On the Timescale of Magma Ocean Solidification and Its Chemical Consequences: 2. Compositional Differentiation Under Crystal Accumulation and Matrix Compaction

Abstract

The solidification of a putative magma ocean sets the stage for subsequent subsolidus mantle convection. Whereas it may have resulted in a compositionally stratified mantle, the efficiency of relevant processes to cause chemical differentiation, such as crystal accumulation and matrix compaction, remains uncertain. The purpose of this study is to present the thermochemical structure of end-member cases where potential differentiation mechanisms are taking full effect. We employ a self-consistent thermodynamic model to make our model consistent in both thermal and chemical aspects. The accumulation of crystals at the base of magma ocean can enrich the upper mantle with iron, but such a global-scale compositional stratification is likely to be quickly eliminated by gravitational instability, leaving small-scale heterogeneities only. On the other hand, the compaction of solid matrix in the deep mantle creates a long-lasting molten layer above the core-mantle boundary. Our results suggest that the efficiency of compaction is the key factor to generate compositional stratification during solidification.