Melting of (Mg,Fe)2SiO4 at the core-mantle boundary of the earth

Science

Volumn 275, Issue 5306, 1997, Pages 1623-1625

  Holland, Kathleen G ^a   Ahrens, Thomas J ^a  

^a CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

MAGNESIUM DERIVATIVE; MINERAL;

ARTICLE; DATA ANALYSIS; GEOLOGY; PACIFIC OCEAN; PRIORITY JOURNAL; ROCK;

CORE/MANTLE BOUNDARY; MAGNESIOWUSTITE; MANTLE MINERAL; PARTIAL MELTING; PEROVSKITE;

EID: 0030620643     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.275.5306.1623     Document Type: Article

References (38)

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2. C. J. Allègre et al., Earth Planet. Sci. Lett. 134, 515 (1995); D. J. Weidner, in Chemistry and Physics of Terrestrial Planets, S. K. Saxena, Ed. (Springer-Verlag, New York, 1986), pp. 251-274; I. Jackson, Earth Planet. Sci. Lett. 62, 91 (1983); A. E. Ringwood, Geochim. Cosmochim. Acta 55, 2083 (1991).
3. C. J. Allègre et al., Earth Planet. Sci. Lett. 134, 515 (1995); D. J. Weidner, in Chemistry and Physics of Terrestrial Planets, S. K. Saxena, Ed. (Springer-Verlag, New York, 1986), pp. 251-274; I. Jackson, Earth Planet. Sci. Lett. 62, 91 (1983); A. E. Ringwood, Geochim. Cosmochim. Acta 55, 2083 (1991).
4. C. J. Allègre et al., Earth Planet. Sci. Lett. 134, 515 (1995); D. J. Weidner, in Chemistry and Physics of Terrestrial Planets, S. K. Saxena, Ed. (Springer-Verlag, New York, 1986), pp. 251-274; I. Jackson, Earth Planet. Sci. Lett. 62, 91 (1983); A. E. Ringwood, Geochim. Cosmochim. Acta 55, 2083 (1991).
5. 3 melting data were measured up to 60 GPa and extrapolated to the pressure of the CMB.
6. E. Knittle and R. Jeanloz, Geophys. Res. Lett. 16, 421 (1989); J. S. Sweeney and D. L. Heinz, in Proceedings of U.S.-Japan Seminar '96, High Pressure-Temperature Research: Properties of Earth and Planetary Materials, M. Manghnani and Y. Syono, Eds. (American Geophysical Union, Washington, DC, in press); D. L. Heinz, E. Knittle, J. S. Sweeney, Q. Williams, R. Jeanloz, Science 264, 279 (1994).
7. E. Knittle and R. Jeanloz, Geophys. Res. Lett. 16, 421 (1989); J. S. Sweeney and D. L. Heinz, in Proceedings of U.S.-Japan Seminar '96, High Pressure-Temperature Research: Properties of Earth and Planetary Materials, M. Manghnani and Y. Syono, Eds. (American Geophysical Union, Washington, DC, in press); D. L. Heinz, E. Knittle, J. S. Sweeney, Q. Williams, R. Jeanloz, Science 264, 279 (1994).
8. E. Knittle and R. Jeanloz, Geophys. Res. Lett. 16, 421 (1989); J. S. Sweeney and D. L. Heinz, in Proceedings of U.S.-Japan Seminar '96, High Pressure-Temperature Research: Properties of Earth and Planetary Materials, M. Manghnani and Y. Syono, Eds. (American Geophysical Union, Washington, DC, in press); D. L. Heinz, E. Knittle, J. S. Sweeney, Q. Williams, R. Jeanloz, Science 264, 279 (1994).
9. A. Zerr and R. Boehler, Nature 371, 506 (1994). The data were measured up to 30 GPa and extrapolated to the pressure of the CMB.
10. D. C. Presnall, in (21), pp. 248-268.
11. 30Si in olivine (between 1430 and 1830 K).
12. J. M. Brown, M. D. Furnish, D. A. Boness, in Shock Waves in Condensed Matter-1987, S. C. Schmidt and N. C. Holmes, Eds. (Elsevier, New York, 1988), pp. 119-122; J. M. Brown, M. D. Furnish, R. G. McQueen, in High-Pressure Research in Mineral Physics, M. H. Manghnani and Y. Syono, Eds. (American Geophysical Union, Washington, DC, 1987), pp. 373-384.
13. J. M. Brown, M. D. Furnish, D. A. Boness, in Shock Waves in Condensed Matter-1987, S. C. Schmidt and N. C. Holmes, Eds. (Elsevier, New York, 1988), pp. 119-122; J. M. Brown, M. D. Furnish, R. G. McQueen, in High-Pressure Research in Mineral Physics, M. H. Manghnani and Y. Syono, Eds. (American Geophysical Union, Washington, DC, 1987), pp. 373-384.
14. G. A. Lyzenga, and T. J. Ahrens, Geophys. Res. Lett. 7, 141 (1980).
15. -1 and 15 ns, respectively, for the previous pyrometer (22).
16. 4.
17. -1 and impacted 0.5-mm-thick Cu, Ti, or Ta driver plates. The planar shock wave induced in the driver plate then propagated into the peridot samples.
18. -1 and impacted 0.5-mm-thick Cu, Ti, or Ta driver plates. The planar shock wave induced in the driver plate then propagated into the peridot samples.
