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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Scientists unearth 20 million years of 'hot spot' magmatism under Cocos   
   plate    
      
     Date:   
         June 20, 2023   
     Source:   
         Georgia Institute of Technology   
     Summary:   
         A team of scientists has observed past episodic intraplate magmatism   
         and corroborated the existence of a partial melt channel at the   
         base of the Cocos Plate. Situated 60 kilometers beneath the Pacific   
         Ocean floor, the magma channel covers more than 100,000 square   
         kilometers, and originated from the Gala'pagos Plume more than 20   
         million years ago, supplying melt for multiple magmatic events --   
         and persisting today.   
      
      
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   FULL STORY   
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   Ten years ago, Samer Naif made an unexpected discovery in Earth's   
   mantle: a narrow pocket, proposed to be filled with magma, hidden some   
   60 kilometers beneath the seafloor of the Cocos Plate.   
      
   Mantle melts are buoyant and typically float toward the surface -- think   
   underwater volcanoes that erupt to form strings of islands. But Naif's   
   imaging instead showed a clear slice of semi-molten rock: low-degree   
   partial melts, still sandwiched at the base of the plate some 37 miles   
   beneath the ocean floor.   
      
   Then, the observation provided an explanation for how tectonic plates   
   can gradually slide, lubricated by partial melting. The study also   
   "raised several questions about why magma is stored in a thin channel --   
   and where the magma originated from," says Naif, an assistant professor   
   in the School of Earth and Atmospheric Sciences at Georgia Institute   
   of Technology.   
      
   Fellow researchers went on to share competing interpretations for the   
   cause of the channel -- including studies that argued against magma   
   being needed to explain the observation.   
      
   So Naif went straight to the source.   
      
   "I basically went on a multiyear hunt, akin to a Sherlock Holmes detective   
   story, looking for clues of mantle magmas that we first observed in the   
   2013 Naturestudy," he says. "This involved piecing together evidence   
   from several independent sources, including geophysical, geochemical,   
   and geological (direct seafloor sampling) data."  Now, the results of   
   that search are detailed in a new Science Advances article, "Episodic   
   intraplate magmatism fed by a long-lived melt channel of distal plume   
   origin," authored by Naif and researchers from the U.S. Geological   
   Survey at Woods Hole Coastal and Marine Science Center, Northern Arizona   
   University, Lamont-Doherty Earth Observatory of Columbia University,   
   the Department of Geology and Geophysics at Woods Hole Oceanographic   
   Institution, and GNS Science of Lower Hutt, New Zealand.   
      
   Zeroing in A relatively young oceanic plate -- some 23 million years   
   old -- the Cocos Plate traces down the western coast of Central America,   
   veering west to the Pacific Plate, then north to meet the North American   
   Plate off the Pacific coast of Mexico.   
      
   Sliding between these two plates caused the devastating 1985 Mexico City   
   earthquake and the 2017 Chiapas earthquake, while similar subduction   
   between the Cocos and Caribbean plates resulted in the 1992 Nicaragua   
   tsunami and earthquake, and the 2001 El Salvador earthquakes.   
      
   Scientists study the edges of these oceanic plates to understand the   
   history and formation of volcanic chains -- and to help researchers and   
   agencies better prepare for future earthquakes and volcanic activity.   
      
   It's in this active area that Naif and fellow researchers recently set out   
   to document a series of magmatic intrusions just beneath the seafloor,   
   in the same area that the team first detected the channel of magma back   
   in 2013.   
      
   Plumbing the depths For the new study, the team combined geophysical,   
   geochemical, and seafloor drilling results with seismic reflection   
   data, a technique used to image layers of sediments and rocks below the   
   surface. "It helps us to see the geology where we cannot see it with   
   our own eyes," Naif explains.   
      
