Zircon Raman dating: Age calculation and data valuation

Zircon Raman dating is a debated concept in thermochronology. It is based on the disruption of the zircon lattice by α-disintegration of ²³⁸U, ²³⁵U, ²³²Th, and their daughter nuclides. This radiation damage leads to broadening of the Raman bands. A date is calculated from the measured Raman bandwidths, and the effective Uranium (eU) content, measured in the same spot. Radiation damage anneals at elevated temperatures; thus the Raman date is interpreted with regard to its closure temperature (T_c) as an event, cooling or mixed age, depending on the thermal history of the sample. We present zircon Raman ages calculated from the widths of the 439, 1008, and 356 cm^-1 Raman bands for samples with different thermal histories. We discuss: (1) criteria for evaluating the Raman data by inter-band comparison; (2) the effect of partial annealing on the dating results; (3) the spatial matching of Raman and eU microanalysis.