Rare earth diffusion kinetics in garnet: Experimental studies and applications

Massimiliano Tirone, Jibamitra Ganguly, Ralf Dohmen, Falko Langenhorst, Richard Hervig, Hans Werner Becker

Research output: Contribution to journalArticle

121 Citations (Scopus)

Abstract

We determined the diffusion coefficient of Sm in almandine garnet as function of temperature at 1 bar and fO2 corresponding that of wüstite-iron buffer, and to a limited extent, that of a few other selected rare earth elements in almandine and pyrope garnets. Both garnets were demonstrated to have metastably survived the diffusion annealing at conditions beyond their stability fields. The experimental diffusion profiles were analyzed by secondary ion mass spectrometry, and in addition, by Rutherford back scattering spectroscopy for two samples. Transmission electron microscopic study of an almandine crystal that was diffusion-annealed did not reveal any near-surface fast diffusion path. Using reasonable approximations and theoretical analysis of vacancy diffusion, the experimental data were used to develop an expression of rare earth element (REE) diffusion coefficient in garnet as a function of temperature, pressure, fO2, ionic radius, and matrix composition. Calculation of the closure temperature for the Sm-Nd decay system in almandine garnet in a metamorphic terrain shows very good agreement with that constrained independently. Modeling of the REE evolution in melt and residual garnet suggests that for dry melting condition, the REE pattern in the melt should commonly conform closely to that expected for equilibrium melting. However, for much lower solidus temperatures that would prevail in the presence of a H2O-CO2 fluid, the concentration of light REE in the melt could be significantly lower than that under equilibrium melting condition. A reported core and rim differences in the REE content of a garnet crystal in a mantle xenolith in kimberlite have been reproduced by assuming that the REE zoning was a consequence of entrapment in a magma derived from an external source for ∼32,000 yr before the eruption.

Original languageEnglish (US)
Pages (from-to)2385-2398
Number of pages14
JournalGeochimica et Cosmochimica Acta
Volume69
Issue number9
DOIs
StatePublished - May 1 2005

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Garnets
Rare earth elements
Rare earths
garnet
rare earth element
experimental study
almandine
kinetics
Kinetics
Melting
melting
melt
crystal
closure temperature
Temperature
Zoning
Crystals
pyrope
xenolith
kimberlite

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Rare earth diffusion kinetics in garnet : Experimental studies and applications. / Tirone, Massimiliano; Ganguly, Jibamitra; Dohmen, Ralf; Langenhorst, Falko; Hervig, Richard; Becker, Hans Werner.

In: Geochimica et Cosmochimica Acta, Vol. 69, No. 9, 01.05.2005, p. 2385-2398.

Research output: Contribution to journalArticle

Tirone, Massimiliano ; Ganguly, Jibamitra ; Dohmen, Ralf ; Langenhorst, Falko ; Hervig, Richard ; Becker, Hans Werner. / Rare earth diffusion kinetics in garnet : Experimental studies and applications. In: Geochimica et Cosmochimica Acta. 2005 ; Vol. 69, No. 9. pp. 2385-2398.
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