Many seismologists and researchers have long believed that Earth has a fast-flowing, well-mixed mantle. But new findings from researchers at Utrecht University in the Netherlands suggest that this theory may need some tweaking. Evidence comes from a pair of submerged continent-sized “out-of-touch” geological islands nestled in a tectonic plate “graveyard” 1,800 feet below the planet’s surface. .
Their study was published on January 22 in the journal naturerelies on the sounds produced during large earthquakes that cause the earth to vibrate like a giant bell. as Along with the university announcement To explain, seismologists study the interiors of planets by analyzing the acoustic signature of these vibrations. Experts can also identify anomalies based on whether an area is out of tune or whether a volume is attenuated.
Over 25 years ago researchers discovered Some of these deep Earth echoes indicated the existence of two underground “supercontinents” hundreds of miles beneath Africa and the Pacific Ocean. At the time, scientists were unsure whether these geological formations near the boundary between Earth’s mantle and core were a temporary phenomenon, or whether they had been there for millions or billions of years. I couldn’t have it. But what they did know was that the mystery surrounding these two men was engulfing them.
“These two large islands are surrounded by a graveyard of tectonic plates that were brought there by a process called ‘subduction,'” study co-author Arwen Deus, a seismologist at Utrecht University, said in a statement Thursday. I explained. During subduction, one tectonic plate moves beneath another, pushing it down nearly 1,900 feet from the Earth’s surface.
The two subcontinents and other regions that slow down seismic waves are known as large-low seismic velocity regions (LLSVP). One of the main reasons why acoustic degradation occurs is the high temperature of the LLSVP compared to the surrounding environment. Duce and his colleagues focused on LLSVP’s ability to “attenuate” seismic waves, referring to the energy loss that occurs as they travel through the Earth. They paid particular attention not only to where the pitch went out of tune, but also to how loud or quiet the sound got as it moved.
“Contrary to our expectations, LLSVP had very little attenuation, which made it sound very loud,” explained study co-author Sujania Talavera-Soza. “However, in cold slab graveyards there was considerable attenuation, making the sounds sound very soft.”
This was in contrast to measurements collected from the upper mantle, which looked as expected (wave attenuation due to high temperatures). Talavera-Sousa compared the difference to running when it’s hot and when it’s cold. When it’s hot, runners tend to run slower and tire more easily than when temperatures are much cooler.
Colleagues suggested moving beyond investigating temperature to investigating the mineralogical composition of LSVP, particularly individual particle size. Granularity turned out to be “much more important,” Duess said.
Deus explained that Slavic Graveyard’s LLSVP is made up of tiny particles formed after minerals recrystallize during each layer’s descent into the planet. Smaller particles mean that there are a lot more particles and a lot more small gaps between them. Sound waves passing through these formations lose energy as they pass through many grain boundaries, resulting in greater attenuation. However, since the two LLSVPs showed little attenuation, their particle size must be much larger.
The large size of the particles also means that these LLSVPs are much older than researchers first hypothesized, potentially reaching at least 500 million years ago and perhaps even more than a billion years old. These mineral particles are even harder and can resist currents in the Earth’s mantle, called mantle convection.
“Ultimately, LLSVP has to be able to withstand mantle convection in some way,” Talavera-Sousa says.
The recent discovery contradicts the description of a highly fluid and well-mixed mantle in most geology textbooks. These potentially significant seismological revisions have implications far beyond the composition, age, and movement of the LLSVP. Understanding how these giant geological formations expand in size and interact with their surroundings will help us better understand Earth’s planetary evolution. It also affects the inner workings of volcanoes and mountains.
“Earth’s mantle is the engine that drives all of these phenomena,” Duss said, citing mantle plumes as an example. These large pockets of molten material rise through the Earth from deep within the Earth’s interior, much like the movement of a lava lamp. When these plumes get close to the surface, they can help trigger volcanic eruptions.
“[W]These mantle plumes are likely originating from the edge of the LLSVP,” Dus said.
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