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An experimental study of Ti and Zr partitioning among zircon, rutile, and granitic melt

Hofmann, Amy E. and Baker, Michael B. and Eiler, John M. (2013) An experimental study of Ti and Zr partitioning among zircon, rutile, and granitic melt. Contributions to Mineralogy and Petrology, 166 (1). pp. 235-253. ISSN 0010-7999. http://resolver.caltech.edu/CaltechAUTHORS:20130807-075459683

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Abstract

In order to evaluate the effect of trace and minor elements (e.g., P, Y, and the REEs) on the high-temperature solubility of Ti in zircon (zrc), we conducted 31 experiments on a series of synthetic and natural granitic compositions [enriched in TiO_2 and ZrO_2; Al/(Na + K) molar ~1.2] at a pressure of 10 kbar and temperatures of ~1,400 to 1,200 °C. Thirty of the experiments produced zircon-saturated glasses, of which 22 are also saturated in rutile (rt). In seven experiments, quenched glasses coexist with quartz (qtz). SiO_2 contents of the quenched liquids range from 68.5 to 82.3 wt% (volatile free), and water concentrations are 0.4–7.0 wt%. TiO_2 contents of the rutile-saturated quenched melts are positively correlated with run temperature. Glass ZrO_2 concentrations (0.2–1.2 wt%; volatile free) also show a broad positive correlation with run temperature and, at a given T, are strongly correlated with the parameter (Na + K + 2Ca)/(Si·Al) (all in cation fractions). Mole fraction of ZrO_2 in rutile (X^(rt)_(ZrO2)) in the quartz-saturated runs coupled with other 10-kbar qtz-saturated experimental data from the literature (total temperature range of ~1,400 to 675 °C) yields the following temperature-dependent expression: ln(X^(rt)_(ZrO2))+ln(ɑ_(SiO2))=2.638(149)−9969(190)/T(K) , where silica activity ɑ_(SiO2) in either the coexisting silica polymorph or a silica-undersaturated melt is referenced to α-quartz at the P and T of each experiment and the best-fit coefficients and their uncertainties (values in parentheses) reflect uncertainties in T and X^(rt)_(ZrO2) . NanoSIMS measurements of Ti in zircon overgrowths in the experiments yield values of ~100 to 800 ppm; Ti concentrations in zircon are positively correlated with temperature. Coupled with values for ɑ^(SiO2) and ɑ_(TiO2) for each experiment, zircon Ti concentrations (ppm) can be related to temperature over the range of ~1,400 to 1,200 °C by the expression: ln(Ti ppm)^(zrc)+ln(ɑ_(SiO2))−ln(ɑ_(TiO2))=13.84(71)−12590(1124)/T(K) . After accounting for differences in ɑ_(SiO2) and ɑ_(TiO2) , Ti contents of zircon from experiments run with bulk compositions based on the natural granite overlap with the concentrations measured on zircon from experiments using the synthetic bulk compositions. Coupled with data from the literature, this suggests that at T ≥ 1,100 °C, natural levels of minor and trace elements in “granitic” melts do not appear to influence the solubility of Ti in zircon. Whether this is true at magmatic temperatures of crustal hydrous silica-rich liquids (e.g., 800–700 °C) remains to be demonstrated. Finally, measured D^(zrc/melt)_(Ti) values (calculated on a weight basis) from the experiments presented here are 0.007–0.01, relatively independent of temperature, and broadly consistent with values determined from natural zircon and silica-rich glass pairs.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1007/s00410-013-0873-6DOIArticle
http://link.springer.com/article/10.1007/s00410-013-0873-6PublisherArticle
http://dx.doi.org/10.1007/s00410-015-1131-x ErrataErratum
http://link.springer.com/article/10.1007%2Fs00410-015-1131-xErrataErratum
Additional Information:© 2013 Springer-Verlag. Received: 1 September 2012. Accepted: 8 March 2013. Published online: 6 April 2013. Communicated by T. L. Grove. The authors thank Yunbin Guan for technical assistance on the NanoSIMS, Rick Hervig (ASU) for assistance on Caltech’s 7f-GEO SIMS during his sabbatical, Chi Ma for assistance on the electron microprobe, and Bruce Watson (RPI) for illuminating conversations regarding methodology and preliminary results. Formal reviews by Calvin Miller and an anonymous reviewer led to substantial improvements to the manuscript. Financial support for this study was provided by NSF award EAR-0910975 to JME and a grant from the Moore Foundation to the Caltech Microanalysis Center.
Funders:
Funding AgencyGrant Number
NSFEAR-0910975
Moore FoundationUNSPECIFIED
Subject Keywords:Rutile; Zircon; Zr-in-rutile thermometry; Ti-in-zircon thermometry; Experimental petrology; Trace-element partitioning; NanoSIMS
Record Number:CaltechAUTHORS:20130807-075459683
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20130807-075459683
Official Citation: An experimental study of Ti and Zr partitioning among zircon, rutile, and granitic melt Amy E. Hofmann, Michael B. Baker… Pages 235-253
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39795
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:07 Aug 2013 22:20
Last Modified:25 Jun 2015 15:46

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