High-Pressure Experimental Study of Tetragonal CaSiO3-Pervoskite to 200 GPa
Abstract
CaSiO3-perovskite is one of the major components in the Earth's lower mantle. The volume percentage of CaSiO3-perovskite is estimated to be 5-8 wt.% in the normal lower mantle but could be up to 22-29 wt.% in the subducting mid-ocean ridge basalts (MORBs). Although cubic CaSiO3-perovskite has been believed to be the stable phase at lower-mantle pressure and temperature condition, recent experimental study has shown that some elements, such as Ti, can elevate the phase transition temperature of CaSiO3-perovskite from the tetragonal to the cubic phase. The structure and equation of state of tetragonal CaSiO3-perovskite are thus of great importance in understanding the composition and material transportation in the lower mantle. Here, we have studied the structure and equation of state of endmember tetragonal CaSiO3-perovskite up to 200 GPa using synchrotron X-ray diffraction at GSECARS of the Advanced Photon Source (APS), Argonne National Laboratory (ANL). The observation of a characteristic peak at 2θ = ~10.0oat high pressures and 300 K allows us to provide the direct evidence to confirm that tetragonal CaSiO3-perovskite crystallize in the I4/mcm structure and is stable up to ~200 GPa at 300 K. Combined with previous experimental results, we have modeled the change in density and sound velocity across the tetragonal to cubic phase transition. These results are important for understanding the density and velocity structure of the Earth's lower mantle.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMMR0160011S
- Keywords:
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- 3909 Elasticity and anelasticity;
- MINERAL PHYSICS;
- 3919 Equations of state;
- MINERAL PHYSICS;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 3672 Planetary mineralogy and petrology;
- MINERALOGY AND PETROLOGY;
- 5430 Interiors;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS