U and Th zonation in Fish Canyon Tuff zircons: implications for a zircon (U-Th)/He standard

Katherine J. Dobson, Finlay M. Stuart, Tim J. Dempster

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55 Citations (Scopus)


The inability to accurately determine the distribution of U and Th in zircon crystals analysed using (U-Th)/He is a major source of error, and limits the confidence in subsequent data interpretation. The Fish Canyon Tuff (FCT) zircon standard shows (U-Th)/He age reproducibility in excess of ±10%. We have tested the extent to which this is due to U and Th zonation using a combination of cathodoluminescence and ion probe analysis of a population of FCT zircons. Primarily we find that FCT zircons exhibit extreme U and Th zonation, and the population has large inter-crystalline variability. Furthermore, the net cathodoluminescence intensity from the FCT zircons is negatively correlated with U and Th concentration, allowing cathodoluminescence emission to be used as a proxy for U and Th zonation. This correlation was exploited to constrain the U and Th zonation within the crystal population, and to show that the poor age reproducibility of the FCT zircons is consistent with the observed zonation.

Original languageEnglish
Pages (from-to)4745-4755
Number of pages11
JournalGeochimica et Cosmochimica Acta
Issue number19
Publication statusPublished - 1 Oct 2008


  • Zircon (U-Th)/He thermochronology
  • Fish Canyon Tuff
  • reproducability
  • zonation


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