The composition of the mantle transition region, characterized by anomalous seismic-wave velocity and density changes at depths of ∼400 to 700 km, has remained controversial. Some have proposed that the mantle transition region has an olivine-rich ‘pyrolite’ composition1,2, whereas others have inferred that it is characterized by pyroxene- and garnet-rich compositions (‘piclogite’), because the sound velocities in pyrolite estimated from laboratory data are substantially higher than those seismologically observed3,4,5. Although the velocities of the olivine polymorphs at these pressures (wadsleyite and ringwoodite) have been well documented, those of majorite (another significant high-pressure phase in the mantle transition region) with realistic mantle compositions have never been measured. Here we use combined in situ X-ray and ultrasonic measurements under the pressure and temperature conditions of the mantle transition region to show that majorite in a pyrolite composition has sound velocities substantially lower than those of earlier estimates, owing to strong nonlinear decreases at high temperature, particularly for shear-wave velocity. We found that pyrolite yields seismic velocities more consistent with typical seismological models than those of piclogite in the upper to middle parts of the region, except for the potentially larger velocity jumps in pyrolite relative to those observed at a depth of 410 km. In contrast, both of these compositions lead to significantly low shear-wave velocities in the lower part of the region, suggesting possible subadiabatic temperatures or the existence of a layer of harzburgite-rich material supplied by the subducted slabs stagnant at these depths.
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Ringwood, A. E. Composition and Petrology of the Earth’s Mantle (McGraw-Hill, New York, 1975)
Bina, C. R. & Wood, B. J. The olivine-spinel transitions: experimental and thermodynamic constraints and implications for the nature of the 400 km seismic discontinuity. J. Geophys. Res. 92, 4853–4866 (1987)
Anderson, D. L. & Bass, J. D. Transition region of the Earth’s upper mantle. Nature 320, 321–328 (1986)
Duffy, T. S., Zha, C. S., Downs, R. T. & Mao, H. K. Elasticity of forsterite up to 16 GPa. Nature 378, 170–173 (1995)
Li, B., Liebermann, R. C. & Weidner, D. J. Elastic moduli of wadsleyite (β-Mg2SiO4) to 7 gigapascal and 873 Kelvin. Science 281, 675–677 (1998)
Irifune, T. & Ringwood, A. E. in High-Pressure Research in Mineral Physics (eds Manghnani, M. & Syono, Y.) 221–230 (Terra/American Geophysical Union, Tokyo/Washington, 1987)
Irifune, T. Absence of an aliminous phase in the upper part of the of the lower mantle. Nature 370, 131–133 (1994)
Irifune, T. & Isshiki, M. Iron partitioning in a pyrolite mantle and nature of the 410-km seismic discontinuity. Nature 392, 702–705 (1998)
Gwanmesia, G. D., Chen, G. & Liebermann, R. C. Sound velocities in MgSiO3-garnet to 8 GPa. Geophys. Res. Lett. 24, 4553–4556 (1998)
Liu, J., Chen, G., Gwanmesia, G. D. & Liebermann, R. C. Elastic wave velocities of pyrope-majorite garnets (Py62Mj38 and Py50Mj50) to 9 GPa. Phys. Earth Planet. Inter. 120, 153–163 (2000)
Sinogeikin, S. V. & Bass, J. D. Elasticity of majorite and a majorite-pyrope solid solution to high pressure: implications for the transition zone. Geophys. Res. Lett. 29 10.1029/2001GL013937 (2002)
Sinogeikin, S. V. & Bass, J. D. Elasticity of pyrope and majorite-pyrope solid solutions to high temperatures. Earth Planet. Sci. Lett. 203, 549–555 (2002)
Ita, L. & Stixrude, L. Petrology, elasticity and composition of the mantle transition zone. J. Geophys. Res. 97, 6849–6866 (1992)
Agee, C. B. Phase transformations and seismic structure in the upper mantle and transition zone. Rev. Mineral. 37, 165–203 (1998)
