The introduction of volatile-rich subducting slabs to the mantle may locally generate large redox gradients, affecting phase stability, element partitioning and volatile speciation1. Here we investigate the redox conditions of the deep mantle recorded in inclusions in a diamond from Kankan, Guinea. Enstatite (former bridgmanite), ferropericlase and a uniquely Mg-rich olivine (Mg# 99.9) inclusion indicate formation in highly variable redox conditions near the 660 km seismic discontinuity. We propose a model involving dehydration, rehydration and dehydration in the underside of a warming slab at the transition zone–lower mantle boundary. Fluid liberated by dehydration in a crumpled slab, driven by heating from the lower mantle, ascends into the cooler interior of the slab, where the H2O is sequestered in new hydrous minerals. Consequent fractionation of the remaining fluid produces extremely reducing conditions, forming Mg-end-member ringwoodite. This fractionating fluid also precipitates the host diamond. With continued heating, ringwoodite in the slab surrounding the diamond forms bridgmanite and ferropericlase, which is trapped as the diamond grows in hydrous fluids produced by dehydration of the warming slab.
This is a preview of subscription content, access via your institution
Subscribe to Nature+
Get immediate online access to Nature and 55 other Nature journal
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Palot, M., Pearson, D. G., Stern, R. A., Stachel, T. & Harris, J. W. Isotopic constraints on the nature and circulation of deep mantle C–H–O–N fluids: carbon and nitrogen systematics within ultra-deep diamonds from Kankan (Guinea). Geochim. Cosmochim. Acta 139, 26–46 (2014).
Stachel, T. Diamonds from the asthenosphere and the transition zone. Eur. J. Miner. 13, 883–892 (2001).
Walter, M. J. et al. Primary carbonatite melt from deeply subducted oceanic crust. Nature 454, 622–625 (2008).
Harte, B., Harris, J. W., Hutchison, M. T., Watt, G. R. & Wilding, M. C. in Mantle Petrology: Field Observations and High Pressure Experimentation: A Tribute to Francis R. (Joe) Boyd (eds Fei, Y., Bertka, C. M. & Mysen, B. O.) 125–153 (The Geochemical Society, 1999).
Stachel, T., Harris, J. W., Brey, G. P. & Joswig, W. Kankan diamonds (Guinea) II: lower mantle inclusion parageneses. Contrib. Mineral. Petrol. 140, 16–27 (2000).
Smith, E. M. et al. Blue boron-bearing diamonds from Earth’s lower mantle. Nature 560, 84–87 (2018).
Stachel, T., Harris, J. W., Aulbach, S. & Deines, P. Kankan diamonds (Guinea) III: δ13C and nitrogen characteristics of deep diamonds. Contrib. Mineral. Petrol. 142, 465–475 (2002).
Regier, M. E. et al. The lithospheric-to-lower-mantle carbon cycle recorded in superdeep diamonds. Nature 585, 234–238 (2020).
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).
Dasgupta, R. & Hirschmann, M. M. The deep carbon cycle and melting in Earth’s interior. Earth Planet. Sci. Lett. 298, 1–13 (2010).
Ringwood, A. E. Phase transformations and differentiation in subducted lithosphere: implications for mantle dynamics, basalt petrogenesis, and crustal evolution. J. Geol. 90, 611–643 (1982).
Brey, G. P., Bulatov, V., Girnis, A., Harris, J. W. & Stachel, T. Ferropericlase—a lower mantle phase in the upper mantle. Lithos 77, 655–663 (2004).
Nestola, F. et al. New accurate elastic parameters for the forsterite-fayalite solid solution. Am. Mineral. 96, 1742–1747 (2011).
Poe, B. T., Romano, C., Nestola, F. & Smyth, J. R. Electrical conductivity anisotropy of dry and hydrous olivine at 8 GPa. Phys. Earth Planet. In. 181, 103–111 (2010).
Nestola, F. et al. First crystal structure determination of olivine in diamond: composition and implications for provenance in the Earth’s mantle. Earth Planet. Sci. Lett. 305, 249–255 (2011).
Angel, R. J., Alvaro, M. & Nestola, F. 40 years of mineral elasticity: a critical review and a new parameterisation of equations of state for mantle olivines and diamond inclusions. Phys. Chem. Mineral. 45, 95–113 (2018).
Angel, R. J., Alvaro, M., Nestola, F. & Mazzucchelli, M. L. Diamond thermoelastic properties and implications for determining the pressure of formation of diamond–inclusion systems. Russian Geol. Geophys. 56, 211–220 (2015).
