One of these domains completely anneals at a higher temperature, and the other remains an open system until rapid cooling at ~21 Ma, interpreted to be related to Miocene unroofing and extension. Domains with higher closure temperatures lie along a different relationship between these two than do those samples with cooler closure temperatures.The transition to the region of lower closure temperatures gives the timing of Miocene extension, unroofing, and cooling. They show that there are two different domains within the K-feldspars that have different diffusivities.
is a radiometric dating method invented to supersede potassium-argon (K-Ar) dating in accuracy.
Ar dating is a major method that researchers have used to understand the structural evolution of the Maria Fold and Thrust Belt.
Oligocene and Miocene extension along low-angle normal faults, associated with metamorphic core complex emplacement, produced the final thermal signal.
Ar closure temperatures are a function of crystal diffusional length-scale, composition and structure, and cooling rate.
Argon-argon dating works because potassium-40 decays to argon-40 with a known decay constant. This led to the formerly-popular potassium-argon dating method.
However, scientists discovered that it was possible to turn a known proportion of the potassium into argon by irradiating the sample, thereby allowing scientists to measure both the parent and the daughter in the gas phase.
Reheating events and diffusion of argon from the boundaries of the grain can result in lower Ar date.
Sometimes, when a large amount of argon has been lost, this is not possible.
In these cases, the age of the first batch of argon released is the age of the reheating event, and the age of the last argon released is the minimum age of initial crystallization.