19. The sample surface in contact with the driver plate is sputter-coated with an opaque layer of Ag to block light that may originate from the shock-heated driver-sample interface [G. Lyzenga, thesis, California Institute of Technology (1982)].
20. Although the sample emits Planck radiation for ∼ 300 ns, radiative losses do not decrease sample temperature [R. Svendsen and T. J. Ahrens, Phys. Rep. 180, 333 (1989)].
21. Corrections for light absorption upon propagation of light through the unshocked sample was conducted as specified [(22); M. B. Boslough, J. Appl. Phys. 58 3394 (1985)]. The ambient transmittance of the sample was measured (15) and used to make this correction.
22. u are the transmission coefficients for the shocked and unshocked materials, respectively. Although ambient-pressure values of transmittance were used to yield a wavelength-dependent emissivity for shocked olivine, this can only be considered an approximation. Both olivine and magnesiowüstite demonstrate marked reddening with increasing pressure at room temperature [M. K. Mao and P. M. Bell, Science 176, 403 (1972); H. K. Mao, Carnegie Inst. Washington Yearb. 72, 554 (1973)].
23. u are the transmission coefficients for the shocked and unshocked materials, respectively. Although ambient-pressure values of transmittance were used to yield a wavelength-dependent emissivity for shocked olivine, this can only be considered an approximation. Both olivine and magnesiowüstite demonstrate marked reddening with increasing pressure at room temperature [M. K. Mao and P. M. Bell, Science 176, 403 (1972); H. K. Mao, Carnegie Inst. Washington Yearb. 72, 554 (1973)].
24. 2 (stishovite) [G. Y. Shen and P. Lazor, J. Geophys. Res. 100, 17699 (1995)]. These extrapolate closely to the melting line of stishovite inferred by Lyzenga et al.; for example, T. J. Ahrens [in Shock Compression of Condensed Matter, S. C. Schmidt and W. C. Tao, Eds. (American Institute of Physics, New York, 1996), pp. 3-8] and R. Boehler (private communication) found good agreement between diamond cell and shock-wave data for the melting of NaCl in the B2 structure at 3100 K and 55 GPa. See T. J. Ahrens, G. Lyzenga, A. C. Mitchell, in High Pressure Research in Geophysics, S. Akimoto and M. H. Manghnani, Eds. (Center for Academic Publication, Tokyo, 1982), pp. 579-594; see also R. Boehler, in Advanced Materials '96, M. Akaishi, Ed. (National Institute for Research in Inorganic Materials, Tsukuba, Japan, 1996), pp. 159-162.
25. 2 (stishovite) [G. Y. Shen and P. Lazor, J. Geophys. Res. 100, 17699 (1995)]. These extrapolate closely to the melting line of stishovite inferred by Lyzenga et al.; for example, T. J. Ahrens [in Shock Compression of Condensed Matter, S. C. Schmidt and W. C. Tao, Eds. (American Institute of Physics, New York, 1996), pp. 3-8] and R. Boehler (private communication) found good agreement between diamond cell and shock-wave data for the melting of NaCl in the B2 structure at 3100 K and 55 GPa. See T. J. Ahrens, G. Lyzenga, A. C. Mitchell, in High Pressure Research in Geophysics, S. Akimoto and M. H. Manghnani, Eds. (Center for Academic Publication, Tokyo, 1982), pp. 579-594; see also R. Boehler, in Advanced Materials '96, M. Akaishi, Ed. (National Institute for Research in Inorganic Materials, Tsukuba, Japan, 1996), pp. 159-162.
26. 2 (stishovite) [G. Y. Shen and P. Lazor, J. Geophys. Res. 100, 17699 (1995)]. These extrapolate closely to the melting line of stishovite inferred by Lyzenga et al.; for example, T. J. Ahrens [in Shock Compression of Condensed Matter, S. C. Schmidt and W. C. Tao, Eds. (American Institute of Physics, New York, 1996), pp. 3-8] and R. Boehler (private communication) found good agreement between diamond cell and shock-wave data for the melting of NaCl in the B2 structure at 3100 K and 55 GPa. See T. J. Ahrens, G. Lyzenga, A. C. Mitchell, in High Pressure Research in Geophysics, S. Akimoto and M. H. Manghnani, Eds. (Center for Academic Publication, Tokyo, 1982), pp. 579-594; see also R. Boehler, in Advanced Materials '96, M. Akaishi, Ed. (National Institute for Research in Inorganic Materials, Tsukuba, Japan, 1996), pp. 159-162.
