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Nitrogen solubility in stishovite under high P-T: formation of “hidden” nitrogen reservoir in the deep mantle via subducting slabs
Ko Fukuyama1*, Hiroyuki Kagi1, Toru Inoue2, 3, Toru Shinmei3,
Sho Kakizawa3, Shunichi Hishita4, Yuji Sano5, Naoto Takahata5
Geochemical Research Center, The University of Tokyo
HiPeR, Hiroshima University
Geodynamics Research Center, Ehime University
National Institute for Materials Science
Atmosphere and Ocean Research Institute, The University of Tokyo
Thank you for your introduction.
Today, I am going to discuss nitrogen behavior in the deep mantle minerals based on high-pressure and high-temperature experiments.

2. We conducted high-pressure experiments under the lower-mantle
Introduction Methods Result and Discussion Conclusion
“Missing” nitrogen
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Depleted (1.68 ppm)
Nitrogen is
Major element in the atmosphere
Essential element of life
Fig. Volatile abundance ratio in the bulk Earth
(Modified from Marty 2012)
I would like to introduce Missing nitrogen which is background of this research .
As you know, nitrogen is Major element in the atmosphere and an　essential element of life.
However, we still cannot fully understand nitrogen behavior in the deep Earth.
This figure shows Volatile abundance in the Bulk Silicate Earth　normalized by the chondrite composition.
You can see that nitrogen and xenon are extremely depleted (指し示す).
In our research, we focused on this depleted nitrogen.
From these backgrounds, We conducted high-pressure experiments under the lower-mantle condition in order to investigate nitrogen incorporation into the minerals
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Depleted nitrogen can be cause by formation of a deep nitrogen reservoir
We conducted high-pressure experiments under the lower-mantle
condition in order to investigate nitrogen incorporation into the minerals

3. High-pressure experiment and nitrogen analysis
Introduction Methods Result and Discussion Conclusion
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High-pressure experiment
Detection of nitrogen with 15N16O-
Orange-3000
GRC, Ehime Univ
NanoSIMS
AORI, Univ. Tokyo
Table. Experimental conditions
Beam diameter: 2 μm
Ion beam: Cs+, Intensity: 2 nA
e- gun intensity: 500 nA
Raster: 10 μm × 10 μm or 5 μm × 5 μm
Au coating thickness: 20 nm
Analysis time (sample): 600s
Standards: 14N-implanted quartz glass
We used this multi-anvil apparatus installed at Geodynamics Research Center, Ehime University for high-pressure experiments.
This table shows that P, T conditions and heating time in 4 representative experiments.
For nitrogen analysis, we used NanoSIMS installed at Atmosphere and Ocean Research Institute, The University of Tokyo.
Here are analysis conditions.
(読まなくてもよい：We have measured nitrogen standard by SIMS. The standards are quartz glass plate implanted 14N+ ion at NIMS)
Pressure
(GPa)
Temperature
(˚C)
Duration
(min)
Run 1 28
1700
120
Run 2
1620
Run 3
1500
Run 4
1400

4. Recovered sample (28 GPa, 1620 ˚C) and nitrogen in stishovite
Introduction Methods Result and Discussion Conclusion
Recovered sample (28 GPa, 1620 ˚C) and nitrogen in stishovite
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TEL = 4 mm
Fe-FeO buffer + water
100 μm
Hydrous melt Mo
Sample
Pt capsule
Sample
W-Re TC b
Sample
(Mg,Co)O
Re heater
〇: Bridgmanite: MgSiO3,
〇: Stishovite: SiO2
5 mm
From this slide, I will show analysis results of recovered samples.
Right figure was BSE image of sample recovered from 28 GPa and 1620 ℃.
Left figure shows cell assembly.
You can see that right figure of position is beyond the TC in the left figure.
Run products consisted of bridgmanite and stishovite.
Nitrogen source (15NH415NO3)
Atmospheric contamination can be distinguished
Fig1. BSE image of a recovered sample
(28 GPa, 1620 ˚C)
Fig2. Cell assembly in this research

5. Mineral proportions in slabs
Introduction Methods Result and Discussion Conclusion
Mineral proportions in slabs
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Higher nitrogen solubility
Hol
Pressure (GPa)
Mineral proportions (Vol%) Ga
ppm N
(Li et al., 2013)
This study:
ppm N
Stishovite
Coe
Fig 1. Nitrogen solubility in stishovite under
different temperatures
These graphs show that mineral proportions in each subducting layers.
You can see that stishovite occupies from 30% to 40% in several subducting layers.
In addition, sediment layer is rich in nitrogen because K(ポタッシウム) ion in the sediment layer can be substituted by NH4 ion.
For these reasons, stishovite can be an important nitrogen carrier into the lower mantle.
That’s all.
In my poster session, I would like to discuss atmosphere-Mantle Coevolution.
Thank you for your　kind attention.
Fig 2. Sediment (Irifune et al., 1994)
Stishovite can be an important nitrogen carrier into the lower mantle
We will discuss atmosphere-Mantle Coevolution