What is ar ar dating
An easier method is to look at the data on age-spectrum plots and assess the reliability of “plateau” sections.
Though definitions of what constitutes a plateau vary, a general guideline is that such sections of the age spectra should contain released, whose ages “overlap”. Two steps can never define a plateau, and such data cannot be evaluated on an isochron diagram.
The plateau age of 100.00 Ma, with a standard error on the mean: of ± 0.22 Ma is found to be unacceptable, with p ~ 0.003 ( lie between ~ 99 and 101
For unmetamorphosed igneous rocks, the latter would normally represent the crystallization age.
The age of have a crystallization age in this range, but it contains excess argon (higher step ages on either side of the “plateau”).
There is no justification for quoting an age of 58.48 Ma with a very small error margin of ±0.18
Thus low-temperature steps normally exhibit ages lower than, or equal to, those of the higher temerature steps.
“Descending staircase” type age spectra may result from two totally different phenomena.