A Systematic Study of the Pressure and Temperature Dependences of H 2 O and Al 2 O 3 Solubility i
Dan Liu, Ya‐Nan Yang, Hongzhan Fei, Fei Wang, Narangoo Purevjav, Yu Ye, Takayuki Ishii, Tomoo KatsuraAbstract
Water transport to Earth’s lower mantle can occur through the high pressure polymorphs of SiO 2 in subducting slabs, while the incorporation of Al 2 O 3 may affect the H 2 O contents and transitions of the SiO 2 phase. Here we systematically investigated the H 2 O and Al 2 O 3 solubility in stishovite and post‐stishovite (CaCl 2 ‐structure) using multi‐anvil apparatus as a function of pressure from 14–27 GPa at 1,900°C, and as a function of temperature from 1,500 to 2,300°C at 27 GPa. It is found that post‐stishovite is stable at higher temperatures and higher pressures. Secondary‐ion mass spectrometry and Fourier transform infrared spectroscopy reveal that stishovite can incorporate 0.5–0.7 wt.% H 2 O and 3.4–5.5 wt.% Al 2 O 3, while post‐stishovite can incorporate 1.1‐2.0 wt.% H 2 O and 8.6–15.1 wt.% Al 2 O 3 . The Al 2 O 3 solubility continuously increases with increasing pressure and temperature. The H 2 O solubility also increases with pressure and temperature, with Al/H ratio of approximately 1.5. Al‐bearing post‐stishovite may retain >1wt.% of H 2 O. The compositional dependence of the stishovite–post‐stishovite transition pressure implies that chemical heterogeneity can shift its depth by several hundred kilometers, providing a plausible explanation for the broad vertical distribution of mid‐mantle seismic scatterers.