A new method for estimating parent rock trace element concentrations from zircon


Chapman, James B.
Gehrels. George E., Ducea
Mihai N., Giesler
Nicky, Pullen

Zircon/bulk rock REE partition coefficients from natural samples correlate with REE concentration in zircon. The correlation is the strongest for the LREE and diminishes with decreasing ionic radius. The relationship between partition coefficient and REE concentration in zircon can be modeled as a power law and the coefficient (α) and exponent (β) terms for each of the REE are empirically determined using new and previously published data. A series of independent tests show that using variable partition coefficients based on the reported α and β terms commonly results in more accurate estimates of bulk rock REE concentrations than average partition coefficients, particularly for the LREE that have previously been difficult to constrain. These results provide a way to account for highly variable REE concentrations in zircon,whichmay be controlled by numerous processes such as surface enrichment, complex substitution mechanisms, or accidental sampling of sub-microscopic inclusions. The proposed method for estimating bulk rock REE concentrations is especially well-suited to detrital zircon investigations where there is no information available on the parent rock composition.

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Fig. 1. Previously published zircon/bulk rock (natural data; Nardi et al., 2013; Reid et al., 2011; Claiborne et al., 2010; Marshall et al., 2009; Sano et al., 2002; Thomas et al., 2002; Bea et al., 1994; Hinton and Upton, 1991; Fujimaki, 1986; Nagasawa, 1970) and zircon/ melt (experimental data; Taylor et al., 2015; Burnham and Berry, 2012; Luo and Ayers, 2009; Rubatto and Hermann, 2007; Watson, 1980) partition coefficients. An identical plot with each data source separated by symbol and color is presented in Appendix 6 in the Supplementary Material. The zircon/bulk rock partition coefficient shown for this study is averaged from each of the median partition coefficients presented in Table 1and the uncertainty is related to the scatter in those values (1σ).

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Chemical Geology 439 (2016) 59–70