Potassium argon dating advantages
The isotopes the KAr system relies on are Potassium (K) and Argon (Ar).Potassium, an alkali metal, the Earth's eighth most abundant element is common in many rocks and rock-forming minerals.Dating of movement on fault systems is also possible with the Ar method.
What simplifies things is that potassium is a reactive metal and argon is an inert gas: Potassium is always tightly locked up in minerals whereas argon is not part of any minerals. So assuming that no air gets into a mineral grain when it first forms, it has zero argon content.Potassium (K) is one of the most abundant elements in the Earth's crust (2.4% by mass).One out of every 10,000 Potassium atoms is radioactive Potassium-40 (K-40).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.Thus, a granite containing all three minerals will record three different "ages" of emplacement as it cools down through these closure temperatures.