2023-08-17 21:12:52
Research by Dr. Sarah Stamps, using 3D thermomechanical modeling, revealed that the African Super Plume, a massive uplift in the mantle, is causing the rifting parallel deformations seen in the East African Rift System. This adds complexity to the debate about the initial forces driving rifting, suggesting a combination of buoyancy forces in the lithosphere and forces of mantle pull. Computer simulations confirm that the African superlayer causes unusual deformations and seismic anisotropy parallel to the fault detected under the East African Rift System. Says geophysicist Dr. This process involves the elongation of the lithosphere, the hard outer layer of the Earth. As it becomes more tense, the upper parts of the lithosphere undergo brittle changes, leading to rock fractures and earthquakes. Stamps, who studies these processes using computer modeling and GPS to map surface motions to millimeter accuracy, compared different patterns of rift continent deformation while playing with Silly Putty. “If you hit cellulite paste with a hammer, it can crack and break,” said Stamps, an associate professor in the Department of Earth Sciences, part of Virginia Tech College of Science. “But if you loosen it slowly, the silly putty stretches. Thus, on different time scales, the Earth’s lithosphere behaves in different ways. Whether expansion or rifting, deformation associated with continental rifting generally follows predictable trend 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 distortions perpendicular to the rift. But after measuring system faults with GPS instruments for more than 12 years, Stamps also noticed distortions in the opposite direction, paralleling system faults. His team at the Laboratory of Geodesy and Tectonic Physics worked to find out why. Assistant Professor Dr. Sarah Stamps. Credit: Virginia Tech In a recent study published in the Journal of Geophysical Research, the team explored the processes driving the East African Rift System using 3D thermal modeling developed by the study’s first author, Tahiri Rajaonarisson, a postdoctoral researcher at New Mexico Tech who received her Ph.D. at Virginia Tech as a member of the Stamps Lab. His models showed that the unusual, parallel fault deformation of the rift system is being driven by the northward mantle flow associated with the African Superpanache, a large mantle uplift rising from the depths of the Earth below southwest Africa and heading northeast across the continent, as it becomes shallower. with its expansion north. Their findings, combined with insights from a study the researchers published in 2021 using Rajaonarisson modeling techniques, could help shed light on the scientific debate about the plate driving forces that dominate the East African Rift System. rift. The buoyancy forces in the lithosphere, the drag forces in the mantle, or both. As a postdoctoral researcher, Stamps began monitoring the unusual parallel deformation of the East African Rift using data from GPS stations that measure signals from more than 30 satellites orbiting Earth, some 25,000 kilometers away. His remarks added a layer of complexity to the controversy surrounding fault system drives. Some scientists consider the East African Rift to be due primarily to buoyancy forces in the lithosphere, which are relatively shallow forces attributed primarily to the elevated topography of the rift system, known as the African Superswell, and density differences in the lithosphere. Others point to horizontal mantle pull forces, deeper forces generated by interactions with the horizontally flowing mantle below East Africa, as the primary driver. The difference A 2021 study found through 3D computer simulations that the fault and its deformation could be driven by a combination of the two forces. Their models showed that buoyancy forces in the lithosphere were responsible for predictable deformation perpendicular to the fault, but these forces could not explain the anomalous deformation parallel to the fault detected by GPS measurements of the stamps. In their recently published study, Rajaonarison again used 3D thermomechanical modeling, this time to focus on the source of the deformations parallel to the crack. His models confirm that the African superlayer is responsible for the unusual deformations as well as the seismic anisotropy parallel to the faulting observed under the East African Rift System. Seismic anisotropy is the orientation or alignment of rocks in a specific 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 north from the African Superpanache, indicating mantle flow as the source. “We say that the mantle flow is not oriented east-west, perpendicular to the fault of some deformation, but it may drive the anomaly northward parallel to the fault,” said Rajaonarisson. “We have confirmed previous ideas that buoyancy forces in the lithosphere are driving the fault, but provide new insights that abnormal deformation may be occurring in East Africa.” Knowing more about the processes involved in continental rifting, including these anomalous ones, will help scientists narrow down the complexity behind continent breakup, something they have been trying for decades. “We are excited about this result from Dr. Rajaonarisson’s numerical modeling because it provides new insights into the complex processes that shape the Earth’s surface through continental rift,” Stamps said. Reference: “A Geodynamic Investigation of Plume-Lithospheric Interactions Below the East African Rift” by Tahir A. Rajaonarison, D.; Sarah Stamps, John Nalipov, Andrew Nibbled and Emmanuelle A. Solid Earth Geophysical Research Journal. doi: 10.1029/2022JB025800
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