Potassium argon dating technique
Dating of movement on fault systems is also possible with the Ar method.
Different minerals have different closure temperatures; biotite is ~300°C, muscovite is about 400°C and hornblende has a closure temperature of ~550°C.
Potassium, an alkali metal, the Earth's eighth most abundant element is common in many rocks and rock-forming minerals.
The quantity of potassium in a rock or mineral is variable proportional to the amount of silica present.
Ar) dating is a radiometric dating method invented to supersede potassium-argon (K/Ar) dating in accuracy.
The older method required splitting samples into two for separate potassium and argon measurements, while the newer method requires only one rock fragment or mineral grain and uses a single measurement of argon isotopes. The sample is then degassed in a high-vacuum mass spectrometer via a laser or resistance furnace.
Minerals usually only record the last time they cooled down below the closure temperature, and this may not represent all of the events which the rock has undergone, and may not match the age of intrusion.The monitor flux can then be extrapolated to the samples, thereby determining their flux.This flux is known as the 'J' and can be determined by the following equation: As the table above illustrates, several "undesirable" reactions occur on isotopes present within every geologic sample.This technique allows the errors involved in K-Ar dating to be checked.Argon–argon dating has the advantage of not requiring determinations of potassium.