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Micas in experimentally shocked gneissPowder-propellant guns are used to shock biotites and muscovites from a gneiss at pressures between 18 and 70 GPa. It is shown that shock in biotite and muscovite can produce homogeneous and devolatilized glasses within microseconds. Shock-deformed micas are found to exhibit fracturing, kinking, and complex extinction patterns over the entire pressure range investigated. Localized melting of micas commences at 33 GPa and reaches completion at 70 GPa. Even though melted biotite and muscovite are opaque optically, they exhibit extensive microvesiculation and flow when observed with the SEM. It is confirmed through electron diffraction that biotite and muscovite have transformed to a glass. The distribution of vesicles in shock-vitrified mica reveals escape of volatiles within the short duration of the shock experiment. It is noted that experimentally shocked biotite and muscovite undergo congruent melting. It is noted that the compositions of the glasses are similar to the unshocked micas except for volatiles (H2O loss and and K loss). These unusual glasses produced from mica can be quenched by rapid cooling conditions during the shock experiment. On the basis of the results, it is pointed out that the extremely low H2O content of tektites can be reconciled with a terrestrial origin by impact.
Document ID
19840043318
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Lambert, P.
(NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Mackinnon, I. D. R.
(NASA Johnson Space Center Houston, TX, United States)
Date Acquired
August 12, 2013
Publication Date
February 15, 1984
Publication Information
Publication: Journal of Geophysical Research, Supplement
Volume: 89
ISSN: 0148-0227
Subject Category
Geophysics
Accession Number
84A26105
Distribution Limits
Public
Copyright
Other

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