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Alkali mobility in shocked basalt

Jeanloz, Raymond and Ahrens, Thomas J. (1976) Alkali mobility in shocked basalt. In: 7th Lunar Science Conference. Geochimica et cosmochimica acta. Supplement. Vol.1. No.7. Pergamon Press , New York, NY, pp. 1623-1632. ISBN 0080217710.

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Plagioclase (An_(45)-An_(55)) in unshocked and experimentally shocked samples of Vacaville basalt was analyzed by electron microprobe. Sodium X-ray intensity measurements were found to be unstable for the diaplectic and shock-fused plagioclases, and for synthetic plagioclase glasses with An ≾ 80. Unstable microprobe analyses have also been reported for shocked chondritic meteorites. That is, sodium is mobilized and volatilized under the electron beam, probably by a thermal mechanism. Crystalline plagioclase, even when shocked to just below the transition pressure to diaplectic glass, gives stable analyses as does synthetic plagioclase glass with An > 80, and shocked calcic plagioclase in Apollo 16 sample 68415. In this study, we conclude that: (i) there is no evidence for selective sodium loss due to the shock process; (ii) sodium mobilization under the electron beam reflects increasingly severe lattice damage for increasing shock pressures; (iii) sodium mobilization is, in any case, not significant for calcic plagioclase. Thus we find no evidence supporting shock-related alkali loss as an important lunar process for impacts generating maximum pressures below about 1 Mbar, corresponding to projectile velocities ~4 km/sec for metallic objects and ⪝6 km/sec for silicate objects.

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Additional Information:© 1976 Lunar and Planetary Institute. We would like to thank Arden Albee, A. A. Chodos, and George Rossman for advice and assistance in this study, as well as W. R. Van Schmus for his critical comments and suggestions. We appreciate technical assistance provided by David Johnson. This research was supported by NASA grants NGL-05-002-105 and NSG-9019. This paper constitutes the Division of Geological and Planetary Sciences Contribution no. 2709.
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Caltech Division of Geological and Planetary Sciences 2709
Series Name:Geochimica et cosmochimica acta. Supplement
Issue or Number:7
Record Number:CaltechAUTHORS:20150902-091954040
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Official Citation:Alkali mobility in shocked basalt Jeanloz, R. & Ahrens, T. J. Lunar Science Conference, 7th, Houston, Tex., March 15-19, 1976, Proceedings. Volume 1. (A77-34651 15-91) New York, Pergamon Press, Inc., 1976, p. 1623-1632
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60024
Deposited By: Ruth Sustaita
Deposited On:11 Sep 2015 18:37
Last Modified:03 Oct 2019 08:52

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