MSGID: 1:317/3 6489426c   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Computer models confirm that the African Superplume is responsible for   
   the unusual deformations as well as rift-parallel seismic anisotropy observed   
   beneath the East African Rift System    
      
     Date:   
         June 13, 2023   
     Source:   
         Virginia Tech   
     Summary:   
         Computer models confirm that the African Superplume is responsible   
         for the unusual deformations, as well as rift-parallel seismic   
         anisotropy observed beneath the East African Rift System.   
      
      
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   FULL STORY   
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   Computer models confirm that the African Superplume is responsible for   
   the unusual deformations as well as rift-parallel seismic anisotropy   
   observed beneath the East African Rift System.   
      
   In continental rifting, there's a mix of stretching and breaking   
   that reaches deep into the Earth, said geophysicist D. Sarah   
   Stamps. Continental rifting involves the stretching of the lithosphere --   
   the outermost, rigid layer of the Earth. As the lithosphere stretches   
   thin, its shallow regions experience brittle deformation, with the   
   breaking of rock and earthquakes.   
      
   Stamps, who studies these processes by using computer modeling and GPS   
   to map surface motions with millimeter precision, compares a rifting   
   continent's different deformation styles with playing with Silly Putty.   
      
   "If you hit Silly Putty with a hammer, it can actually crack and break,"   
   said Stamps, associate professor in the Department of Geosciences,   
   part of the Virginia Tech College of Science. "But if you slowly pull   
   it apart, the Silly Putty stretches. So on different time scales,   
   Earth's lithosphere behaves in different ways."  Whether in stretching   
   or breaking, the deformation that comes with continental rifting usually   
   follows predictable directional patterns in relation to the rift: The   
   deformation tends to be perpendicular to the rift. The East African Rift   
   System, the Earth's largest continental rift system, has those rift-   
   perpendicular deformations. But after measuring the rift system with GPS   
   instruments for more than 12 years, Stamps also observed deformation that   
   went in the opposite direction, parallel to the system's rifts. Her team   
   at the Geodesy and Tectonophysics Labhas worked to find out why.   
      
   In a recent study published in theJournal of Geophysical Research, the   
   team explored the processes behind 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   
   earned his Ph.D.   
      
   at Virginia Tech as a member of Stamps's lab. His models showed that the   
   rift system's unusual, rift-parallel deformation is driven by northward   
   mantle flow associated with the African Superplume, a massive upwelling   
   of mantle that rises from deep within the Earth beneath southwest Africa   
   and goes northeast across the continent, becoming more shallow as it   
   extends northward.   
      
   Their findings, combined with insights from a study the researchers   
   published in 2021 using Rajaonarison's modeling techniques, could help   
   clear up scientific debate on which plate-driving forces dominate the   
   East African Rift System, accounting for both its rift-perpendicular and   
   rift-parallel deformation: lithospheric buoyancy forces, mantle traction   
   forces, or both.   
      
   As a postdoctoral researcher, Stamps began observing the East African   
   Rift System's unusual, rift-parallel deformation using data from GPS   
   stations that measured signals from more than 30 satellites orbiting   
   Earth, from about 25,000 kilometers away. Her observations have added   
   a layer of complexity to the debate around what drives the rift system.   
      
   Some scientists see the rifting in East Africa as driven primarily   
   by lithospheric buoyancy forces, which are relatively shallow forces   
   attributed mainly to the rift system's high topography, known as the   
   African Superswell, and to density variations in the lithosphere. Others   
   point to horizontal mantle traction forces, the deeper forces arising   
   from interactions with mantle flowing horizontally beneath East Africa,   
   as the primary driver.   
      
   The team's 2021 study found through 3D computational simulations that   
   the rift and its deformation could be driven by a combination of the   
   two forces. Their models showed that lithospheric buoyancy forces were   
   responsible for the more predictable, rift-perpendicular deformation,   
   but those forces couldn't account for the anomalous, rift-parallel   
   deformation picked up by Stamps's GPS measurements.   
      
   In their newly 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 Superplume 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 rocks' alignment followed the direction of the African   
   Superplume's northward mantle flow, which suggests mantle flow as   
   their source.   
      
   "We are saying that the mantle flow is not driving the east-west, rift-   
   perpendicular direction of some of the deformations, but that it may   
   be causing the anomalous northward deformation parallel to the rift,"   
   Rajaonarison said.   
      
   "We confirmed previous ideas that lithospheric buoyancy forces are driving   
   the rift, but we're bringing new insight that anomalous deformation can   
   happen in East Africa."  Learning more about the processes involved in   
   continental rifting, including these anomalous ones, will help scientists   
   chip away at the complexity behind the breaking of a continent, which   
   they've been attempting for decades. "We're 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 rifting," Stamps said.   
      
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   ==========================================================================   
   Story Source: Materials provided by Virginia_Tech. Original written by   
   Suzanne Irby. Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Tahiry A. Rajaonarison, D. Sarah Stamps, John Naliboff, Andrew   
      Nyblade,   
         Emmanuel A. Njinju. A Geodynamic Investigation of   
         Plume‐Lithosphere Interactions Beneath the East African   
         Rift. Journal of Geophysical Research: Solid Earth, 2023; 128 (4)   
         DOI: 10.1029/2022JB025800   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230613190839.htm   
      
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