Effect of Fe2+ on garnet-melt trace element partitioning: Experiments in FCMAS and quantification of crystal-chemical controls in natural systems

Wim Van Westrenen, Jonathan D. Blundy, Bernard J. Wood

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Garnet-melt trace element partitioning experiments were performed in the system FeO-CaO-MgO-Al2O3-SiO2 (FCMAS) at 3 GPa and 1540°C, aimed specifically at studying the effect of garnet Fe2+ content on partition coefficients (D(Grt/Melt)). D(Grt/Melt), measured by SIMS, for trivalent elements entering the garnet X-site show a small but significant dependence on garnet almandine content. This dependence is rationalised using the lattice strain model of Blundy and Wood [Blundy, J.D., Wood, B.J., 1994. Prediction of crystal-melt partition coefficients from elastic moduli. Nature 372, 452-454], which describes partitioning of an element i with radius r(i) and valency Z in terms of three parameters: the effective radius of the site r0(Z), the strain-free partition coefficient D0(Z) for a cation with radius r0(Z), and the apparent compressibility of the garnet X-site given by its Young's modulus E(X)(Z). Combination of these results with data in Fe-free systems [Van Westrenen, W., Blundy, J.D., Wood, B.J., 1999. Crystal-chemical controls on trace element partitioning between garnet and anhydrous silicate melt. Am. Mineral. 84, 838-847] and crystal structure data for spessartine, andradite, and uvarovite, leads to the following equations for r0(3 +) and E(X)(3 +) as a function of garnet composition (X) and pressure (P): r0(3 +) [Å] = 0.930X(Py) + 0.993X(Gr) + 0.916X(Alm) + 0.946X(Spes) + 1.05(X(And)+X(Uv)) - 0.005(P[GPa] - 3.0)(±0.005Å) E(x)(3 +) [GPa] = 3.5 x 1012 (1.38 + r0(3 +) [Å])-26.7(±30GPa) Accuracy of these equations is shown by application to the existing garnet-melt partitioning database, covering a wide range of P and T conditions (1.8 GPa < P < 5.0 GPa; 975°C < T < 1640°C). D(Grt/Melt) for all 3 + elements entering the X-site (REE, Sc and Y) are predicted to within 10-40% at given, P, T, and X, when D(Grt/Melt) for just one of these elements is known. In the absence of such knowledge, relative element fractionation (e.g. D(Sm)(Grt/Melt)/D(Nd)(Grt/Melt)) can be predicted. As an example, we predict that during partial melting of garnet peridotite, group A eclogite, and garnet pyroxenite, r0(3 +) for garnets ranges from 0.939 ± 0.005 to 0.953 ± 0.009 Å. These values are consistently smaller than the ionic radius of the heaviest REE, Lu. The above equations quantify the crystal-chemical controls on garnet-melt partitioning for the REE, Y and Sc. As such, they represent a major advance en route to predicting D(Grt/Melt) for these elements as a function of P, T and X. (C) 2000 Elsevier Science B.V. All rights reserved.

LanguageEnglish
Pages189-201
Number of pages13
JournalLithos
Volume53
Issue number3-4
DOIs
Publication statusPublished - 2000

Fingerprint

chemical control
Garnets
Trace Elements
garnet
partitioning
trace element
melt
crystal
Crystals
experiment
Experiments
partition coefficient
Wood
rare earth element
effect
Elastic moduli
spessartine
andradite
Silicates
almandine

Keywords

  • Crystal chemistry
  • Experimental studies
  • Garnet group
  • Partitioning
  • Trace elements

