Bridge connecting the surface and the interior of the earth -dive board

Author:Stone Popular Science Studio Time:2022.09.12

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As we all know, the earth, as a more special planet in the solar system, has a sector structure movement. The sector structure movement has always been the focus and difficulty of scientists' research. The main driving force of the structure of the plate is magma activity, and the material inside the earth can spray the surface through magma activities. So is there a way to enable surface substances to enter the earth?

The structure movement of the sector provides a bridge for material entry into the earth. At the boundary of some sectors, some plates can move inside the earth due to squeezing and gravity. Scientists call such plates dive plates.

The dive board can be transported near the tables to the crust or even 1000 km. So what kind of composition and nature of dive plates enter the earth.

First of all, we make a simple introduction to the dive board. The dive plate can be divided into five layers, from top to bottom, which are sedimentary layers, basalt rock layers, Fanghui olive rock layers, Erhui olive rock formations, and losing mantle layers.

We can see that each layer of the dive plate has different components. The main ingredients of the following 3 layers and the mantle ingredients are almost the same. The main ingredients are olives, single -diarrhea and trapezi pyroxyl. Today we mainly introduce the hoods.

The trapezi pyroxyl (space group PBCA) is the main composition of minerals in the mantle. As the temperature and pressure rise, the trapezi pyroxyin minerals will change complex phase change. At room temperature, the iconic pyroxin will undergo multiple phase changes with the rise of pressure, and previous studies believe that the different FE content in the trapezi pyroxin will change its phase boundary. Different FE contents except pure iron end element converted from the orthogonal structure (space group PBCA) to a single inclined structure (space group P21/C) phase change pressure of 10-14 GPA, and the pressure continued to rise The second phase change will occur at 25-30 GPA after high (dera et al., 2013). The trapezi pyroxin itself has the symmetrical properties of the silicon ion tetraonal. The increase in the number of coordination after phase change under a certain pressure will change the symmetry method, which will cause changes in its structure and nature. FE2+and other transition metal ions have a strong impact on the phase change pressure and high -pressure structure of the poor calcium pyroxyl system.

Found

Therefore, we selected a lymic pyroxin containing a certain amount of FE for high -pressure experiments. Vajrayana exerted force on the sample cavity. On a small countertop (400 μm in diameter, pressure p = f/s, generally 400 μm of diamond we can. To achieve 40 GPA, interested students can calculate how much pressure are required) to perform high pressure under the experiment. The following is a schematic diagram of our experiments and the sample diagram of experiments conducted in the US Advanced Light Agen National Laboratory, including 2 samples, passing pressure medium, stress calibration material platinum and ruby.

Through diamond to increase the pressure on the top of the anvil and combine the synchronous radiation device to obtain the diffraction signal of the sample, we found that the trapezi pyroxin has changed in the 15 GPA, from the trapezine structure to a single inclined structure.

So how can such a phase transformation happen inside the earth? We can see by the phase diagram of the iconic pylori under high temperature and high pressure. Since the phase change can only occur at low temperature, only some low -temperature dive plates have the conditions for the phase change.

Xu et al., 2018

And through Bourin scattering (below, the Bourin scattered lighting platform) obtained the wave speed change of the iconic pyroxin under high -pressure conditions. It can be seen that it softened with the increase of the longitudinal waves and horizontal wave waves.

Through the experimental data obtained above and combined with thermodynamic parameters, we effectively restrained the wave speed characteristics of the iconic pylori under the internal conditions of the dive plate, and compared with the low -speed wedge inside the dive plate obtained by the relevant seismic observation (the gray below in the figure (the gray below Line representatives only consider the low -speed wedge of sub -stable olives. The red line represents the low -speed wedge of the trapezi pyroxin, and it is more consistent with the observation of the seismic after adding the icing prescription).

In the end, we believe that the low -speed wedge inside the dive board is not only composed of sub -stable olives, but consisting of sub -stable olives and trapezi pyroxyl, which updates the understanding of the low -wave speed abnormal area inside the dive plate sheet. Essence

Reference

DERA, P., FINKELSTEIN, G. J., Duffy, T. S., DOWNS, R. T., Meng, Y., PRAKAPENKA, TKACHEV, S. (2013). Metastable High-Presses of Orthoferrossilite FS (82), PHST Earth and Planetary Interiors, 221, 15-21, 10.1016/J.Pepi.2013.06.006.

Li, L., Sun, N., SHI, W., MAO, Z., YU, Y., ZHANG, Y., Lin, J.-F. (2022). Elastic Anomalies the α-β phase transition in orthopyroxene: Implication for the metastable wedge in the cold subduction slab. Geophysical Research Letters, 49, e2022GL099366. https://doi.org/10.1029/2022GL099366Ringwood, A. E., Irifune, T. (1988). Nature of the 650 km seismic Discontinuity: Implications for Mantle Dynamics and Differentiation, Nature, 331 (6152), 131-136, 10.1038/331131a0.

XU, J., ZHANG, D., FAN, D., ZHANG, J. S., Hu, Y., GUO, X., et al. (2018). Phase transitions in organoenstative and subduction zone dynamics: effects of water and transition Metal Ions, Journal of Geophysical Research: Solid Earth, 123 (4), 2723-2737, 10.1002/2017jb015169.

这篇论文以“Elastic anomalies across the α-β phase transition in orthopyroxene: Implication for the metastable wedge in the cold subduction slab”为题，发表于地球科学领域国际著名学术期刊Geophysical Research Letters。 The author of the communications is Professor Maozhu of the School of Earth and Space Sciences of China University of Science and Technology. The co -authors include special associate researchers Sun Ningyu, Dr. Shi Weigang, Master Yu Yingxin, Professor Lin Junfu and Dr. Zhang Yannao at the University of Texas University, and Dr. Zhang Yannao. Related experiments are completed in the High -temperature and high -pressure mineral laboratory of the University of Science and Technology of China, the synchronous radiation light source in Shanghai, and the US Advanced Light Agen National Laboratory. This work is funded by the Chinese Academy of Sciences Strategic Pioneer B Project (Grant No. XDB41000000), the National Natural Science Foundation (Grant No. 41590621), and the central university's basic scientific research business fee (Grant No. WK2080000144).