Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Redox state of the deep upper mantle recorded by nickel-rich diamond inclusions

Nature Geoscience (2025)Cite this article

Subjects

A Publisher Correction to this article was published on 25 September 2025

This article has been updated

Abstract

The redox state of Earth’s mantle is governed by the oxidation state of iron and carbon and influences key physical and chemical mantle parameters. Mantle xenoliths, and experimental and thermodynamic studies reveal a decrease in oxygen fugacity with depth, down to ~250 km. A further more modest drop is linked to the predicted stabilization of nickel-rich metallic alloy at 250–300 km. However, garnets from 250–500 km record more oxidized conditions, and no nickel-rich alloy has been reported from these depths to account as natural evidence for the predictions. Here we report nickel–iron metallic nanoinclusions and Ni-rich carbonate microinclusions in two diamonds from the Voorspoed mine, South Africa. Various pressure indicators confirm their origin in the deep upper mantle or the shallow transition zone (280–470 km). The coexistence of nickel-rich metal and carbonate indicates a reaction between oxidized carbonatitic melt and reduced metal-bearing peridotite that led to nickel enrichment and diamond growth. This reaction captures a snapshot of the dynamics of metasomatism, including the formation of intermediate products that may later react. The diamonds provide direct evidence for nickel-rich alloy at its predicted depth within the mantle. They also indicate the presence of deep carbonatitic–silicic melts, which episodically oxidize small volumes of the mantle and play a role in the formation of kimberlites and alkali basalts.

Access through your institution
Buy or subscribe

This is a preview of subscription content, access via your institution

Access options

Access through your institution

Buy this article

  • Purchase on SpringerLink
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: N2 nanoinclusions with Ni–Fe metallic phase in their apex.
Fig. 2: Ni–Fe carbonate microinclusions in diamond ON-VRS-664.
Fig. 3: Constraints on source pressure and a model for diamond formation.
Fig. 4: A conceptual model illustrating deep-mantle metasomatic redox reaction involving Ni-rich phases and diamond formation in the deep upper mantle.

Similar content being viewed by others

Data availability

Source data for this paper are provided in Supplementary Tables and Supplementary Figs. 1–11 and can be found on the EarthChem Library at https://doi.org/10.60520/IEDA/113984 (ref. 77).

Change history

References

  1. Ballhaus, C., Berry, R. F. & Green, D. H. High pressure experimental calibration of the olivine–orthopyroxene–spinel oxygen geobarometer: implications for the oxidation state of the upper mantle. Contrib. Mineral. Petrol. 107, 27–40 (1991).

    Article  CAS  Google Scholar 

  2. Frost, D. J. & McCammon, C. A. The redox state of Earth’s mantle. Annu. Rev. Earth Planet. Sci. 36, 389–420 (2008).

    Article  CAS  Google Scholar 

  3. O’Neill, H. S. C. & Wall, V. J. The olivine–orthopyroxene–spinel oxygen geobarometer, the nickel precipitation curve, and the oxygen fugacity of the Earth’s upper mantle. J. Petrol. 28, 1169–1191 (1987).

    Article  Google Scholar 

  4. Rohrbach, A. et al. Metal saturation in the upper mantle. Nature 449, 456–458 (2007).

    Article  CAS  Google Scholar 

  5. Zhang, Z., von der Handt, A. & Hirschmann, M. M. An experimental study of Fe–Ni exchange between sulfide melt and olivine at upper mantle conditions: implications for mantle sulfide compositions and phase equilibria. Contrib. Mineral. Petrol. 173, 19 (2018).

    Article  Google Scholar 

  6. Rohrbach, A. & Schmidt, M. W. Redox freezing and melting in the Earth’s deep mantle resulting from carbon–iron redox coupling. Nature 472, 209–212 (2011).

    Article  CAS  Google Scholar 

  7. McCammon, C. & Kopylova, M. G. A redox profile of the slave mantle and oxygen fugacity control in the cratonic mantle. Contrib. Mineral. Petrol. 148, 55–68 (2004).

    Article  CAS  Google Scholar 

  8. Stagno, V. Carbon, carbides, carbonates and carbonatitic melts in the Earth’s interior. J. Geol. Soc. 176, 375–387 (2019).

