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

Anno: 2022

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

Affiliazione autori: Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai, China; School of Physical Sciences, University of Science and Technology of China, Hefei, China; School of Earth and Space Sciences, Peking University, Beijing, China; National Institute of Optics (INO-CNR), European Laboratory for Non-Linear Spectroscopy (LENS), Sesto Fiorentino, Italy; Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany; Department of Earth Science, Graduate School of Science, Tohoku University, Sendai, 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


Volume: 49 (15)      Da Pagina: e2021GL097178-1  A: e2021GL097178-10

Maggiori informazioni: 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.
DOI: 10.1029/2021GL097178