Without getting into the detailed mumbo-jumbo of the topic, I will say that science does not dispute that Argon mobility can and will influence radiometric dating results. This influence can often be corrected or compensated for, or even found to be useful.
Looking at metamorphic rocks. Metamorphic recrystalization can and does cause Argon migration. Most likely, if you do a Uranium/Lead dating of this rock, you will get an older date, than that from a Potassium/Argon dating. Does this mean that all the dates are invalid? No. It means that the U/Pb date is that of the formation of the protolith, the rock that was, before metamorphism. The K/Ar date is that of the metamorphic event. Two different, but equally valid and significant dates, of the same rock.
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