Physics
Scientific paper
Jun 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994pepi...83..197k&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 83, Issue 3-4, p. 197-216.
Physics
8
Scientific paper
To constrain the composition of the Moon we have calculated the stable phase assemblages and their seismic properties by the method of minimization of Gibbs free energy, to determine whether various compositional models are consistent with the seismic observations for the lunar lower mantle at depths between 500 and 1000 km. P-Wave and S-wave velocities have been calculated for a series of proposed bulk composition models. Compositional models for the Moon (impactor composition, Orgueil composition, etc.) and Earth-like compositions (lherzolite and pyrolite) have been considered. It is found that impactor and Orgueil models are unlikely for the lower mantle. Within reasonable temperature adjustment in the temperature profile, all of the terrestrial compositional models come close to the seismic data below the 500 km discontinuity. It is found that a composition enriched in Al2O3 (up to about 6 wt.%) and having pyrolite content of the other major oxides (`lunar pyrolite') is adequate to describe the seismic properties of the lunar lower mantle. Within the uncertainty of calculations and resolution of seismic data, an Al-rich model with a terrestrial Ol/Px ratio and unusually enriched in garnet gives the best fit to the lunar lower-mantle seismic properties. Despite the uncertainty of the seismic data it is shown that none of the analysed compositional models satisfies the seismic constraints simultaneously in the middle and lower mantle. Phase changes in any model considered are not able to explain the nature of the 500 km discontinuity. It is concluded that the lunar mantle is chemically stratified.
Fabrichnaya O. B.
Kuskov Oleg L.
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