Angel, R. J., Mazzucchelli, M. L., Alvaro, M. & Nestola, F. EosFit-Pinc: a simple GUI for host–inclusion elastic thermobarometry. Am. Mineral. 102, 1957–1960 (2017).
Katsura, T., Yoneda, A., Yamazaki, D., Yoshino, T. & Ito, E. Adiabatic temperature profile in the mantle. Phys. Earth Planet. Int. 183, 212–218 (2010).
Hasterok, D. & Chapman, D. S. Heat production and geotherms for the continental lithosphere. Earth Planet. Sci. Lett. 307, 59–70 (2011).
Cayzer, N. J., Odake, S., Harte, B. & Kagi, H. Plastic deformation of lower mantle diamonds by inclusion phase transformations. Eur. J. Mineral. 20, 333–339 (2008).
Wood, B. J. Phase transformations and partitioning relations in peridotite under lower mantle conditions. Earth Planet. Sci. Lett. 174, 341–354 (2000).
Davies, R. M., Griffin, W. L., O’Reilly, S. Y. & Doyle, B. J. Mineral inclusions and geochemical characteristics of microdiamonds from the DO27, A154, A21, A418, DO18, DD17 and Ranch Lake kimberlites at Lac de Gras, Slave Craton, Canada. Lithos 77, 39–55 (2004).
Kaminsky, F. V. et al. Superdeep diamonds from the Juina area, Mato Grosso State, Brazil. Contrib. Miner. Petrol. 140, 734–753 (2001).
Tappert, R., Stachel, T., Harris, J. W., Shimizu, N. & Brey, G. P. Mineral inclusions in diamonds from the Panda kimberlite, Slave province, Canada. Eur. J. Miner. 17, 423–440 (2005).
Hayman, P. C., Kopylova, M. G. & Kaminsky, F. V. Lower mantle diamonds from Rio Soriso (Juina area, Mato Grosso, Brazil). Contrib. Miner. Petrol. 149, 430–445 (2005).
Regier, M. E. et al. An oxygen isotope test for the origin of Archean mantle roots. Geochemical Perspect. Lett. 9, 6–10 (2018).
Vance, J. A. & Dungan, M. A. Formation of peridotites by deserpentinization in the Darrington and Sultan areas, Cascade Mountains, Washington. Bull. Geol. Soc. Am. 88, 1497–1508 (1977).
Kitamura, M., Shen, B., Banno, S. & Morimoto, N. Fine textures of laihunite, a nonstoichiometric distorted olivine-type mineral. Am. Mineral. 69, 154–160 (1984).
Blondes, M. S., Brandon, M. T., Reiners, P. W., Page, F. Z. & Kita, N. T. Generation of forsteritic olivine (Fo99·8) by subsolidus oxidation in basaltic flows. J. Petrol. 53, 971–984 (2012).
Frost, D. J. & McCammon, C. A. The redox state of Earth’s mantle. Annu. Rev. Earth Planet. Sci. 36, 389–420 (2008).
Shahar, A. et al. High-temperature Si isotope fractionation between iron metal and silicate. Geochim. Cosmochim. Acta 75, 7688–7697 (2011).
Schmidt, M. W., Gao, C., Golubkova, A., Rohrbach, A. & Connolly, J. A. Natural moissanite (SiC) – a low temperature mineral formed from highly fractionated ultra-reducing COH-fluids. Prog. Earth Planet. Sci. 1, 27 (2014).
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).
Ryabchikov, I. D. & Kaminsky, F. V. Oxygen potential of diamond formation in the lower mantle. Geol. Ore Depos. 55, 1–12 (2013).
McCammon, C. A., Stachel, T. & Harris, J. W. Iron oxidation state in lower mantle mineral assemblages II. Inclusions in diamonds from Kankan, Guinea. Earth Planet. Sci. Lett. 222, 423–434 (2004).
Otsuka, K., Longo, M., McCammon, C. A. & Karato, S. Ferric iron content of ferropericlase as a function of composition, oxygen fugacity, temperature and pressure: implications for redox conditions during diamond formation in the lower mantle. Earth Planet. Sci. Lett. 365, 7–16 (2013).
Shirey, S. B., Wagner, L. S., Walter, M. J., Pearson, D. G. & van Keken, P. E. Slab transport of fluids to deep focus earthquake depths – thermal modeling constraints and evidence from diamonds. AGU Adv. 2, e2020AV000304 (2021).
Van der Hist, R., Engdahl, R., Spakman, W. & Nolet, G. Tomographic imaging of subducted lithosphere below northwest Pacific island arcs. Nature 353, 37–43 (1991).
