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.
Thus, discretion and interpretation of age dating is essential.
Ar after cooling past the closing temperature and that this was properly sampled during analysis.
The abundance of Ar is unlikely to provide the age of intrusions of granite as the age typically reflects the time when a mineral cooled through its closure temperature.
However, in a metamorphic rock that has not exceeded its closure temperature the age likely dates the crystallization of the mineral.
Therefore, unlike the conventional K/Ar technique, absolute abundances need not be measured.
Instead, the ratios of the different argon isotopes are measured, yielding more precise and accurate results.
Argon–argon dating has the advantage of not requiring determinations of potassium.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.Additional advantages of the single isotopic measurements of the K.However, because each of these parameters is difficult to determine independantly, a mineral standard, or monitor, of known age is irradiated with the samples of unknown age.
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Therefore, mafic rocks and minerals often contain less potassium than an equal amount of silicic rock or mineral.