14:00 〜 14:15
[SIT14-13] Revaluation of nitrogen storage capacity in the lower mantle by ferropericlase forming solid solution with iron oxynitride.
★Invited Papers
キーワード：高温高圧実験、二次イオン質量分析、”missing” nitrogen、フェロペリクレース、鉄酸窒化物
Nitrogen is one of essential elements of life and the most abundant element in the Earth’s atmosphere. However, nitrogen is depleted by one magnitude compared to other volatile such as carbon and hydrogen and its behaviour has remained unclear in the deep mantle (Marty et al. 2012). Moreover, nitrogen solubility in ferropericlase, the secondary most abundant mineral in the lower mantle, was previously estimated to be significantly low (~17 ppm, Rustioni et al., 2024).
In this research, we investigated effect of iron content on nitrogen solubility in ferropericlase. High-pressure and high-temperature experiments were conducted using multi-anvil apparatus (Orange-3000) installed at Geodynamics Research Center, Ehime University. The pressure condition was 28 GPa and temperature conditions ranged from 1400 ℃ to 1600 ℃. Fe-FeO buffer was used to control the redox state equal to the lower mantle. Nitrogen in recovered samples were analyzed using a secondary ionization mass spectrometer (NanoSIMS, Cameca) installed at Atmosphere and Ocean Research Institute, The University of Tokyo.
Here we report that nitrogen solubility in ferropericlase exponentially increases with increasing its iron content the lower-mantle conditions. This is because ferropericlase can form solid solution with iron oxynitride (FeOxNy, x + y ≈ 1, e.g., Grafouté et al., 2007) with NaCl-crystal structure equal to B1-type ferropericlase. Our results shows that nitrogen storage capacity of the whole lower mantle only by nitrogen-rich ferropericlase with (Mg0.79, Fe0.21)O0.99N0.01 is 300 times larger than the mass of present atmospheric nitrogen in assuming that Fe/(Mg + Fe) of ferropericlase is close to 0.21 as reported in Narygina et al. (2011). Such ferropericlase should play an important role in formation of deep "hidden" nitrogen reservoir during solidification of magma ocean. Our hypothesis that such mafic lower-mantle minerals can store large amount of nitrogen in the deep mantle is consistent with geochemical observations (e.g., Marty 1995).
In this research, we investigated effect of iron content on nitrogen solubility in ferropericlase. High-pressure and high-temperature experiments were conducted using multi-anvil apparatus (Orange-3000) installed at Geodynamics Research Center, Ehime University. The pressure condition was 28 GPa and temperature conditions ranged from 1400 ℃ to 1600 ℃. Fe-FeO buffer was used to control the redox state equal to the lower mantle. Nitrogen in recovered samples were analyzed using a secondary ionization mass spectrometer (NanoSIMS, Cameca) installed at Atmosphere and Ocean Research Institute, The University of Tokyo.
Here we report that nitrogen solubility in ferropericlase exponentially increases with increasing its iron content the lower-mantle conditions. This is because ferropericlase can form solid solution with iron oxynitride (FeOxNy, x + y ≈ 1, e.g., Grafouté et al., 2007) with NaCl-crystal structure equal to B1-type ferropericlase. Our results shows that nitrogen storage capacity of the whole lower mantle only by nitrogen-rich ferropericlase with (Mg0.79, Fe0.21)O0.99N0.01 is 300 times larger than the mass of present atmospheric nitrogen in assuming that Fe/(Mg + Fe) of ferropericlase is close to 0.21 as reported in Narygina et al. (2011). Such ferropericlase should play an important role in formation of deep "hidden" nitrogen reservoir during solidification of magma ocean. Our hypothesis that such mafic lower-mantle minerals can store large amount of nitrogen in the deep mantle is consistent with geochemical observations (e.g., Marty 1995).