    Article  CAS  Google Scholar 

  9. Woodland, A. B. & Koch, M. Variation in oxygen fugacity with depth in the upper mantle beneath the Kaapvaal craton, Southern Africa. Earth Planet. Sci. Lett. 214, 295–310 (2003).

    Article  CAS  Google Scholar 

  10. Smith, E. M. et al. Large gem diamonds from metallic liquid in Earth’s deep mantle. Science 354, 1403–1405 (2016).

    Article  CAS  Google Scholar 

  11. Smith, E. M. et al. Blue boron-bearing diamonds from Earth’s lower mantle. Nature 560, 84–87 (2018).

    Article  CAS  Google Scholar 

  12. Kiseeva, E. S. et al. Oxidized iron in garnets from the mantle transition zone. Nat. Geosci. 11, 144–147 (2018).

    Article  CAS  Google Scholar 

  13. Stagno, V., Ojwang, D. O., McCammon, C. A. & Frost, D. J. The oxidation state of the mantle and the extraction of carbon from Earth’s interior. Nature 493, 84–88 (2013).

    Article  Google Scholar 

  14. Palyanov, Y. N. et al. Mantle–slab interaction and redox mechanism of diamond formation. Proc. Natl Acad. Sci. USA 110, 20408–20413 (2013).

    Article  CAS  Google Scholar 

  15. Shirey, S. B. et al. in Deep Carbon: Past to Present (eds Orcutt, B. N. et al.) Ch. 3 (Cambridge Univ. Press, 2019).

  16. Tschauner, O. et al. Long-term relaxation of orientational disorder and structural modifications in molecular nitrogen at high pressure. J. Chem. Phys. https://doi.org/10.1063/5.0219186 (2024).

  17. Rohrbach, A., Ghosh, S., Schmidt, M. W., Wijbrans, C. H. & Klemme, S. The stability of Fe–Ni carbides in the Earth’s mantle: evidence for a low Fe–Ni–C melt fraction in the deep mantle. Earth Planet. Sci. Lett. 388, 211–221 (2014).

    Article  CAS  Google Scholar 

  18. Navon, O. et al. Solid molecular nitrogen (δ-N2) inclusions in Juina diamonds: exsolution at the base of the transition zone. Earth Planet. Sci. Lett. 464, 237–247 (2017).

    Article  CAS  Google Scholar 

  19. Nadolinny, V. A. et al. A study of 13C hyperfine structure in the EPR of nickel-nitrogen-containing centres in diamond and correlation with their optical properties. J. Phys. Condens. Matter 11, 7357 (1999).

    Article  CAS  Google Scholar 

  20. Meng, Y., Newville, M., Sutton, S., Rakovan, J. & Mao, H.-K. Fe and Ni impurities in synthetic diamond. Am. Mineral. 88, 1555–1559 (2003).

    Article  CAS  Google Scholar 

  21. Jablon, B. M. & Navon, O. Most diamonds were created equal. Earth Planet. Sci. Lett. 443, 41–47 (2016).

    Article  CAS  Google Scholar 

  22. Weiss, Y., Czas, J. & Navon, O. Fluid inclusions in fibrous diamonds. Rev. Mineral. Geochem. 88, 475–532 (2022).

    Article  CAS  Google Scholar 

  23. Hemley, R. J. in High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto (eds Manghnani, M. H. & Syono, Y.) 347–359 (Terra Scientific Publishing, 1987).

  24. Wang, A., Kuebler, K. E., Jolliff, B. L. & Haskin, L. A. Raman spectroscopy of Fe–Ti–Cr oxides, case study: Martian meteorite EETA79001. Am. Mineral. 89, 665–680 (2004).

    Article  CAS  Google Scholar 

  25. Hutchison, M. T., Hursthouse, M. B. & Light, M. E. Mineral inclusions in diamonds: associations and chemical distinctions around the 670-km discontinuity. Contrib. Mineral. Petrol. 142, 119–126 (2001).

    Article  CAS  Google Scholar 

  26. Kimura, F., Kojitani, H. & Akaogi, M. High-pressure and high-temperature phase relations in the systems KAlSiO4-MgAl2O4 and CaAl2O4-MgAl2O4: stability fields of NAL phases. Phys. Earth Planet. Inter. 310, 106632 (2021).

