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Shock wave equation of state of enstatite

Watt, J. Peter and Ahrens, Thomas J. (1986) Shock wave equation of state of enstatite. Journal of Geophysical Research B, 91 (B7). pp. 7495-7503. ISSN 0148-0227. doi:10.1029/JB091iB07p07495.

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Shock compression data are reported for hot-pressed Bamble bronzite (En_(86)) loaded to pressures between 104 and 161 GPa. When compared to earlier shock wave data on En_(90) at lower pressures and to static compression data, our data require the presence of a phase change. In P-ρ space the data yield two distinct trajectories, which cannot be explained by experimental error. The higher-density data, corrected for porosity and a small amount of metallic iron impurity, agree with a theoretical En_(86) high-pressure phase Hugoniot calculated from static compression equation of state data for perovskite (pv) structure silicates when experimental errors and uncertainties in the equation of state parameters are considered. All the En86 data can be described by a calculated Hugoniot if the first pressure derivative of the MgSiO_3 (pv) bulk modulus is taken as 4.5 ± 1.0. Combining the present preferred data with recent shock wave data for single-crystal forsterite, we find that En_(86) is slightly more dense than Fo86 at pressures above 110 GPa. Comparison of the forsterite and enstatite data with the Preliminary Reference Earth Model (PREM) lower mantle densities, with corrections applied for the higher shock temperatures relative to lower mantle temperatures, shows that PREM densities are satisfied by olivine or pyroxene stoichiometries with Mg mole fractions from 0.82 to 0.90. These values are lower than estimates of 0.90 to 0.95 developed from extrapolating static compression data to lower mantle conditions.

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Additional Information:Copyright 1986 by the American Geophysical Union. (Received March 21, 1984; revised October 21, 1985; accepted February 13, 1986.) Paper number 4B5042. We appreciate the careful construction and execution of the experiments by E. Gelle and M. Long. C. G. $ammis kindly made available samples of his Bamble bronzite. J. J. Papike supplied a copy of his pyroxene composition calculation program. We acknowledge useful discussions with J. M. Vizgirda and helpful comments from E. S. Gaffney and an anonymous reviewer. Computing support was provided by the Office of Computer Services and the Department of Geology, Rensselaer Polytechnic Institute. Supported by National Science Foundation grant EAR 80-18819. Contribution 4019, Division of Geological and Planetary Sciences, California Institute of Technology.
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NSFEAR 80-18819
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Caltech Division of Geological and Planetary Sciences4019
Issue or Number:B7
Record Number:CaltechAUTHORS:20141030-112207870
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Official Citation:Watt, J. P., and T. J. Ahrens (1986), Shock wave equation of state of enstatite, J. Geophys. Res., 91(B7), 7495–7503, doi:10.1029/JB091iB07p07495.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51064
Deposited By: George Porter
Deposited On:30 Oct 2014 18:36
Last Modified:10 Nov 2021 19:05

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