2023-06-21 04:28:08
A team of researchers led by Virginia Tech geophysicist Sarah Stamps has gained new insight into unusual seismic activity within the world’s largest continental rift system. They found that the unusual deformations of the crustobserved in the rift system are primarily caused by the African Superplume – a tremendous upward movement from the Earth’s mantle.
Outermost crust is behaving strangely
Continental rifting is a geological process in which the lithosphere (the outer layer of the earth’s crust) is greatly stretched. However, the East African Rift system here shows an unusual pattern of deformations parallel to the rift. This phenomenon has puzzled geophysicists for years. Stamps’ team, which also includes the first author of the Studyowned by New Mexico Tech’s Tahiry Rajaonarison, has been studying these “anomalous deformations” for more than a decade, using GPS technology to precisely measure surface movements.
In analogy to bouncy kitt described Stamps the diverse deformation patterns observed on a rifting continent. “If you hit bouncy putty with a hammer, it can crack and break,” said the scientist from Virginia Tech’s Department of Earth Sciences. “But if you slowly pull it apart, the bouncy putty stretches. So, on different timescales, Earth’s lithosphere behaves differently.”
Researchers used advanced 3D thermomechanical modeling techniques to determine the source of these unusual deformations. They found that the African superplume, a giant mantle upwelling originating deep beneath Southwest Africa and moving northeast across the continent, is the driving force behind the unusual rift-parallel deformations and seismic anisotropy in the East African Rift System.
Die lithosphere is the outermost solid layer of the earth. It consists of the earth’s crust and the uppermost part of the underlying mantle. Together, these two layers form the lithosphere. It is divided into several large and small plates known as tectonic plates. These plates move slowly on the underlying, tougher part of Earth’s mantle known as the asthenosphere. The movement of these plates is responsible for the formation of earthquakes, volcanoes and mountain formations.
“We have confirmed previous assumptions”
Seismic anisotropy describes how rocks align in response to influences such as mantle flows, melt pockets, or pre-existing structures in the lithosphere. In the case of the outermost crust at the East African Rift System, the orientation follows the direction of the northward flow of the African superplume, which the team has identified as the source.
The team’s findings offer valuable insight into the debate over the forces driving the East African Rift System. While there is general agreement that lithospheric upwelling forces play an important role in the expected deformation perpendicular to the rift, these forces do not explain the anomalous deformation parallel to the rift.
“We say that mantle flow does not drive the east-west direction perpendicular to the rift of some deformations, but that it may drive the anomalous northward-directed deformation parallel to the rift. We have confirmed previous assumptions that lithospheric upwelling forces drive the rift, but we bring new evidence that anomalous deformations may occur in East Africa.”
Tahiry Rajaonarison
Quellen: „A Geodynamic Investigation of Plume-Lithosphere Interactions Beneath the East African Rift“ (Journal of Geophysical Research: Solid Earth, 2023); Virginia Polytechnic Institute and State University
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