Hydrogen-bearing iron peroxide and the origin of ultralow-velocity zones

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Ultralow-velocity zones (ULVZs) at Earth’s core–mantle boundary region have important implications for the chemical composition and thermal structure of our planet, but their origin has long been debated1,2,3. Hydrogen-bearing iron peroxide (FeO2Hx) in the pyrite-type crystal structure was recently found to be stable under the conditions of the lowermost mantle4,5,6. Using high-pressure experiments and theoretical calculations, we find that iron peroxide with a varying amount of hydrogen has a high density and high Poisson ratio as well as extremely low sound velocities consistent with ULVZs. Here we also report a reaction between iron and water at 86 gigapascals and 2,200 kelvin that produces FeO2Hx. This would provide a mechanism for generating the observed volume occupied by ULVZs through the reaction of about one-tenth the mass of Earth’s ocean water in subducted hydrous minerals with the effectively unlimited reservoir of iron in Earth’s core. Unlike other candidates for the composition of ULVZs7,8,9,10,11,12, FeO2Hx synthesized from the superoxidation of iron by water would not require an extra transportation mechanism to migrate to the core–mantle boundary. These dense FeO2Hx-rich domains would be expected to form directly in the core–mantle boundary region and their properties would provide an explanation for the many enigmatic seismic features that are observed in ULVZs1,13,14.

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  1. 1.

    & Seismic detection of a thin laterally varying boundary layer at the base of the mantle beneath the central-Pacific. Geophys. Res. Lett. 23, 977–980 (1996)

  2. 2.

    & Evidence for partial melt at the core–mantle boundary north of Tonga from the strong scattering of seismic waves. Nature 391, 682–685 (1998)

  3. 3.

    & in Treatise on Geophysics 2nd edn, Vol. 7, 461–519 (Elsevier, 2015)

  4. 4.

    et al. FeO2 and FeOOH under deep lower-mantle conditions and Earth’s oxygen–hydrogen cycles. Nature 534, 241–244 (2016)

  5. 5.

    et al. Dehydrogenation of goethite in Earth’s deep lower mantle. Proc. Natl Acad. Sci. USA 114, 1498–1501 (2017)

  6. 6.

    , , & The pyrite-type high-pressure form of FeOOH. Nature 547, 205–208 (2017)

  7. 7.

    & Seismic evidence for partial melt at the base of Earth’s mantle. Science 273, 1528–1530 (1996)

  8. 8.

    , & Sediments at the top of Earth’s core. Science 290, 1338–1342 (2000)

  9. 9.

    & Subducted banded iron formations as a source of ultralow-velocity zones at the core-mantle boundary. Nature 434, 371–374 (2005)

  10. 10.

    et al. Iron-rich post-perovskite and the origin of ultralow-velocity zones. Science 312, 564–565 (2006)

  11. 11.

    , & Very low sound velocities in iron-rich (Mg,Fe)O: implications for the core-mantle boundary region. Geophys. Res. Lett. 37, L15304 (2010)

  12. 12.

    , , & Origins of ultra-low velocity zones through slab-derived metallic melt. Proc. Natl Acad. Sci. USA 113, 5547–5551 (2016)

  13. 13.

    & Inferences on ultralow-velocity zone structure from a global analysis of SPdKS waves. J. Geophys. Res. 109, 2156–2202 (2004)

  14. 14.

    , & Tracking deep mantle reservoirs with ultra-low velocity zones. Earth Planet. Sci. Lett. 299, 1–9 (2010)

  15. 15.

    , & Continent-sized anomalous zones with low seismic velocity at the base of Earth’s mantle. Nat. Geosci. 9, 481–489 (2016)

  16. 16.

    , , , & Mega ultra low velocity zone and mantle flow. Earth Planet. Sci. Lett. 364, 59–67 (2013)

  17. 17.

    , , , & Melting of iron at Earth’s inner core boundary based on fast X-ray diffraction. Science 340, 464–466 (2013)

  18. 18.

    & Direct shock compression experiments on premolten forsterite and progress toward a consistent high-pressure equation of state for CaO-MgO-Al2O3-SiO2-FeO liquids. J. Geophys. Res. 118, 5738–5752 (2013)

  19. 19.

    & Preliminary reference Earth model. Phys. Earth Planet. Inter. 25, 297–356 (1981)

  20. 20.