Billen, M. I. Deep slab seismicity limited by rate of deformation in the transition zone. Sci. Adv. 6, eaaz7692 (2020).
Pearson, D. G. et al. Hydrous mantle transition zone indicated by ringwoodite included within diamond. Nature 507, 221–224 (2014).
Zhu, F., Li, J., Liu, J., Dong, J. & Liu, Z. Metallic iron limits silicate hydration in Earth’s transition zone. Proc. Natl Acad. Sci. 116, 22526–22530 (2019).
Van der Meer, D. G., van Hinsbergen, D. J. J. & Spakman, W. Atlas of the underworld: slab remnants in the mantle, their sinking history, and a new outlook on lower mantle viscosity. Tectonophysics 723, 309–448 (2018).
Harte, B. Diamond formation in the deep mantle: the record of mineral inclusions and their distribution in relation to mantle dehydration zones. Miner. Mag. 74, 189–215 (2010).
Moussallam, Y. et al. Mantle plumes are oxidised. Earth Planet. Sci. Lett. 527, 115798 (2019).
Kaminsky, F. V. et al. Oxidation potential in the Earth’s lower mantle as recorded by ferropericlase inclusions in diamond. Earth Planet. Sci. Lett. 417, 49–56 (2015).
Kiseeva, E. S. et al. Oxidized iron in garnets from the mantle transition zone. Nat. Geosci. 11, 144–147 (2018).
Kawamoto, T. Hydrous phase stability and partial melt chemistry in H2O-saturated KLB-1 peridotite up to the uppermost lower mantle conditions. Phys. Earth Planet. Inter. 143, 387–395 (2004).
Wenz, M. D. et al. Fast identification of mineral inclusions in diamond at GSECARS using synchrotron X-ray microtomography, radiography and diffraction. J. Synchrotron Radiat. 26, 1763–1768 (2019).
Golubkova, A., Schmidt, M. W. & Connolly, J. A. D. Ultra-reducing conditions in average mantle peridotites and in podiform chromitites: a thermodynamic model for moissanite (SiC) formation. Contrib. Mineral. Petrol. 171, 41 (2016).
Holland, T. J. B. & Powell, R. An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids. J. Metamorph. Geol. 29, 333–383 (2011).
Smith, E. M. et al. Heavy iron in large gem diamonds traces deep subduction of serpentinized ocean floor. Sci. Adv. 7, eabe9773 (2021).
Fichtner, C. E., Schmidt, M. W., Liebske, C., Bouvier, A. S. & Baumgartner, L. P. Carbon partitioning between metal and silicate melts during Earth accretion. Earth Planet. Sci. Lett. 554, 116659 (2021).
Wade, J. & Wood, B. J. Core formation and the oxidation state of the Earth. Earth Planet. Sci. Lett. 236, 78–95 (2005).
This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge the support of GeoSoilEnviroCARS (Sector 13), which is supported by the US National Science Foundation (NSF) – Earth Sciences (EAR-1128799), and the Department of Energy, Geosciences (DE-FG02-94ER14466), and staff scientists M. Newville, T. Lanzirotti and M. Rivers. S.D.J. acknowledges support from NSF grant no. EAR-1853521. NSERC Discovery grants to R.W.L., D.G.P. and T.S. funded aspects of this research. The authors acknowledge A. Rohrbach and K. Kiseeva for very valuable comments that prompted a re-think of our fO2 estimate and formation model.
The authors declare no competing interests.
Peer review information
Nature thanks Kate Kiseeva and Arno Rohrbach for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
Reference spectrum of enstatite is in solid red line (RRUFF ID: R070641). The data reduction software is OMNIC 9 (Thermo Fisher Scientific Inc.).
Extended Data Fig. 2 X-ray tomographic image of KK203, collected at GSECARS, showing no cracks leading to inclusions.
The entire diamond could not fit into the field of view.
Extended Data Fig. 3 Calculated values of log fO2 relative to the IW buffer at 10, 15, and 20 GPa and 1,200, 1,400, and 1,800 °C necessary to stabilize a (Mg,Fe)2SiO4 polymorph with Mg# = 99.9.
The different values at each condition reflect the range of assumed activities of Fe and SiO2 (see text for details). The stars denote the case with both activities equal to one. See tabulated values in the accompanying spreadsheet for details of the calculations.
About this article
Cite this article
Nestola, F., Regier, M.E., Luth, R.W. et al. Extreme redox variations in a superdeep diamond from a subducted slab. Nature 613, 85–89 (2023). https://doi.org/10.1038/s41586-022-05392-8