The 560-km seismic discontinuity, crucial for understanding Earth's interior, has garnered attention. However, the cause of this discontinuous surface has not been convincingly explained.

An international team of scientists, including Joshua M.R. Muir from the Institute of Geochemistry, CAS;  LIU Xi from Peking University; ZHANG Zhigang  from the Institute of Geology and Geophysics, CAS; and Mingda Lü from Michigan State University, has uncovered the cause of the seismic discontinuity at 560 kilometers deep within the Earth's mantle. Researchers identified the phase transition of defect-bearing ringwoodite as the key factor behind this geological phenomenon.

The team used first-principles calculations to study the stability of defect-bearing ringwoodite under mantle transition zone conditions. this study discovered that defects present in ringwoodite significantly lower the phase transition temperature between normal and inverse ringwoodite, enabling inverse ringwoodite to stably exist within the mantle transition zone. This phase transition process is highly correlated with the formation of the 560-kilometer seismic discontinuity.

Lead author Xuwei Zhao, a PhD candidate at Peking University, highlighted that defects in ringwoodite lower the transition temperature between normal and inverse ringwoodite.

Their findings challenge the traditional view that ringwoodite's structure is stable and unrelated to the seismic discontinuity at this depth. This reduction allows inverse ringwoodite to exist under mantle transition zone conditions, contributing to the observed seismic discontinuity at 560 kilometers.

The study was published online in the journal Geoscience Frontiers.

"The discovery provides new insights into Earth's internal structure and helps refine mantle mineralogy models. It also offers important clues for understanding the internal structure and evolution of Earth-like planets," said Prof. Xi Liu,

Fig 1:(Left Panel): Structure of Earth's layers and changes in seismic wave velocity. (Middle Panel): Mineral composition near the mantle transition zone and variations in seismic wave velocity.(Right Panel): Depths of seismic discontinuities near the mantle transition zone in certain regions of   the Earth.（Image by IGCAS)

Fig2：Phase diagrams of pure ringwoodite and defect-bearing ringwoodite.

Contact: ZHANG Feiwu. Institute of Geochemistry, Chinese Academy of Sciences

Email:zhangfeiwu@mail.gyig.ac.cn