Persistence of davemaoite at lower-mantle conditions

Abstract

The lower mantle occupies over half of Earth’s volume, and accordingly, its mineralogy is crucial in determining the structure and dynamics of Earth. Davemaoite, the calcium silicate perovskite, was believed to coexist with bridgmanite in the lower mantle and is considered essential for understanding the chemical evolution and dynamics of Earth’s lower mantle. However, the presence of davemaoite is challenged due to the potential for high calcium silicate solubility in bridgmanite. Here we use an ultrahigh-pressure multi-anvil technique to show experimentally that the calcium solubility in bridgmanite is insufficient to eliminate davemaoite under mantle conditions, including typical mantle pressure, temperature and chemical compositions. We conclude that davemaoite has been stable in Earth’s lower mantle since its formation. Due to the limited calcium solubility in bridgmanite, davemaoite-enriched domains are expected at the core–mantle boundary. These domains could serve as the principal reservoir for incompatible elements in the lower mantle and may be the source for some ocean island basalts. Furthermore, our study offers an explanation for the observed large low-shear-wave-velocity provinces at the bottom of the lower mantle. These provinces may consist of davemaoite-enriched materials crystallized from basal magma ocean in early Earth history. The calcium silicate perovskite mineral davemaoite probably persisted since lower-mantle formation and may form davemaoite-enriched domains at the core–mantle boundary, according to an experimental study at lower-mantle conditions.