Hidden molten rock layer found beneath Earth’s tectonic plates

Researchers have discovered a previously unknown layer of partially molten rock beneath the Earth’s crust.

The discovery could help scientists learn more about the movements of Earth’s tectonic plates, which created not only mountains and earthquakes but also the right chemical and physical conditions to support life on early Earth. It also helps in creating environment.

The outermost layer of our planet is the crust—the one we live on—and below that is the mantle, outer core, and inner core. The world’s oceans and continents sit on 15 large blocks that move and shift, called tectonic plates, that make up the lower crust and upper mantle.

The newly identified molten layer lies 100 miles (161 km) below Earth’s surface. This layer is part of the asthenosphere, which sits beneath the tectonic plates. The asthenosphere exists as a soft layer of solid but weak rock that can cause tectonic plates to move and shift.

Researchers have wondered what factors make the asthenosphere soft and considered molten rock to be part of the equation. Although the Earth’s interior is mostly solid, rocks can shift and move slowly over time.

Jonlin Hua, a postdoctoral fellow at the Jackson School of Geosciences at the University of Texas at Austin, was studying seismic images of the Earth’s mantle beneath Turkey for his doctoral research when he encountered partially molten rock. See the signs. He began his work in 2020 while a doctoral student at Brown University.

Scientists had previously seen parts of this rock layer and thought it was an anomaly, but Hua and his fellow researchers found evidence that it had a wider presence.

The research team confirmed that the asthenosphere is composed of both solid and molten rock, and although the latter is partially molten, it does not contribute to the movement of the plates, nor does it facilitate their movement. makes

“When we think about the melting of something, we intuitively think that melting should play a large role in the adhesion of the material,” Hua said. “But what we found is that where the melt fraction is quite high, the effect on mantle flow is very small.”

In the mantle, convection, or heat transfer, occurs as warmer, less dense material rises and cooler, denser material sinks. Researchers believe that the presence and movement of solid rocks contributes to plate movement.

One of the biggest challenges in studying Earth’s interior is collecting data because most of it can only be collected at the surface, and directly sampling the planet’s interior is difficult, Hua said.

“Therefore, scientists are using seismic waves generated by earthquakes that travel deep into the Earth’s interior to study the motions of seismic waves on these inner layers, which hospital “It’s like CT scans,” Hua said.

He collected more than 700 images taken from seismic detectors around the world and created a global map of the asthenosphere.

Analyzing the data, Hua looked at how seismic waves travel through different materials beneath the Earth’s crust, including changes in speed, direction and arrival time at detection locations. The presence of melt in the partially molten crust meant that seismic waves moved more slowly.

Molten rock appeared on seismic readings in regions where the asthenosphere reached its highest temperature, about 2,640 degrees Fahrenheit (1,450 degrees Celsius).

Hua is the lead author of the study detailing the findings, which was published Monday in the journal Nature Geoscience.

“This study is fundamental to the understanding that the asthenosphere — the fragile mantle beneath tectonic plates that enables the plates to move — is indeed fragile,” said Karen M. Fisher, Distinguished Professor of Geological Sciences at Brown University. In a statement

“Ultimately, it provides evidence that other factors such as temperature and pressure variations can control the strength of the asthenosphere and make it quite vulnerable to plate tectonics.”

The findings could help researchers understand how different layers beneath the Earth work.

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