Cite this

Van Westrenen, Wim ; Blundy, Jonathan D. ; Wood, Bernard J. / Effect of Fe2+ on garnet-melt trace element partitioning : Experiments in FCMAS and quantification of crystal-chemical controls in natural systems. In: Lithos. 2000 ; Vol. 53, No. 3-4. pp. 189-201.
@article{dcdab5672de04242883545e80a725c98,
title = "Effect of Fe2+ on garnet-melt trace element partitioning: Experiments in FCMAS and quantification of crystal-chemical controls in natural systems",
abstract = "Garnet-melt trace element partitioning experiments were performed in the system FeO-CaO-MgO-Al2O3-SiO2 (FCMAS) at 3 GPa and 1540°C, aimed specifically at studying the effect of garnet Fe2+ content on partition coefficients (D(Grt/Melt)). D(Grt/Melt), measured by SIMS, for trivalent elements entering the garnet X-site show a small but significant dependence on garnet almandine content. This dependence is rationalised using the lattice strain model of Blundy and Wood [Blundy, J.D., Wood, B.J., 1994. Prediction of crystal-melt partition coefficients from elastic moduli. Nature 372, 452-454], which describes partitioning of an element i with radius r(i) and valency Z in terms of three parameters: the effective radius of the site r0(Z), the strain-free partition coefficient D0(Z) for a cation with radius r0(Z), and the apparent compressibility of the garnet X-site given by its Young's modulus E(X)(Z). Combination of these results with data in Fe-free systems [Van Westrenen, W., Blundy, J.D., Wood, B.J., 1999. Crystal-chemical controls on trace element partitioning between garnet and anhydrous silicate melt. Am. Mineral. 84, 838-847] and crystal structure data for spessartine, andradite, and uvarovite, leads to the following equations for r0(3 +) and E(X)(3 +) as a function of garnet composition (X) and pressure (P): r0(3 +) [{\AA}] = 0.930X(Py) + 0.993X(Gr) + 0.916X(Alm) + 0.946X(Spes) + 1.05(X(And)+X(Uv)) - 0.005(P[GPa] - 3.0)(±0.005{\AA}) E(x)(3 +) [GPa] = 3.5 x 1012 (1.38 + r0(3 +) [{\AA}])-26.7(±30GPa) Accuracy of these equations is shown by application to the existing garnet-melt partitioning database, covering a wide range of P and T conditions (1.8 GPa < P < 5.0 GPa; 975°C < T < 1640°C). D(Grt/Melt) for all 3 + elements entering the X-site (REE, Sc and Y) are predicted to within 10-40{\%} at given, P, T, and X, when D(Grt/Melt) for just one of these elements is known. In the absence of such knowledge, relative element fractionation (e.g. D(Sm)(Grt/Melt)/D(Nd)(Grt/Melt)) can be predicted. As an example, we predict that during partial melting of garnet peridotite, group A eclogite, and garnet pyroxenite, r0(3 +) for garnets ranges from 0.939 ± 0.005 to 0.953 ± 0.009 {\AA}. These values are consistently smaller than the ionic radius of the heaviest REE, Lu. The above equations quantify the crystal-chemical controls on garnet-melt partitioning for the REE, Y and Sc. As such, they represent a major advance en route to predicting D(Grt/Melt) for these elements as a function of P, T and X. (C) 2000 Elsevier Science B.V. All rights reserved.",
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}

Effect of Fe2+ on garnet-melt trace element partitioning : Experiments in FCMAS and quantification of crystal-chemical controls in natural systems. / Van Westrenen, Wim; Blundy, Jonathan D.; Wood, Bernard J.

In: Lithos, Vol. 53, No. 3-4, 2000, p. 189-201.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Effect of Fe2+ on garnet-melt trace element partitioning

T2 - Lithos

AU - Van Westrenen, Wim

AU - Blundy, Jonathan D.

AU - Wood, Bernard J.

