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The post-spinel transition pressure in Mg2SiO4 was determined with a Kawai-type multi-anvil press combined with in-situ X-ray diffraction. We obtained the highest transition pressure of 23.6-23.9 GPa at 1700 K so far by our advanced multianvil technology, such as forced pumping during heating and anvil tapering [Ishii et al. 2016, 2017, 2019]. This is a complete agreement with the pressure of the 660-km discontinuity at an expected mantle temperature of 2000 K. The present study resolved a question of 20 years’ standing, a discrepancy between the post-spinel transition pressure and the 660-km discontinuity depth, and indicate the applicability of the widely accepted models of the mantle. The lower pressures reported by previous studies are experimental artifacts due to the pressure drop upon heating.

Takayuki Ishii, Rong Huang, Hongzhan Fei, Iuliia Koemets, Zhaodong Liu, Fumiya Maeda, Liang Yuan, Lin Wang, Dmitry Druzhbin, Takafumi Yamamoto, Shrikant Bhat, Robert Farla, Takaaki Kawazoe, Noriyoshi Tsujino, Eleonora Kulik, Yuji Higo, Yoshinori Tange, Tomoo Katsura (2018) Complete agreement of the post-spinel transition with the 660-km seismic discontinuity. Scientific Reports 8, 6358. doi: 10.1038/s41598-018-24832-y (Open Access)