Superhydrous B (shy B) is a dense hydrous magnesium silicate (DHMS) phase, for which experimental studies have indicated a large stability field along cold subduction geotherms in the Earth’s transition zone and top region of the lower mantle. The rheological properties of shy B may therefore be relevant to the rheology and possibly the deep seismic characteristics of subduction zones. Samples of shy B have been synthesized and deformed in a multianvil apparatus at 20 GPa and at temperatures 1000–1100 °C. The resulting dislocations have been characterized by transmission electron microscopy (TEM) with the weak-beam dark-field (WBDF) and the large-angle convergent-beam electron diffraction (LACBED) techniques. We emphasize the role of (010) plane in the plasticity of phase shy B. We report that [100] and [001] glide in (010), and also climb of [100]. We also observe 〈101〉 glide in (010) and {111} planes under high stress conditions.

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