Ultrasonic shear wave velocities of MgSiO3 perovskite at 8 GPa and 800 K and lower mantle composition

Science

Volumn 281, Issue 5377, 1998, Pages 677-679

  Sinelnikov, Yegor D ^a   Chen, Ganglin ^a   Neuville, Daniel R ^b   Vaughan, Michael T ^a   Liebermann, Robert C ^a  

^a STONY BROOK UNIVERSITY   (United States)

^b INSTITUT DE PHYSIQUE DU GLOBE DE PARIS   (France)

Author keywords

[No Author keywords available]

Indexed keywords

MAGNESIUM SILICATE;

PEROVSKITE; S-WAVE; SEISMIC VELOCITY;

ACOUSTICS; ARTICLE; ELASTICITY; GEOLOGY; INTERFEROMETRY; PRESSURE; PRIORITY JOURNAL; SHEAR RATE; TEMPERATURE; ULTRASOUND;

EID: 0032584706     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: None     Document Type: Article

References (33)

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11. The primitive mantle material called pyrolite was proposed by A. E. Ringwood [Composition of the Earth's Mantle (McGraw-Hill, New York, 1975), p. 295] to produce a typical basaltic magma on fractional melting. The initially proposed composition was one part of basalt and four parts of dunite.
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14. -2 GPa/K [for example, (2); E. Knittle et al., Nature 319, 214 (1986); H. K. Mao et al., J. Geophys. Res. 96, 8069 (1991); L. Stixrude, R. J. Hemley, Y. Fei, H. K. Mao, Science 257, 1099 (1992)].
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18. Recently, we have adapted ultrasonic interferometry techniques to a DIA-type, cubic anvil, high-pressure apparatus (SAM-85) installed on the superconducting wiggler beamline (X17B1) at the National Synchroton Light Source of the Brookhaven National Laboratory [G. Chen, R. C. Liebermann, D. J. Weidner, Science 280, 1913 (1998)].
19. In ultrasonic interferometry, a burst of high-frequency signal is applied to the piezoelectric transducer. The resultant elastic wave, propagating inside the sample, produces a series of echoes. The travel time of an elastic wave through the sample is measured by observing constructive and destructive interferences among overlapped echoes as a function of carrier frequency.
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21. The largest uncertainties in travel times (±1%) originated from the anomalous travel-time dispersion. To minimize this dispersion, we chose a sufficiently large frequency window in our interference data, over which all collected travel times had a comparable dispersion shape. The travel times were averaged over a chosen frequency window to obtain G as a function of pressure and temperature. Discrepancies occurred for the data collected under initial compression at room temperature because of nonhydrostatic stresses. The deviation from hydrostatic conditions was accounted for by estimating pressures from subsets {200, 420} and {222, 220} of salt diffraction lines and by assigning the corresponding difference to a pressure uncertainty of the measurements.
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27. p ≈ 2 throughout the lower mantle [for example, A. Hales and H. Doyle, Geophys. J. R. Astron. Soc. 13, 403 (1967); J. Woodhouse and A. Dziewonski, Philos. Trans. R. Soc. London Ser. A 328, 291 (1989): X. Li et al., Geophys. J. Int. 105, 649 (1991); G. Robertson and J. Woodhouse, ibid. 123, 85 (1995)].
28. p ≈ 2 throughout the lower mantle [for example, A. Hales and H. Doyle, Geophys. J. R. Astron. Soc. 13, 403 (1967); J. Woodhouse and A. Dziewonski, Philos. Trans. R. Soc. London Ser. A 328, 291 (1989): X. Li et al., Geophys. J. Int. 105, 649 (1991); G. Robertson and J. Woodhouse, ibid. 123, 85 (1995)].
29. p ≈ 2 throughout the lower mantle [for example, A. Hales and H. Doyle, Geophys. J. R. Astron. Soc. 13, 403 (1967); J. Woodhouse and A. Dziewonski, Philos. Trans. R. Soc. London Ser. A 328, 291 (1989): X. Li et al., Geophys. J. Int. 105, 649 (1991); G. Robertson and J. Woodhouse, ibid. 123, 85 (1995)].
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32. The inclusion of Fe was assumed to reduce perovskite's G in a manner similar to the reduction of G in magnesiowüstite (5, 6).
33. We thank the personnel who contributed to the execution of these ultrasonic experiments in SAM-85 at the National Synchroton Light Source (NSLS) of the Brookhaven National Laboratory: H. Kagi, J. Liu, H. Schay, K. Baldwin, P. Hoversen, B. Vitale, C. Koleda, and B. Huebsch. We especially thank Y. Fei and B. Mysen at the Geophysical Laboratory for helping with the Raman spectroscopy measurements; J. Hastings and D. Siddons at the NSLS for their technical support at the beamline X17B1, where this work was performed; J. Chen and D. Weidner for their support and encouragement in this new project; and Y. Wang for providing the pressure-volume-temperature data. These high-pressure experiments were conducted with the joint support of the State University of New York at Stony Brook and the NSF Science and Technology Center for High Pressure Research under Earth Sciences Division grant EAR 89-20239. This research was also supported by NSF grants to R.C.L. (EAR 93-04502 and 96-14612). This is Mineral Physics Institute contribution 226.