PY - 2000

Y1 - 2000

N2 - Garnet-melt trace element partitioning experiments were performed in the system FeO-CaO-MgO-Al2O3-SiO2 (FCMAS) at 3 GPa and 1540°C, aimed specifically at studying the effect of garnet Fe2+ content on partition coefficients (D(Grt/Melt)). D(Grt/Melt), measured by SIMS, for trivalent elements entering the garnet X-site show a small but significant dependence on garnet almandine content. This dependence is rationalised using the lattice strain model of Blundy and Wood [Blundy, J.D., Wood, B.J., 1994. Prediction of crystal-melt partition coefficients from elastic moduli. Nature 372, 452-454], which describes partitioning of an element i with radius r(i) and valency Z in terms of three parameters: the effective radius of the site r0(Z), the strain-free partition coefficient D0(Z) for a cation with radius r0(Z), and the apparent compressibility of the garnet X-site given by its Young's modulus E(X)(Z). Combination of these results with data in Fe-free systems [Van Westrenen, W., Blundy, J.D., Wood, B.J., 1999. Crystal-chemical controls on trace element partitioning between garnet and anhydrous silicate melt. Am. Mineral. 84, 838-847] and crystal structure data for spessartine, andradite, and uvarovite, leads to the following equations for r0(3 +) and E(X)(3 +) as a function of garnet composition (X) and pressure (P): r0(3 +) [Å] = 0.930X(Py) + 0.993X(Gr) + 0.916X(Alm) + 0.946X(Spes) + 1.05(X(And)+X(Uv)) - 0.005(P[GPa] - 3.0)(±0.005Å) E(x)(3 +) [GPa] = 3.5 x 1012 (1.38 + r0(3 +) [Å])-26.7(±30GPa) Accuracy of these equations is shown by application to the existing garnet-melt partitioning database, covering a wide range of P and T conditions (1.8 GPa < P < 5.0 GPa; 975°C < T < 1640°C). D(Grt/Melt) for all 3 + elements entering the X-site (REE, Sc and Y) are predicted to within 10-40% at given, P, T, and X, when D(Grt/Melt) for just one of these elements is known. In the absence of such knowledge, relative element fractionation (e.g. D(Sm)(Grt/Melt)/D(Nd)(Grt/Melt)) can be predicted. As an example, we predict that during partial melting of garnet peridotite, group A eclogite, and garnet pyroxenite, r0(3 +) for garnets ranges from 0.939 ± 0.005 to 0.953 ± 0.009 Å. These values are consistently smaller than the ionic radius of the heaviest REE, Lu. The above equations quantify the crystal-chemical controls on garnet-melt partitioning for the REE, Y and Sc. As such, they represent a major advance en route to predicting D(Grt/Melt) for these elements as a function of P, T and X. (C) 2000 Elsevier Science B.V. All rights reserved.

AB - Garnet-melt trace element partitioning experiments were performed in the system FeO-CaO-MgO-Al2O3-SiO2 (FCMAS) at 3 GPa and 1540°C, aimed specifically at studying the effect of garnet Fe2+ content on partition coefficients (D(Grt/Melt)). D(Grt/Melt), measured by SIMS, for trivalent elements entering the garnet X-site show a small but significant dependence on garnet almandine content. This dependence is rationalised using the lattice strain model of Blundy and Wood [Blundy, J.D., Wood, B.J., 1994. Prediction of crystal-melt partition coefficients from elastic moduli. Nature 372, 452-454], which describes partitioning of an element i with radius r(i) and valency Z in terms of three parameters: the effective radius of the site r0(Z), the strain-free partition coefficient D0(Z) for a cation with radius r0(Z), and the apparent compressibility of the garnet X-site given by its Young's modulus E(X)(Z). Combination of these results with data in Fe-free systems [Van Westrenen, W., Blundy, J.D., Wood, B.J., 1999. Crystal-chemical controls on trace element partitioning between garnet and anhydrous silicate melt. Am. Mineral. 84, 838-847] and crystal structure data for spessartine, andradite, and uvarovite, leads to the following equations for r0(3 +) and E(X)(3 +) as a function of garnet composition (X) and pressure (P): r0(3 +) [Å] = 0.930X(Py) + 0.993X(Gr) + 0.916X(Alm) + 0.946X(Spes) + 1.05(X(And)+X(Uv)) - 0.005(P[GPa] - 3.0)(±0.005Å) E(x)(3 +) [GPa] = 3.5 x 1012 (1.38 + r0(3 +) [Å])-26.7(±30GPa) Accuracy of these equations is shown by application to the existing garnet-melt partitioning database, covering a wide range of P and T conditions (1.8 GPa < P < 5.0 GPa; 975°C < T < 1640°C). D(Grt/Melt) for all 3 + elements entering the X-site (REE, Sc and Y) are predicted to within 10-40% at given, P, T, and X, when D(Grt/Melt) for just one of these elements is known. In the absence of such knowledge, relative element fractionation (e.g. D(Sm)(Grt/Melt)/D(Nd)(Grt/Melt)) can be predicted. As an example, we predict that during partial melting of garnet peridotite, group A eclogite, and garnet pyroxenite, r0(3 +) for garnets ranges from 0.939 ± 0.005 to 0.953 ± 0.009 Å. These values are consistently smaller than the ionic radius of the heaviest REE, Lu. The above equations quantify the crystal-chemical controls on garnet-melt partitioning for the REE, Y and Sc. As such, they represent a major advance en route to predicting D(Grt/Melt) for these elements as a function of P, T and X. (C) 2000 Elsevier Science B.V. All rights reserved.

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KW - Experimental studies

KW - Garnet group

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KW - Trace elements

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