Talk:Criticism of RATE’s helium diffusion data
Contamination
I think you should spend more time on assuming that contamination is even possible. To quote Humphreys on this issue:
“It is doubtful that such fluids could travel very far. First, the granodiorite is presently dry and well-consolidated, even at the surface. Second, the overlying rock puts the Jemez Granodiorite under in situ pressures hundreds to thousands of times greater than atmospheric pressure. Those factors would mean that the interface widths between minerals would be microscopic, perhaps only an Angstrom (the diameter of a hydrogen atom) or so. Henke needs to show—preferably with experimental data in a peer-reviewed scientific journal—just how far the helium could travel in this rock unit during the time he thinks is available. That would determine how close his conduits of magma would have to be. Then he would have to show geological evidence that conduits of basalt (solidified volcanic magma) presently exist within that distance of the borehole.”
“Next, Henke would have to show that the concentration (atoms or nanomoles per cc) of helium in the magmatic fluids could have been high enough to do the job. Our 15 ncc/µg value for Q0 in the zircons means there were at least 3140 nanomoles of helium per cubic centimeter in the zircons originally. (Henke’s value of “41” ncc/µg in item 6 above would require even more helium, 8590 nmol/cc.) The concentration in the assumed fluids would have to exceed that value in order to transfer helium from the fluid into the zircons. Yet the concentration of helium produced by uranium decay in typical basalt[ \l "12"] (and hence in basaltic magmatic fluids) would be less than 80 nmol/cc, more than forty times too small. No transfer would take place. So Henke’s scenario requires extraordinary amounts of helium in his magmatic fluids.”
“But let’s assume for the sake of argument that the helium somehow gets into the zircons. Now it has to stay there. The magmatic fluids would raise the temperature of the zircons considerably higher than their present temperature, and temperatures would remain high for dozens of millennia. As I showed in ICC 2003, section 7, the zircons would then lose essentially all their helium—contrary to what we observe. Moreover, most of the helium outside the zircons has to disappear somehow, so that the biotite concentration would drop to its present low level, hundreds of times less than the concentrations in the zircons.”--Nlawrence 23:47, 27 February 2007 (EST)
