Part of the Pacific Ocean found at a depth of more than 400 kilometers under China

Part of the Pacific Ocean found at a depth of more than 400 kilometers under China
Part of the Pacific Ocean found at a depth of more than 400 kilometers under China
Anonim

The record depth of submersion of the edge of the lithospheric plate was recorded by Chinese geophysicists. Using a distributed network of seismographs, scientists have discovered a layer of oceanic crust at depths ranging from 410 to 660 kilometers. What was the bottom of the Pacific Ocean millions of years ago is now hiding under mainland China.

At the junction of the lithospheric plates, subduction zones arise - one of the plates advances on the other. And the edge of the one that turns out to be below smoothly descends into the mantle. Along the way, the crustal rocks heat up and lose the lightest chemical elements, as well as their compounds. In addition to the formation of large-scale geological structures, this process is responsible for the enrichment of the mantle with water, carbon and other substances.

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One of the models of the geological structure of the discovered anomaly in the vertical section / © Wang, X., Chen, QF., Niu, F. et al. Distinct slab interfaces imaged within the mantle transition zone. Nat. Geosci. (2020).

Previously, blocks of oceanic crust were found at depths of about 200 kilometers. Due to their strength and colossal heat capacity, fragments of the lithosphere partially retained their structure even under the influence of high pressure and heat in the bowels of the Earth. Consequently, they have a different temperature and density from the surrounding matter. This leads to re-reflection and refraction of seismic waves at the boundary of such formations. Which helps geologists find them.

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Map of the explored region of mainland China. Small triangles - seismic stations (different types are highlighted in colors); large red triangles - volcanoes; dotted black lines - boundaries of anomalies at depths from 450 to 600 kilometers (boundaries 600 and 500 are marked); bold black numbered geodesic lines - vertical slices along which the modeling was carried out / © Wang, X., Chen, QF., Niu, F. et al. Distinct slab interfaces imaged within the mantle transition zone. Nat. Geosci. (2020).

In a new scientific paper, Chinese scientists describe the discovery of fragments of oceanic crust at depths of 410 to 660 kilometers. It is published in the peer-reviewed journal Nature Geoscience. A team from the leading geological institutes of the Middle Kingdom analyzed data from more than 300 seismological stations. By the way sensors located throughout the country recorded waves from many earthquakes, it was possible to make a "tomogram" of the subsoil.

In northeastern China, the stations detected two anomalies in the propagation of seismic waves. They were located much deeper than any known formation that could cause similar effects. Then scientists built several of the most probable models describing such characteristic changes in the fluctuations of the earth's interior. Based on modeling and analysis of observational data, fragments of the ancient lithosphere became the most likely explanation.

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The location of the epicenters of earthquakes that occurred during the observations. The color shows the approximate azimuth of seismic wave propagation in relation to the anomaly / © Wang, X., Chen, QF., Niu, F. et al. Distinct slab interfaces imaged within the mantle transition zone. Nat. Geosci. (2020).

Depending on the direction of movement of seismic waves, they propagate in different ways, are reflected and change their speed at the boundary of rocks with different densities and temperatures. As observations continued over a long period of time, the data included waves emanating from earthquake hypocenters throughout Eurasia, as well as in the North and Southwest Pacific.

This discovery allows you to take a fresh look at tectonic processes. The assumptions that fragments of the oceanic lithosphere can penetrate into the mantle to great depths have been made earlier. However, now there is a clear confirmation of this. Until there is an opportunity to "plunge" into the bowels so deeply, all research is carried out by indirect methods. Observations then complement the models, and each new bit of information can move geology forward significantly.

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