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I have on idea if it has a separate name since most magma would have it. That being said diffusion would be a huge problem so you could only date young magma or see which crystals are least affect. But hey its a moot point unless you can go sample a piece of magma.
To be a bit more precise here. Radiometric ages give us cooling ages, and not solidification ages. A given mineral has a 'trapping' temperature above which daughter elements are mobile, even in the solid state. Most of those temperatures would be below the temperature that the rock is solid (called the 'solidus'). Hence each mineral would give a different age based on its trapping temperature and its cooling history.
This, of course, would confuse YECs...
There are ways around this mineral issue based on isochron dating and whole rock methods, but it has been very long since I studied them and I'm too lazy to look up the information. I think that RAZD has it handy.
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