Journal
GEOPHYSICAL RESEARCH LETTERS
Volume 49, Issue 15, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2021GL097178
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Funding
- National Natural Science Foundation of China (NSFC) [41902033, 42150103]
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This study reports the formation of an Al-rich Nt-phase in model hydrated basalts, suggesting its potential role as a water carrier in subducted oceanic crust to the deep lower mantle.
Subducted oceanic crust is enriched in free silica. Although being one of the silica polymorphs at lower-mantle pressures, niccolite-type phase (Nt-phase) has not been documented in multicomponent metabasaltic or metasediment compositions relevant to subducting oceanic crust. Here, we report the formation of an Al-rich Nt-phase (similar to 24.4 to 32.4 wt% Al2O3), coexisting with Al-depleted bridgmanite (similar to 6.4 to 7.6 wt% Al2O3), delta-phase, and iron-rich phase in model hydrated basalts over the pressure-temperature range of 84-113 GPa and 1,800-2,200 K. Infrared spectroscopy of a pure synthetic Al-rich Nt-phase shows OH bending and stretching vibrations at high pressures, indicative of its hydrous nature. This study suggests that Al-rich Nt-phase can serve as a potential water carrier in subducted oceanic crust to the deep lower mantle.
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