A mass of oceanic crust sinks into the Earth’s mantle
In Geology 101, like a sugar-coated puzzle, the interior of the Earth is divided into neat layers. However, some of the Earth’s middle layers turned out to be like peanuts in the Caramel Sea. Seismic data reveals that masses of the oceanic crust are embedded deep in the planet’s liquid mantle, forming large masses in one of their smooth layers.
The authors of the new study found these “pieces of peanuts” in the sticky coat under East Asia. Their findings, in addition to being very interesting, may affect the formation and displacement patterns of the oceanic crust.
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How did the mass of the oceanic crust get into this layer? The lithosphere is the hard outer layer of the Earth, surrounding the fissured crust and the warm upper mantle. The warm mantle spins and circulates, the crust moves to the surface, the oceanic crust sinks to that depth (a process called subduction), and huge magma smoke rises towards the surface.
“Earth The crustal movements of the lithosphere and the deep convection in the mantle reveal this, ”said Zikhun Feng, lead author of the study and postdoctoral fellow at the University of Science and Technology of China.
However, geologists know little about the behavior of deeper areas of the mantle, although they can affect mantle circulation.
The team wanted to create a more detailed picture of the mantle structure and composition and its relationship to mantle circulation, specifically the transition zone between the upper and lower mantle. Fen and his colleagues focused on the region below China, where the crust of northern China sits above a portion of the Pacific oceanic crust buried deep in the mantle. This region of the Pacific plate is considered “stagnation” because it appears to float in the mantle rather than sink beyond the transition layer. They wanted to better understand what goes on in the mantle transition layer and how stagnant plaques affect circulation.
Traditionally, seismologists have studied the structure of the mantle using seismic waves (waves passing through the earth). earthquakeFen said. However, these earthquakes don’t just happen anytime, anywhere. To work around this limitation, Feng’s team used more than 200 existing seismographs to record ambient seismic noise, small daily vibrations that are not associated with a particular epicenter.
The seismic waves could reveal “imprints of the deep mantle circulation,” Fen told Live Science. This is because seismic waves move differently through materials of different densities and properties. And these properties can be altered by other phenomena such as the descent of the oceanic crust. The rising mantle plume also disturbs the Earth’s interior, providing a variety of seismic measurements.
In a new study, researchers accumulated the seismographic measurements from these instruments to see how seismic waves behaved in the mantle of the transition zone where the upper and lower mantle meet. (The lower mantle is warmer, deeper, and more under pressure than the upper mantle.)
They found a strong seismic wave discontinuity, a change in seismic velocity, in the 410 mile (660 km) deep mantle, at the bottom of the transition zone between the upper and lower mantle. Based on these waves, they concluded that some of the marine plates were “clustered” at the bottom of this area, preventing the Pacific plate from diving further. The researchers hypothesized that when the oceanic crust meets denser rocks at this depth, it would stop descending into the mantle and spread laterally within the transition mantle. , Chemically separated into different mineral compositions. This chemical separation creates a “thick” region of the mantle with a complex structure. This area is slightly different from the rest of the mantle, pyrolite (a rock of about three parts). peridotitis some basalts).
“Our results provide direct evidence that isolated oceanic crusts are trapped in the mantle transition zone,” says Feng.
The new study provides information on mantle circulation, including the behavior of stagnant slabs in the transition zone, Fen said. Understanding the nature of mantle heterogeneity “provides important information about the mantle’s cyclical process and ultimately the evolution of the Earth,” he said.
Their results were published in the journal on May 5. Nature Communication..
Originally published in Live Science.