Reaction between Forsterite and Nitrogen Fluid at High Pressure and High Temperature


Behavior of nitrogen in the deep Earth still remains unrevealed. Geochemical data suggest that substantial amount of nitrogen could be stored in the deep Earth. In this study, reactions between forsterite (Mg2SiO4) and molecular nitrogen (N2) were investigated at high pressure and high temperature using laser-heating diamond anvil cells (DACs). Pressure in the DAC was estimated from Raman spectra of nitrogen before heating and the initial pressure was set at 5 GPa. Pelleted sample of powder forsterite or a single crystal of forsterite was loaded in the DAC with N2 fluid. A carbon dioxide laser (λ = 10.64 μm, <100 W) and a fiber laser (λ = 1.019 μm, <100 W) were used to heat forsterite in the temperature range from 1300 to 3500 K. An SEM image on the surface of the recovered forsterite crystal after the laser heating showed a stepwise texture which strongly suggests the dissolution of forsterite into the N2 fluid. The EDS chemical mapping showed that Mg-rich area and Si-poor area overlapping each other, which suggests the preferential dissolution of MgO component and its precipitation from the N2 fluid. X-ray diffraction patterns of the powder and single crystal forsterite samples after the reaction showed reflections assignable to orthopyroxene (MgSiO3) and periclase (MgO). The present experimental results indicate that Mg2SiO4 incongruently melts into MgSiO3 and MgO in N2 fluid. Moreover, N1s XPS spectra collected from a single crystal of forsterite after the reaction with N2 fluid revealed three components assignable to \({\text{NH}}_{4}^{ + },\) N2, and N3–. The present study provides a new clue to the reaction between forsterite and molecular nitrogen under the upper mantle condition.

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We are sincerely grateful to Drs. Konstantin Litasov and Andrei Shiryaev for their review comments which greatly improved the manuscript.


This research was supported by JSPS-RDBR bilateral program and JSPS KAKENHI Grant Numbers 15K13600, 15H05828. Synchrotron X-ray diffraction measurements were performed under the approval of the Photon Factory Program Advisory Committee (Proposal numbers 2015G694 and 2017G644). SEM analyses were performed under the collaborative research project of PRIUS, Geodynamic Research Center, Ehime University. XPS measurements were conducted at Advanced Characterization Nanotechnology Platform of the University of Tokyo, supported by “Nanotechnology Platform” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

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Correspondence to Hiroyuki Kagi.

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Kagi, H., Kubo, T., Shinozaki, A. et al. Reaction between Forsterite and Nitrogen Fluid at High Pressure and High Temperature. Geochem. Int. 57, 956–963 (2019).

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  • nitrogen
  • forsterite
  • incongruent melting
  • diamond anvil cell (DAC)