(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.
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.
Hypothetical profiles of argon concentrations through the grain, and associated step-heating results.
(a) A constant concentration profile indicates no diffusion or later heating events. (b) Recent diffusive loss of Ar yields a staircase-type profile.
This could even be the case when the K-Ar and Ar-Ar analyses yield "dates" compatible with other radioisotopic "dating" systems and/or with fossil "dating" based on evolutionary assumptions.
Furthermore, there would be no way of knowing, because the Ar not from radioactive decay, except of course by external assumptions about the ages of the rocks.
For more than three decades potassium-argon (K-Ar) and argon-argon (Ar-Ar) dating of rocks has been crucial in underpinning the billions of years for Earth history claimed by evolutionists. Lassen plagioclase, California (AD 1915) 0.11±0.03 Ma Sunset Crater basalt, Arizona (AD 1064-1065) 0.27±0.09 Ma; 0.25±0.15 Ma Akka Water Fall flow, Hawaii (Pleistocene) 32.3±7.2 Ma Kilauea Iki basalt, Hawaii (AD 1959) 8.5±6.8 Ma Mt.