Use of Cathodoluminescence for U-Pb Zircon Dating by Ion Microprobe: Some Examples from the Western Alps

Abstract

The first report on cathodoluminescence (CL) of zircon goes back to the second half of the nineteenth century (Crookes 1879), however, only in the last 40 years has this phenomenon been addressed more frequently. The main CL emission bands have been related to different trace elements such as Mn and V (Leverenz 1968), Hf and Y (Ono 1976), Dy (e.g. Mariano 1978), Gd and Tb (e.g. Ohnenstetter et al. 1991). These elements would act as “activators” and enhance the “intrinsic” luminescence of pure zircon by non-stoichiometry, lattice damage or by structural defects (Marshall 1988). It has also been pointed out that elements such as Y can have a “quenching” effect on CL of zircon (Ohnenstetter et al. 1991) as they reduce the CL emission. A second approach to CL relates to the studies of CL zoning patterns to assist in the interpretation of U-Pb dating. This tool has proved to be indispensable when combined with U-Pb zircon dating by ion microprobe (e.g. SHRIMP). CL allows the identification of different types of zircon domains that then may be dated in situ by SHRIMP, with spatial resolutions between ca. 30 µm (e.g. Gebauer et al. 1988) and 15–20 µm (e.g. Gebauer 1996; Vavra et al. 1996).