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

Dobson, K.J., Stuart, F.M. and Dempster, T.J. (2008) U and Th zonation in Fish Canyon Tuff zircons: implications for a zircon (U–Th)/He standard. Geochimica et Cosmochimica Acta, 72(19), pp. 4745-4755. (doi: 10.1016/j.gca.2008.07.015)

Abstract

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.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Dempster, Dr Tim and Stuart, Professor Fin and Dobson, Dr Katherine
• Authors: Dobson, K.J., Stuart, F.M., and Dempster, T.J.
• Subjects: Q Science > QE Geology
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre; College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Geochimica et Cosmochimica Acta
• ISSN: 0016-7037
• ISSN (Online): 1872-9533
• Published Online: 03 August 2008