    & The difficulty for subducted oceanic crust to accumulate at the Earth’s core-mantle boundary. J. Geophys. Res. 118, 1807–1816 (2013)

  21. 21.

    et al. Evidence for primordial water in Earth’s deep mantle. Science 350, 795–797 (2015)

  22. 22.

    et al. The stability of hydrous silicates in Earth’s lower mantle: experimental constraints from the systems MgO–SiO2–H2O and MgO–Al2O3–SiO2–H2O. Chem. Geol. 418, 16–29 (2015)

  23. 23.

    Fluid processes in subduction zones. Science 248, 329–337 (1990)

  24. 24.

    , , & Subduction factory: 4. Depth-dependent flux of H2O from subducting slabs worldwide. J. Geophys. Res. 116, 2156–2202 (2011)

  25. 25.

    Hydrogen partitioning into molten iron at high pressure: implications for Earth’s core. Science 278, 1781–1784 (1997)

  26. 26.

    et al. Stable magnesium peroxide at high pressure. Sci. Rep. 5, 13582 (2015)

  27. 27.

    et al. Discovery of Fe7O9: a new iron oxide with a complex monoclinic structure. Sci. Rep. 6, 32852 (2016)

  28. 28.

    et al. Hydrogenation of iron in the early stage of Earth’s evolution. Nat. Commun. 8, 14096 (2017)

  29. 29.

    et al. Iron isotopic fractionation between silicate mantle and metallic core at high pressure. Nat. Commun. 8, 14377 (2017)

  30. 30.

    et al. X-ray diffraction and Mössbauer spectroscopy study of fcc iron hydride FeH at high pressures and implications for the composition of the Earth’s core. Earth Planet. Sci. Lett. 307, 409–414 (2011)

  31. 31.

    , , & The laser micro-machining system for diamond anvil cell experiments and general precision machining applications at the High Pressure Collaborative Access Team. Rev. Sci. Instrum. 86, 072202 (2015)

  32. 32.

    et al. Advanced flat top laser heating system for high pressure research at GSECARS: application to the melting behavior of germanium. High Press. Res. 28, 225–235 (2008)

  33. 33.

    , , , & New developments in laser-heated diamond anvil cell with in situ synchrotron x-ray diffraction at High Pressure Collaborative Access Team. Rev. Sci. Instrum. 86, 072201 (2015)

  34. 34.

    et al. Toward an internally consistent pressure scale. Proc. Natl Acad. Sci. USA 104, 9182–9186 (2007)

  35. 35.

    and PHOENIX: evaluation of nuclear resonant scattering data. Hyperfine Interact. 125, 149–172 (2000)

  36. 36.

    & Pressure calibration of diamond anvil Raman gauge to 410 GPa. J. Phys. Conf. Ser. 215, 012195 (2010)

  37. 37.

    & Second-order elastic constants of a solid under stress. Proc. Phys. Soc. 85, 523–532 (1965)

  38. 38.

    & Quasiharmonic thermal elasticity of crystals: an analytical approach. Phys. Rev. B 83, 184115 (2011)

  39. 39.

    et al. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials. J. Phys. Condens. Matter 21, 395502 (2009)

  40. 40.

    Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994)

  41. 41.

    & From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, (1999)

  42. 42.

    & Efficient pseudopotentials for plane-wave calculations. II. Operators for fast iterative diagonalization. Phys. Rev. B 43, 8861–8869 (1991)

  43. 43.

    , & Band theory and Mott insulators: Hubbard U instead of Stoner I. Phys. Rev. B 44, 943–954 (1991)

  44. 44.

    , & Lattice dynamics calculations for ferropericlase with internally consistent LDA+U method. J. Geophys. Res. 117, B12202 (2012)

  45. 45.

    & Thermodynamic properties of (Mg,Fe2+)SiO3 perovskite at the lower-mantle pressures and temperatures: an internally consistent LSDA+U study. Geophys. J. Int. 190, 310–322 (2012)

  46. 46.

    & Ab initio investigation on the high-temperature thermodynamic properties of Fe3+-bearing MgSiO3 perovskite. J. Geophys. Res. 118, 83–91 (2013)

  47. 47.

    & Linear response approach to the calculation of the effective interaction parameters in the LDA+U method. Phys. Rev. B 71, 035105 (2005)

  48. 48.

