4:15 PM - 4:30 PM
[SMP38-16] Al substitution mechanism in anhydrous bridgmanite in low Al content
Keywords:anhydrous bridgmanite, Al substitution mechanism
The high pressure synthesis experiments were conducted at 28 GPa and 1600-1700℃ for 1hour using a Kawai-type multi-anvil apparatus. Four different Al content samples were prepared as the starting materials along the ideal substitution line of Tschermak (Al=0.025, 0.05, 0.1, 0.15 mol) and oxygen-vacancy (Al=0.025, 0.05, 0.075, 0.1 mol) substitutions, respectively (when total cation of 2).
These results show that both Tschermak and oxygen-vacancy substitution bridgmanites can exist in low Al content in anhydrous condition. We found the possible compositional area for Al-bearing anhydrous bridgmanite. The maximum Al content for pure oxygen-vacancy substitution bridgmanite is less than 0.025 mol in total cation of 2. Our result shows that hydration in Al-bridgmanite should occur easily if hydrogen exists in the system (lower mantle) in pyrolite (MgO-excess) composition. In MgO excess condition as pyrolite, oxygen-vacancy substitution favors in Al- bridgmanite in low Al content, if no hydrogen. On the other hand in SiO2 excess condition as MORB and sediment, Tschermak substitution favors in Al-bridgmanite.