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Effects of Shock Pressures on Calcic Plagioclase

Gibbons, Rex V. and Ahrens, Thomas J. (1977) Effects of Shock Pressures on Calcic Plagioclase. Physics and Chemistry of Minerals, 1 (1). pp. 95-107. ISSN 0342-1791.

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Samples of single crystal calcic plagioclase (labradorite, An63, from Chihuahua, Mexico) have been shock-loaded to pressures up to 496 kbar. Optical and electron microscopic studies of the recovered samples show the effects of increasing shock pressures on this mineral. At pressures up to 287 kbar, the recovered specimens are still essentially crystalline, with only a trace amount of optically unresolvable glass present at 287 kbar. Samples recovered after shock-loading to pressures between 300 and 400 kbar are almost 100% diaplectic glasses; that is formed by shock transformation presumably in the solid-state. Above about 400 kbar, glasses with refractive indices similar to thermally fused glass were produced. The general behavior of the index of refraction with shock pressures agrees closely with previous work, however, the absence of planar features is striking. At pressures less than 300 kbar, the most prominent physical feature is the pervasive irregular fracturing caused by the shock crushing, although some (001) and (010) cleavages are observed. No fine-scale shock deformation structures, i.e. planar features, were noted in any of the specimens. We conclude, in contrast to previous studies of shocked rocks that planar features are not necessarily definitive shock indicators, in contrast to diaplectic glass (e.g., maskelynite) and high-pressure phases, but are rather likely indicative of the local heterogeneous dynamic stress experienced by plagioclase grains within shocked rocks.

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Additional Information:© 1977 Springer-Verlag. Received August 13, 1976. Contribution No. 2469. Division of Geological and Planetary Sciences. California Institute of Technology. Pasadena. California 91125, U.S.A. This research was sponsored by NASA under grant NGL-05-002-105. We appreciate the hospitality and assistance of Dr. E.C.T. Chao and J.A. Best while doing interference microscopy at Dr. Chao's laboratory at the United States Geological Survey, Washington. DC. We also appreciate the help of Professor J.M. Christie for the transmission electron microscopy carried out at the University of California. Los Angeles and U.S. Steel Research Center. Monroeville. Pennsylvania. We are appreciative of the critical reviews and comments of Fred Horz. Dieter Stöffler, Raymond Jeanloz, John D. Kleeman. and John C. Jamieson.
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Caltech Division of Geological and Planetary Sciences2469
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Official Citation:Effects of shock pressures on calcic plagioclase A Gibbons, Rex V., Ahrens, Thomas J. Physics and Chemistry of Minerals v.1, n.1 P 95-107
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:62015
Deposited On:10 Nov 2015 17:24
Last Modified:12 Oct 2020 22:03

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