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Rates and mechanism of Y, REE, and Cr diffusion in garnet

  • William D. Carlson EMAIL logo
Published/Copyright: April 2, 2015
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American Mineralogist
From the journal American Mineralogist Volume 97 Issue 10

Abstract

Numerical simulation of the evolution of stranded diffusion profiles in partially resorbed garnet crystals from the aureole of the Makhavinekh Lake Pluton, Labrador, yields quantitative determinations of rates of diffusion of Y, rare earth elements (REEs), and Cr at ~700-900 °C, 0.53 GPa. Diffusion coefficients for these trivalent cations are 0.5-1.5 log10 units smaller than those for major divalent cations measured in the same crystals, but diffusivities for trivalent cations are all equal to one another to within ±0.25 log10 unit. Integration of these new data with previously published results resolves some prior inconsistencies, and defines the dependence of diffusivities for Y, the REEs, and Cr on temperature, pressure, and oxygen fugacity, while accounting for minor effects of ionic radius and host-crystal composition. Nd, Sm, and Eu-elements that are strongly depleted in rims of relict garnet crystals due to preferential partitioning out of garnet during resorption-evolve small but distinct maxima from initially nearly flat profiles; this “uphill diffusion” results from cross-coupling with Y and the other REEs, which are strongly concentrated in relict garnet rims by resorption. The weak dependence of diffusivity on ionic radius and host-crystal composition, the near-equivalence of diffusivities of Y+REEs with that of Cr, and the strong positive cross-coupling among Y+REEs are all explained by a diffusion mechanism that links the mobility of VIIIY+REEs with that of VIAl; this is likely a consequence of the dominance of the menzerite-(Y) component as a means of incorporating Y+REEs in the garnet structure. However, the variety of possible substitution mechanisms that may enable Y+REE incorporation into garnet, and the degree to which each may be favored in different regimes of temperature, pressure, and oxygen fugacity, imply a potential for great complexity, as the net diffusional flux may result from the superposed effect of multiple diffusion mechanisms, each with different kinetics.

Keywords : Diffusion; garnet; rare earth elements; yttrium; chromium
Received: 2012-1-15
Accepted: 2012-7-2
Published Online: 2015-4-2
Published in Print: 2012-10-1

© 2015 by Walter de Gruyter Berlin/Boston

Articles in the same Issue

  1. MSA Roebling medal lecture. Mineralogy, petrology, U-Pb geochronology, and geologic evolution of the Dabie-Sulu classic ultrahigh-pressure metamorphic terrane, East-Central China
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  17. Elastic and anelastic anomalies due to spin-state transitions in orthorhombic perovskite from isoelectronic behavior of Co3+ and Fe2+
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  24. Krasheninnikovite, KNa2CaMg(SO4)3F, a new mineral from the Tolbachik volcano, Kamchatka, Russia
  25. Crystal structure of pseudojohannite, with a revised formula, Cu3(OH)2[(UO2)4O4(SO4)2](H2O)12
  26. Letter. A natural photoelectrochemical cell for water splitting: Implications for early Earth and Mars
  27. Letter. In situ observation of the breakdown of magnetite (Fe3O4) to Fe4O5 and hematite at high pressures and temperatures
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https://doi.org/10.2138/am.2012.4108
Keywords for this article
Diffusion; garnet; rare earth elements; yttrium; chromium

Articles in the same Issue

  1. MSA Roebling medal lecture. Mineralogy, petrology, U-Pb geochronology, and geologic evolution of the Dabie-Sulu classic ultrahigh-pressure metamorphic terrane, East-Central China
  2. Brittle-ductile microfabrics in naturally deformed zircon: Deformation mechanisms and consequences for U-Pb dating
  3. In situ hot-stage AFM study of the dissolution of the barite (001) surface in water at 30–55 °C
  4. A multi-domain gem-grade Brazilian apatite
  5. High-temperature structural behaviors of anhydrous wadsleyite and forsterite
  6. Rates and mechanism of Y, REE, and Cr diffusion in garnet
  7. EPR discrimination of microcrystalline calcite geomaterials
  8. Crystal chemistry of Bi- and Mn-bearing vesuvianite from Långban, Sweden
  9. Cation ordering in Pb2+-bearing, Mn3+-rich pargasite from Långban, Sweden
  10. Long-term solid-phase fate of co-precipitated U(VI)-Fe(III) following biological iron reduction by Thermoanaerobacter
  11. The sulfur speciation in S-bearing minerals: New constraints by a combination of electron microprobe analysis and DFT calculations with special reference to sodalite-group minerals
  12. Simultaneous sound velocity and density measurements of NaCl at high temperatures and pressures: Application as a primary pressure standard
  13. The temperature and compositional dependence of disordering in Fe-bearing dolomites
  14. Quantifying crystallization and devitrification of rhyolites by means of X-ray diffraction and electron microprobe analysis
  15. Reactions of strontium anorthite with H2O+CaCl2 fluids at 500 °C and high pressure: Kinetic information from in situ synchrotron-radiation XRF analyses of the fluid
  16. Solubility of xenotime in a 2 M HCl aqueous fluid from 1.2 to 2.6 GPa and 300 to 500 °C
  17. Elastic and anelastic anomalies due to spin-state transitions in orthorhombic perovskite from isoelectronic behavior of Co3+ and Fe2+
  18. Accurate determination of ferric iron in garnets by bulk Mössbauer spectroscopy and synchrotron micro-XANES
  19. Re-investigation of the crystal structure of enstatite under high-pressure conditions
  20. Second-order P6̄c2-P31c transition and structural crystallography of the cyclosilicate benitoite, BaTiSi3O9, at high pressure
  21. High-pressure structural studies of eskolaite by means of single-crystal X-ray diffraction
  22. Almandine: Lattice and non-lattice heat capacity behavior and standard thermodynamic properties
  23. Witzkeite: A new rare nitrate-sulphate mineral from a guano deposit at Punta de Lobos, Chile
  24. Krasheninnikovite, KNa2CaMg(SO4)3F, a new mineral from the Tolbachik volcano, Kamchatka, Russia
  25. Crystal structure of pseudojohannite, with a revised formula, Cu3(OH)2[(UO2)4O4(SO4)2](H2O)12
  26. Letter. A natural photoelectrochemical cell for water splitting: Implications for early Earth and Mars
  27. Letter. In situ observation of the breakdown of magnetite (Fe3O4) to Fe4O5 and hematite at high pressures and temperatures
  28. Letter. The crystal structure of bartelkeite, with a revised chemical formula, PbFeGeVI(Ge2IVO7) (OH)2·H2O, isotypic with high-pressure P21/m lawsonite
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