At Mesquite Mountain, the plateau ages for the hornblende indicate closure at around 80 Ma, the initial phase of thrusting and uplift.
Biotites and potassium feldspar have 0% Ar intercept ages around 20-30 Ma, indicative of early Miocene cooling during extension and unroofing in the Colorado River Extensional Corridor.
The transition to the region of lower closure temperatures gives the timing of Miocene extension, unroofing, and cooling.
method is based upon the decay of radioactive potassium-40 to radioactive argon-40 in minerals and rocks; potassium-40 also decays to calcium-40.
Sometimes, when a large amount of argon has been lost, this is not possible.
To address the first of these, Knapp and Heizler (1990) select multiple mineral phases to analyze.
(c) A reheating event yields another staircase-like profile; the 0% value is the age of the reheating event, and the 100% value is the minimum age of initial crystallization of the sample. Knapp and Heizler (1990) use argon-argon thermochronometry to date the thermal history of the Maria Fold and Thrust Belt.
In doing so, they find that basement-involved deformation of the crust around 80–90 Ma caused regional heating of the crust.
The potassium-argon age of some meteorites is as old as 4,500,000,000 years, and volcanic rocks as young as 20,000 years old have been measured by this method.
Ar) dating is a radiometric dating method invented to supersede potassium-argon (K/Ar) dating in accuracy.