Low-temperature thermal evolution of the Azov Massif (Ukrainian Shield-Ukraine) - Implications for interpreting (U-Th)/He and fission track ages from cratons

Our results reveal apparent inconsistencies between AFT and AHe data: the AHe ages corrected for alpha ejection according to the standard procedure [Farley, K.A., Wolf, R.A., Silver, L.T., 1996. The effect of long alpha-stopping distances on (U-Th)/He ages. Geochim. Cosmochim. Acta 60(21), 4223-4229.; Farley, K.A., 2002. (U-Th)/He dating: Techniques, calibrations, and applications. Mineral. Soc. Am. Rev. Mineral. Geochem. 47, 819-844] are older than corresponding AFT ages. In order to test the relevance of alpha ejection correction, mechanical abrasion of several apatite grains was applied. We found that in case of relatively slow cooling, alpha ejection correction of raw (U-Th)/He ages leads to erroneously high ages. This shows that alpha ejection correction should be used with caution. We propose that this correction should only be applied to samples with a fast cooling history, whereas it should not be applied to slowly cooled samples and to samples whose thermal history is not constrained by other means.