Scientists have debated for decades as to what forces allow the planet's tectonic plates to slide across the Earth's mantle. Now, researchers have found a layer of liquefied molten rock in Earth's mantle, which could potentially be that cause of the tectonic movements. This discovery will also improve our understanding of basic geologic functions of the planet and that of volcanism and earthquakes.
Scientists discovered this magma layer at the Middle America trench off Nicaragua's shores. They imaged a 25 kilometer (15.5 mile) thick layer of partially melted mantle rock below the edge of the Cocos plate where it moves beneath Central America. Advanced seafloor electromagnetic imaging technology pioneered at Scripps Institution of Oceanography SIO was used for the purpose.
These images were captured during a 2010 expedition aboard the research vessel Melville. After deploying a vast array of seafloor instruments that recorded natural electromagnetic signals to map features of the crust and mantle, the scientists realized they had found magma in a surprising place. Kerry Key of the Scripps Institution of Oceanography (SIO) said,
"This was completely unexpected. We went out looking to get an idea of how fluids are interacting with plate subduction, but we discovered a melt layer we weren't expecting to find."
Credits: Scripps Institution of Oceanography
The research was funded by the National Science Foundation (NSF), and is reported in this week's issue of the journal Natureby Samer by Naif, Kerry Key, and Steven Constable of the Scripps Institution of Oceanography (SIO), and Rob Evans of the Woods Hole Oceanographic Institution. Bil Haq, program director in NSF's Division of Ocean Sciences said,
"This new image greatly enhances our understanding of the role that fluids, both seawater and deep subsurface melts, play in controlling tectonic and volcanic processes."
Previously, studies had suggested that dissolved water in mantle minerals results in a more ductile mantle that would facilitate tectonic plate motions, but for many years clear images and data required to confirm or deny this idea were lacking. Naif said,
"Our data tell us that water can't accommodate the features we are seeing. The information from the new images confirms the idea that there needs to be some amount of melt in the upper mantle. That's what's creating this ductile behavior for plates to slide."
These results will provide deeper insights into the structure of the tectonic plate boundary and thereby improve our understanding of plate tectonics. Key said, "One of the longer-term implications of our results is that we are going to understand more about the plate boundary, which could lead to a better understanding of earthquakes." The researchers are now trying to find the source that supplies the magma in the newly discovered layer.
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