40Ar/39Ar ages of detrital muscovite and whole-rock slate/phyllite, Narragansett Basin, RI-MA, USA: implications for rejuvenation during very low-grade metamorphism
Article Abstract:
The 40Ar/39Ar dating method has proven effective in determining the source of detrital muscovite and in identifying the low-grade metamorphic processes of clastic sedimentary rocks. The results of the dating method on the muscovite and whole-rock slate/phyllite samples found in the Narragansett Basin, Rhode Island, suggest that temperatures of 270 to 285 degrees centigrade slightly rejuvenate clastic muscovite rocks while temperatures of over 325 degrees completely rejuvenate the detrital muscovite rocks. Moreover, total rejuvenation has occurred in the 2Md white mica elements of whole-rock slate/phyllite samples in the uppermost levels of the middle anchizone.
Publication Name: Contributions to Mineralogy and Petrology
Subject: Earth sciences
ISSN: 0010-7999
Year: 1992
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White K-mica evolution from phengite to muscovite in shales and shale matrix melange, Diablo Range, California
Article Abstract:
The evolution of K-mica from phengite to muscovite composition in shales and shale-matrix melanges of the Diablo Range, California, occurs perpendicular to c* rather than parallel to c*. During evolution, surface free energy, strain energy, Gibbs free energy and defects in the crystal decrease. Muscovitic crystal has less defects and longer areas with no defect than phengitic crystal. The illite crystallinity values of the crystals are due to many small phengitic coherent scattering domains and a few large muscovite scattering domains.
Publication Name: Contributions to Mineralogy and Petrology
Subject: Earth sciences
ISSN: 0010-7999
Year: 1996
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40Ar/39Ar thermochronology using alkali felspars: real thermal history or mathematical mirage of microtexture?
Article Abstract:
The inventory of real defect microtextures that have been observed by electron microscopy in plutonic alkali feldspars is presented. The Multiple Diffusion Domain theory of Ar loss that is based on the 40Ar/39Ar technique assumes that Ar diffuses in Nature over geological time from the same domains and by the same processes that regulate its diffusion under laboratory settings. The nature of possible diffusion domains and the fast pathways for diffusion between them are described.
Publication Name: Contributions to Mineralogy and Petrology
Subject: Earth sciences
ISSN: 0010-7999
Year: 1999
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