    Article  CAS  Google Scholar 

  27. Thomson, A. R. et al. Origin of sub-lithospheric diamonds from the Juina-5 kimberlite (Brazil): constraints from carbon isotopes and inclusion compositions. Contrib. Mineral. Petrol. 168, 1081 (2014).

    Article  Google Scholar 

  28. Pamato, M. G. et al. Hexagonal Na0.41[Na0.125Mg0.79Al0.085]2[Al0.79Si0.21]6O12 (NAL phase): crystal structure refinement and elasticity. Am. Mineral. 99, 1562–1569 (2014).

    Article  Google Scholar 

  29. Harte, B. Diamond formation in the deep mantle: the record of mineral inclusions and their distribution in relation to mantle dehydration zones. Mineral. Mag. 74, 189–215 (2010).

    Article  CAS  Google Scholar 

  30. Walter, M. J., Thomson, A. R. & Smith, E. M. Geochemistry of silicate and oxide inclusions in sublithospheric diamonds. Rev. Mineral. Geochem. 88, 393–450 (2022).

    Article  CAS  Google Scholar 

  31. Aulbach, S. & Jacob, D. E. Major- and trace-elements in cratonic mantle eclogites and pyroxenites reveal heterogeneous sources and metamorphic processing of low-pressure protoliths. Lithos 262, 586–605 (2016).

    Article  CAS  Google Scholar 

  32. Kempe, Y. et al. Trace element and Sr-Nd-Pb isotope compositions of diamond-forming fluids in Voorspoed diamonds. Miner. Petrol. https://doi.org/10.1007/s00710-025-00940-2 (2025).

  33. Olijnyk, H. High pressure X‐ray diffraction studies on solid N2 up to 43.9 GPa. J. Chem. Phys. 93, 8968–8972 (1990).

    Article  CAS  Google Scholar 

  34. Schneider, H., Häfner, W., Wokaun, A. & Olijnyk, H. Room temperature Raman scattering studies of external and internal modes of solid nitrogen at pressures 8 ≤ P ≤ 54 GPa. J. Chem. Phys. 96, 8046–8053 (1992).

    Article  CAS  Google Scholar 

  35. Belak, J., Etters, R. D. & LeSar, R. Thermodynamic properties and equation of state of dense fluid nitrogen. J. Chem. Phys. 89, 1625–1633 (1988).

    Article  CAS  Google Scholar 

  36. Strąk, P. & Krukowski, S. Molecular nitrogen–N2 properties: the intermolecular potential and the equation of state. J. Chem. Phys. 126, 194501 (2007).

    Article  Google Scholar 

  37. Katsura, T. A revised adiabatic temperature profile for the mantle. J. Geophys. Res. Solid Earth 127, e2021JB023562 (2022).

    Article  CAS  Google Scholar 

  38. Hanson, R. & Jones, L. Infrared and Raman studies of pressure effects on the vibrational modes of solid CO2. J. Chem. Phys. 75, 1102–1112 (1981).

    Article  CAS  Google Scholar 

  39. Lu, R. & Hofmeister, A. Infrared fundamentals and phase transitions in CO2 up to 50 GPa. Phys. Rev. B 52, 3985 (1995).

    Article  CAS  Google Scholar 

  40. Liu, L.-g Compression and phase behavior of solid CO2 to half a megabar. Earth Planet. Sci. Lett. 71, 104–110 (1984).

    Article  CAS  Google Scholar 

  41. Belonoshko, A. & Saxena, S. K. A molecular dynamics study of the pressure–volume–temperature properties of supercritical fluids: II. CO2, CH4, CO, O2, and H2. Geochim. Cosmochim. Acta 55, 3191–3208 (1991).

    Article  CAS  Google Scholar 

  42. Li, Y., Vočadlo, L., Edgington, A. & Brodholt, J. P. Equation of state for CO and CO2 fluids and their application on decarbonation reactions at high pressure and temperature. Chem. Geol. 559, 119918 (2021).

    Article  CAS  Google Scholar 

  43. Chuliá-Jordán, R. et al. Phase stability of natural Ni0.75Mg0.22Ca0.03CO3 gaspeite mineral at high pressure and temperature. J. Phys. Chem. C. 124, 19781–19792 (2020).

