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Soon after the initial studies on He-diffusion in apatite pointed out the use of the (U-Th)/ He system for low temperature geochronology (Zeitler et al. 1987; Wolf et al. 1996; Warnock et al. 1997), the potential value of forward modeling for refined interpretation of (U-Th)/He dating was indicated (Wolf et al. 1998). While the first studies provided evidence for the low closure temperature (TC, Dodson 1973) of the (U-Th)/He system in apatite for monotonously cooling systems, the latter study investigated the sensitivity of the (U-Th)/He system for a wide range of geologically feasible heating/cooling scenarios. Forward modeling of He-accumulation in minerals expanded the use of the (U-Th)/He geochromometer to geological systems that do not fit one of the main conditions for the meaningful application of the closure temperature concept, i.e. monotonous cooling at a constant rate through TC. Forward modeling can help to give a meaning to apparent (U-Th)/He-ages from rocks with cooling histories with protracted residence time in the helium partial retention zone (HePRZ; e.g., ~40–85 °C in apatite; Wolf et al. 1998), where the closure temperature is undefined (Fig. 1⇓).