Direct dating of gold by radiogenic helium
Humphreys cannot make any claim regarding my inappropriate use of a multi-domain diffusion model, because I have replicated the results of my original old-earth model with a simpler single-domain diffusion model. Although such modeling does not prove such a mechanism for these non-Arrhenius effects, it suggests that only a small proportion of gas resides in domains that exhibit anomalously high diffusivity, and therefore this phenomenon may not significantly affect the bulk closure temperature or He diffusion properties of most natural zircons.
This model relies on the high-temperature steps of a diffusion experiment, and therefore makes no claims about the retention of loosely bound helium. If that is indeed the quote that Humphreys is referring to, then I would argue that he is the one who is misquoting Reiners.
The background concentration is not well constrained by the data, but a sensitivity analysis shows that the results do not significantly change over that range, and that all observables can be matched by the model.
I can put together a more formal presentation if you wish. Originally posted by Poster 5 Oh that is fine thanks, no need for too much more detail!
There is nothing in his statement or experiment to preclude the possibility of helium remaining after the initial ramp.
It was just a topic that was outside of the scope of this particular study.
The bottom line is that good agreement to the measured helium retention of Gentry is obtained for both experimental sources for the diffusion parameters, provided that the high-temperature data is used to extract the single-domain diffusion model.
If one insists that the low-temperature data be included, as Humphreys did, then a multi-domain diffusion model must be used instead.
(Humphreys, 2008) Regardless of whether one considers this statement by Humphreys to be right or wrong, this latest result renders it completely irrelevant. Which part of which quote does he think you overlooked and what is he talking about and what is your response to his criticism? Originally Posted by Reiners Zircons with a wide range of ages and radiation dosages exhibited approximately the same degree of non-Arrhenius behavior in initial diffusion steps.Second, the statement about the loose helium being gone after the initial ramp are not in the quote by Reiners!