Post-perovskite phase transition and the nature of the D″ layer

Abstract

Recent experimental and theoretical studies have shown that MgSiO3 perovskite, a predominant mineral in the lower mantle, transforms to a post-perovskite phase at pressure and temperature conditions expected in the D″ region. The D″ layer has long been the most enigmatic region in the Earth's interior, due to a number of large seismic anomalies that are not consistent with the known properties of MgSiO3 perovskite. Discovery of a phase transformation from perovskite to post-perovskite significantly improves our understanding of the nature of the Earth's lowermost mantle. In addition, the post-perovskite phase transition destabilizes the hot thermal boundary layer at the base of the mantle and induces extensive formation of mantle plumes, because it has a large positive Clapeyron slope. If the plumes originate in the core-mantle boundary (CMB) region, chemical compositions of such plumes are naturally distinct from the bulk of the mantle. The D″ layer most likely has significant chemical heterogeneities at various scales caused by accumulation of subducted slabs, partial melting, and reaction with the outer core. © 2007 Springer.