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Diffusion of Ar-40 in muscovite

Harrison, Timothy; Celerier, Julien; Aikman, Amos; Hermann, Joerg; Heizler, Matthew T.

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Hydrothermal treatment of closely sized muscovite aggregates in a piston-cylinder apparatus induced 40Ar* loss that is revealed in 40Ar/39Ar step heating spectra. Age spectra and Arrhenius data, however, differ from that expected from a single diffusion length scale. A numerical model of episodic loss assuming the presence of multiple diffusion domains yields excellent fits between synthetic and actual degassing spectra. We used this model to isolate 40Ar* loss from the grains that remained...[Show more]

dc.contributor.authorHarrison, Timothy
dc.contributor.authorCelerier, Julien
dc.contributor.authorAikman, Amos
dc.contributor.authorHermann, Joerg
dc.contributor.authorHeizler, Matthew T.
dc.date.accessioned2015-12-10T21:56:33Z
dc.identifier.issn1872-9533
dc.identifier.urihttp://hdl.handle.net/1885/39485
dc.description.abstractHydrothermal treatment of closely sized muscovite aggregates in a piston-cylinder apparatus induced 40Ar* loss that is revealed in 40Ar/39Ar step heating spectra. Age spectra and Arrhenius data, however, differ from that expected from a single diffusion length scale. A numerical model of episodic loss assuming the presence of multiple diffusion domains yields excellent fits between synthetic and actual degassing spectra. We used this model to isolate 40Ar* loss from the grains that remained intact during hydrothermal treatment at 10 kbar permitting calculation of diffusion coefficients in the temperature range 730-600 °C. Diffusion data generated in this manner yield an activation energy (E) of 63 ± 7 kcal/mol and frequency factor (Do) of 2.3 (+ 70; - 2.2) cm2/s. Experiments at 20 kbar yield diffusivities lower by about an order of magnitude and correspond to an activation volume of ∼14 cm3/mol. Together, these parameters predict substantially greater retentivity of Ar in muscovite than previously assumed and correspond to a closure temperature (Tc) of 425 °C for a 100 μm radius grain cooling at 10 °C/Ma at 10 kbar (Tc = 405 °C at 5 kbar. Age and log (r/ro) spectra for the run products show strong correlations indicating that muscovites can retain Ar diffusion boundaries and mechanisms that define their natural retentivity during vacuum step heating. This may permit the application of high resolution, continuous 40Ar/39Ar thermochronology to low grade, regionally metamorphosed terranes.
dc.publisherPergamon-Elsevier Ltd
dc.sourceGeochimica et Cosmochimica Acta
dc.subjectKeywords: argon isotope; diffusion; experimental mineralogy; hydrothermal alteration; muscovite; numerical model; temperature profile; thermochronology
dc.titleDiffusion of Ar-40 in muscovite
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume73
dc.date.issued2009
local.identifier.absfor040203 - Isotope Geochemistry
local.identifier.ariespublicationu4047674xPUB178
local.type.statusPublished Version
local.contributor.affiliationHarrison, Timothy, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationCelerier, Julien, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationAikman, Amos, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationHermann, Joerg, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationHeizler, Matthew T. , New Mexico Tech
local.description.embargo2037-12-31
local.bibliographicCitation.issue4
local.bibliographicCitation.startpage1039
local.bibliographicCitation.lastpage1051
local.identifier.doi10.1016/j.gca.2008.09.038
dc.date.updated2016-02-24T10:31:38Z
local.identifier.scopusID2-s2.0-58549111123
local.identifier.thomsonID000263633300012
CollectionsANU Research Publications

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