Physics – Space Physics
Scientific paper
Feb 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983rvgsp..21...51j&link_type=abstract
Reviews of Geophysics and Space Physics, vol. 21, Feb. 1983, p. 51-74. Research supported by Harvard University and Alfred P. S
Physics
Space Physics
222
Earth Mantle, Earth Planetary Structure, Geochemistry, Mineralogy, Phase Transformations, Planetary Composition, Chemical Equilibrium, Elastic Properties, Laser Heating, Petrology, Phase Diagrams, Seismology, Temperature Effects
Scientific paper
Theoretical petrology techniques were employed to investigate the phase equilibria and physical properties of the minerals present in the earth's mantle. Available high-pressure-temperature phase equilibrium data for the mineral formations were combined according to a pressure scale using calibration points defined by a reanalysis of the coesite-stishovite equilibrium. Attention was given to the temperature dependence of mineral composition in the analysis of the seismic discontinuities at 400 and 670 km depths. A discontinuous reaction of olivine and gamma-spinel to form a beta-phase was found to account for the 400 km discontinuity. However, if the 400 km temperatures are higher than 800-1200 C, then reactions involving magnesiowuestite, perovskite, and stishovite are also possible. Experimental discrepancies persist for the possible reactions at 670 km depth, the boundary of the lower mantle, particularly in considering silicate, ilmenite, gamma-spinel, and silicate perovskite. Further laboratory trials involving laser heating of a diamond cell are recommended, and methods for detecting chemical stratification below 670 km are suggested.
Jeanloz Raymond
Thompson Alan Bruce
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