Letter | Published:

Early differentiation and volatile accretion recorded in deep-mantle neon and xenon

Nature volume 486, pages 101104 (07 June 2012) | Download Citation

Abstract

The isotopes 129Xe, produced from the radioactive decay of extinct 129I, and 136Xe, produced from extinct 244Pu and extant 238U, have provided important constraints on early mantle outgassing and volatile loss from Earth1,2. The low ratios of radiogenic to non-radiogenic xenon (129Xe/130Xe) in ocean island basalts (OIBs) compared with mid-ocean-ridge basalts (MORBs) have been used as evidence for the existence of a relatively undegassed primitive deep-mantle reservoir1. However, the low 129Xe/130Xe ratios in OIBs have also been attributed to mixing between subducted atmospheric Xe and MORB Xe, which obviates the need for a less degassed deep-mantle reservoir3,4. Here I present new noble gas (He, Ne, Ar, Xe) measurements from an Icelandic OIB that reveal differences in elemental abundances and 20Ne/22Ne ratios between the Iceland mantle plume and the MORB source. These observations show that the lower 129Xe/130Xe ratios in OIBs are due to a lower I/Xe ratio in the OIB mantle source and cannot be explained solely by mixing atmospheric Xe with MORB-type Xe. Because 129I became extinct about 100 million years after the formation of the Solar System, OIB and MORB mantle sources must have differentiated by 4.45 billion years ago and subsequent mixing must have been limited. The Iceland plume source also has a higher proportion of Pu- to U-derived fission Xe, requiring the plume source to be less degassed than MORBs, a conclusion that is independent of noble gas concentrations and the partitioning behaviour of the noble gases with respect to their radiogenic parents. Overall, these results show that Earth’s mantle accreted volatiles from at least two separate sources and that neither the Moon-forming impact nor 4.45 billion years of mantle convection has erased the signature of Earth’s heterogeneous accretion and early differentiation.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

References

  1. 1.

    , & Rare gas systematics: formation of the atmosphere, evolution and structure of the Earth’s mantle. Earth Planet. Sci. Lett. 81, 127–150 (1987)

  2. 2.

    Neon and xenon isotopes in MORB: implications for the earth-atmosphere evolution. Earth Planet. Sci. Lett. 94, 45–56 (1989)

  3. 3.

    & Seawater subduction controls the heavy noble gas composition of the mantle. Nature 441, 186–191 (2006)

  4. 4.

    & Isotope systematics of noble gases in the Earth’s mantle: possible sources of primordial isotopes and implications for mantle structure. Phys. Earth Planet. Inter. 148, 13–38 (2005)

  5. 5.

    & Preserving noble gases in a convecting mantle. Nature 459, 560–563 (2009)

  6. 6.

    & Geochemical constraints on mantle dynamics in the Hadean. Earth Planet. Sci. Lett. 238, 17–30 (2005)

  7. 7.

    & Origin of noble gases in the terrestrial planets. Rev. Mineral. Geochem. 47, 191–246 (2002)

  8. 8.

    & Mass transfer of helium, neon, argon and xenon through a steady-state upper mantle. Geochim. Cosmochim. Acta 59, 4921–4937 (1995)

  9. 9.

    & Early crust on top of the Earth’s core. Phys. Earth Planet. Inter. 148, 109–130 (2005)

  10. 10.

    , & Helium isotopic systematics of oceanic islands and mantle heterogeneity. Nature 297, 43–47 (1982)

  11. 11.

    , , & A multiple-system study of the geochemical evolution of the mantle with force-balanced plates and thermochemical effects. Earth Planet. Sci. Lett. 276, 1–13 (2008)

  12. 12.

    & Compositional heterogeneity in the bottom 1000 kilometers of Earth’s mantle: toward a hybrid convection model. Science 283, 1885–1888 (1999)

  13. 13.

    & Evolution of helium isotopes in the Earth’s mantle. Nature 436, 1107–1112 (2005)

  14. 14.

    Rogue mantle helium and neon. Science 319, 943–945 (2008)

  15. 15.

    Helium isotopic evidence for episodic mantle melting and crustal growth. Nature 446, 900–903 (2007)

  16. 16.

    et al. Upside-down differentiation and generation of a ‘primordial’ lower mantle. Nature 463, 930–933 (2010)

  17. 17.

    , & Rare gas systematics in popping rock: isotopic and elemental compositions in the upper mantle. Science 279, 1178–1181 (1998)

  18. 18.

    , , , & The nature of pristine noble gases in mantle plumes. Science 288, 1036–1038 (2000)

  19. 19.

    , , & Resolving atmospheric contaminants in mantle noble gas analyses. Geochem. Geophys. Geosyst. 4, 1023 (2003)

  20. 20.

    , , & Neon isotopes constrain convection and volatile origin in the Earth’s mantle. Nature 433, 33–38 (2005)

  21. 21.

    & A determination of the neon isotopic composition of the deep mantle. Earth Planet. Sci. Lett. 225, 77–88 (2004)

  22. 22.

    & Primordial helium and neon in the Earth — a speculation on early degassing. Geophys. Res. Lett. 25, 1951–1954 (1998)

  23. 23.

    et al. Primordial noble cases from Earth’s mantle: identification of a primitive volatile component. Science 285, 2115–2118 (1999)

  24. 24.

    , & Chondritic-like xenon trapped in Archean rocks: a possible signature of the ancient atmosphere. Earth Planet. Sci. Lett. 308, 298–306 (2011)

  25. 25.

    , & Plutonium-fission xenon found in Earth’s mantle. Science 280, 877–880 (1998)

  26. 26.

    , , , & Heterogeneous accretion and the moderately volatile element budget of Earth. Science 328, 884–887 (2010)

  27. 27.

    Early silicate Earth differentiation. Annu. Rev. Earth Planet. Sci. 39, 31–58 (2011)

  28. 28.

    & Equilibration in the aftermath of the lunar-forming giant impact. Earth Planet. Sci. Lett. 262, 438–449 (2007)

  29. 29.

    , , , & Diamonds sampled by plumes from the core–mantle boundary. Nature 466, 352–355 (2010)

  30. 30.

    , & He, Ne and Ar systematics in single vesicles: mantle isotopic ratios and origin of the air component in basaltic glasses. Earth Planet. Sci. Lett. 274, 142–150 (2008)

Download references

Acknowledgements

I thank D. Graham for supplying the Iceland sample, and K. Zahnle, C. Langmuir, S. Stewart and R. Parai for comments. Reviews by C. Ballentine, B. Marty and D. Porcelli helped to improve the paper. This work was supported by NSF grant EAR 0911363.

Author information

Affiliations

  1. Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA

    • Sujoy Mukhopadhyay

Authors

  1. Search for Sujoy Mukhopadhyay in:

Competing interests

The author declares no competing financial interests.

Corresponding author

Correspondence to Sujoy Mukhopadhyay.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    This file contains Supplementary Figures 1-4, Supplementary Tables 1-7 and Supplementary References.

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/nature11141

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.