Texture development and TEM analysis of deformed CaIrO3: Implications for the D″ layer at the core-mantle boundary

Abstract

CaIrO3 is an isostructural analog for MgSiO3 post-perovskite (ppv), likely the dominant mineral phase in the D″ layer. At high temperature CaIrO3 undergoes a phase transition to a perovskite (pv) structure. We have performed deformation experiments of CaIrO3 pv and ppv with the deformation-DIA apparatus. The deformed pv does not display any discernable texture even after strong coaxial shortening. In contrast, ppv displays a strong lattice preferred orientation (LPO) with the a-axis parallel to the shear direction and the b-axis perpendicular to the shear plane. Calculation of the seismic properties predicts a shear wave splitting with a maximum of 2.7% in the shear plane, which is qualitatively compatible with seismic measurements. Ppv displayed a high density of (010)[100] dislocations, consistent with the textural results. Thus, our experiments on CaIrO3 pv and ppv are compatible with a seismically isotropic lower mantle and anisotropic D″ layer in the Earth. Copyright 2007 by the American Geophysical Union.