Mineral Physics Constraints on a Uniform Mantle Composition
- 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
Weidner, D. J. and Ito, E. (1987) Mineral Physics Constraints on a Uniform Mantle Composition, 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/GM039p0439
- 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
A comparison of seismic data with those from mineral physics demonstrates that the earth's mantle may be of homogeneous chemical composition. In particular, the pyrolite model is compatible with the available data. The test of any model centers on matching the seismic velocity values at the base of the upper mantle, the magnitude of the velocity jump at 400 km, the velocity gradient in the transition zone, and the characteristics of the 670 km discontinuity. When testing a chemical model it is critical to consider the uncertainties of all of the model parameters. Thus the hypothesis includes the chemical variables and the assumptions concerning the physical properties.
Interdependence of chemical and physical variables are examined with reference to various tests afforded by seismic data. The 400 km discontinuity and the transition zone gradient are extremely sensitive to the pressure derivative of the shear moduli of the stable phases and phase transitions in the pyroxene systems. The sensitivity to these parameters is so great as to severely limit the chemical resolution of the seismic data. The expected composition range for the lower mantle results in a mineralogy which ranges from 80% (by volume) of perovskite with 20% magnesio-wustite to pure perovskite. The differences in the resulting velocities is extremely small relative to those introduced from uncertainties in the physical properties.
Further mineral physics data are necessary to resolve the chemical characteristics of the mantle. In particular, the pressure derivatives of the elastic moduli of the high pressure phases are needed. In addition, more data on the phase equilibria of the pyroxene systems, particularly with sodium and calcium, are important. It is also important to evaluate the resolution of the seismic data. The mineralogical models center on the magnitude of velocity discontinuities and velocity gradients. The interdependence of these variables needs to be more clearly elucidated.