In Geology 101, like a sugar-coated jawbreaker, 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 sea of caramel. Seismic data reveal that oceanic crust masses are anchored deep into the planet’s liquid mantle, forming large masses in one of their smooth layers.
The authors of the new study found those “peanut chunks” in the sticky mantle beneath East Asia. Their findings, in addition to being very interesting, can affect models of how the oceanic crust is formed and moved.
How did the mass of the oceanic crust get into that layer? The lithosphere is the hard outer layer of the Earth, surrounding the cracked crust and the hot upper mantle. The hot mantle rotates and circulates, the crust moves on the surface, the oceanic crust subducts to that depth (a process called subduction), and a huge magma smoke rises toward the surface.
“Earth The lithosphere’s crustal movements and deep convection in the mantle reveal it, “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 how deeper areas of the mantle behave, even though they can affect the circulation of the mantle.
The team wanted to create a more detailed picture of the structure and composition of the mantle and its relationship to the mantle circulation, especially the transition zone between the upper and lower mantle. Fen and colleagues focused on the region below China, where the crust of northern China sits above a portion of the oceanic Pacific 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 sinking beyond the transition layer. They wanted to better understand what is happening in the transition layer in the mantle and how stagnant slabs affect the circulation.
Traditionally, seismologists have studied the structure of the mantle using seismic waves (waves traveling through the earth). earthquakeSaid Fen. However, these earthquakes do not occur anytime, anywhere. To work around this limitation, Feng’s team used over 200 existing seismographs to record ambient seismic noise, small daily vibrations that are not associated with a particular epicenter.
Seismic waves could reveal “footprints of the deep mantle circulation,” Fen told Live Science. This is because seismic waves travel differently through materials of different densities and properties. And these properties can be altered by other phenomena such as oceanic crust descent. The rising mantle plume also disturbs the interior of the Earth, providing a variety of seismic measurements.
In a new study, researchers piled up seismograph measurements from these instruments to see how seismic waves behaved in the transition zone mantle where the upper and lower mantle meet. (The lower mantle is hotter, deeper and more pressured than the upper mantle.)
They found a sharp discontinuity of seismic waves, a change in seismic velocity, within the 410 mile (660 km) deep mantle, at the bottom of the transition zone between the upper and lower mantle. Based on those waves, they concluded that some of the marine slabs were “bunched” at the bottom of this zone, preventing the Pacific Plate from diving further. The researchers hypothesized that when the oceanic crust encounters denser rocks at that depth, it would stop descending into the mantle and spread laterally within the transitional mantle. , Chemically separated to 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, the pyrolite (a rock of about three parts). Peridotite Some basalts).
“Our findings provide direct evidence that isolated oceanic crusts are trapped within the mantle transition zone,” says Feng.
The new study provides insights into the circulation of the mantle, including how stagnant slabs behave within the transition zone, Fen said. Understanding the nature of mantle heterogeneity “provides important insights into the mantle’s cyclical process and, ultimately, the evolution of the Earth,” he said.
Their findings were published in the journal on May 5th. Nature Communications..
Initially published in Live Science.
A mass of oceanic crust is digging into the Earth’s mantle
Source link A mass of oceanic crust is digging into the Earth’s mantle