Elasticity of single‐crystal superhydrous phase B at simultaneous high pressure‐temperature conditions

• Published in: Geophysical research letters 2016-08, Vol.43 (16), p.8458-8465
• Main Authors: Li, Xinyang, Mao, Zhu, Sun, Ningyu, Liao, Yifan, Zhai, Shuangmeng, Wang, Yi, Ni, Huaiwei, Wang, Jingyun, Tkachev, Sergey N., Lin, Jung‐Fu
• Format: Article
• Language: English
• Subjects: Anisotropy; Anomalies; Diffraction; Elasticity; GEOSCIENCES; High pressure; high P‐T; Lower mantle; low‐velocity layer; Mantle; Seismic analysis; single crystal elasticity; Single crystals; Slabs; superhydrous phase B; Temperature; Transition zone; water; X-ray diffraction
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2016GL070027

We investigated the combined effect of pressure and temperature on the elasticity of single‐crystal superhydrous phase B (Shy‐B) using Brillouin scattering and X‐ray diffraction up to 12 GPa and 700 K. Using the obtained elasticity, we modeled the anisotropy of Shy‐B along slab geotherms, showing that Shy‐B has a low anisotropy and cannot be the major cause of the observed anisotropy in the region. Modeled velocities of Shy‐B show that Shy‐B will be shown as positive velocity anomalies at the bottom transition zone. Once Shy‐B is transported to the topmost lower mantle, it will exhibit a seismic signature of lower velocities than topmost lower mantle. We speculate that an accumulation of hydrous phases, such as Shy‐B, at the topmost lower mantle with a weight percentage of ~17–26% in the peridotite layer as subduction progresses could help explain the observed 2–3% low shear velocity anomalies in the region. Key Points We determine elasticity of single‐crystal Shy‐B at simultaneous high P‐T conditions The anisotropy of Shy‐B is small and cannot be the major cause for the observed seismic anisotropy in the slab regions Shy‐B has lower velocities than those of the topmost lower mantle and could explain the observed low‐velocity layer in the region