Layering in the Mantle: To Be Or Not To Be

Abstract

One of the most perplexing and compelling problems in deep Earth geophysics is the possibility of mantle layering induced dynamically by the presence of the endothermic spinel to Perovskitite plus magnesiumüstite phase transition, a change in bulk composition or a change in viscosity between the upper and lower mantle, or any combination of these. Recent models of mantle convection indicate that the Clapeyron slope of the phase transition (-3 ± lMPa/K) is strong enough to produce a dynamically layered mantle. One key feature common to these studies is that the variation of thermal expansively with depth is assumed to be near that found by Chopelas and Boehler (1989] for magnesiumüstite. Recent measurements of the thermal expansively of Perovskitite have been made and the results are not in agreement. Weirder et. al. [1993] find a thermal expansively profile that is similar to that of magnesiumüstite in the lower mantle. Stixrude et al. [1992] find a thermal expansively that is much higher than that of magnesiumüstite at mantle temperatures.