Pyroxene-Garnet Transformation: Thermochemistry and Elasticity of Garnet Solid Solutions, and Application to a Pyrolite Mantle
- Murli H. Manghnani and
- Yasuhiko Syono
Published Online: 21 MAR 2013
Copyright © 1987 by Terra Scientific Publishing Company (TERRAPUB), Tokyo.
High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto
How to Cite
Akaogi, M., Navrotsky, A., Yagii, T. and Akimoto, S.-I. (1987) Pyroxene-Garnet Transformation: Thermochemistry and Elasticity of Garnet Solid Solutions, and Application to a Pyrolite Mantle, 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/GM039p0251
- Published Online: 21 MAR 2013
- Published Print: 1 JAN 1987
Print ISBN: 9780875900667
Online ISBN: 9781118664124
- Mineralogy and Crystal Chemistry;
- Phase transformations;
- High Pressure-High Temperature Research
Thermochemical properties and equations of state of garnet solid solutions in the system Mg4Si4O12-Mg3Al2Si3O12 were investigated. Based on high-temperature solution calorimetry experiments, the enthalpy of the pyroxene-garnet transition of Mg4Si4O12 was estimated to be about 146 kJ/mol. The phase relations, calculated from the thermochemical data, among pyroxene, garnet, and spinel (or modified spinel) plus stishovite in the system Mg4Si4O12-Mg3Al2Si3O12 were generally consistent with the phase diagrams determined experimentally. The bulk modulus of the garnet solid solution in this system was measured by hydrostatic compression experiments using synchrotron radiation and X-ray diffraction techniques. With increasing Mg4Si4O12 component, the bulk modulus of the garnet solid solution was found to decrease slightly relative to pyrope. Using the new phase equilibria and elasticity data, density and bulk sound velocity profiles were calculated for the pyroxene-garnet system, as well as for pyrolite. The bulk sound velocity distribution of the pyroxene-garnet system showed no sharp increase in velocity in the mantle down to 670 km. The density and bulk sound velocity of pyrolite at depths of 220–670 km were in general agreement with the seismological velocity and density profiles when the new elasticity data for the garnet solid solution were used.