How accurate is Radiometric Dating?

[Paleophyte]

Metamorphism typically isn't a problem for Rb-Sr ages because the closure temperatures for most minerals are high enough that any event hot enough to reset them becomes pretty obvious. We actually use the closure temperatures of different minerals to produce different ages that result in chronologies of metamorphic events.

K-Ar and Ar-Ar systematics are much more prone to resetting or loss at lower temperatures and are rarely used much anymore except on pristine materials or when trying to actually track low temperature events. That's because the argon daughter product is a noble gas and doesn't bind into any crystal structure, so the system is leaky as hell.

For really robust ages go with U-Pb concordia ages in zircon. You get two independent uranium decay series working side by side in a mineral that gleefully refuses to reset in anything up to and including having its host rock melt. On a bright day you can pull a Th-Pb date as a bonus. Just make sure you aren't analyzing detrital grains by accident or you're totally buggered.

I think the problem with using Rb-Sr to date the time of closure temperature is both Rb and Sr are alkaline elements can be diffusion into or out of the parent mineral by carbonated hydrothermal fluids at below closure temperatures.    So lower grade metamorphism that exposes the rock to hydrothermal fluids can alter RN-Sr dating results without subjecting the rocks to closure temperature again.

Not typically a problem. The closure temperature is where the daughter product is no longer capable of diffusing within the mineral grains. Below that any fluids that might be lurking are either left stripping a few atoms off the grain boundaries or producing large degrees of metasomatism. The former is negligible and the latter is pretty obvious. Single grain, fractional grain, and in situ analyses can be used to check for this type leakage.