Research by D. Sarah Stamps, using 3D thermomechanical modeling, revealed that the African Superpanache, a massive upwelling of the mantle, causes unusual rift-parallel deformations seen in the East African Rift system. This adds complexity to the debate around the primary forces driving rifting, suggesting a combination of lithospheric pushing forces and mantle pulling forces.
Computer simulations confirm that the African Superpanache causes unusual deformations and rift-parallel seismic anisotropy detected beneath the East African Rift system.
Continental rifting involves a combination of stretching and fracturing that penetrates deep into the Earth, says geophysicist D. Sarah Stamps. This process involves the elongation of the lithosphere, the rigid outer layer of the Earth. As it becomes more tense, the upper parts of the lithosphere undergo fragile changes, leading to rock fractures and earthquakes.
Stamps, who studies these processes using computer modeling and GPS to map surface motion with millimeter precision, compares the different styles of deformation of a fractured continent with a game with Silly Putty.
“If you hit Silly Putty with a hammer, it can crack and shatter,” said Stamps, an associate professor in the Department of Geosciences at Virginia Tech College of Science. “But if you take it apart slowly, Silly Putty stretches. Thus, at different time scales, the earth’s lithosphere behaves in different ways.
Whether stretching or rifting, the deformation that accompanies continental rifting generally follows predictable directional patterns relative to the rift: deformation tends to be perpendicular to the rift. The East African Rift System, the largest continental rift system on Earth, exhibits these deformations perpendicular to the rift. But after measuring the fault system with GPS instruments for more than 12 years, Stamps also observed deformation that ran in the opposite direction, parallel to the faults in the system. His team from the geodesy and tectonophysics laboratory sought to understand why.
Assistant Professor D. Sarah Stamps. Credit: Virginia Tech
In a recent study published in the Geophysical Research Journal, the team explored the processes driving the East African Rift system using 3D thermomechanical modeling developed by the study’s first author, Tahiry Rajaonarison, a postdoctoral researcher at New Mexico Tech who has obtained his doctorate. at Virginia Tech as a member of Stamps’ lab. His models showed that the unusual, parallel deformation of the rift system is caused by northward mantle flow associated with the African Superpanache, a massive upwelling of the mantle that rises from deep within the Earth beneath the southwest of Africa and heads northeast across the continent, becoming more shallow. as it expands north.
Their results, combined with information from a study published by the researchers in 2021 using Rajaonarison’s modeling techniques, could help clarify the scientific debate about the driving forces of the plates that dominate the East African Rift System, explaining to the times its deformation perpendicular and parallel to the rift. : lithospheric pushing forces, mantle pulling forces, or both.
As a postdoctoral researcher, Stamps began observing the unusual, parallel deformation of the East African Rift System using data from GPS stations that measured signals from more than 30 Earth-orbiting satellites, at about 25,000 kilometers away. His observations added a layer of complexity to the debate about what drives the fault system.
Rifting in East Africa is considered by some scientists to be primarily due to lithospheric buoyancy forces, which are relatively shallow forces attributed primarily to the elevated topography of the rift system, known as the African Superswell, and variations density in the lithosphere. Others point to horizontal mantle pulls, the deeper forces resulting from interactions with the mantle flowing horizontally beneath East Africa, as the main driver.
The 2021 team’s study found, through 3D computer simulations, that the fault and its deformation could be caused by a combination of the two forces. Their models showed that lithospheric buoyancy forces were responsible for the more predictable perpendicular-to-rift deformation, but these forces could not explain the anomalous rift-parallel deformation detected by Stamps’ GPS measurements.
In his recently published study, Rajaonarison again used 3D thermomechanical modeling, this time to focus on the source of the rift-parallel deformations. His models confirm that the African Superpanache is responsible for the unusual deformations as well as rift-parallel seismic anisotropy observed beneath the East African Rift System.
Seismic anisotropy is the orientation or alignment of rocks in a particular direction in response to mantle flow, melt pockets, or pre-existing structural fabrics in the lithosphere, Stamps said. In this case, the rock alignment followed the direction of mantle flow from the African Superpanache to the north, suggesting that mantle flow is the source.
“We say that the mantle flow does not direct some deformation in the east-west direction, perpendicular to the rift, but it can cause anomalous deformation northward parallel to the rift,” Rajaonarison said. “We have confirmed previous ideas that lithospheric buoyancy forces are the source of the fault, but we bring new information that anomalous deformation may be occurring in East Africa. »
Learning more about the processes involved in the breakup of continents, including these anomalous processes, will help scientists understand the complexity behind the breakup of a continent, something they have been trying for decades. “We are excited about this result from Dr. Rajaonarison’s numerical modeling because it provides new insights into the complex processes shaping the Earth’s surface through continental rifting,” Stamps said.
2023-08-25 17:08:20
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