One of Africa's Tectonic Plates Is Rotating in a Different Direction to All the Others

A small tectonic plate that is forming on the continent of Africa is rotating in the opposite direction to all the others, and scientists believe they now know the reason why.

The microplate, or rift branch, known as the Victoria plate, is one of several sections of the East African Rift System—a newly developing tectonic boundary, where the African plate is in the process of splitting in two. The Victoria plate is moving counterclockwise, in contrast to the other microplates, Rovuma and Lwandle, further to the south.

"The East Africa Rift System has long been recognized as a place of continental break up," Anne Glerum, a Geodynamic Modeler at the German Research Centre for Geosciences GFZ, told Newsweek. "The landscape itself is the beautiful evidence of this process, with its deep valleys and high rift shoulders that are easily visible from space."

Glerum is lead author of a study published in Nature Communications that examines the movement of the microplates. She said global satellite positioning systems have shown how the Victoria microplate moves in the opposite direction to the others for the last two years. What is behind this is debated.

tectonic plates
Image depicting Earth's tectonic plates. The East Africa Rift System may lead the African plate to be split in two. iStock

Previously, it was thought the rotation direction was related to mantle plumes beneath the surface. This is where hot rock from Earth's mantle is thought to rise upwards. Glerum and colleagues had been studying the East Africa Rift System because it is "a textbook example" of active continental rifting. "Looking at geological maps of the system, we noted the peculiar geometry of the two curved, overlapping rift branches and the mobile belts," she said.

They started looking at what could be causing the unusual rotation of the Victoria microplate that could be tested with software. Findings showed the movement was related to the lithosphere—the solid, outer part of Earth—rather than a mantle plume. They found certain regions of the lithosphere were weaker and stronger, and these differences were the primary driver behind the direction of rotation. The differences in lithospheric strength led to curved rift branches that were being rotated by the movements of the major tectonic plates.

The team now plans to continue studying the East Africa Rift System to develop more realistic models that incorporate other contributing factors, like mantle plumes.

What will happen to the East Africa Rift System and its microplates in the future is not known, but Glerum said the rifting may continue until the African plate breaks up and a new ocean forms. "The same has happened to the north of the [East Africa Rift System], where new oceanic crust has formed in the Red Sea and the Gulf of Aden," she said. "If a break-up is successful, it is likely that only the Western or the Eastern Branch...will become a new ocean basin, but which one will be the winner is impossible to predict in the moment. Of course, the rift system could also fail and never reach breakup."

Africa
Africa from space. iStock
One of Africa's Tectonic Plates Is Rotating in a Different Direction to All the Others | Tech & Science