“Rock under the fire!” A former piece of the Pacific floor depicted deep in China

In northeastern China, seismic imaging revealed the boundaries of a tectonic plate (blue) և top (X1) և bottom (X2) that had previously sat on the Pacific floor and stretched to the Earth’s transition zone, which is about 254-410 miles away. 410-660 kilometers below the Earth’s surface. Loan Image: N. New / Rice University

The study offers clues about the fate of tectonic plates that sink deep into the Earth’s crust.

In a study that gives the term “stone floor” a new meaning, seismic researchers have found a part of the Earth’s surface layer or rocky slab of the lithosphere that stretched more than 400 miles northeast of China through tectonic obedience. ,

The study, published by a team of Chinese-American researchers Natural geography, offers new evidence of what happens to water-rich oceanic tectonic plates as they line the Earth’s crust beneath the continents.

Fenglin New, seismologist at Rice University, says the study provides seismic images of the first high-resolution seismic boundaries above a rocky or lithospheric tectonic plate. down և extends to 10 410 miles (660 kilometers).

“Many studies suggest that the slab is actually deformed a lot in the transition zone of the membrane, it becomes soft, so it is easily deformed,” Niu said. The extent to which the plate deforms or retains its shape may explain why it blends into the cap and has a cooling effect.

Fenglin New

Fenglin is Professor of Earth, Planet and Earth Sciences at New Rice University. Loan Thanks to Rice University

The mantle of the earth burns like heat in a furnace. Heat rises from the Earth’s core through the crust in the center of the oceans, where tectonic plates form. From there, heat flows through the mantle, freezing as it travels to the continents, where it falls back into the nucleus to collect more heat, rising, and filling the convective region.

Previous studies have examined the extent of plate abduction in the crust, but few have seen deeper than 125 miles (200 kilometers) – none of the current study, which used more than 67,000 measurements collected from 313 regional seismic stations in northeast China. : The work, which was carried out jointly with the China Earthquake Administration, was led by Qi-Fu Chen, a correspondent for the Chinese Academy of Sciences.

The study examines fundamental questions about the processes that have shaped the Earth’s surface over billions of years. Mantle convection drives the movements of the Earth’s tectonic plates, the rigidly intertwined pieces of the Earth’s surface that are in constant motion as they soar to the top of the asthenosphere, the upper mantle, and the liquid part of the inner planet.

Where tectonic plates meet, they are shaken and crushed, releasing seismic energy. In extreme fires, it can cause devastating earthquakes and tsunamis, but most seismic movements are too weak for people to feel without tools. Scientists can use seismometers to measure the magnitude and location of seismic disturbances. And because seismic waves are accelerating in some rocks and slowing in others, scientists can use them to create images of the Earth’s interior, much like a doctor doing an ultrasound scan to see what’s inside a patient.

Niue, Professor of Rice Earth, Environment and Planet Science, has been a leader in seismic imaging for more than two decades. When he was awarded the title of Doctor. More than 20 years ago in training in Aponia, researchers were assembling dense networks of seismic stations to collect the first detailed images of the submerged slab boundaries of a Pacific plate, the same plate pictured in a study published this week.

“Japan Aponia is where the Pacific Ocean reaches a depth of about 100 kilometers,” New said. “There is a lot of water in this slab, it produces a very partial melt. It produced arc volcanoes that helped create the Japan Aponia. But we are still debating whether that water is completely released at that depth. “There is more and more evidence that some of the water stays in the plate to go much deeper.”

Northeast China offers one of the best places to visit to see if it is right. The region is located about 1,000 kilometers from the trench of Aponia, where the plate of the Pacific Ocean begins to sink into the interior of the planet. In 2009, with funding from the National Science Foundation, scientists from the University of Texas at Austin, the Earthquake Administration of China, the Tokyo University Earthquake Research Institute, and the Japan Earthquake Prediction Research Center in Tohoku, Japan. The university began installing broadband seismometers in the region.

“We are putting 140 stations there. Of course, the more stations, the better the solution,” Niu said. “The Chinese Academy of Sciences has installed additional stations so that they can get a more subtle, detailed image.”

During the new study, the data from the stations revealed the “upper” and “lower” borders of the Pacific plate, falling down at an angle of 25 degrees in the transition zone of the membrane. Deployment in this zone is important for the study of mantle convection, as the transition zone lies beneath the asthenosphere at depths where increased pressure causes the mantle ores to undergo abrupt phase changes. These phases of minerals behave very differently in seismic profiles, just as liquid water and solid ice behave very differently, even though they are made up of identical molecules. Because phase changes in the mantle transition zone occur at specific pressures և temperatures, geologists can use them as a thermometer to measure the temperature in the mantle.

Niu said that the fact that the top and bottom of the slab were visible indicates that the slab did not completely mix with the surrounding mantle. He said the thermal signatures of the partially melted parts of the slab under the slab were also indirect evidence that the slab had moved some of its water to the transition zone.

“The problem is to explain how these hot materials can be dumped deeper into the mantle,” New said. “It is still a question. “Because they are hot, they are strong.”

That swim should act as a lifeline by pushing the bottom of the sinking slab. Niu said the answer to this question may be that holes have formed in the deformable slab, which allows the hot melt to rise while the slab is sinking.

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

The holes could also explain the appearance of volcanoes like Changbayshan on the border between China and North Korea.

“It’s 1,000 kilometers from the plate boundary,” New said. “We do not really understand the mechanism of this type of volcano. But the melt rising from the holes in the slab may be a possible explanation. ”

Reference. “Clear Slab Interfaces Pictured in the Slab contraction joints” – Xin Wang, i-fu Feng Chen, Fenglin Niu, Shenji Wei, ey yeyuan Nin, Juan Li, Weijun Wang, Johannes Buchen և Lijun Liu, 2020 November 9, Natural geography,
DOI: 10.1038 / s41561-020-00653-5:

The study was co-authored by Xin Wang իայի Juan Lin of the Chinese Academy of Sciences, Shenji Wei of Nanyang Technological University, Singapore, Weijun Wang of the China Earthquake Administration, Johannes Buchen of the California Institute of Technology, and Lijun Lu University. In Urbana-Champaign, Illinois. The study was funded by the Chinese Academy of Sciences (XDB18000000) and the National Natural Science Foundation of China (91958209, 41974057, 41130316).

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