Abstract
The 400-km seismic discontinuity has traditionally been ascribed to the isochemical transformation of α-olivine to the β-modified-spinel structure in a mantle of peridotitic bulk composition1–6. It has recently been proposed7,8 that the observed seismic velocity increase at 400km depth is too abrupt and too small to result from a phase change in olivine but instead requires that the transition zone be chemically distinct in bulk composition from the uppermost mantle. By requiring phase relations in the Mg2SiO4-Fe2SiO4 system to be internally consistent thermodynamically, we find that the α–β transition in olivine of mantle (Mg0.9Fe0.1)2SiO4 composition is extremely sharp, occurring over a depth interval (isothermal) of ∼6 km. The magnitude of the predicted velocity increase is in agreement with that observed seismically9,10 if the transition zone is composed of ∼60–70% olivine. Thus, our results indicate that seismic velocities across the 400-km discontinuity are consistent with a transition zone of homogeneous peridotitic composition and do not require chemical stratification.
This is a preview of subscription content, access via your institution
Access options
Subscribe to this journal
Receive 51 print issues and online access
$199.00 per year
only $3.90 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Bernai, J. D. Observatory 59, 268 (1936).
Ringwood, A. E. Composition and Petrology of the Earth's Mantle (McGraw-Hill, New York, 1975).
Liu, L. in The Earth: Its Origin, Structure and Evolution (ed. McElhinny, M. W.) 177–202 (Academic, New York, 1979).
Jeanloz, R. & Thompson, A. B., Rev. Geophys. Space Phys. 21, 51–74 (1983).
Navrotsky, A. & Akaogi, M. J. geophys. Res. 89, 10135–10140 (1984).
Weidner, D. J., Geophys. Res. Lett. 12, 417–420 (1985).
Bass, J. D. & Anderson, D. L. Geophys. Res. Lett. 11, 237–240 (1984).
Anderson, D. L. & Bass, J. D. Nature 320, 321–328 (1986).
Walck, M. C. Geophys. R. R. astr. Soc. 76, 697–723 (1984).
Grand, S. P. & Helmberger, D. V. Geophys. J. R. ast. Soc. 76, 399–438 (1984).
Bina, C. R. & Wood, B. J. Geophys. Res. Lett. 11, 955–958 (1984).
Suito, K. in High Pressure Research—Applications to Geophysics (eds Manghnani, M. H. & Akimoto, S.) 255–266 (Academic, New York, 1977).
Kawada, K. . thesis, Univ. Tokyo (1977).
Sawamoto, H. Phys. Chem. Miner. 13, 1–10 (1986).
Watanabe, H. . in High Pressure Research in Geophysics (eds Akimoto, S. & Manghnani, M. H.) 441–464 (Center for Academic Publications, Tokyo, 1982).
Weidner, D. J., Sawamoto, H., Sasaki, S. & Kumazawa, M. J. geophys. Res. 89, 7852–7860 (1984).
Wood, B. J. & Kleppa, O. J. Geochim. cosmochim. Acta 45, 529–534 (1981).
Akimoto, S. & Fujisawa, H. J. geophys. Res. 73, 1467–1479 (1968).
Ringwood, A. E. & Major, A. Phys. Earth planet. Inter. 3, 89–108 (1970).
Yagi, T., Bell, P. M. & Mao, H.-K. Yb. Carnegie Inst. Wash. 78, 614–618 (1979).
Bina, C. R. & Wood, B. J. J. geophys. Res. (submitted).
Anderson, O. L., Schreiber, E., Liebermann, R. C. & Soga, N. Rev. Geophys. Space Phys. 6, 491–524 (1968).
Birch, F. J. geophys. Res. 57, 227–286 (1952).
Wood, B. J. & Holloway, J. R. Geochim. cosmochim. Acta 48, 159–176 (1984).
Watt, J. P., Davies, G. F. & O'Connell, R. J. Rev. Geophys. Space Phys. 14, 541–563 (1976).
Sumino, Y. & Anderson, O. L. in CRC Handbook of Physical Properties of Rocks Vol. III (ed. Carmichael, R. S.) 39–138 (CRC, Boca Raton, 1984).
Lees, A. C., Bukowinski, M. S. T. & Jeanloz, R. J. geophys. Res. 88, 8145–8159 (1983).
Muirhead, K. J. geophys. Res. 90, 2057–2059 (1985).
Ingate, S. F., Ha, J. & Muirhead, K. J., Geophys. J.R. astr. Soc. 86, 57–61 (1986).
Leven, J. H. Phys. Earth planet. Inter. 38, 9–27 (1985).
Silver, P. G., Carlson, R. W., Bell, P. & Olsen, P. Eos 66, 1193–1198 (1985).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Bina, C., Wood, B. The 400-km seismic discontinuity and the proportion of olivine in the Earth's upper mantle. Nature 324, 449–451 (1986). https://doi.org/10.1038/324449a0
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1038/324449a0
This article is cited by
-
Iron partitioning in a pyrolite mantle and the nature of the 410-km seismic discontinuity
Nature (1998)
-
Elasticity of forsterite to 16 GPa and the composition of the upper mantle
Nature (1995)
-
Mutually consistent estimates of upper mantle composition from seismic velocity contrasts at 400 km depth
Pure and Applied Geophysics PAGEOPH (1993)
-
The elastic properties of single-crystal fayalite as determined by dynamical measurement techniques
Pure and Applied Geophysics PAGEOPH (1993)
-
Stress dependence of the mechanism of the olivine–spinel transformation
Nature (1989)
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.