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Shock compression of feldspars

Ahrens, Thomas J. and Petersen, C. F. and Rosenberg, J. T. (1969) Shock compression of feldspars. Journal of Geophysical Research, 74 (10). pp. 2727-2746. ISSN 0148-0227.

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Hugoniot data for oligoclase and microcline to 670 and 580 kb and release adiabat data for oligoclase were obtained by means of the inclined mirror and immersed-foil-reflected-light techniques, respectively. Oligoclase and microcline have Hugoniot elastic limits in the range of 40–55 and 80–85 kb. These limits increase slightly with increasing driving shock pressure. Above the elastic limit, extending to ∼300 and ∼400 kb, transition regions of anomalously high compression are observed for microcline and oligoclase. These data and the data of McQueen, Marsh, and Fritz for albitite and anorthosite indicate that at successively higher shock pressures within this region, the feldspars gradually transform to a high-pressure, high-density polymorph. This polymorph probably corresponds to the rutile-like hollandite structure obtained in high-pressure quenching experiments by Kume, Matsumoto, and Koizumi (in KAlGe_3O_8) and by Ringwood, Reid, and Wadsley (in KAlSo_3O_8, microcline). In the hollandite structure germanium or silicon is in octahedral coordination with oxygen. The zero-pressure density and the Birch-Murnaghan equation of state parameters for the adiabat and isotherm are calculated for the high-pressure polymorphs of oligoclase, microcline, anorthosite, and albitite. The release adiabat centered at 180 kb indicates that at this shock pressure some (∼15%) of the hollandite phase forms but apparently reverts to a lower-density phase on pressure release. Release adiabat curves centered at 272 and 417 kb and calculated postshock temperatures indicate that material of feldspar composition recovered from meteorite and laboratory impacts is converted to the hollandite structure upon shock compression; upon pressure release this material probably reverts to the low-density maskelynite form.

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Additional Information:Copyright 1969 by the American Geophysical Union. (Received September 6, 1968; revised January 27, 1969.) We greatly appreciate the help of E. C. T. Chao, U.S. Geological Survey, in providing encouragement as well as specimens and analyses of the oligoclase material. We have profited from discussions of various aspects of this work with A. E. Ringwood, D. L. Anderson, and O. F. Tuttle as well as from the suggestions of one of the reviewers. This research was supported in part by the National Aeronautics and Space Administration under NASr-49(24) and the Defense Atomic Support Agency under DASA 01-68-C-0069. The experiments were performed at Stanford Research Institute. Contribution 1563, Division of Geological Sciences, California Institute of Technology, Pasadena, California 91109. Ahrens, T. J., C. F. Petersen, and J. T. Rosenberg (1969), Correction to paper by Thomas J. Ahrens, C. F. Petersen, and J. T. Rosenberg, ‘Shock compression of feldspars’, J. Geophys. Res., 74(22), 5353–5353, doi:10.1029/JB074i022p05353.
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Defense Atomic Support Agency (DASA)DASA 01-68-C-0069
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Caltech Division of Geological Sciences1563
Issue or Number:10
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Official Citation:Ahrens, T. J., C. F. Petersen, and J. T. Rosenberg (1969), Shock compression of feldspars, J. Geophys. Res., 74(10), 2727–2746, doi:10.1029/JB074i010p02727.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51440
Deposited By: George Porter
Deposited On:07 Nov 2014 21:09
Last Modified:03 Oct 2019 07:33

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