Transformational Weakening During the Perovskite-Post Perovskite Phase Transition in CaIrO3
Abstract
The D" layer plays a fundamental role in core - mantle interactions. The recent discovery of a CaIrO3 structured phase of MgSiO3, the so called post-perovskite (ppv) phase, significantly altered our understanding of the seismic and dynamic properties of the D". Here we report results of a study of the rheology during transformation from pv to pvv. The experiments were performed using the D-DIA on the X17B2 beamline at NSLS. A sample of presintered perovskite structured CaIrO3 was deformed, along with a MgO stress calibrant, during heating at 3 GPa and up to 1000°C in a 8mm D-DIA assembly. The stress was measured by X-ray diffraction from the MgO sample and a proxy for the phase proportions was the relative strengths of unique perovskite and post-perovskite diffraction peaks from the CaIrO3 sample. The strain was measured by X-radiography, from the position of Platinum foils placed above, between and below the two samples. From this data the viscosity of the CaIrO3 sample can be calculated as well as the progress of the reaction. During the transformation to post-perovskite we observed a two fold weakening of the pv and ppv mixture; followed by an increase in the strength of the mixture to greater than that of that starting perovskite-structured material. If MgSiO3 behaves in the same way during pv - ppv transformation it will cause a viscous decoupling between the lower mantle and the D". This in turn has major implications for the topography that can be supported at the top of the D" layer.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFMMR52A..08H
- Keywords:
-
- 3621 Mantle processes (1038);
- 3630 Experimental mineralogy and petrology;
- 3902 Creep and deformation;
- 3924 High-pressure behavior;
- 3954 X-ray;
- neutron;
- and electron spectroscopy and diffraction