Abstract
The phase boundary between wadsleyite and ringwoodite in Mg2SiO4 has been determined in situ using a multi-anvil apparatus and synchrotron X-rays radiation at SPring-8. In spite of the similar X-ray diffraction profiles of these high-pressure phases with closely related structures, we were able to identify the occurrence of the mutual phase transformations based on the change in the difference profile by utilizing a newly introduced press-oscillation system. The boundary was located at ~18.9 GPa and 1,400°C when we used Shim’s gold pressure scale (Shim et al. in Earth Planet Sci Lett 203:729–739, 2002), which was slightly (~0.8 GPa) lower than the pressure as determined from the quench experiments of Katsura and Ito (J Geophys Res 94:15663–15670, 1989). Although it was difficult to constrain the Clapeyron slope based solely on the present data due to the kinetic problem, the phase boundary [P (GPa)=13.1+4.11×10−3×T (K)] calculated by a combination of a P–T position well constrained by the present experiment and the calorimetric data of Akaogi et al. (J Geophys Res 94:15671–15685, 1989) reasonably explains all the present data within the experimental error. When we used Anderson’s gold pressure scale (Anderson et al. in J Appl Phys 65:1535–1543, 1989), our phase boundary was located in ~18.1 GPa and 1,400°C, and the extrapolation boundary was consistent with that of Kuroda et al. (Phys Chem Miner 27:523–532, 2000), which was determined at high temperature (1,800–2,000°C) using a calibration based on the same pressure scale. Our new phase boundary is marginally consistent with that of Suzuki et al. (Geophys Res Lett 27:803–806, 2000) based on in situ X-ray experiments at lower temperatures (<1,000°C) using Brown’s and Decker’s NaCl pressure scales.
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Acknowledgements
We thank K. Kuroda, N. Nishiyama, T. Ueda, Y. Tanimoto, M. Miyashita, S. Matsushita, K. Kawamura, T. Futagami, Y. Okajima for their assistance during the present in situ X-ray diffraction experiments. We also thank R.P. Rapp for valuable comments in this manuscript. Constructive comments by T. Yagi and an anonymous reviewer were greatly helpful to improve the manuscript. This work was supported in part by Grants-in-Aid for Scientific Research from Ministry of Education, Science, Sport, and Culture, Japan to T. Inoue. This work was also partly supported by the Earthquake Research Institute cooperative research program of University of Tokyo to T. Inoue. In situ X-ray diffraction experiments were carried out using the SPEED-1500 at SPring-8 (proposal No. 1998A0144-ND-np, 1999A0101-CD-np, 1999B0412-ND-np, 2000A0009-CD-np)
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Inoue, T., Irifune, T., Higo, Y. et al. The phase boundary between wadsleyite and ringwoodite in Mg2SiO4 determined by in situ X-ray diffraction. Phys Chem Minerals 33, 106–114 (2006). https://doi.org/10.1007/s00269-005-0053-y
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DOI: https://doi.org/10.1007/s00269-005-0053-y