   First, the researchers observed an abundance of widespread intraplate   
   magmatism. "Volcanism where it is not expected," Naif says, "basically   
   away from plate boundaries: subduction zones and mid-ocean ridges."   
   Think Hawaii, where "a mantle plume of hot, rising material melts during   
   its ascent, and then forms the Hawaii volcanic chain in the middle of   
   the Pacific Ocean," just as with the Cocos Plate, where the team imaged   
   the volcanism fed by magma at the lithosphere-asthenosphere boundary --   
   the base of the sliding tectonic plates.   
      
   "Below it is the convecting mantle," Naif adds. "The tectonic plates   
   are moving around on Earth's surface because they are sliding on the   
   asthenosphere below them."  The researchers also found that this channel   
   below the lithosphere is regionally extensive -- over 100,000 square   
   kilometers -- and is a "long-lived feature that originated from the   
   Gala'pagos Plume," a mantle plume that formed the volcanic Gala'pagos   
   islands, supplying melt for a series of volcanic events across the past   
   20 million years, and persisting today.   
      
   Importantly, the new study also suggests that these plume-fed melt   
   channels may be widespread and long-lived sources for intraplate magmatism   
   itself -- as well as for mantle metasomatism, which happens when Earth's   
   mantle reacts with fluids to form a suite of minerals from the original   
   rocks.   
      
   Connecting the (hot spot) dots "This confirms that magma was there in   
   the past -- and some of it leaked through the mantle and erupted near   
   the seafloor," Naif says, "in the form of sill intrusions and seamounts:   
   basically volcanoes located on the seafloor."  The work also provides   
   compelling supporting evidence that magma could still be stored in the   
   channel. "More surprising is that the erupted magma has a chemical   
   fingerprint that links its source to the Gala'pagos mantle plume."   
   "We learned that the magma channel has been around for at least 20   
   million years, and on occasion some of that magma leaks to the seafloor   
   where it erupts volcanically," Naif adds.   
      
   The team's identified source of the magma, the Gala'pagos Plume, "is more   
   than 1,000 kilometers away from where we detected this volcanism. It is   
   not clear how magma can stay around in the mantle for such a long time,   
   only to leak out episodically."  Plume hunters wanted The evidence that   
   the team compiled is "really quite subtle and requires a detailed and   
   careful study of a suite of seafloor observations to connect the dots,"   
   Naif says. "Basically, the signs of such volcanism, while they are quite   
   clear here, also require high resolution data and several different   
   types of data to be able to detect such subtle seafloor features."  So,   
   "if we can see such subtle clues of volcanism here," Naif explains, "it   
   means a similar, careful analysis of high resolution data in other parts   
   of the seafloor may lead to similar discoveries of volcanism elsewhere,   
   caused by other mantle plumes."  "There are numerous mantle plumes dotted   
   across the planet. There are also numerous seamounts -- at least 100,000   
   of them! -- covering the seafloor, and it is anyone's guess how many of   
   them formed in the middle of the tectonic plates because of magma sourced   
   from distant mantle plumes that leaked to the surface."  Naif looks   
   forward to continuing that search, from seafloor to asthenosphere.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Volcanoes # Geology # Earthquakes # Natural_Disasters   
             o Fossils_&_Ruins   
                   # Fossils # Origin_of_Life # Early_Climate # Paleontology   
       * RELATED_TERMS   
             o Mantle_plume o Oceanic_trench o Yellowstone_Caldera o   
             Ice_sheet o Ocean o Mid-ocean_ridge o Tunguska_event o River   
      
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   Story Source: Materials provided by Georgia_Institute_of_Technology. Note:   
   Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Samer Naif, Nathaniel C. Miller, Donna J. Shillington, Anne Be'cel,   
         Daniel Lizarralde, Dan Bassett, Sidney R. Hemming. Episodic   
         intraplate magmatism fed by a long-lived melt channel of distal   
         plume origin.   
      
         Science Advances, 2023; 9 (23) DOI: 10.1126/sciadv.add3761   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230620174452.htm   
      
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