    Article  Google Scholar 

  44. Angel, R. J., Alvaro, M. & Nestola, F. Crystallographic methods for non-destructive characterization of mineral inclusions in diamonds. Rev. Mineral. Geochem. 88, 257–305 (2022).

    Article  CAS  Google Scholar 

  45. Fux, M., Schmidt, M. W. & Liebske, C. The reduced alloy in Earth’s upper mantle: experimental constraints on Fe–Ni–S–C(–O) melt compositions and deep mantle oxygen fugacity (5–16 GPa). Earth Planet. Sci. Lett. 645, 118955 (2024).

    Article  CAS  Google Scholar 

  46. Miller, W. G. R., Holland, T. J. B. & Gibson, S. A. Garnet and spinel oxybarometers: new internally consistent multi-equilibria models with applications to the oxidation state of the lithospheric mantle. J. Petrol. 57, 1199–1222 (2016).

    Article  CAS  Google Scholar 

  47. Davis, F. A., Tangeman, J. A., Tenner, T. J. & Hirschmann, M. M. The composition of KLB-1 peridotite. Am. Mineral. 94, 176–180 (2009).

    Article  CAS  Google Scholar 

  48. McDonough, W. F. & Sun, S. S. The composition of the Earth. Chem. Geol. 120, 223–253 (1995).

    Article  CAS  Google Scholar 

  49. Herzberg, C., Vidito, C. & Starkey, N. A. Nickel–cobalt contents of olivine record origins of mantle peridotite and related rocks. Am. Mineral. 101, 1952–1966 (2016).

    Article  Google Scholar 

  50. Witt-Eickschen, G. & O’Neill, H. S. C. The effect of temperature on the equilibrium distribution of trace elements between clinopyroxene, orthopyroxene, olivine and spinel in upper mantle peridotite. Chem. Geol. 221, 65–101 (2005).

    Article  CAS  Google Scholar 

  51. Eggler, D. H. & Lorand, J. P. Mantle sulfide geobarometry. Geochim. Cosmochim. Acta 57, 2213–2222 (1993).

    Article  CAS  Google Scholar 

  52. Bulanova, G., Griffin, W. L., Ryan, C., Shestakova, O. Y. & Barnes, S.-J. Trace elements in sulfide inclusions from Yakutian diamonds. Contrib. Mineral. Petrol. 124, 111–125 (1996).

    Article  CAS  Google Scholar 

  53. Bulanova, G. P. et al. Mineral inclusions in sublithospheric diamonds from Collier 4 kimberlite pipe, Juina, Brazil: subducted protoliths, carbonated melts and primary kimberlite magmatism. Contrib. Mineral. Petrol. 160, 489–510 (2010).

    Article  CAS  Google Scholar 

  54. Lei, J., Sen, S., Li, Y. & ZhangZhou, J. Carbon in the deep upper mantle and transition zone under reduced conditions: insights from high-pressure experiments and machine learning models. Geochim. Cosmochim. Acta 332, 88–102 (2022).

    Article  CAS  Google Scholar 

  55. Zhang, Z., Qin, T., Pommier, A. & Hirschmann, M. M. Carbon storage in Fe–Ni–S liquids in the deep upper mantle and its relation to diamond and Fe–Ni alloy precipitation. Earth Planet. Sci. Lett. 520, 164–174 (2019).

    Article  CAS  Google Scholar 

  56. Thomson, A. R., Walter, M. J., Kohn, S. C. & Brooker, R. A. Slab melting as a barrier to deep carbon subduction. Nature 529, 76–79 (2016).

    Article  CAS  Google Scholar 

  57. Giuliani, A., Schmidt, M. W., Torsvik, T. H. & Fedortchouk, Y. Genesis and evolution of kimberlites. Nat. Rev. Earth Environ. 4, 738–753 (2023).

    Article  CAS  Google Scholar 

  58. ROCK, N. M. S. The nature and origin of ultramafic lamprophyres: alnöites and allied rocks. J. Petrol. 27, 155–196 (1986).

    Article  CAS  Google Scholar 

  59. Kirstein, L. A. et al. Volatiles and intraplate magmatism: a variable role for carbonated and altered oceanic lithosphere in ocean island basalt formation. J. Petrol. https://doi.org/10.1093/petrology/egad022 (2023).