Vacher, P., Mocquet, A. & Sotin, C. Computation of seismic profiles from mineral physics: the importance of the non-olivine components for explaining the 660 km depth discontinuity. Phys. Earth Planet. Inter. 106, 275–298 (1998)
Nishihara, Y. & Takahashi, E. Phase relation and physical properties of an Al-depleted komatiite to 23 GPa. Earth Planet. Sci. Lett. 190, 65–77 (2001)
Higo, Y., Inoue, T., Irifune, T., Funakoshi, K. & Li, B. Elastic wave velocities of (Mg0. 91Fe0. 09)2SiO4 ringwoodite under P-T condition of the mantle transition region. Phys. Earth Planet. Inter. (in the press)
Li, B. Compressional and shear wave velocities of ringwoodite γ-Mg2SiO4 to 12 GPa. Am. Mineral. 88, 1312–1317 (2003)
Higo, Y., Inoue, T., Li, B., Irifune, T. & Liebermann, R. C. The effect of iron on the elastic properties of ringwoodite at high pressure. Phys. Earth Planet. Inter. 159, 276–285 (2006)
Sinogeikin, S. V., Bass, J. B. & Katsura, T. Single-crystal elasticity of ringwoodite to high pressure and high temperature: implication for 520 km seismic discontinuity. Phys. Earth Planet. Inter. 136, 41–66 (2003)
Masters, G., Laske, G., Bolton, H. & Dziewonski, A. M. in Earth’s Deep Interior: Mineral Physics and Seismic Tomography From the Atomic to the Global Scale (eds Karato, S., Forte, A. M., Liebermann, R. C., Masters, G., Stixrude, L.) 63–87 (AGU, Washington DC, 2000)
Akaogi, M., Ito, E. & Navrotsky, A. Olinine-modified spinel-spinel transitions in the system Mg2SiO4-Fe2SiO4: calorimetric measurements, thermochemical calculation, and geophysical application. J. Geophys. Res. 94, 15671–15685 (1989)
Cammarano, F., Goes, S., Vacher, P. & Giardini, D. Inferring upper-mantle temperatures from seismic velocities. Phys. Earth Planet. Inter. 138, 197–222 (2003)
Dziewonski, A. M. & Anderson, D. L. Preliminary reference Earth model. Phys. Earth Planet. Inter. 25, 297–356 (1981)
Kennet, B. L. N., Engdahl, E. R. & Buland, R. Constraints on seismic velocities in the Earth from traveltimes. Geophys. J. Int. 122, 108–124 (1995)
Fukao, Y., Widiyantoro, S. & Obayashi, M. Stagnant slabs in the upper and lower mantle transition region. Rev. Geophys. 39, 291–323 (2001)
Anderson, O. L., Issak, D. G. & Yamamoto, S. Anharmonicity and the equation of state for gold. J. Appl. Phys. 65, 1534–1543 (1989)
Decker, D. J. High-pressure equation of state for NaCl, KCl, and CsCl. J. Appl. Phys. 42, 3239–3244 (1971)
Li, B., Kung, J. & Liebermann, R. C. Modern techniques in measuring elasticity of Earth materials at high pressure and high temperature using ultrasonic interferometry in conjunction with synchrotron X-ray radiation in multi-anvil apparatus. Phys. Earth Planet. Inter. 98, 79–91 (2004)
We thank B. Li, R. C. Liebermann, J. Kung, I. Jackson for their help and advice in ultrasonic techniques, T. Shinmei, A. Yamada, T. Kunimoto, Y. Tange, N. Nishiyama for their assistance in synchrotron experiments, and C. A. McCammon and I. Jackson for comments on the manuscript. This paper was written while T. Irifune was on leave at the Bayreuth Geoinstitute, and supported by the Humboldt Foundation. This study is based on a research proposal to SPring-8 with a Grant-in-Aid for Scientific Research from the Japanese government (to T. Irifune).
Author Contributions T. Irifune directed the research project and wrote the manuscript. Y.H. did most of the experiments and analyses of the data with the help of T. Inoue, Y.K. and K.F. The TEM and XRD analyses of the recovered sample were conducted by H.O. and T. Inoue, respectively. All authors discussed the results and commented on the manuscript.
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Irifune, T., Higo, Y., Inoue, T. et al. Sound velocities of majorite garnet and the composition of the mantle transition region. Nature 451, 814–817 (2008) doi:10.1038/nature06551
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