Elastic anisotropy of experimental analogues of perovskite and post-perovskite help to interpret D′′ diversity

Abstract

Recent studies show that the D′′ layer, just above the Earth's core–mantle boundary, is composed of MgSiO3 post-perovskite and has significant lateral inhomogeneity. Here we consider the D′′ diversity as related to the single-crystal elasticity of the post-perovskite phase. We measure the single-crystal elasticity of the perovskite Pbnm-CaIrO3 and post-perovskite Cmcm-CaIrO3 using inelastic X-ray scattering. These materials are structural analogues to same phases of MgSiO3. Our results show that Cmcm-CaIrO3 is much more elastically anisotropic than Pbnm-CaIrO3, which offers an explanation for the enigmatic seismic wave velocity jump at the D′′ discontinuity. Considering the relation between lattice preferred orientation and seismic anisotropy in the D′′ layer, we suggest that the c axis of post-perovskite MgSiO3 aligns vertically beneath the Circum-Pacific rim, and the b axis vertically beneath the Central Pacific.

Anisotropy in the lowermost mantle beneath the Indian Ocean Geoid Low from ScS splitting measurements

“…We feel that experiments done at high temperatures on analog materials [Yamazaki et al, 2006] are more reliable [Karato, 2008] and the experimentally determined LPO patterns for CaTiO 3 postperovskite [Yamazaki et al, 2006] are consistent with the seismological observations [Wookey and Kendall, 2007]. Recently, Yoneda et al [2014] studied the pv and ppv-CaIrO 3 single-crystal elasticity based on the mineral physics experiments on analog materials to interpret the D 00 layer anisotropy. This study proposed a postperovskite (ppv) LPO model to explain anisotropy in the D 00 layer, consistent with the seismic observations.…”

“…Recently, Yoneda et al . [] studied the pv and ppv‐CaIrO 3 single‐crystal elasticity based on the mineral physics experiments on analog materials to interpret the layer anisotropy. This study proposed a postperovskite (ppv) LPO model to explain anisotropy in the layer, consistent with the seismic observations.…”

Effect of cation substitution on bridgmanite elasticity: A key to interpret seismic anomalies in the lower mantle

“…Inelastic X-ray scattering with a single crystal sample in conjunction with an analysis based on Christoffel’s equation has been recently used for accurate determination of elastic moduli 16 54 55 56 . This technique has been adopted to data along high-symmetry directions about samples at high-pressure and high-temperature conditions 55 56 .…”

“…This technique has been adopted to data along high-symmetry directions about samples at high-pressure and high-temperature conditions 55 56 . In this study, we did not limit data along high-symmetry directions, but measured rather redundant data at off-symmetry positions to determine C ij precisely and to utilize all measured data with an analyzer array 16 54 (see Fig. 1 ).…”

Crystal structure of post-perovskite-type CaIrO3reinvestigated: new insights into atomic thermal vibration behaviors

“…Meanwhile, CaIrO 3 is known to be one of the few post-perovskite-type compounds stable at ambient conditions (Rodi & Babel, 1965;McDaniel & Schneider, 1972). The postperovskite-type CaIrO 3 has attracted much attention in the field of Earth science as an excellent low-pressure analogue of the post-perovskite-type MgSiO 3 (see, for example, Niwa et al, 2007;Tsuchiya & Tsuchiya, 2007;Yoneda et al, 2014).…”