  60. Mazza, S. E. et al. Sampling the volatile-rich transition zone beneath Bermuda. Nature 569, 398–403 (2019).

    Article  CAS  Google Scholar 

  61. Weiss, Y., Class, C., Goldstein, S. L. & Hanyu, T. Key new pieces of the HIMU puzzle from olivines and diamond inclusions. Nature 537, 666–670 (2016).

    Article  CAS  Google Scholar 

  62. Howell, D. et al. μ-FTIR mapping: distribution of impurities in different types of diamond growth. Diam. Relat. Mater. 29, 29–36 (2012).

    Article  CAS  Google Scholar 

  63. Howell, D., Weiss, Y., Smit, K. V., Loudin, L. & Nestola, F. DiaMap: new applications for processing IR spectra of fluid-rich diamonds and mapping diamonds containing isolated nitrogen (type Ib) and boron (type IIb). In Proc. International Kimberlite Conference: Extended Abstracts 11, abstr. 11IKC-4457 (2017); https://doi.org/10.29173/ikc3831

  64. Klinger, M. More features more tools more CrysTBox. J. Appl. Crystallogr. 50, 1226–1234 (2017).

    Article  CAS  Google Scholar 

  65. Pertlik, F. Structures of hydrothermally synthesized cobalt(II) carbonate and nickel(II) carbonate. Acta Crystallogr. C 42, 4–5 (1986).

    Article  Google Scholar 

  66. Prescher, C. & Prakapenka, V. B. DIOPTAS: a program for reduction of two-dimensional X-ray diffraction data and data exploration. High. Press. Res. 35, 223–230 (2015).

    Article  CAS  Google Scholar 

  67. Kraus, W. & Nolze, G. POWDER CELL—a program for the representation and manipulation of crystal structures and calculation of the resulting X-ray powder patterns. J. Appl. Crystallogr. 29, 301–303 (1996).

    Article  CAS  Google Scholar 

  68. Putz, H., Schön, J. & Jansen, M. Combined method for ab initio structure solution from powder diffraction data. J. Appl. Crystallogr. 32, 864–870 (1999).

    Article  CAS  Google Scholar 

  69. Tamura, N. in Strain and Dislocation Gradients from Diffraction: Spatially-Resolved Local Structure and Defects (eds Barabash, R. I. & Ice, G.) Ch. 4 (World Scientific, 2014).

  70. Tomlinson, E. L. & Holland, T. J. B. A thermodynamic model for the subsolidus evolution and melting of peridotite. J. Petrol. https://doi.org/10.1093/petrology/egab012 (2021).

  71. Robie, R. A. & Hemingway, B. S. Thermodynamic Properties of Minerals and Related Substances at 298.15 K and 1 bar (105 Pascals) Pressure and at Higher Temperatures Vol. 2131 (US Government Printing Office, 1995).

  72. Zhang, D. et al. High-pressure behavior of liebenbergite: the most incompressible olivine-structured silicate. Am. Mineral. 104, 580–587 (2019).

    Article  Google Scholar 

  73. Brosh, E. Modeling of the thermophysical properties of Fe–Ni alloys with application to calculation of high-pressure phase equilibria. Calphad 51, 365–366 (2015).

    Article  Google Scholar 

  74. van de Walle, A., Nataraj, C. & Liu, Z.-K. The thermodynamic database database. Calphad 61, 173–178 (2018).

    Article  Google Scholar 

  75. Swartzendruber, L. J., Itkin, V. P. & Alcock, C. B. The Fe–Ni (iron–nickel) system. J. Phase Equilibria 12, 288–312 (1991).

    Article  CAS  Google Scholar 

  76. Cacciamani, G., Dinsdale, A., Palumbo, M. & Pasturel, A. The Fe–Ni system: thermodynamic modelling assisted by atomistic calculations. Intermetallics 18, 1148–1162 (2010).

