Previous studies have shown patches of melt (partial melting) at similar depths. However, a research team led by the University of Texas at Austin has elucidated for the first time the global spread of the melt layer and its role in plate tectonics.
Its lava layers lie at a depth of about 160 km below the surface and lie beneath the crustal plate in the upper mantle.AsthenosphereIt forms part of the (rock astrophysic). The asthenosphere is important for plate tectonics because it forms a relatively soft boundary, allowing plates to move through the mantle.
However, it is still not well understood why it is soft. Scientists previously thought lava might be a factor. However, the present study shows that the melt does not significantly affect the flow of mantle rocks.
“When you have something melted, we instinctively think that the melt plays a big role in the viscosity of the material,” said a postdoctoral fellow at the University of Texas Jackson School of Earth Sciences, who led the study.Junlin FarrYes. “What we found was that even in areas where the melt fraction is fairly high, the effect on mantle flow is negligible.”
The study, which Farr began as a graduate student at Brown University, suggests that heat and rock convection in the mantle are the main factors affecting plate movement. The Earth’s interior is mostly solid, but over time, rocks move and flow like honey.
Structural drawing of the asthenosphere (JUNLIN HUA/UT JACKSON SCHOOL OF GEOSCIENCES)
Finding that the melt layer doesn’t affect plate tectonics removes one troubling variable from computer models of the Earth, says co-author and Jackson professor.Torsten BeckerYes.
“You can’t rule out localized melt effects,” says Becker, who designs geodynamic models at the University of Texas Geophysical Laboratory. “Nevertheless, we believe that these melt observations are a marker of what is happening inside the Earth and do not necessarily contribute positively.”
The idea of looking for new layers in the Earth’s interior arose when Farr, in his doctoral work, explored the mantle beneath Turkey.portrait of seismologyIt was when I was looking into
Intrigued by the signs of partially molten rock beneath the crust, Farr collected similar images from other seismic stations, eventually forming a world map of the asthenosphere. What he and his colleagues thought to be the exception was in fact commonplace around the world, appearing invariably in images of places where the asthenosphere was the hottest.
The next surprise was that heCompare melt maps with seismic measurements of crustal motionThere was no correlation between the two, even though the melt layer covered nearly half of the Earth.
“This work is important because understanding the properties of the asthenosphere and why it is soft is fundamental to understanding plate tectonics,” said Farr as co-author and professor at Brown University when he began his PhD. Karen Fischer, a seismologist who was a supervisor, said.
this research”Asthenospheric low-velocity zone consistent with globally prevalent partial melting‘ is published in the journal Nature Geoscience.
