The researchers collected gas samples for their study from a hot spring in the Gwisho region of Zambia. – P. Vivien-Neal/Kalahari Geo-Energy and MC Daly/University of Oxford, UK
The results are only preliminary because the samples came from only six sites in a highly concentrated area. But the researchers also sampled two hot springs about 60 miles (95 kilometers) from the suspected rift valley and found no similar increase in helium-3 ratios.
Because as tectonic plates stretch and begin to break apart, material from the Earth’s mantle can reach the surface, the team believes this new geochemical data could serve as an early signal suggesting the formation of new plate boundaries.
Economic benefits
Tectonic plates are huge slabs of solid rock that range in size from hundreds to thousands of miles and can be up to about 120 miles (190 kilometers) thick. Ever since these plates formed early in Earth’s history, they have been sliding across the Earth’s mantle at a rate comparable to the growth of a fingernail. About 200 million years ago, shifting plates began to separate Pangea into today’s continents. The plates are still moving, and this movement drives geological processes such as earthquakes and volcano formation.
The boundaries between plates are mostly on the ocean floor, where they can slide past each other, squeeze together or drift apart. The borders are also areas of greatest seismic and volcanic activity.
Active, developing rifts can become plate boundaries—but not necessarily. “These cracks often start and stop, or they can expand a little and then stop again. It’s hard to predict what will happen,” Carolit said.
Africa already has a well-developed rift valley that is tens of millions of years old. The Great Rift Valley has several volcanoes and is seismically active. However, it takes a long time for new rifts to develop this way and then become plate boundaries. “In the fastest case, this could happen within a few million years. In the slowest case, it could take 10 or 20 million years,” said study co-author Mike Daly, visiting professor of earth sciences at the University of Oxford.
“Southern Africa is going to break apart, but before that you’re going to start seeing more earthquakes, and some volcanic activity, lava flowing out. You’re going to start to get very deep fissures, and water is going to start to stagnate in them, so you’re going to have lakes and eventually seas like you have in East Africa today,” he added.
In the near term, however, Zambia could benefit economically from harnessing energy—geothermal power plants are emerging in the region. The landlocked country might even be able to collect helium, which is in high demand and has a variety of applications in the medical and technology industries.
A bird’s eye view of the Kafue River swamps in Zambia. – D’Agostini/Getty Images
To confirm these findings, the researchers are collecting more gas from a wider geographic area along the suspected rift, and they are already working on a new study to get broader results.
Answer basic questions
Folarin Kolawole, an assistant professor in the Department of Earth and Environmental Sciences at Columbia University in New York who was not involved in the study, calls the findings novel and exciting because they provide “strong evidence” that fluids flow directly up from the mantle to the surface through newly formed rift zones.
“The key significance of the new plate boundary in Southwest Africa is that we now have an established pathway for the continent to break apart from East Africa, through Botswana and Namibia, to the Atlantic Ocean,” he added in an email.
The sample size is limited, but the results are still significant, said UC Davis’ Atkwana. “They provide strong geochemical evidence that the Kafue Rift is still active at depth, even though magma has not yet reached the surface,” she wrote in an email.
However, Atekwana added that more evidence is needed along the entire proposed boundary to determine whether the helium signal in the mantle is continuous or just localized. “This is an important piece of evidence, not a final conclusion. It supports the hypothesis of early rifting, but confirmation of new plate boundaries requires full plate boundary-scale testing,” she said.
“This doesn’t mean that Africa is going to break apart tomorrow; these processes continue for millions of years. But from a scientific perspective, it’s like capturing a plate boundary at its birth.”
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