MSGID: 1:317/3 63e1d3f4   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Scientists detect molten rock layer hidden under Earth's tectonic plates   
      
      
     Date:   
         February 6, 2023   
     Source:   
         University of Texas at Austin   
     Summary:   
         Scientists have discovered a new layer of partly molten rock under   
         the Earth's crust that might help settle a long-standing debate   
         about how tectonic plates move. The molten layer is located about   
         100 miles from the surface and is part of the asthenosphere, which   
         is important for plate tectonics because it forms a relatively soft   
         boundary that lets tectonic plates move through the mantle. The   
         researchers found, however that the melt does not appear to   
         notably influence the flow of mantle rocks. Instead, they say,   
         the discovery confirms that the convection of heat and rock in   
         the mantle are the prevailing influence on the motion of the plates.   
      
      
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   FULL STORY   
   ==========================================================================   
   Scientists have discovered a new layer of partly molten rock under the   
   Earth's crust that might help settle a long-standing debate about how   
   tectonic plates move.   
      
      
   ==========================================================================   
   Researchers had previously identified patches of melt at a similar   
   depth. But a new study led by The University of Texas at Austin revealed   
   for the first time the layer's global extent and its part in plate   
   tectonics.   
      
   The research was published Feb. 6, 2023, in the journal Nature Geoscience.   
      
   The molten layer is located about 100 miles from the surface and is part   
   of the asthenosphere, which sits under the Earth's tectonic plates in   
   the upper mantle. The asthenosphere is important for plate tectonics   
   because it forms a relatively soft boundary that lets tectonic plates   
   move through the mantle.   
      
   The reasons why it is soft, however, are not well understood. Scientists   
   previously thought that molten rocks might be a factor. But this study   
   shows that melt, in fact, does not appear to notably influence the flow   
   of mantle rocks.   
      
   "When we think about something melting, we intuitively think that the   
   melt must play a big role in the material's viscosity," said Junlin Hua,   
   a postdoctoral fellow at UT's Jackson School of Geosciences who led the   
   research. "But what we found is that even where the melt fraction is   
   quite high, its effect on mantle flow is very minor."  According to the   
   research, which Hua began as a graduate student at Brown University, the   
   convection of heat and rock in the mantle are the prevailing influence   
   on the motion of the plates. Although the Earth's interior is largely   
   solid, over long periods of time, rocks can shift and flow like honey.   
      
   Showing that the melt layer has no influence on plate tectonics means   
   one less tricky variable for computer models of the Earth, said coauthor   
   Thorsten Becker, a professor at the Jackson School.   
      
   "We can't rule out that locally melt doesn't matter," said Becker,   
   who designs geodynamic models of the Earth at the Jackson School's   
   University of Texas Institute for Geophysics. "But I think it drives us   
   to see these observations of melt as a marker of what's going on in the   
   Earth, and not necessarily an active contribution to anything."  The idea   
   to look for a new layer in Earth's interior came to Hua while studying   
   seismic images of the mantle beneath Turkey during his doctoral research.   
      
   Intrigued by signs of partly molten rock under the crust, Hua compiled   
   similar images from other seismic stations until he had a global map of   
   the asthenosphere. What he and others had taken to be an anomaly was in   
   fact commonplace around the world, appearing on seismic readings wherever   
   the asthenosphere was hottest.   
      
   The next surprise came when he compared his melt map with seismic   
   measurements of tectonic movement and found no correlation, despite the   
   molten layer encompassing almost half the Earth.   
      
   "This work is important because understanding the properties of   
   the asthenosphere and the origins of why it's weak is fundamental   
   to understanding plate tectonics," said coauthor Karen Fischer, a   
   seismologist and professor at Brown University who was Hua's Ph.D. advisor   
   when he began the research.   
      
   The research was funded by the U.S. National Science   
   Foundation. Collaborating institutions included the UT Oden Institute   
   for Computational Engineering and Sciences and Cornell University.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Geology # Earthquakes # Natural_Disasters #   
                   Earth_Science # Tsunamis # Environmental_Issues #   
                   Atmosphere # Ozone_Holes   
       * RELATED_TERMS   
             o Crust_(geology) o Mantle_plume o Mid-ocean_ridge o Volcano   
             o Earth o Lithosphere o Basalt_rock o Earthquake   
      
   ==========================================================================   
   Story Source: Materials provided by University_of_Texas_at_Austin. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Junlin Hua, Karen M. Fischer, Thorsten W. Becker, Esteban Gazel,   
      Greg   
         Hirth. Asthenospheric low-velocity zone consistent with globally   
         prevalent partial melting. Nature Geoscience, 2023; DOI:   
         10.1038/s41561- 022-01116-9   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230206130628.htm   
      
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