Scientists detect molten rock layer hidden under Earth's tectonic plates

Scientists have found a new layer of partially molten rock beneath the Earth's crust. This could help to settle a long-standing dispute about how tectonic plates move. The molten layer, which is about 100 miles below the surface, is part of the a...

Researchers had previously found patches of melt at the same depth. A new study by The University of Texas at Austin has revealed the global extent of the layer and its role in plate tectonics.

The molten layer, located approximately 100 miles from the surface, is part of the asthenosphere. It is located under the Earth's tectonic plate in the upper mantle. Because it provides a relatively soft boundary that allows tectonic plates to move through the mantle, the asthenosphere plays an important role in plate tectonics.

It is not yet clear why it is so soft. Scientists had previously believed that molten rocks could be a factor. This study shows that melt does not appear to significantly influence the flow mantle rock.

Junlin Hua, a postdoctoral fellow from UT's Jackson School of Geosciences, who led the research, said, "When we think of something melting, it is intuitively thought that the melt must play a large role in the material’s viscosity. But what we found was that even when the melt fraction is high, its effect is very minimal on the mantle flow.

Hua's research, which he began while a Brown University graduate student, shows that the dominant influence on the motions of the plates is the convection heat and rock in mantle. Although the Earth's interior remains largely solid, rocks can shift and flow over long periods of times.

Becker, who is responsible for geodynamic models of Earth at the University of Texas Institute for Geophysics' Jackson School, said that "we can't rule out the possibility that locally melt doesn’t matter. But it drives me to see these observations about melt as a marker for what's happening in the Earth and not necessarily an active contribution.

Hua was intrigued by the signs of partially molten rock beneath the crust and began to compile similar images from other seismic stations until creating a global map for the asthenosphere. He was wrong to believe that an anomaly was commonplace all over the globe, as seismic readings showed it everywhere the asthenosphere was hottest." This work is important because understanding how the asthenosphere works and its origins is crucial to understanding plate tectonics," said Karen Fischer, coauthor and a Brown University professor and seismologist who was Hua’s Ph. D advisor.