27. 2 (stishovite) [G. Y. Shen and P. Lazor, J. Geophys. Res. 100, 17699 (1995)]. These extrapolate closely to the melting line of stishovite inferred by Lyzenga et al.; for example, T. J. Ahrens [in Shock Compression of Condensed Matter, S. C. Schmidt and W. C. Tao, Eds. (American Institute of Physics, New York, 1996), pp. 3-8] and R. Boehler (private communication) found good agreement between diamond cell and shock-wave data for the melting of NaCl in the B2 structure at 3100 K and 55 GPa. See T. J. Ahrens, G. Lyzenga, A. C. Mitchell, in High Pressure Research in Geophysics, S. Akimoto and M. H. Manghnani, Eds. (Center for Academic Publication, Tokyo, 1982), pp. 579-594; see also R. Boehler, in Advanced Materials '96, M. Akaishi, Ed. (National Institute for Research in Inorganic Materials, Tsukuba, Japan, 1996), pp. 159-162.
28. 2 (stishovite) [G. Y. Shen and P. Lazor, J. Geophys. Res. 100, 17699 (1995)]. These extrapolate closely to the melting line of stishovite inferred by Lyzenga et al.; for example, T. J. Ahrens [in Shock Compression of Condensed Matter, S. C. Schmidt and W. C. Tao, Eds. (American Institute of Physics, New York, 1996), pp. 3-8] and R. Boehler (private communication) found good agreement between diamond cell and shock-wave data for the melting of NaCl in the B2 structure at 3100 K and 55 GPa. See T. J. Ahrens, G. Lyzenga, A. C. Mitchell, in High Pressure Research in Geophysics, S. Akimoto and M. H. Manghnani, Eds. (Center for Academic Publication, Tokyo, 1982), pp. 579-594; see also R. Boehler, in Advanced Materials '96, M. Akaishi, Ed. (National Institute for Research in Inorganic Materials, Tsukuba, Japan, 1996), pp. 159-162.
29. 3 (Pv) is melting from a superheated state and the temperature drop is not easily explained by the onset of polymorphism in olivine.
30. D. C. Presnall and M. J. Walter, J. Geophys. Res. 98, 1977 (1993).
31. E. Garnero and D. V. Helmberger, Phys. Earth Planet. Inter. 91, 161 (1995); E. J. Garnero, S. P. Grand, D. V. Helmberger, Geophys. Res. Lett. 20, 1843 (1993); Q. Williams and E. J. Garnero, Science 273, 1528 (1996). The ultralow-velocity zone is 40 km thick and is marked by a 10% decrease in P-wave velocity that is explained by (i) a 30% partial melt if spherical or tubule melting geometry is assumed or (ii) a 5% partial melt if a grain-wetting model is assumed.
32. E. Garnero and D. V. Helmberger, Phys. Earth Planet. Inter. 91, 161 (1995); E. J. Garnero, S. P. Grand, D. V. Helmberger, Geophys. Res. Lett. 20, 1843 (1993); Q. Williams and E. J. Garnero, Science 273, 1528 (1996). The ultralow-velocity zone is 40 km thick and is marked by a 10% decrease in P-wave velocity that is explained by (i) a 30% partial melt if spherical or tubule melting geometry is assumed or (ii) a 5% partial melt if a grain-wetting model is assumed.
33. E. Garnero and D. V. Helmberger, Phys. Earth Planet. Inter. 91, 161 (1995); E. J. Garnero, S. P. Grand, D. V. Helmberger, Geophys. Res. Lett. 20, 1843 (1993); Q. Williams and E. J. Garnero, Science 273, 1528 (1996). The ultralow-velocity zone is 40 km thick and is marked by a 10% decrease in P-wave velocity that is explained by (i) a 30% partial melt if spherical or tubule melting geometry is assumed or (ii) a 5% partial melt if a grain-wetting model is assumed.
34. R. Jeanloz and S. Morris, Annu. Rev. Earth Planet. Sci. 14, 377 (1986); R. Boehler, ibid. 24, 15 (1996).
35. R. Jeanloz and S. Morris, Annu. Rev. Earth Planet. Sci. 14, 377 (1986); R. Boehler, ibid. 24, 15 (1996).
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38. Research supported by NSF. Division of Geological and Planetary Science, California Institute of Technology, contribution 5672. We thank A. Scherer for the use of his sputtering apparatus, and G. Rossman for the use for of his optical transmission apparatus. We thank P. Wyllie, E. Ohtani, D. Stevenson, M. Gurnis, D. Helmberger, and the reviewers for comments. We also thank E. Gelle, M. Long, and A. Devora for their help in conducting the laboratory experiments.