Slip Systems in MgSiO 3 Post-Perovskite: Implications for D ′′ Anisotropy

• Published in: Science (American Association for the Advancement of Science) Vol. 329; no. 5999; pp. 1639 - 1641
• Main Authors: Miyagi, Lowell, Kanitpanyacharoen, Waruntorn, Kaercher, Pamela, Lee, Kanani K. M., Wenk, Hans-Rudolf
• Format: Journal Article
• Language: English
• Published: 24.09.2010
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1192465

Slippery When Squeezed The behavior of seismic waves as they pass through Earth's interior depends on the physical properties of major mineral phases at depth. If such minerals are anisotropic—that is, they influence seismic waves preferentially depending on crystallographic orientation—interpreting the structure of a region becomes more challenging. In the lowermost mantle, near the boundary with the outer core, deformation of MgSiO 3 post-perovskite may affect anisotropy. Miyagi et al. (p. 1639 ) solved previous experimental limitations to show that, when squeezed at high pressures, MgSiO 3 post-perovskite weakens and breaks along its (001) lattice plane. When modeled, this deformation pattern produces anisotropic structures that are consistent with seismic data collected from this region. The major mineral phase in the lower mantle deforms preferentially along one lattice plane. Understanding deformation of mineral phases in the lowermost mantle is important for interpreting seismic anisotropy in Earth’s interior. Recently, there has been considerable controversy regarding deformation-induced slip in MgSiO 3 post-perovskite. Here, we observe that (001) lattice planes are oriented at high angles to the compression direction immediately after transformation and before deformation. Upon compression from 148 gigapascals (GPa) to 185 GPa, this preferred orientation more than doubles in strength, implying slip on (001) lattice planes. This contrasts with a previous experiment that recorded preferred orientation likely generated during the phase transformation rather than deformation. If we use our results to model deformation and anisotropy development in the D ′′ region of the lower mantle, shear-wave splitting (characterized by fast horizontally polarized shear waves) is consistent with seismic observations.