Estimation of a maximum Lu diffusion rate in a natural eclogite garnet

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State: Public
Version: Final published version
Serval ID
serval:BIB_D9A1C51B9D4B
Type
Article: article from journal or magazin.
Collection
Publications
Institution
Title
Estimation of a maximum Lu diffusion rate in a natural eclogite garnet
Journal
Swiss Journal of Geosciences
Author(s)
Skora S., Baumgartner L.P., Mahlen N.J., Lapen T.J., Johnson C.M., Bussy F.
ISSN-L
1661-8726
Publication state
Published
Issued date
2008
Peer-reviewed
Oui
Volume
101
Pages
637-650
Language
english
Abstract
Lutetium zoning in garnet within eclogites from the Zermatt-Saas Fee
zone, Western Alps, reveal sharp, exponentially decreasing central
peaks. They can be used to constrain maximum Lu volume diffusion in
garnets. A prograde garnet growth temperature interval of 450-600 A
degrees C has been estimated based on pseudosection calculations and
garnet-clinopyroxene thermometry. The maximum pre-exponential diffusion
coefficient which fits the measured central peak is in the order of D-0=
5.7*10(-6) m(2)/s, taking an estimated activation energy of 270 kJ/mol
based on diffusion experiments for other rare earth elements in garnet.
This corresponds to a maximum diffusion rate of D (600 A degrees C) =
4.0*10(-22) m(2)/s. The diffusion estimate of Lu can be used to
estimate the minimum closure temperature, T-c, for Sm-Nd and Lu-Hf age
data that have been obtained in eclogites of the Western Alps,
postulating, based on a literature review, that D (Hf) < D (Nd) < D (Sm)
a parts per thousand currency sign D (Lu). T-c calculations, using the
Dodson equation, yielded minimum closure temperatures of about 630 A
degrees C, assuming a rapid initial exhumation rate of 50A degrees/m.y.,
and an average crystal size of garnets (r = 1 mm). This suggests that
Sm/Nd and Lu/Hf isochron age differences in eclogites from the Western
Alps, where peak temperatures did rarely exceed 600 A degrees C must be
interpreted in terms of prograde metamorphism.
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01/10/2012 19:07
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20/08/2019 15:58
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