    : A program to calculate phonons using the small displacement method. Comput. Phys. Commun. 180, 2622–2633 (2009)

  49. 49.

    , , & Structural properties of ordered high-melting-temperature intermetallic alloys from first-principles total-energy calculations. Phys. Rev. B 41, 10311–10323 (1990)

  50. 50.

    & Efficient iteractive schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996)

  51. 51.

    & First principle phonon calculations in materials science. Scr. Mater. 108, 1–5 (2015)

  52. 52.

    et al. Atoms, molecules, solids, and surfaces: applications of the generalized gradient approximation for exchange and correlation. Phys. Rev. B 46, 6671–6687 (1992)

  53. 53.

    , & Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996)

  54. 54.

    , , , & Electron-energy-loss spectra and the structural stability of nickel oxide: an LSDA+U study. Phys. Rev. B 57, 1505–1509 (1998)

  55. 55.

    , & Metal-insulator transition and the role of electron correlation in FeO2. Phys. Rev. B 95, 075144 (2017)

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We thank A. Shahar for providing the 57Fe-enriched hematite (Fe2O3 with 57Fe of >96.5%) powder samples. We acknowledge C. Kenney-Benson, L. X. Yang, T. T. Gu, B. Li, W. G. Yang, Y. Wu, B. Chen, E. Ohtani, X. Y. Tong and M. M. Li for experimental assistance and discussion, and E. Greenberg for beamline technical support. NRIXS and XRD measurements were performed at the High Pressure Collaborative Access Team (HPCAT 16-IDB and 16-IDD), Advanced Photon Source, Argonne National Laboratory. Some of the XRD experiments were performed at GeoSoilEnviroCARS (Sector 13ID-D) at the Advanced Photon Source. HPCAT operations are supported by the Department of Energy (DOE)-NNSA under award DE-NA0001974, with partial instrumentation funding by NSF. Y.X., P.C. and Y.M. acknowledge the support of the DOE-BES/DMSE under award DE-FG02-99ER45775. GeoSoilEnviroCARS is supported by the National Science Foundation (NSF)—Earth Sciences (EAR-1128799) and the DOE Geosciences (DE-FG02-94ER14466). Use of the Advanced Photon Source was supported by the US DOE, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC02-06CH11357. W.L.M., Q.H. and J.L. acknowledge support from the Geophysics Program by the NSF (EAR 1446969) and the Deep Carbon Observatory. H.-K.M. and Q.H. were supported by NSF grants EAR-1345112 and EAR-1447438. This work was also partially supported by the National Natural Science Foundation of China (grant number U1530402). Some of the computations were conducted at the Supercomputing Center of the University of Science and Technology of China. Z.W. and W.W. acknowledge the support of the Natural Science Foundation of China (41590621) and State Key Development Program of Basic Research of China (2014CB845905). We thank M. Walter for comments and suggestions.

Author information

Author notes

    • Jin Liu
    •  & Qingyang Hu

    These authors contributed equally to this work.


  1. Department of Geological Sciences, Stanford University, Stanford, California 94305, USA

    • Jin Liu
    • , Qingyang Hu
    •  & Wendy L. Mao
  2. Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China

    • Qingyang Hu
    • , Duck Young Kim
    •  & Ho-Kwang Mao
  3. Laboratory of Seismology and Physics of Earth’s Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China

    • Zhongqing Wu
    •  & Wenzhong Wang
  4. High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439, USA

    • Yuming Xiao
    • , Paul Chow
    •  & Yue Meng
  5. Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60437, USA

    • Vitali B. Prakapenka
  6. Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015, USA

    • Ho-Kwang Mao
  7. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA

    • Wendy L. Mao


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J.L., Q.H., Y.X., Y.M., V.B.P. and P.C. carried out the experiment. J.L., W.L.M. and H.-K.M. performed the experimental data analysis. D.Y.K., Q.H., Z.W. and W.W. performed the theoretical simulation. H.-K.M. and W.L.M. conceived and designed the project and directed the calculations and experiments. J.L., W.L.M. and H.-K.M. wrote the manuscript. All authors contributed to the discussion of the results and revision of the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Ho-Kwang Mao or Wendy L. Mao.

Reviewer Information Nature thanks M. Walter and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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