Scientists have identified an old piece of the Pacific Ocean – an ancient remnant of a beach long before that – that stretched a few miles beneath China as it pulled down into the Earth’s transition zone.
This rocky slab, used to mark the lower part of the Pacific Ocean, is a remnant of the lithosphere of the ocean, the outermost layer of the earth’s surface, composed of the upper part of the crust and the hardest outer parts of the upper crust.
In the lithosphere it is not always noticed to enjoy the views above. The upper surface layer consists of a number of fragmented tectonic plates, which gradually move closer to the surface and occasionally move with each other.
During this collision a geological process called subduction can occur, where one plate is forced into the subduction zones below the other and moves deeper into the planet.
A new study has found that scientists in China and the United States have now witnessed this epic phenomenon at a greater depth than observation.
Earlier, scientists searched the boundary at a depth of about 200 kilometers (about 125 miles) and recorded negligent slabs.
Now, for a vast network of more than 300 seismic stations spread across northeastern China, the researchers found the phenomenon at a much lower location, with imaging parts of the tectonic plate pushing towards the middle of the mantle under the Pacific Ocean – the layer transition zone, 410 below the Earth’s surface. At a depth of kilometers (254–410 miles).
To explain the sunken slab, the team identified the velocity discrepancies of the two earthquakes, many areas underground where seismic waves encountered inconsistencies. In this case, two inconsistencies were encountered, which the team says are related to both the upper and lower sides of the plunging plate.
“Based on seismological detailed analysis, the above isolation was interpreted as the moho isolation of the submolded slab,” said Qiu-Fu Chen, a geophysicist at the Chinese Academy of Sciences.
“Low segregation may occur due to partial melting of the sub-slab athens in aquatic conditions in the sea part of the slab.”
The subduction of the plate can be seen in the process below the china, but the subduction zone itself is located far to the east, with the slab located at a relatively shallow 25 degree angle.
“Japan is located where the Pacific plate reaches a depth of about 100 kilometers,” said Fenglin Niu, a seismologist at Rice University.
Thanks to the new imaging, scientists are getting a better idea of what happens to a sub-adobe slab when it reaches this part of the transformation zone, including how it deforms and how much water is lost from the oceanic crust.
“Many studies suggest that the slab actually deforms so much in the mantle transition zone that it becomes soft, so it deforms easily,” New says.
“We are still debating whether this water is being released completely from this depth. There is evidence that a portion of the water is located inside the plate to go much deeper.”
The investigation is reported Nature Geoscience.
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