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Shock temperatures of SiO_2 and their geophysical implications

Lyzenga, Gregory A. and Ahrens, Thomas J. and Mitchell, Arthur C. (1983) Shock temperatures of SiO_2 and their geophysical implications. Journal of Geophysical Research B, 88 (B3). pp. 2431-2444. ISSN 0148-0227. doi:10.1029/JB088iB03p02431.

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The temperature of SiO_2 in high-pressure shock states has been measured for samples of single-crystal α-quartz and fused quartz. Pressures between 60 and 140 GPa have been studied using projectile impact and optical pyrometry techniques at Lawrence Livermore National Laboratory. Both data sets indicate the occurrence of a shock-induced phase transformation at ∼70 and ∼50 GPa along the α- and fused quartz Hugoniots, respectively. The suggested identification of this transformation is the melting of shock-synthesized stishovite, with the onset of melting delayed by metastable superheating of the crystalline phase. Some evidence for this transition in conventional shock wave equation of state data is given, and when these data are combined with the shock temperature data, it is possible to construct the stishovite-liquid phase boundaries. The melting temperature of stishovite near 70 GPa pressure is found to be 4500 K, and melting in this vicinity is accompanied by a relative volume change and latent heat of fusion of ∼2.7% and ∼2.4 MJ/kg, respectively. The solid stishovite Hugoniot centered on α-quartz is well described by the linear shock velocity-particle velocity relation, u_s = 1.822 up + 1.370 km/s, while at pressures above the melting transition, the Hugoniot centered on α-quartz has been fit with u_s = 1.619 u_p + 2.049 km/s up to a pressure of ∼200 GPa. The melting temperature of stishovite near 100 GPa suggests an approximate limit of 3500 K for the melting temperature of SiO_2-bearing solid mantle mineral assemblages, all of which are believed to contain Si^(4+) in octahedral coordination with O^(2−). Thus 3500 K is proposed as an approximate upper limit to the melting point and the actual temperature in the earth's mantle. Moreover, the increase of the melting point of stishovite with pressure at 70 GPa is inferred to be ∼11 K/GPa. Using various adiabatic temperature gradients in the earth's mantle and assuming creep is diffusion controlled in the lower mantle, the current results could preclude an increase of viscosity by more than a factor of 10^3 with depth across the mantle.

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Alternate Title:Shock temperatures of SiO2 and their geophysical implications
Additional Information:Copyright 1983 by the American Geophysical Union. (Received May 5, 1981; revised October 1, 1982; accepted December 3, 1982.) Paper number 2B1880. We appreciate the cooperation and collaboration of the personnel at Lawrence Livermore Laboratory (LLL) in use of the light gas gun and related facilities, especially that of W. J. Nellis. J. Trainor and M. B. Boslough provided valuable assistance in obtaining pyrometer calibrations. We also appreciate the helpful discussions and suggestions of J. Shaner, R. G. McQueen, J. N. Fritz, and J. W. Hopson of Los Alamos Scientific Laboratory in providing their data in preprint form. We also thank R. Jeanloz, E. Stolper, D. L. Anderson, and C. G. Sammis for helpful discussions and suggestions. The technical assistance of J. R. Long, E. Gelle, and M. Long of Caltech and that of D. Bakker, J. Samuels, and W. C. Wallace of LLL is gratefully acknowledged. Support was provided through NSF grant EAR78-12942. Contribution 3433, Division of Geological and Planetary Sciences, California Institute of Technology.
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Caltech Division of Geological and Planetary Sciences3433
Issue or Number:B3
Record Number:CaltechAUTHORS:20141031-124350963
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Official Citation:Lyzenga, G. A., T. J. Ahrens, and A. C. Mitchell (1983), Shock temperatures of SiO2 and their geophysical implications, J. Geophys. Res., 88(B3), 2431–2444, doi:10.1029/JB088iB03p02431.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51126
Deposited By: George Porter
Deposited On:31 Oct 2014 20:33
Last Modified:10 Nov 2021 19:06

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