Kinetics and detectability of the bridgmanite to post-perovskite transformation in the Earth's D″ layer

• Published in: Nature communications Vol. 10; no. 1; pp. 5680 - 9
• Main Authors: Langrand, Christopher, Andrault, Denis, Durand, Stéphanie, Konôpková, Zuzana, Hilairet, Nadège, Thomas, Christine, Merkel, Sébastien
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 12.12.2019; Nature Publishing Group; Nature Portfolio
• Series: Nature Communications
• Subjects: 704/2151/330; 704/2151/508; Astrophysics; Chemical Sciences; Condensed Matter; Earth mantle; Earth Sciences; Geophysics; Humanities and Social Sciences; Kinetics; Lower mantle; Material chemistry; Materials Science; multidisciplinary; Perovskites; Phase transitions; Physics; Science; Science (multidisciplinary); Sciences of the Universe; Transition layers
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-13482-x

Bridgmanite, the dominant mineral in the Earth’s lower mantle, crystallizes in the perovskite structure and transforms into post-perovskite at conditions relevant for the D ″ layer. This transformation affects the dynamics of the Earth’s lowermost mantle and can explain a range of seismic observations. The thickness over which the two phases coexist, however, can extend over 100 km, casting doubt on the assignment of the observed seismic boundaries. Here, experiments show that the bridgmanite to post-perovskite transition in (Mg 0.86 ,Fe 0.14 )SiO 3 is fast on geological timescales. The transformation kinetics, however, affects reflection coefficients of P and S waves by more than one order of magnitude. Thick layers of coexisting bridgmanite and post-perovskite can hence be detected using seismic reflections. Morever, the detection and wave period dependence of D ″ reflections can be used to constrain significant features of the Earth’s lowermost mantle, such as the thickness of the coexistence layer, and obtain information on temperature and grain sizes. The D ″ layer in the Earth’s lower mantle involves a seismic discontinuity which is often assigned to a mineral phase transition to post-perovskite, however, as this phase transition occurs over broad region the assignment of seismic boundaries remains unclear. Here, the authors find that due to the kinetics of the bridgmanite to post-perovskite transformation, thick transition layers can be detected by seismic reflections, unlike previously thought.