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Shock wave compression of iron-silicate garnet

Graham, Earl K. and Ahrens, Thomas J. (1973) Shock wave compression of iron-silicate garnet. Journal of Geophysical Research, 78 (2). pp. 375-392. ISSN 0148-0227. doi:10.1029/JB078i002p00375.

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Shock wave Hugoniot data have been obtained for almandine-garnet of composition (Fe_(0.79), Mg_(0.14), Ca_(0.04), Mn_(0.03)) Al_2Si_3O_(12) to pressures of >650 kb. The Hugoniot data indicate the onset of a high-pressure phase at 195 ± 20 kb. Equation-of-state systematics and crystal chemical data (stemming largely from analog compounds) suggest that the high-pressure phase occurs in an ‘ilmenitelike’ structure with an initial density of 4.44 ± 0.04 g/cm^3. This value represents an increase of about 6% over the initial garnet density of 4.180 ± 0.005 g/cm^3. The adiabatic bulk modulus K_0^s and its first pressure derivative (∂K^s/∂P)_T were calculated for the high-pressure phase and found to be 3.19 ± 0.39 Mb and 2.6 ± 0.7, respectively. The major source of probable error in these values results from the indicated uncertainty in the initial density of the high-pressure phase. These results strongly suggest that upper mantle minerals are likely to occur in the ilmenite structure over a substantial part of the lower mantle.

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Additional Information:Copyright 1973 by the American Geophysical Union. (Received January 31, 1972; revised September 25, 1972.) We appreciate the valuable suggestions and technical assistance of J. H. Lower, Rex V. Gibbons, D. Johnson, D. Newbigging, and A. Chodos concerning various aspects of this work. J. N. Fritz's critical comments on our original manuscript also are appreciated. This research was supported by NSF grant GA21396 and NASA grant NGL-05-002-105. Contribution 2093, Division of Geological Sciences, California Institute of Technology.
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Caltech Division of Geological and Planetary Sciences2093
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Official Citation:Graham, E. K., and T. J. Ahrens (1973), Shock wave compression of iron-silicate garnet, J. Geophys. Res., 78(2), 375–392, doi:10.1029/JB078i002p00375.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51408
Deposited By: George Porter
Deposited On:07 Nov 2014 16:08
Last Modified:10 Nov 2021 19:10

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