Discovery of Oceanic Crust Rocks Subducted Deep into the Earth: Integration of Experiments, Theoretical Calculations, and Seismic Observations Reveals Plates Reach Near the Core

This is a joint research result press release from Meiji University, the Japan Synchrotron Radiation Research Institute (JASRI), the University of Tokyo, and Okayama University.

June 13, 2026 National University Corporation Okayama University

https://www.okayama-u.ac.jp/

◆ Summary

A research group consisting of Associate Professor Ryosuke Sinmyo and graduate student S. Maitani (at the time) of the School of Science and Technology, Meiji University; Senior Researcher Saori Kawaguchi (at the time, currently Specially Appointed Associate Professor at Kyoto University) of the Japan Synchrotron Radiation Research Institute (JASRI); Associate Professor Kenshi Kawai and graduate students R. Sato (at the time) and K. Otsuru (at the time) of the Graduate School of Science, the University of Tokyo; Senior Researchers Hiroshi Sakuma and Shigeru Suehara of the National Institute for Materials Science (NIMS); and Associate Professor Takayuki Ishii of the Institute for Planetary Materials, Okayama University, has obtained new evidence showing that rocks subducted into the Earth's interior along with oceanic plates have reached the vicinity of the "core-mantle boundary" at a depth of approximately 2,900 km. The group achieved this by combining experiments simulating the deep Earth, atomic-level theoretical calculations, and seismic observations.

On the Earth's surface, oceanic plates subduct into the Earth's interior from trenches. It has long been thought that rocks originating from subducted plates are carried deep into the mantle over hundreds of millions of years. However, directly demonstrating whether they actually reach the core-mantle boundary near the Earth's center has remained difficult.

The key to this study is silicon dioxide (SiO2), which is abundant in subducted oceanic crust. Under the extremely high pressure and temperature of the deep Earth, SiO2 changes its crystal structure, transforming into a high-density structure called "seifertite" in the lowermost mantle. Since this phase transition characteristically affects the propagation of seismic waves, it serves as a marker for finding rocks subducted deep into the Earth.

In this study, the research group first determined precisely the pressures and temperatures at which SiO2 transforms into seifertite through high-temperature, high-pressure experiments and quantum beam measurements at the large synchrotron radiation facility SPring-8. Next, they verified the validity of the experimental results and the effects of metastable phases (which had been an issue in previous studies) using atomic-level quantum theoretical calculations. Furthermore, by analyzing vast seismic waveform data and comparing them with the seismic velocity structures beneath Central America and Hawaii, they showed that the mineral changes obtained in the laboratory correspond to seismic velocity anomalies observed in the actual deep Earth.

This study was conducted with support from JSPS KAKENHI grants 19H01989, 23H01277, JP23K25970, JP24K07171, JP23KJ0651, 23K19067, 24K00735, and 24KJ2052. The research results were published in the Nature portfolio journal "Scientific Reports."

This announcement was released on June 10, 2026.

◆ Publication Information Journal: Scientific Reports Paper Title: Cold SiO2-rich slabs reaching the CMB revealed by the seifertite phase boundary Authors: Sinmyo R., Kawaguchi SI., Sato R., Otsuru, K., Kawai K., Sakuma H., Suehara S., Ishii T., Maitani S. Research Institutions: Meiji University, Japan Synchrotron Radiation Research Institute (JASRI), the University of Tokyo, National Institute for Materials Science (NIMS), Okayama University, etc. Research Details: The seifertite phase boundary of SiO2 was determined using high-speed X-ray diffraction experiments at SPring-8 and theoretical calculations. By comparing this boundary with seismic velocity structures, the study showed that SiO2-rich rocks originating from subducted oceanic plates likely reach the core-mantle boundary. DOI: https://doi.org/10.1038/s41598-026-54731-6 Publication Date: May 30, 2026 (Saturday, Japan Time)

◆ Detailed Information Discovery of Oceanic Crust Rocks Subducted Deep into the Earth: Integration of Experiments, Theoretical Calculations, and Seismic Observations Reveals Plates Reach Near the Core

https://www.okayama-u.ac.jp/up_load_files/press_r8/press20260610-1.pdf

◆ Contact Information

<Regarding Research and Paper> Ryosuke Sinmyo, Department of Physics, School of Science and Technology, Meiji University

Saori Kawaguchi, Hydrogen Energy Materials and Next-Generation Battery Research and Development Unit (OI-HAB), Growth Strategy Headquarters, Kyoto University

Kenshi Kawai, Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo

Takayuki Ishii, Institute for Planetary Materials, Okayama University

<Regarding Press Coverage and Others> Public Relations Division, Management Planning Department, Meiji University TEL: 03-3296-4