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The effect of halogens on Zr diffusion and zircon dissolution in hydrous metaluminous granitic melts. (Articolo in rivista)

Type

Prodotto della ricerca (Classe)
Articolo in rivista (Classe)

Label

The effect of halogens on Zr diffusion and zircon dissolution in hydrous metaluminous granitic melts. (Articolo in rivista) (literal)

Anno

2002-01-01T00:00:00+01:00 (literal)

Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#doi

10.1007/s00410-001-0328-3 (literal)

Alternative label

BAKER D.R.; CONTE A.M.; FREDA C.; OTTOLINI L. (2002)
The effect of halogens on Zr diffusion and zircon dissolution in hydrous metaluminous granitic melts.
in Contributions to mineralogy and petrology; Springer Verlag, New York NY (Stati Uniti d'America)
(literal)

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BAKER D.R.; CONTE A.M.; FREDA C.; OTTOLINI L. (literal)

Pagina inizio

666 (literal)

Pagina fine

678 (literal)

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This study demonstrated the effects of halogens, F and Cl, on the diffusion of Zr in differently hydrated silicic melts. It has provided the foundation for estimates of the rates of zircon dissolution and the concentrations of Zr necessary for the saturation of silicic melts with zircon. These values can then be used, for example, to investigate the duration of melting events in the lower crust. In addition, the results can be used to determine solubilities of zircon in the melts for use as potential geothermometers and to investigate the formation of complexes between Zr and halogens through comparisons of diffusion coefficients determined in this study and in previous, halogen-free, studies. Contribution to Mineralogy and Petrology is an international journal that publish only high-quality papers dealing with geochemistry, petrology and genesis of igneous, metamorphic and sedimentary rocks and experimental petrology and mineralogy. (literal)

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142 (literal)

Rivista

Contributions to mineralogy and petrology (Rivista)

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Impact factor 2.534 (literal)

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6 (literal)

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The paper complements earlier studies on the dissolution of zircon, apatite and monazite and on the diffusion of their essential structural components in felsic melts that constrain the effect of these minerals on the trace element chemistry of hydrous granitic and rhyolitic melts. Among accessories, zircon has been of major interest because it is a major sink of HFSE and REE. In this study the effects of halogens, F and Cl, with and without water, on the diffusion of Zr away from dissolving zircon crystals in a felsic melt has been investigated to verify the rates at which this mineral dissolves and the geological implications based upon those rates. One of these is trace element model for HFSE and REE in granite and rhyolite petrogenesis because of the observed correlation between HFSE and halogen contents in numerous felsic rocks. The results of this study, combined with previous ones, demonstrate that the addition of halogens at amounts comparable to those of F- and Cl-enriched natural metaluminous felsic rocks exert a small effect on the solubility of zircon and the diffusion of Zr in the melt at temperatures greater than 800°C; thus they probably can not explain the observed possible correlation between Zr and halogens. On the contrary, due to the reduced zircon solubility and Zr diffusion in the chlorinated melt at lower temperature, during crustal melting, small amount of chlorine can affect the dissolution of zircon and diffusion of zirconium in the melt. (literal)

Note

ISI Web of Science (WOS) (literal)

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Baker D.R. a); Conte A. M. b); Freda C. c); Ottolini L. d); a) Earth and Planetary Sciences, McGill University, 3450 rue University, Montreal, QC H3A 2°7, Canada; b) CNR-IGG Sezione di Roma c/o Dip. Scienze della Terra, Università \"La Sapienza\", P.le A. Moro, 5, 00185 Roma; c) INGV, Via di Vigna Murata, 605, 00143 Roma; d) CNR-IGG Sezione di Pavia, Via Ferrata, 1, 27100 Pavia; (literal)

Titolo

The effect of halogens on Zr diffusion and zircon dissolution in hydrous metaluminous granitic melts. (literal)

Abstract

Diffusion of Zr and zircon solubility in hydrous, containing approximately 4.5 wt% H2O, metaluminous granitic melts with halogens, either 0.35 wt% Cl (LCl) or 1.2 wt% F (MRF), and in a halogen-free melt (LCO) were measured at 1.0 GPa and temperatures between 1050 and 1400 °C in a piston-cylinder apparatus using the zircon dissolution technique. Arrhenius equations for Zr diffusion in each hydrous melt composition are, for LCO with 4.4 ± 0.4 wt% H2O:D = 2.28 ±0.03x10-8 exp(-140.1±33.9/RT), for LCl with 4.5 ± 0.5 wt% H2O:D = 2.33 ±0.05x10-4 exp(-254.8±64.1/RT), and for MRF with 4.9 ± 0.3 wt% H2O:D = 2.54 ±0.03x10-5 exp(223.8±15.5/RT). Solubilities determined by the dissolution technique were reversed for LCO + 4.5±0.5 wt% H2O by crystallization of a Zr-enriched glass of LCO composition at 1200 and 1050 °C at 1.0 GPa.The solubility data were used to calculate partition coefficients of Zr between zircon and hydrous melt which are given by the following expressions, for LCO:lnD Zr-zircon/melt = 1.63(10000/T) 5.78, for LCl:lnD Zr-zircon/melt = 1.47(10000/T) 4.75, and for MRF by:lnD Zr-zircon/melt = 1.47(10000/T) 4.91. Experiments on the same compositions, but with water contents down to 0.5 wt% demonstrated reductions in both the diffusion coefficient of Zr and zircon solubility in the melt. The addition of halogens at the concentration levels studied to metaluminous melts has a small effect on either the diffusion of Zr in the melt or the solubility of zircon at all water concentrations and temperatures investigated. At 800 °C the calculated diffusion coefficient of Zr is lowest in LCl, 9 x 10exp-17 mexp2/s, and is highest in LCO, 4 x 10exp-15 mexp2/s. Extrapolation of the halogen-free solubility data to a magmatic temperature of 800 °C yields solubilities approximately one-third of those directly measured in similar compositions, predicted by earlier studies of zircon dissolution, and based upon analyses of natural rocks. This discrepancy is attributed to the higher oxygen fugacity of the experiments of this study compared to previous studies and nature, and the effect of oxygen fugacity on the structural role of iron in the melt which in turn affects zircon solubility, but does not significantly affect Zr diffusion. (literal)

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