Computer simulations confirm that the African superplume is causing the anomalous deformation and rift-parallel seismic anisotropy detected under the East African Rift system.
Geophysicist D. Sarah Stamps explains that continental fissures involve a combination of stretching and breaking that penetrates deep into the Earth’s interior. This process involves the stretching of the lithosphere, the hard outer layer of the Earth. As the tension in the lithosphere increases, the upper part of the lithosphere undergoes brittle changes, causing rock fractures and earthquakes.
Stamps uses computer modeling to study these processes and GPS Compare different deformation styles of rift continents to playing with Silly Putty to map surface motion with millimeter precision.
“If you hit silly putty with a hammer, it can actually crack and break,” says Stamps, an associate professor in the Earth Sciences Department of the Virginia Tech School of Science. “But if you pull them apart slowly, the silly putty will stretch. So the Earth’s lithosphere behaves differently on different timescales.”
Deformations associated with continental cracks, whether stretched or ruptured, usually follow predictable directional patterns for cracks. That is, the deformation tends to be perpendicular to the crack. The Earth’s largest continental rift system, the East African Rift System, shows deformation perpendicular to the rift. But after more than 12 years of his using GPS instruments to measure the crack system, Stamps also observed deformation going in the opposite direction, parallel to the crack in the system. Her team at the Institute of Geodesy and Geophysics has been working to find out why.
In a recent study published in Geophysical Research Journal, the team used 3D thermomechanical modeling developed by the study’s lead author, New Mexico Tech Postdoctoral Fellow and Ph.D. Did. Studied at Virginia Tech as a member of Stamps’ lab. His model suggests that the anomalous parallel rift deformation of the rift system is associated with a northward-facing African superplume that rises from deep Earth below southwestern Africa, advances northeast across the continent, and becomes shallower. It is shown that it is caused by mantle flow. as it extends north.
Their findings, combined with insights from a study published in 2021 by the researchers using Rajaonarison’s modeling techniques, suggest which plate-driving forces govern the East African Rift system and which are perpendicular to the Rift Valley. It may help clarify scientific debates about how to explain both deformation and deformation parallel to the rift valley. : lithospheric buoyancy, mantle traction, or both.
As a postdoctoral fellow, Stamps used data from a GPS station that measured signals from more than 30 satellites orbiting the Earth about 25,000 kilometers away to identify anomalous parallel rift deformations in the East African rift system. started observing. Her observations further complicated the debate about what drives the rift system.
Some scientists believe that the cracks in East Africa are primarily caused by lithospheric buoyancy. This buoyancy is primarily a relatively shallow force resulting from high fissured topography, known as the African superswell, and density changes in the lithosphere. Others point to horizontal mantle traction, a deeper force arising from interaction with the mantle flowing horizontally beneath East Africa, as the main driving force.
team’s 2021 survey Through 3D computational simulations, they discovered that cracks and their deformation can be caused by a combination of two forces. Their model showed that lithospheric buoyancy forces were responsible for the more predictable crack-perpendicular deformation, whereas those forces explained the anomalous crack-parallel deformation detected by Stumps’ GPS measurements. couldn’t.
In a newly published study, Rajaonarison again used 3D thermomechanical modeling, this time focusing on the causes of parallel crack deformation. His model confirms that the African superplume is responsible for the anomalous deformation and seismic anisotropy parallel to the rift observed under the East African rift system.
According to Stamps, seismic anisotropy is the orientation or alignment of rocks in specific directions in response to mantle flows, melt pockets, or existing structural structures within the lithosphere. In this case, the rock placement follows the direction of the northward mantle flow of the African superplume, suggesting that the mantle flow is its source.
“We say that mantle flows may not be driving some deformation east-west, perpendicular to the rift valley, but may be causing anomalous northward deformation parallel to the rift valley. We are doing it,” Rajaonarison said. “We confirmed previous ideas that lithospheric buoyancy drives cracks, but provide new insight that anomalous deformation can occur in East Africa.”
Learning more about the processes involved in continental rifts, including these anomalies, will help shed light on the complexities behind decades of attempts by scientists to create continental rifts. “We are excited about this result from Dr. Rajaonarison’s numerical modeling because it provides new information about the complex processes that shape the Earth’s surface through continental cracks.” said Stamps.
References: Tahiri A. Rajaonarison, D. Sara Stamps, John Narivov, Andrew Nyblade, Emmanuel A. Njinju, “Geodynamic Investigation of Plume-Lithosphere Interactions Under the East African Rift,” March 27, 2023, Geophysical Research Journal Solid Earth.
DOI: 10.1029/2022JB025800