Micas in experimentally shocked gneiss

Lambert, P. & Mackinnon, I.D.R. (1984) Micas in experimentally shocked gneiss. Journal of Geophysical Research, 89, Suppl(B), pp. 685-699.

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Abstract

Biotites and muscovites from a gneiss have been experimentally shocked between 18 and 70 GPa using powder-propellant guns at NASA Johnson Space Center and at the California Institute of Technology. This study shows that shock in biotite and muscovite can produce homogeneous and devolatilized glasses within microseconds. Shock-deformed micas display fracturing, kinking, and complex extinction patterns over the entire pressure range investigated. However, these deformation features are not a sensitive pressure indicator. Localized melting of micas begins at 33 GPa and goes to completion at 70 GPa. Melted biotite and muscovite are optically opaque, but show extensive microvesiculation and flow when observed with the SEM. Electron diffraction confirms that biotite and muscovite have transformed to a glass. The distribution of vesicles in shock-vitrified mica shows escape of volatiles within the short duration of the shock experiment. Experimentally shocked biotite and muscovite undergo congruent melting. Compositions of the glasses are similar to the unshocked micas except for volatiles (H2O loss and K loss). These unusual glasses derived from mica may be quenched by rapid cooling conditions during the shock experiment. Based on these results, the extremely low H2O content of tektites may be reconciled with a terrestrial origin by impact. Release of volatiles in shock-melted micas affects the melting behavior of coexisting dry silicates during the short duration of the shock experiment. Transportation and escape of volatiles released from shock-melted micas may provide plausible mechanisms for the origin of protoatmospheres on terrestrial planets, hydrothermal activity on phyllosilicate-rich meteorite parent bodies, and fluid entrapment in meteorites.

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ID Code: 55646
Item Type: Journal Article
Refereed: Yes
Additional Information: GeoRef, Copyright 2009, American Geological Institute.
1985-062979
Keywords: biotite, electron probe data, experimental studies, geomorphology, geophysics, gneisses, high pressure, impact features, metamorphic rocks, meteor craters, mica group, muscovite, optical properties, pressure, regional metamorphism, SEM data, sheet silicates, shock metamorphism, textures
DOI: 10.1029/JB089iS02p0B685
ISSN: 0148-0227
Subjects: Australian and New Zealand Standard Research Classification > EARTH SCIENCES (040000) > GEOLOGY (040300) > Igneous and Metamorphic Petrology (040304)
Australian and New Zealand Standard Research Classification > EARTH SCIENCES (040000) > GEOLOGY (040300) > Mineralogy and Crystallography (040306)
Divisions: Current > Institutes > Institute for Future Environments
Deposited On: 30 Jan 2013 22:58
Last Modified: 30 Jan 2013 22:58

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