Thus, a granite containing all three minerals will record three different "ages" of emplacement as it cools down through these closure temperatures.
Ar (argon), the atom typically remains trapped within the lattice because it is larger than the spaces between the other atoms in a mineral crystal.
But it can escape into the surrounding region when the right conditions are met, such as change in pressure and/or temperature.
The amount of Argon sublimation that occurs is a function of the purity of the sample, the composition of the mother material, and a number of other factors.
These factors introduce error limits on the upper and lower bounds of dating, so that final determination of age is reliant on the environmental factors during formation, melting, and exposure to decreased pressure and/or open-air.
Heating causes the crystal structure of the mineral (or minerals) to degrade, and, as the sample melts, trapped gases are released.
The gas may include atmospheric gases, such as carbon dioxide, water, nitrogen, and argon, and radiogenic gases, like argon and helium, generated from regular radioactive decay over geologic time.Potassium is a common element found in many materials, such as micas, clay minerals, tephra, and evaporites.In these materials, the decay product Ar is able to escape the liquid (molten) rock, but starts to accumulate when the rock solidifies (recrystallizes).If so, then the K-Ar and Ar-Ar "dating" of crustal rocks would be similarly questionable.When muscovite (a common mineral in crustal rocks) is heated to 740°-860°C under high Ar pressures for periods of 3 to 10.5 hours it absorbs significant quantities of Ar, producing K-Ar "ages" of up to 5 billion years, and the absorbed Ar is indistinguishable from radiogenic argon ( In other experiments muscovite was synthesized from a colloidal gel under similar temperatures and Ar pressures, the resultant muscovite retaining up to 0.5 wt% Ar at 640°C and a vapor pressure of 4,000 atmospheres.This is approximately 2,500 times as much Ar as is found in natural muscovite.