Anisotropy of Earth's D layer and stacking faults in the MgSiO3 post-perovskite phase

• Published in: Nature Vol. 438; no. 7071; pp. 1142 - 1144
• Main Authors: OGANOV, Artem R, MARTONAK, Roman, LAIO, Alessandro, RAITERI, Paolo, PARRINELLO, Michele
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 22.12.2005; Nature Publishing Group
• Subjects: Anisotropy; Earth; Earth sciences; Earth, ocean, space; Earthquakes, seismology; Exact sciences and technology; Fault lines; Geochemistry; Internal geophysics; Mineralogy; Plate tectonics; Seismology; Solid-earth geophysics, tectonophysics, gravimetry; Topography; perovskite; oxides; lower mantle; textures; simulation; anisotropy; seismology; phase transitions; Earth interior; S-waves; polytypism; preferred orientation; enthalpy; core-mantle boundary; transition zones; crystallography; slip; techniques; plastic deformation; discontinuities; seismic waves
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature04439

The post-perovskite phase of (Mg,Fe)SiO3 is believed to be the main mineral phase of the Earth's lowermost mantle (the D'' layer). Its properties explain numerous geophysical observations associated with this layer-for example, the D'' discontinuity, its topography and seismic anisotropy within the layer. Here we use a novel simulation technique, first-principles metadynamics, to identify a family of low-energy polytypic stacking-fault structures intermediate between the perovskite and post-perovskite phases. Metadynamics trajectories identify plane sliding involving the formation of stacking faults as the most favourable pathway for the phase transition, and as a likely mechanism for plastic deformation of perovskite and post-perovskite. In particular, the predicted slip planes are {010} for perovskite (consistent with experiment) and {110} for post-perovskite (in contrast to the previously expected {010} slip planes). Dominant slip planes define the lattice preferred orientation and elastic anisotropy of the texture. The {110} slip planes in post-perovskite require a much smaller degree of lattice preferred orientation to explain geophysical observations of shear-wave anisotropy in the D'' layer.