Abstract
Fe-bearing phase E coexisting with ringwoodite and wadsleyite has been synthesized at near-geotherm temperatures in hydrous KLB-1 peridotite compositions held at 18 and 19 GPa, and 1400 °C for 27 h. The long heating duration time of syntheses implies that phase E can be a stable component of the mantle under hydrous conditions. Single-crystal X-ray diffraction analyses show that the M1 octahedral site is 72.1-75.2 at% occupied, whereas the M2 and tetrahedral Si sites are 2.4-2.9 at% and 18.9-19.8 at% occupied, respectively. The M1 site occupancies show a positive correlation with Fe/Mg molar ratios, indicating that Fe mainly occupies the M1 site in the phase E structure. High-pressure Raman spectroscopy shows that the framework Raman frequencies of Fe-bearing phase E increase continuously with increasing pressures up to 19 GPa at room temperature, and there is no indication for a major change in the crystal structure. If transition-zone regions adjacent to subducting slabs are hydrated by fluids generated at the top of the lower mantle, Fe-bearing phase E is expected to occur at wadsleyite-ringwoodite phase transition boundary (about 520 km) as an important phase for incorporating water.
Original language | English (US) |
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Pages (from-to) | 1620-1624 |
Number of pages | 5 |
Journal | American Mineralogist |
Volume | 104 |
Issue number | 11 |
DOIs | |
State | Published - Nov 26 2019 |
Keywords
- Phase E
- X-ray diffraction
- high-pressure Raman spectroscopy
- transition zone
ASJC Scopus subject areas
- Geophysics
- Geochemistry and Petrology