Journal
GEOPHYSICAL RESEARCH LETTERS
Volume 49, Issue 16, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2022GL098353
Keywords
Al-bearing superhydrous phase B; phase D; phase stability; high pressure and temperature; deep Earth water cycle
Categories
Funding
- Center for Molecular Water Science (CMWS) as part of the early science program (DESY)
- Center for Molecular Water Science (CMWS) as part of the early science program (GFZ)
- Projekt DEAL
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This study investigates the phase stability of Al-bearing superhydrous phase B (shy-B) and its impact on the water cycle in the deep Earth. It reveals that the incorporation of Al expands the stability range and allows the coexistence of phase D even at normal mantle geotherm conditions. The study highlights the importance of Al in dense hydrous magnesium silicates for understanding the water cycle.
In this study, we investigated the phase stability of Al-free and Al-bearing superhydrous phase B (shy-B) up to 55 GPa and 2500 K. In comparison with Al-free shy-B, the incorporation of 11.7 wt.% Al2O3 in shy-B expands the stability by similar to 400-800 K at 20-30 GPa. The determined dehydration boundary for Al-bearing phase D indicates that it could be present even at normal mantle geotherm conditions at 30-40 GPa. Up to 23.8 mol.% Al2O3 can be dissolved into the structures of akimotoite and bridgmanite as a result of the decomposition reactions of Al-bearing shy-B and phase D between 20 and 40 GPa. Results of further experiments indicate that delta-AlOOH is the stable hydrous phase coexisting with Al-depleted bridgmanite at pressures above 52 GPa. This study shows that the incorporation of Al in dense hydrous magnesium silicates can have a profound impact on our picture of the water cycle in the deep Earth.
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