    Article  CAS  Google Scholar 

  77. Kempe, Y. et al. Nickel-Rich Inclusions in Sublithospheric Diamonds from Voorspoed, South Africa Version 1.0. (IEDA, 2025); https://doi.org/10.60520/IEDA/113984

  78. Day, H. W. A revised diamond-graphite transition curve. Am. Mineral. 97, 52–62 (2012).

    Article  CAS  Google Scholar 

  79. Young, D. et al. Diatomic melting curves to very high pressure. Phys. Rev. B 35, 5353 (1987).

    Article  CAS  Google Scholar 

  80. Nimis, P., Preston, R., Perritt, S. H. & Chinn, I. L. Diamond’s depth distribution systematics. Lithos 376, 105729 (2020).

    Article  Google Scholar 

Download references

Acknowledgements

We thank A. Radko for help with the Raman analyses, W. Liu (Advanced Photon Source (APS), Argonne National Laboratory) and S. Atray, N. Tamura, H. Bechtel and S. Gilbert-Corder (Advanced Light Source (ALS), Lawrence Berkeley Laboratory) for help with the synchrotron beamline analyses, and E. Brosh for calculating the Fe–Ni alloy a–x relations. I. Chinn and De Beers Consolidated Mines are thanked for the donation of diamonds used in this study and R. Hamman and G. Bartlette for selecting them. We thank E. Stolper, R. Angel and A. Matthews for discussions, and A. Meltzer and O. Elazar for moral support. This research was supported by the Israel Science Foundation grant numbers 2015/18 and 779/22 to Y.W. and NSF-BSF grant number 2020639 to O.N. Use of the APS and the ALS was supported by the US DOE-BES contracts DE-AC02-06CH11357 and DE-AC02-05CH11231.

Author information

Authors and Affiliations

  1. The Freddy and Nadine Herrmann Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel

    Yael Kempe, Oded Navon & Yaakov Weiss

  2. The Harvey M. Krueger Family Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem, Israel

    Sergei Remennik

  3. Department of Geoscience, University of Nevada, Las Vegas, NV, USA

    Oliver Tschauner

  4. Department of Earth Sciences, University of Cambridge, Cambridge, UK

    Tim J. B. Holland

Authors
  1. Yael Kempe
    View author publications

    Search author on:PubMed Google Scholar

  2. Sergei Remennik
    View author publications

    Search author on:PubMed Google Scholar

  3. Oliver Tschauner
    View author publications

    Search author on:PubMed Google Scholar

  4. Oded Navon
    View author publications

    Search author on:PubMed Google Scholar

  5. Tim J. B. Holland
    View author publications

    Search author on:PubMed Google Scholar

  6. Yaakov Weiss
    View author publications

    Search author on:PubMed Google Scholar

Contributions

Y.K. and Y.W. conceived of and developed the project. Y.K. performed the EPMA, FTIR and Raman analyses, and Y.K. and S.R. performed STEM analyses, all at HUJI. O.T. performed the synchrotron X-ray analyses at ANL and LBL. T.J.B.H. carried out the thermodynamic calculations. Y.K. wrote the first draft of the paper and together with Y.W. wrote the present version. S.R. and O.T. helped describe the STEM and X-ray methods and results, and Y.K., T.J.B.H. and O.N. described the thermodynamic calculations. All authors contributed intellectually to the paper.

Corresponding authors

Correspondence to Yael Kempe or Yaakov Weiss.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Geoscience thanks Maya Kopylova, Robert Nicklas and J. ZhangZhou for their contribution to the peer review of this work. Primary Handling Editor: Alison Hunt, in collaboration with the Nature Geoscience team.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Photographs of slabs cut through the central part of the diamonds.

The clouds in the center of the two slabs carry nano- and microinclusions (see Figs. 1 and 2 of the main text). Larger mineral inclusions, up to 20 μm in size surround the cloud of diamond ON-VRS-664 (see Extended Data Fig. 4 and Supplementary Data 6–9).

Extended Data Fig. 2 X-ray diffraction (XRD) spectrum of the inclusions in the diamond clouds.

a. ON-VRS-664 shows three major lines that fit those of δ-N2 and yield a volume of 26.37 ± 4 Å3 corresponding to pressure of 8.1 GPa at room temperature. Other peaks and shoulders fit CO2 under pressure of 8 GPa and gaspeite. Because of the difference in composition between the trapped and the reference gaspeite, no pressure could be estimated based on that phase. See Supplementary Data 2, Supplementary Fig. 2.3 for the full spectrum. b. X-ray diffraction of the high Ni concentration zone in the inclusions cloud of diamond ON-VRS-866. The lines are fitted by diffractograms of deltanitrogen (δ-N2, main phase), taenite (metallic, Ni-rich phase), and possibly Ni11N2 (or (Ni,Fe)11N2), an ordered supercell of fcc-type Ni with some sites unoccupied and some sites occupied by nitrogen.

