Report for the Joint Use/Research of the Institute for Planetary Materials,Okayama University
2020 fiscal year first term / second term / others
26/May/2021
Category:

International Joint Research

Name of the research project: The coupling of water and fluorine in bridgmanite
Principal applicant: Xiang Wu
Affiliated institution and department: State Key Laboratory of Geological Processes and Mineral
Resources, China University of Geosciences (Wuhan), Wuhan 430074, China.
Collaborator
Name: Takashi Yoshino
Affiliated institution and department: Institute for Planetary Materials, Okayama University,Misasa, Tottori 682-0193, JapanResearch report:1) Please write the research report with free format, but include followings: research purpose, actuallyconducted research, and research outcomes. If necessary, you can add another pages.

H2O solubility in bridgmanite, the most abundant mineral in the Earth’s lower mantle, is still indebate, yet it has far-reaching impacts on the physical behavior of the mantle and our planet’sevolution. Previous studies suggested that bridgmanite can contain either low (a few ppm wt, nearor less than the detection limit) or high (~2,000 ppm wt) water concentrations at the presence of Feand Al (e.g. Panero et al., 2014; Fu et al., 2019). Yoshino and Jaseem. (2018) reported that H
solubility in bridgmanite correlates with the F solubility (Figure 1), suggests that certain amounts ofH2O (up to 4948 ppm, which is much higher than what we observed before) could be incorporated
into the bridgmanite in the presence of F. However, they did not take Fe (the most abundanttransition metal in the Earth’s mantle) into their account where Fe 2+ may reduce the solubility of F
in minerals (named Fe2+-F acoidance rule) (e.g. Mason, 1992). To explore H2O, F solubility and thecoupling of H2O and F in the natural Earth’s lower mantle, we have synthesized two stishovite andfour bridgmanite with different compositions at 24 GPa and 1973 K for 3 hours. Their
microstructures were examined by scanning electron microscopy (Figure 2) and their chemicalcompositions were determined with an electron microprobe analyzer (EMPA) (Table 1). The run
product phases were identified by Raman Spectrum (Figure 3) and micro-focused X-ray
diffractometer. Stishovite with small grain size of ~50 μm and bridgmanite with small grain size of~100 μm.

EMPA results show that F solubility in stishovite are under detection limit, but (Al,Fe)-richbridgmanite (1K3277) can contain a large amount of F (range from 4225 ppm to 9735 ppm). We
also found the distinct OH‐stretching peak at 3580 cm-1 using Raman spectrum, indicating thatbridgmanite from Run 1K3277a and b contain H2O in its structure. The volume of stishovites are
46.891(3) and 46.822(3) Å3 for 1K3277a and b decided by a micro-focused X-ray diffractometer,and they contain ~1.25 wt% H2O calculated by the equation: C (H2O, wt %) = 4.64 ×ΔV from Nisret al. (2017). Our results show that stishovites can only carry a large amount of H2O to Earth’s
lower mantle, and (Al,Fe)-bearing bridgmanite in the uppermost lower mantle may be a reservoir
for fluorine and water.
To quantitative analysis H2O solubility in bridgmanite, we are going to use NanoSIMs byco-operating with Dr. Jing Yang from Carnegie Institution of Washington. Also, Mössbauer
Spectroscopy is needed to study the Fe2+/ Fe3+ in bridgmanite and the effects of valence state of ironon solubility of F and H. Moreover, high-pressure and high-temperature X-ray diffraction andBrillouin scattering should be carried to studied the effects of F and H on the elastic properties ofbridgmanite at lower mantle conditions.
Table 1. Chemical compositions of bridgmanite and stishovite.
Run #1K3277a1K3277b

1K3277a1K3277b

5K3542a5K3542b

Phase

Stishovite

Stishovite

Bridgmanite

Bridgmanite

Bridgmanite

Bridgmanite

F000.9735

0.42250.1123

0.075

Al2O3

3.69854.564516.842

15.916

3.2707

6.626

MgO

0.03350.028

28.28927.263537.712335.0477

SiO2

95.08392.87140.3555

39.8475

55.5877

51.5263

FeO

0.0295

0.097

9.264

12.4115

2.9507

7.641

Total

98.8445

98.194595.72495.86199.6337

100.916

Figure 2. Scanning electron micrographs (SEM) of 1K3277 and 5K3542, Sto = Stishovite, Brg = bridgmanite.

Figure 3. Unpolarized Raman spectra of bridgmanite. The black line represents the dates from Fu et al., 2019 andthe red and blue line represent the date from 1K32771a and 1K32771b, respectively. There also have sharp
vibrational bands at 3580 cm-1.

References:Fu, S.Y., Yang, J., Karato, S.-I., Vasiliev, A., Presniakov, M.Y., Gavrilliuk, A.G., et al. (2019). Water
Concentration in Single‐Crystal (Al,Fe)‐Bearing Bridgmanite Grown From the Hydrous Melt:
Implications for Dehydration Melting at the Topmost Lower Mantle. Geophysical Research
Letters, 46, 10346–10357.
Nisr, C., Shim, S.H., Leinenweber, K., & Chizmeshya, A. (2017). Raman spectroscopy ofwater-rich stishovite and dense high-pressure silica up to 55 GPa. American Mineralogist, 102,2180–2189.
Panero, W.R., Pigott, J.S., Reaman, D.M., Kabbes, J.E., Liu, Z.X. (2014). Dry (Mg,Fe)SiO3
perovskite in the Earth’s lower mantle. Journal of Geophysical Research: Solid Earth, 120,894–908.
Yoshino. T., & Jaseem, V. (2018). Solubility in bridgmanite: A potential fluorine reservoir in theEarth’s mantle. Earth and Planetary Science Letters, 504, 106–114.

2) For the workshop, please write the report for the workshop. Also, attach the program, abstracts, and listof the participants etc.

3) Please add Collaborator's Name, Affiliated institution and department as needed.

Name: Prof. Takashi Yoshino, Dr. Ran Wang
Affiliated institution and department: Institute for Planetary Materials, Okayama University,
Misasa, Tottori 682-0193, Japan
Name: Prof. Xiang Wu, M.D. Xiang Li
Affiliated institution and department: State Key Laboratory of Geological Processes and MineralResources, China University of Geosciences (Wuhan), Wuhan 430074, China.
Name: Dr. Jing Yang
Affiliated institution and department: Geophysical Laboratory, Carnegie Institution ofWashington, Washington, DC, USA