The Activation Energy of the Back Transformation of Silicate Perovskite to Enstatite

  1. Murli H. Manghnani and
  2. Yasuhiko Syono
  1. E. Knittle and
  2. R. Jeanloz

Published Online: 21 MAR 2013

DOI: 10.1029/GM039p0243

High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto

High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto

How to Cite

Knittle, E. and Jeanloz, R. (1987) The Activation Energy of the Back Transformation of Silicate Perovskite to Enstatite, in High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto (eds M. H. Manghnani and Y. Syono), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM039p0243

Author Information

  1. Department of Geology and Geophysics, University of California, Berkeley, Ca 94720, USA

Publication History

  1. Published Online: 21 MAR 2013
  2. Published Print: 1 JAN 1987

ISBN Information

Print ISBN: 9780875900667

Online ISBN: 9781118664124

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Keywords:

  • Mineralogy and Crystal Chemistry;
  • Phase transformations;
  • High Pressure-High Temperature Research

Summary

The activation energy for the back transformation of (Mg0.9Fe0.1) SiO3 in the perovskite structure to the enstatite structure has been measured at zero pressure. The activation energy is 70 (±20) kJ/mole, small in comparison with values for creep, diffusion and phase transitions in many other silicates. We suggest that the transition may be activated by movement of the central Mg ion (or the corresponding vacancy) through the four oxygen ions of the dodecahedral face of the perovskite structure. From a simple harmonic model of the amplitudes of vibration of Mg-O bonds at elevated temperature, this mobility of the Mg ions is expected to occur with an activation energy of 60 kJ/mole (in accord with our measurement) and an activation volume near 1 cm−1/mole. Implications of the small value of the activation energy for silicate perovskite are as follows: 1) there should be no kinetic hindrance to the perovskite phase transition in the earth; 2) any silicate perovskite emplaced on the earth's surface in a xenolith would revert to enstatite in a geologically brief time (3–100 years), therefore minimizing the chances of finding this high-pressure phase as a natural sample on the earth's surface.