Hydrogen site analysis of hydrous ringwoodite in mantle transition zone by pulsed neutron diffraction

Narangoo Purevjav, Takuo Okuchi, Naotaka Tomioka, Jun Abe, Stefanus Harjo

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Hydrogen site positions and occupancies in the crystal structure of synthetic hydrous ringwoodite have been determined for the first time by high-resolution neutron powder diffraction conducted at the pulsed neutron source at Japan Proton Accelerator Research Complex (J-PARC). It is demonstrated that hydrogen exchanges not only with Mg or Fe but also with Si cations to form hydroxyl and hydrogen bonding, both within the relevant octahedra or tetrahedra created by their surrounding oxygen anions. The hydrated octahedra shrink, whereas the hydrated tetrahedra expand. The occurrence of simultaneous hydration of octahedra and tetraheda is thus unambiguously confirmed, whereby the latter plays an especially unique role in reducing seismic velocity and for enhancing the electrical conductivity of ringwoodite at high pressures and temperatures. These results provide distinctive implications for discussing the physical properties of hydrous ringwoodite occurring in the mantle transition zone and evaluating the actual water content in the zone. Key Points Hydrogen site positions in ringwoodite crystal structure are first determinedHydrogen exchanges not only with Mg or Fe but also with Si in the structureThe nature of deep mantle water stored in the transition zone is revealed

Original languageEnglish
Pages (from-to)6718-6724
Number of pages7
JournalGeophysical Research Letters
Volume41
Issue number19
DOIs
Publication statusPublished - Oct 16 2014

Keywords

  • hydrogen
  • hydrous minerals
  • mantle transition zone
  • neutron diffraction
  • ringwoodite

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)

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