A review of the present state of the absolute calibration for zircon fission track geochronometry using the external detector method




The authors have developed and demonstrated an independent calibration of zircon fission track dating with the external detector method. During the past two decades, investigations have continued concerning the issues of the absolute age calibration of fission track dating. The derivation of accurate fission track age equations has been made possible by taking into account the relationships between the latent and etched track lengths. Our dating exercise involving 10 zircon reference samples supports our claim that absolute age determinations can be carried out based on the following three parameters: (1) the 238U spontaneous fission decay constant of 8.5 × 10−17 a−1f) which is recommended by the IUPAC; (2) thermal neutron fluence values based on pre-irradiated IRMM540 dosimeter glass, which is equivalent to the Au and Co metal activation monitors in the 1990 IUGS recommendation; and (3) a [GQR] correction value of 1.35 which has been experimentally determined for the combination of zircon external surfaces irradiated with mica external detectors. Independent measurements of uranium concentration by the fission track method were also tested. A new method of fission track dating that uses mass spectrometry for uranium measurements was simulated with success using our zircon data. We propose that the Fission Track Community reassesses the situation and formulates a new recommendation, in which the established independent method is placed on at least an equal footing with the standard-based method.