A part of the Earth’s surface lies 400 miles below China


The researchers reported that the process of tectonic subduction has drawn Earth’s surface layer, or lithosphere, over 400 miles west of northeastern China.

Study in Nature Geoscience Water-rich marine tectonic plates provide new evidence about what happens as they are drawn through continents beneath the Earth.

Seismologist Fanglin Niu of Rice University, who is the study’s co-related author, says that it is the first high-, top and bottom of a rocky, or lithospheric, tectonic plate within a key known as the mantle transition zone. Provides seismic images with resolution. , Which starts at about 254 miles (410 kilometers) from the Earth’s surface and extends for about 410 miles (660 kilometers).

“A lot of studies show that the slab actually deteriorates so much in the mantle transition zone, that it softens, so it deteriorates easily,” says Niu. It is important to explain how and why the slab is deformed or retains its shape, and how it mixes with the mantle and has a cooling effect.

Earth’s mantle conducts heat like an oven. The heat from the Earth’s core passes through the gorge at the center of the oceans, where tectonic plates are formed. From there, heat flows through the mantle, cooling as it moves toward the continents, where it falls back to the core to complete more heat, rise and convection cycles.

Previous studies have examined the boundaries of sub-slabs in Mantle, but some are more than 125 miles (200 kilometers) deep and none with the resolution of the current study, which collected 67,000 from 313 regional seismic stations in northeast China. Uses more measurements than. The work, which took place in collaboration with the China Earthquake Administration, was led by Chinese Academy of Sciences co-related author Qiu-fu Chen.

Pieces of the earth’s surface

Fundamental questions have been asked about the processes shaping the Earth’s surface over billions of years in research. Mantle convection increases the speed of Earth’s tectonic plates, rigid interlocked pieces of the Earth’s surface that are in constant motion, as they float in the asthenosphere, the topmost mantle layer, and the most fluid part of the inner planet.

Where tectonic plates meet, they emit seismic energy, join and grind together. In extreme cases, it can cause catastrophic earthquakes and tsunamis, but most seismic motion is too faint for humans to feel without instruments. Using a seismometer, scientists can measure the magnitude and location of seismic disturbances. And because seismic waves move in some types of rock and move slower in others, scientists can use them to create images of the Earth’s interior, in the same way a doctor can use ultrasound that a patient can use. Be for the image inside.

“Japan is located at a place where the Pacific plate reaches a depth of about 100 kilometers,” says Niu, a professor of Earth, Environment and Planetary Sciences at Rice. “There is a lot of water in this slab, and it produces a lot of partial melt. This arc produces volcanoes that help form Japan. But, we are still debating whether this water is completely released at that depth. There is increasing evidence that a portion of water remains inside the plate to go deeper. “

Northeast China offers one of the best vantage points to examine whether this is true or not. The region is about 1,000 kilometers from the moat of Japan where the Pacific plate enters the interior of the planet. In 2009, Niu and scientists from the University of Texas at Austin, the China Earthquake Administration, the Earthquake Research Institute of the University of Tokyo and the Research Center for Forecasting Earthquakes and Volcanic Eruptions in Tohoku, Japan, began installing broadband seismometers in the area.

“We keep 140 stations there, and certainly more stations are better for resolution,” Niu says. “The Chinese Academy of Sciences installed additional stations so that they could obtain a finer, more detailed image.”

Slabs in mantle

In the new study, data from stations shows both the upper and lower boundaries of the Pacific plate, downward at an angle of 25 ° within the mantle transition zone. Placement within this region is important for the study of mantle convection because the transition zone lies beneath the asthenosphere, at depths where pressure increases cause specific mantle minerals to undergo dramatic phase changes. These phases of minerals behave very differently in seismic profiles, such that liquid water and solid ice behave very differently, even though they are composed of similar molecules. Because phase changes in mantle transform zones occur at specific pressures and temperatures, geologists can use them as thermometers to measure temperature.

Niu calls the fact that both the top and bottom of the slab are visible, evidence that the slab is not completely mixed with the surrounding mantle. He states that the heat signature of the partially molten portion of the mantle under the slab also provides indirect evidence that the slab transported some of its water to the transition zone.

“The problem is illustrating how these hot materials can be dropped into the deeper part of the mantle,” says Niu. “It is still a question. Because they are warm, they are warm. “

This surge should act like a life saver, pushing the underside of the sinking slab upwards. Niu says that the answer to this question may be that the holes appear in the defective slab, which may increase hot melting when the slab is submerged.

“If you have a hole, the melt will come out,” he says. “That’s why we think the slab can go deep.”

Holes can also point out the presence of volcanoes like Changbishan on the border between China and North Korea.

“This plate is 1,000 kilometers from the border,” Niu says. “We don’t really understand the mechanism of such volcanoes. But a possible explanation could be a rise from holes in the slab. “

The coauthors are from the Chinese Academy of Sciences, Nanyang Technological University, Singapore, China Earthquake Administration, California Institute of Technology and Urban-University of Urban-Champagne. The funding came from the Chinese Academy of Sciences and the National Natural Science Foundation of China.

Source: Rice University

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