Equations of State of Superhydrous Phase B with Varying Mg, Al and Fe Contents: Implications for Water Transport in the Mantle

Dense Hydrous Magnesium Silicates (DHMSs), as potential important water reservoirs in the Earth's interior, are critical for understanding the global water cycle, mantle composition and dynamic processes. Superhydrous phase B (shy-B), as a member of the DHMSs family, is considered an important hydrous phase in the mantle transition zone (MTZ) and even in the uppermost lower mantle (ULM) due to its high water content. Given the abundance of aluminum (Al) and iron (Fe) in the mantle, investigating their effects on the physical properties of shy-B better approximates realistic Earth's interior conditions. In this study, structural characterization and physical property analysis of synthesized Al-bearing shy-B, Fe-bearing shy-B and Fe-Al-bearing shy-B were performed under high pressure using a diamond anvil cell combined with synchrotron radiation single-crystal X-ray diffraction, infrared absorption spectroscopy and Raman scattering spectroscopy. Based on the Birch-Murnaghan (BM) equation of state fitting, the effects of different Al and Fe contents on the bulk modulus of shy-B were quantified, and the variations of density and bulk velocity with pressure were further derived, providing constraints for modeling the geodynamic processes of water subduction and transport.