Geologists discover that the fragmentation of Africa is advancing faster than expected

More than 200 million years ago, the current continents were part of a single supercontinent. Over time, the tectonic plates have separated to form the known Earth. These plates continue to move extremely slowly: where they converge they form mountains, while where they separate, seas or oceans are born. On the African continent, a team of geologists from Columbia University (USA) has observed that its fragmentation will occur sooner than expected by discovering an active crack that has reached a "critical threshold", which will cause the separation of two plates and the creation of a new ocean.

This process is taking place in the East African Rift system, where the African plate is splitting into a huge Nubian plate to the west, which comprises most of the continent, and the much smaller Somali plate, which encompasses much of the eastern coast and the island of Madagascar. "We have discovered that the fracture in this area is more advanced, and the crust is thinner, than anyone had recognized," says geoscientist and lead author of the study, Christian Rowan, in a statement.

In the Turkana Rift, a low-lying, 500-kilometer-wide region spanning Kenya and Ethiopia and part of the East African Rift System, the African and Somali plates are moving apart at a rate of about 4.7 millimeters annually. As the researchers explain, during this process, the Earth's crust stretches horizontally, causing it to deform and fracture, thus releasing magma from the depths.

To carry out this discovery, published in the journal Nature Communications, the team analyzed seismic measurements previously made in the region and calculated the thickness of the crust in that area. The results showed that this cortex is much thinner than the researchers expected. Specifically, only about 13 kilometers thick in the center of the crack, when the crust is more than 35 kilometers thick at the edges of the rift region.

For scientists, when the crust in a rift zone thins below 15 kilometers, it enters a phase called "narrowing," and once that point is reached, continental breakup is practically inevitable. "The thinner the crust is, the weaker it is, which favors the continuity of the rifting process," explains Rowan, referring to the formation of rifts where the crust stretches.

The Turkana rift began to open about 45 million years ago, and researchers estimate that the narrowing began after an episode of widespread volcanic eruptions about 4 million years ago. For this reason, they calculate that this phase will be completed in a few million years—since it develops on a geological time scale—and then we will move on to the next phase, oceanization, that is, the formation of a new ocean.

It will then be when the magma will rise through the cracks and create a new seabed for the waters that will penetrate from the Indian Ocean, located to the north.

In addition, the scientists also found evidence of an earlier period of fracturing that did not culminate in continental breakup, but which weakened and thinned the crust, thus contributing to the current phase of fracturing. "This challenges some of the more traditional ideas about how continents break up," Rowan says.