Abstract
Abstract. Texture, plastic deformation, and phase transformation mechanisms in perovskite and post-perovskite are of general interest for our understanding of the Earth's mantle. Here, the perovskite analogue NaCoF3 is deformed in a resistive-heated diamond anvil cell (DAC) up to 30 GPa and 1013 K. The in situ state of the sample, including crystal structure, stress, and texture, is monitored using X-ray diffraction. A phase transformation from a perovskite to a post-perovskite structure is observed between 20.1 and 26.1 GPa. Normalized stress drops by a factor of 3 during transformation as a result of transient weakening during the transformation. The perovskite phase initially develops a texture with a maximum at 100 and a strong 010 minimum in the inverse pole figure of the compression direction. Additionally, a secondary weaker 001 maximum is observed later during compression. Texture simulations indicate that the initial deformation of perovskite requires slip along (100) planes with significant contributions of {110} twins. Following the phase transition to post-perovskite, we observe a 010 maximum, which later evolves with compression. The transformation follows orientation relationships previously suggested where the c axis is preserved between phases and hh0 vectors in reciprocal space of post-perovskite are parallel to [010] in perovskite, which indicates a martensitic-like transition mechanism. A comparison between past experiments on bridgmanite and current results indicates that NaCoF3 is a good analogue to understand the development of microstructures within the Earth's mantle.
Highlights
Earth’s lower mantle is believed to be composed predominantly of bridgmanite, i.e., (Mg,Fe)SiO3 in the perovskite structure (Tschauner et al, 2014)
The deformation and transformation of perovskite and post-perovskite phases are important for a number of processes in the deep Earth (Cížková et al, 2010; Nakagawa and Tackley, 2011; Tackley, 2012), including the development of crystallographic preferred orientation (Yamazaki and Karato, 2007; McCormack et al, 2011; Hunt et al, 2016), known as texture, which can lead to seismic anisotropy (Cobden et al, 2015; Walker et al, 2018b)
NaCoF3 crystallizes in the perovskite structure at ambient conditions
Summary
Earth’s lower mantle is believed to be composed predominantly of bridgmanite, i.e., (Mg,Fe)SiO3 in the perovskite structure (Tschauner et al, 2014). Numerical modeling has been implemented in order to investigate deformation mechanisms in perovskite and post-perovskite (e.g., Ferré et al, 2007; Carrez et al, 2007; Mainprice et al, 2008; Metsue et al, 2009; Boioli et al, 2017; Carrez et al, 2017) This allows for the study of the effect of chemistry, pressure, and temperature and the effects of strain rate on perovskite and post-perovskite deformation, which can not be measured in experiments using current experimental techniques. We use a resistive-heated radial DAC combined with synchrotron radiation at pressures and temperatures between 1.1 and 29.6 GPa and 300 and 1013 K, respectively, to observe in situ texture development and phase change from a perovskite to a post-perovskite structure in NaCoF3 We use these data to model plastic deformation and deformation mechanisms in perovskite. These results can help us to better understand the deformation and phase transformation in perovskite and post-perovskite phases and will lead to greater knowledge of deep mantle dynamics
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