Formation of an Al-Rich Niccolite-Type Silica in Subducted Oceanic Crust: Implications for Water Transport to the Deep Lower Mantle

Year: 2022

Authors: Liu L., Yuan H., Yao Y., Yang Z., Gorelli F.A., Giordano N., He L., Ohtani E., Zhang L.

Autors Affiliation: Ctr High Pressure Sci & Technol Adv Res HPSTAR, Shanghai, Peoples R China; Univ Sci & Technol China, Sch Phys Sci, Hefei, Peoples R China; Peking Univ, Sch Earth & Space Sci, Beijing, Peoples R China; European Lab NonLinear Spect LENS, Natl Inst Opt INO CNR, Sesto Fiorentino, Italy; Deutsch Eleckt Synchrotron DESY, Hamburg, Germany; Tohoku Univ, Dept Earth Sci, Grad Sch Sci, Sendai, Miyagi, Japan.

Abstract: 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

Journal/Review: GEOPHYSICAL RESEARCH LETTERS

Volume: 49 (15)      Pages from: e2021GL097178-1  to: e2021GL097178-10

More Information: This work was supported from the National Natural Science Foundation of China (NSFC) (Grant Nos 41902033 and 42150103). The authors acknowledge Deutsches Elektronen Synchrotron (DESY, Hamburg, Germany), a member of the Helmholtz Association HGF, and Shanghai Synchrotron Radiation Facility (SSRF) for the provision of experimental facilities. Portions of this research were carried out at the light source PETRA III at DESY. Portions of this work were performed at BL15U1 and BL06B1 at SSRF. The authors appreciate comments from the two anonymous reviewers.
KeyWords: HIGH-PRESSURE; PHASE-RELATIONS; ULTRAHYDROUS STISHOVITE; INFRARED-ABSORPTION; TRANSITION ZONE;
DOI: 10.1029/2021GL097178

Citations: 5
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