Reflection properties of phase transition and compositional change models of the 670-km discontinuity

Details Reflection properties of phase transition and compositional change models of the 670-km discontinuity Reflection properties of phase transition and compositional change models of the 670-km discontinuity

Oct 1983

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983jgr....88.8145l&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 88, Oct. 10, 1983, p. 8145-8159. Research supported by the Alfred P. Sloa

Physics

94

Discontinuity, Earth Mantle, Earth Planetary Structure, Seismology, Chemical Composition, Mineralogy, Phase Transformations, Reflectance

Scientific paper

The way in which phase transition and compositional change models match the seismic data for the transition zone is investigated. In addition to comparing densities and velocities, special attention is given to the question whether the models proposed here are consistent with the observed P-prime 670 P-prime reflections. On the basis of a direct calculation of the change in seismic properties through phase transitions for plausible mantle mineralogies, it is found that models involving only phase transitions produce reflections much smaller than those inferred from the observed P-prime 670 P-prime. It is noted that a discontinuous change in chemical composition, coupled with a phase change, is most likely to produce reflections of the appropriate size, especially for an increase in silica in the lower mantle. It is found, however, that the absolute value of the velocity in the transition zone is difficult to match with the models used here. Although a convecting mantle with a chemical discontinuity would have boundary layers arising from thermal and chemical diffusion across the discontinuity, it is shown that the effect of the boundary layers on seismic velocities in the transition region is likely to be within the uncertainties of the seismic observations.

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