Micro‐Raman spectroscopy and SEM/EDX applied to improve the zircon fission track method used for dating geological formations

Abstract

The zircon mineral is widely studied in geochronology. In the case of the fission track method (FTM), the age is determined by the density of fission tracks at the zircon surface, which can be observed with an optical microscope after an appropriate chemical treatment (etching). The etching must be isotropic at the zircon grain surface to be used in the FTM, which leads those zircon grains whose etching is anisotropic to be discarded. The only reason for this discarding is the nonuniform morphology of the surface grain seen by optical microscopy, that is, no further physicochemical analysis is performed. In this work, combining micro-Raman and scanning electron microscopy (SEM) to study the etching anisotropy, it was shown that zircon grains that present at least one area at the surface where the density of fission track is uniform can be used in the FTM. The micro-Raman showed characteristic spectra of the standard zircon sample either from the areas where there are tracks or from where there are not. The only difference found was in the Raman bandwidths, which were broader for the areas with higher density of fission tracks. This suggests simply a decrease in the relative percentage of the crystalline/amorphous phases at these areas. The SEM/energy dispersive spectrometry (EDX) showed that there were no significant differences in the principal chemical composition at the areas with and without fission tracks.

Fission track and U–Pb in situ dating applied to detrital zircon from the Vale do Rio do Peixe Formation, Bauru Group, Brazil

“…In the last decade, the fission track method (FTM) in zircon, in which the fission track age and its thermal history can be determined, has experienced rapid growth and widespread application in the Earth Sciences (Yamada et al, 2003;Hasebe and Watanabe, 2004;Garver, 2003;Dias et al, 2009). Some of the most exciting advances in geochronology have been driven by Laser Ablation Multicollector Inductively Coupled Plasma Mass Spectrometers (LA-MC-ICP-MS).…”

Recent advances in linear and nonlinear Raman spectroscopy. Part IV

“…In the case of the fission track method (FTM), the age is determined by the density of fission tracks at the zircon surface, which can be observed with an optical microscope after an appropriate chemical etching. Dias et al 164 combined micro‐Raman and SEM to study the etching anisotropy and thereby determine the age of zircon minerals by the FTM method. Frost et al 165 carried out a Raman spectroscopic study of the uranyl tellurite mineral moctezumite PbUO 2 (TeO 3 ) 2 .…”

A new approach for electron microprobe zircon fission track thermochronology

“…In the past decade, fission track thermochronology (FTT) in zircon has experienced rapid growth and widespread application in the earth sciences (Yamada et al, 2003;Hasebe and Watanabe, 2004;Garver, 2003;Bernet et al, 2004aBernet et al, , 2009Dias et al, 2009Dias et al, , 2011. The most widely used approach is the external detector method (EDM), in which age is obtained by counting both the fossil ( 238 U spontaneous fission) and the induced ( 235 U induced fission) tracks using an optical microscope.…”