Extended Data Fig. 3 TEM images of selected area diffraction patterns taken from a single (Ni,Fe)CO3 microinclusion at different orientations.

The solution of these diffraction patterns and the angles between their orientations are in good agreement with the crystallographic structure of trigonal NiCO3 phase with lattice parameters a = b = 4.6117 Å, c = 14.735 Å (ICSD# 61067)65. Pattern of ZA [0001] contain double diffraction due to orientation relationship between diamond and gaspeite crystal structure. Additional diffraction patterns are presented in Supplementary Data 4, Supplementary Figs. 4.3-4.5.

Extended Data Fig. 4 Raman spectra of mineral inclusions in diamond ON-VRS-664.

a. Coesite (a photo of one of the inclusions is shown). All spectra are shifted from the one-atmosphere peak at ~520 cm−1 (RRUFF #X050094). b. Ulvöspinel – the Raman spectrum is very close to that of a synthetic ulvöspinel (Fe2TiO4)24. The spectrum of magnetite (RRUFF Project database number R060191) is shown for comparison. c. Na-Al pyroxene – the upper left inclusion in the photo. Raman peaks at 362, 681 and 1020 cm−1 resemble those of a high-pressure Na-Al pyroxene11 at 348, 680 and 1021 cm−1; the two peaks at 825 and 857 cm−1 fit those of olivine (RRUFF Project database number X050085), suggesting that the two phases co-occupy the inclusion. d. The Raman spectrum was collected before the inclusion was exposed. Two of the peaks fall close to two of the four peaks associated with a Na-NAL phase28, the other two do not show in the present spectrum of the K-NAL inclusions. e. A spectrum collected from the inclusion cloud in diamond ON-VRS-664. The peaks at ~1140 cm−1 correspond to the main line of Mg-gaspeite at a pressure of more than 13.6 GPa43. The photo presents a representative gaspeite microinclusion.

Extended Data Fig. 5 Pressure estimation of the diamond source.

Diamond symbols: internal pressure at room temperature (black dashed line) recorded by the various trapped phases in the inclusions. Blue diamonds: 8.4 and 8.7 GPa (shift of Raman lines) and 8.1 GPa (not shown) based on the X-ray peak. The blue lines: isochores (equal-volume lines) of fluid N2 at high pressure and temperature. The volume was determined based on the pressure in the deltanitrogen inclusions in the two diamonds and the EOS of solid δ-N234. It was extrapolated to high temperatures using the EOS of fluid N235,36. Volume change due to thermal expansion and compressibility of the diamond were neglected and would lead to somewhat higher pressure if included18. Cyan diamond: solid CO2-I at 8 GPa based on the shift of the FTIR line38 (Supplementary Data 5, Supplementary Fig. 5.2) Cyan lines: isochores for fluid CO2, using the volume calculated using the EOS of CO2-I40 and of fluid CO2 (a41, b42). Brown diamond and line: The maximum internal pressure at room temperature (3-9 GPa, by the Raman spectra) and the isomeke for coesite in diamond (the line along which the diamond and the coesite have the same P, T and volume, calculated using the software of Angel et al.44). Dashed grey line – the diamond graphite phase boundary78, Black line – the melting curve of solid N279. Orange line – the 38 mW/m2 geotherm80 connected to the mantle adiabate37. Orange thick line – the inferred possible range of pressure and temperature for the two diamonds.

Supplementary information

Supplementary Data

Supplementary Data 1–11, including all analysis data of the diamonds and inclusions (FTIR, EPMA, TEM, Raman, thermodynamic calculations and XRD).

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Kempe, Y., Remennik, S., Tschauner, O. et al. Redox state of the deep upper mantle recorded by nickel-rich diamond inclusions. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01791-4

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1038/s41561-025-01791-4

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing