Fission-track Analysis of Detrital Zircon

Abstract

Zircon has become one of the most important minerals for studying sediment provenance and the exhumation history of orogenic belts. The reason for this utility is that zircon is common in many igneous, metamorphic, and sedimentary rocks, it is resistant to weathering and abrasion, and it can be dated with various isotopic methods having reasonable high concentrations of uranium and thorium (Fig. 1⇓). Techniques used to date detrital zircon include U/Pb and (U-Th)/He dating, but in this chapter we focus exclusively on fission-track (FT) analysis. Figure 1. Suite of detrital zircon showing the whole spectrum of zircon shapes and colors that encountered in detrital samples. This particular samples is a suite of zircon from a single sandstone sample of the Eocene Ukelayet Flysch, Northern Kamchatka, Russia. Several end members are worth noting (see text for discussion): Very well-rounded grains are likely to be polycyclic; Colorless with little damage and/or low REE; Colorless and euhedral; Grains of the red series; Grains of the yellow series. FT analysis allows age determination of single zircon grains that may have cooling ages between several hundred thousand to a billion years or more. The datable range depends on individual uranium content and cooling history of a zircon grain. Fission tracks in zircon have an effective annealing temperature of ~240 °C ± 30 °C in natural systems (Hurford 1986; Brandon et al. 1998; Bernet et al. 2002). Therefore most detrital zircon are fairly resistant to thermal annealing in typical sedimentary basins after deposition, while the other low-temperature thermochronometers anneal at lower temperatures common in sedimentary basins (i.e., Helium dating and apatite FT) and therefore more readily have compromised provenance information (Fig. 2⇓). Consequently, the strength of detrital zircon fission-track (DZFT) analysis lies in the fact that this method provides robust cooling ages of source …