Nitrides and carbonitrides from the lowermost mantle and their importance in the search for Earth’s “lost” nitrogen

Kaminsky, Felix V.; Wirth, Richard

doi:10.2138/am-2017-6101

Cited by 50 publications

(45 citation statements)

References 64 publications

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“…These support that Fe 7 N 3 forms continuous solid solution with Fe 7 C 3 under inner core conditions. Indeed, Fe 7 (C,N) 3 has been found as inclusions in diamond (Kaminsky & Wirth, ).…”

Section: Discussionmentioning

confidence: 99%

Melting Curve and Equation of State of β‐Fe₇N₃: Nitrogen in the Core?

et al. 2019

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The chemical composition of carbonaceous chondrites permits up to 0.5 ± 0.4 wt% N in the Earth's core, which potentially affects the melting temperature, density profile, and phase relation of the core iron alloy. Here we have determined the melting curve and the high-temperature equation of state (EoS) of β-Fe 7 N 3 , which is stable above 40 GPa as the most Fe-rich iron-nitride. Experiments were performed in a laser-heated diamond-anvil cell up to 136 GPa, together with synchrotron X-ray diffraction measurements. We found that multiple melting criteria gave similar melting temperatures: (1) the appearance of diffuse X-ray scattering, (2) discontinuity in the laser power versus temperature relation, and (3) the reduction in diffraction peak intensity from solid. The validity of these melting criteria was confirmed by textural observation of recovered samples. We also observed rapid recrystallization at temperatures lower than the melting temperatures. The results demonstrate that β-Fe 7 N 3 melts congruently at about 3,100 K at 135 GPa, lower than the melting temperatures of FeSi and FeO and similar to that of FeS. The thermal EoS indicates that the density of Fe 7 (C,N) 3 matches the observed inner core density. Combining the melting curve and the EoS of β-Fe 7 N 3 , we also obtain the EoS of liquid Fe 7 N 3 . It shows that the density and compressibility of Fe + 10 wt% N is compatible with the outer core density profile. It supports the presence of some nitrogen in the liquid and solid parts of the core, although its concentration is difficult to constrain from the core density.

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“…These support that Fe 7 N 3 forms continuous solid solution with Fe 7 C 3 under inner core conditions. Indeed, Fe 7 (C,N) 3 has been found as inclusions in diamond (Kaminsky & Wirth, ).…”

Section: Discussionmentioning

confidence: 99%

Melting Curve and Equation of State of β‐Fe₇N₃: Nitrogen in the Core?

et al. 2019

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“…Hence, arguments both against and in favor of nitrogen sequestration in the core exist from various geochemical considerations. The presence of nitrogen during core-mantle differentiation of Earth is also potentially supported by recent findings of nitride and carbonitride inclusions in lower mantle diamond (Kaminsky & Wirth, 2017) if lower mantle domains preserve memory of inefficient core formation. For example, nitrogen may be delivered during core formation in the form of relatively refractory nitrides rather than less stable organics (Rubin & Choi, 2009), minimizing the volatility-induced loss.…”

Section: Introductionmentioning

confidence: 69%

“…Moreover, a fraction of terrestrial core growth might have happened through near-disequilibrium merger of a differentiated planetary embryo (e.g., Li, Marty, et al, 2016;Rudge et al, 2010), in which case merger of a nitride-rich metallic core of more exotic composition formed from a different bulk composition could take place. The presence of nitrogen during core-mantle differentiation of Earth is also potentially supported by recent findings of nitride and carbonitride inclusions in lower mantle diamond (Kaminsky & Wirth, 2017) if lower mantle domains preserve memory of inefficient core formation. Furthermore, although N is shown to be moderate to mildly siderophile or even lithophile, D alloy=silicate N is known only at shallow magma ocean conditions and it remains an open question whether N becomes much more siderophile at deep magma ocean conditions.…”

Section: Introductionmentioning

confidence: 69%

“…Because it is evident that the light elements play a crucial role in the dynamics of the core, it is critical to put constraint on the concentration and the chemistry of the light elements and how it affects the structure, phase relations, elasticity, and transport properties of liquid and solid iron alloys at high pressures and temperatures (Badro et al, 2014(Badro et al, , 2016Buffett & Seagle, 2010;Helffrich, 2014;Huang et al, 2011). Owing to the large mass fraction of the Earth's core, even with a small concentration of a given light element, core may become a significant reservoir of that element in the bulk Earth (Dasgupta, 2013;Dasgupta & Hirschmann, 2010;Kaminsky & Wirth, 2017;Marty, 2012). Several candidates including H, C, O, Si, and S have received attention as possible light elements in the liquid outer and solid inner core (Birch, 1964;Chen et al, 2014;Hirose et al, 2013;Li & Fei, 2003;Poirier, 1994;Ringwood, 1977;Stixrude et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

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Nitrogen Content in the Earth's Outer Core

Bajgain

Mookherjee

Dasgupta

et al. 2019

Geophysical Research Letters

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Using first principles molecular dynamic simulations, we explore the effects of nitrogen (N) on the density and sound velocity of liquid iron and evaluate its potential as a light element in the Earth's outer core. Our results suggest that Fe‐N melt cannot simultaneously explain the density and seismic velocity of the Earth's outer core. Although ~2.0 wt.% N can explain the bulk sound velocity of the outer core, such N content only lowers the density of liquid Fe by ~3%. Matching both the velocity and density by the other light elements limits the N in the core to ≪2.0 wt.%. Our finding suggests that nitrogen is a minor to trace element in the Earth's core and is consistent with the geochemical mass balance with terrestrial abundance of N and alloy‐silicate partitioning data, which suggest that there cannot be significant N in the core.

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“…The uprising interest to iron nitrides is due to their recent ndings in meteorites and deep mantle rocks. [6][7][8][9] Fe 7 C 3 and Fe 7 N 3 stoichiometries are considered as potential inner core constituents among known Fe-C and Fe-N compounds. In the case of Fe 7 C 3 , this assumption is based on the experimental results, showing that this compound crystallizes rst from the iron melt at pressures of 130 GPa, and also on the close correspondence of its density to that of the Earth's core.…”

Section: Introductionmentioning

confidence: 99%