Hydrogen incorporation mechanism in the lower-mantle bridgmanite

Narangoo Porevjav, Naotaka Tomioka, Shigeru Yamashita, Keiji Shinoda, Sachio Kobayashi, Kenji Shimizu, Motoo Ito, Suyu Fu, Jesse Gu, Christina Hoffmann, Jung Fu Lin, Takuo Okuchi

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Bridgmanite, the most abundant mineral in the lower mantle, can play an essential role in deep-Earth hydrogen storage and circulation processes. To better evaluate the hydrogen storage capacity and its substitution mechanism in bridgmanite occurring in nature, we have synthesized high-quality single-crystal bridgmanite with a composition of (Mg0.88Fe0.052+Fe0.053+Al0.03)(Si0.88Al0.11H0.01)O3 $\begin{array}{} \displaystyle {\rm (Mg_{0.88}Fe^{2+}_{0.05}Fe^{3+}_{0.05}Al_{0.03})(Si_{0.88}Al_{0.11}H_{0.01})O_3} \end{array}$ at nearly water-saturated environments relevant to topmost lower mantle pressure and temperature conditions. The crystallographic site position of hydrogen in the synthetic (Fe,Al)-bearing bridgmanite is evaluated by a time-of-flight single-crystal neutron diffraction scheme, together with supporting evidence from polarized infrared spectroscopy. Analysis of the results shows that the primary hydrogen site has an OH bond direction nearly parallel to the crystallographic b axis of the orthorhombic bridgmanite lattice, where hydrogen is located along the line between two oxygen anions to form a straight geometry of covalent and hydrogen bonds. Our modeled results show that hydrogen is incorporated into the crystal structure via coupled substitution of Al3+ and H+ simultaneously exchanging for Si4+, which does not require any cation vacancy. The concentration of hydrogen evaluated by secondary-ion mass spectrometry and neutron diffraction is ~0.1 wt% H2O and consistent with each other, showing that neutron diffraction can be an alternative quantitative means for the characterization of trace amounts of hydrogen and its site occupancy in nominally anhydrous minerals.

Original languageEnglish
Pages (from-to)1036-1044
Number of pages9
JournalAmerican Mineralogist
Volume109
Issue number6
DOIs
StatePublished - Jun 25 2024

Funding

This work was supported by the Japan Society for the Promotion of Science (Post-doctoral Fellowship for Research in Japan Grant Number P17331, and KAKENHI Grant Numbers 17H01172, 18K18795, 18H04468, 20H01965 and 21H04519). J.F.L. acknowledges support from the Geophysics Program and the Cooperative Studies of The Earth's Deep Interior Program (CSEDI) of the National Science Foundation (EAR-2001381; EAR-1916941). A portion of this research at the Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. This work was supported in part by the Joint Use Program at IPM, by the Kochi Core Center Open Facility System (KOFS) under the MEXT foundation, and by the collaboration research project of Integrated Radiation and Nuclear Science, Kyoto University (R3148, R4011, and R5007).

FundersFunder number
Basic Energy Sciences
MEXT foundation
U.S. Department of Energy
Scientific User Facilities Division
Institute for Research in Fundamental Sciences
Japan Society for the Promotion of Science18H04468, 17H01172, 20H01965, P17331, 21H04519, 18K18795
Japan Society for the Promotion of Science
Kyoto UniversityR4011, R5007, R3148
Kyoto University
National Science FoundationEAR-2001381, EAR-1916941
National Science Foundation

    Keywords

    • Bridgmanite
    • hydrogen substitution
    • lower mantle
    • neutron diffraction

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