Discovery of an unknown “sticky” layer hidden under the Earth’s tectonic plates

A new study has found that about 150 kilometers (93 miles) below the Earth’s surface lies an unknown layer of molten rock that could help scientists learn more about the movements of Earth’s tectonic plates.

Finding this viscous layer will help researchers better understand how tectonic plates “float” above this mantle layer, study lead author Gonlin Hua, a researcher with a PhD in geosciences at the University of Texas at Austin, told Live Science.

The molten rock is found in the asthenosphere (asthenosphere or flow zone), the uppermost layer of the mantle between about 80 km (50 miles) and 200 km (124 miles) below the Earth’s surface.

The only way to explore this layer of the mantle is through seismic waves. Scientists can use wave data from seismic stations around the world and look for subtle changes in waveforms that indicate the types of material the waves travel through.

Previously, scientists learned from such studies that some parts of the asthenosphere were hotter than others, and patchy melting zones were found, Hua said. But little was known about how deep and extensive the melt was.

To find out, Hua and his colleagues collected data from thousands of seismic waves detected at 716 stations around the world. They found that instead of retaining small patches of melt, the asthenosphere appears to contain a partially melted layer that extends across the globe under at least 44 percent of the planet.

The researchers found that this area is widespread throughout the world and may be much larger because they were unable to investigate under the ocean, which likely covers a layer of melt that covers a much larger area than the continents.

Oddly enough, this molten layer does not seem to affect the movements of tectonic plates. The scientists found that melting regions did not affect the mantle’s viscosity or tendency to flow.

“These molten rocks plus hard rocks don’t deform as easily as hard rocks alone,” Hua said. “So, contrary to expectations, these magmas, although present, will not affect how easily tectonic plates move through the asthenosphere.” .

According to the authors of the study, this is useful information for building computer models of plate movement.

“We can’t rule out that local melting doesn’t matter,” Thorsten Becker, a geophysicist at the University of Austin and one of the study’s authors, said in a statement. “But I think it encourages us to consider these melting observations as a sign that something is happening.” in the ground, not necessarily an active participant in anything.”

Hua added that there is still a lot of work to be done to map this molten mantle layer.

He continued: “In this study, we mainly use seismic instruments on the continents, and although we also used some instruments from ocean islands, there is definitely some data gap in the ocean. Therefore, other instruments will be used in the subsequent study. data types or seismic instruments at the bottom of the oceans fill this gap.”

The researchers published their findings Feb. 6 in the journal Nature Geoscience.

Source: Living Science