Common phases to be used for argon-argon dating are white micas, biotite, varieties of potassium feldspar (especially sanidine because it is potassium-rich), and varieties of amphibole. This can be used to solve equation 2 for the sample.
Second, the sample is irradiated along with a standard of a known age. A major advantage of the argon-argon method is that the sample can be heated incrementally.
However, in many instances, the published “ages” have no merit, as they fail the simple statistical tests that should be applied to all such data. In these experiments, a sample is heated in steps of increasing laboratory extraction temperature, until all the argon is released.
The argon released in each step is measured to calculate a “step age” with an associated analytical error.
Some of the problems of K-Ar dating can be avoided by the use of the related Ar-Ar dating method.
In this article we shall explain how this method works and why it is superior to the K-Ar method.
Dalrymple, referring to metamorphism and melting of rocks in the crust, has commented: "If the rock is heated or melted at some later time, then some or all the In a recent study 128 Ar isotopic analyses were obtained from ten profiles across biotite grains in high-grade metamorphic rocks, and apparent Ar-Ar "ages" within individual grains ranged from 161Ma-514Ma.
Thus under certain conditions Ar can be incorporated into minerals which are supposed to exclude Ar when they crystallize. envisage noble gases from the mantle (and the atmosphere) migrating and circulating through the crust, so there should be evidence of excess in crustal rocks and their constituent minerals could well be the norm rather than the exception.
Ar dating is a major method that researchers have used to understand the structural evolution of the Maria Fold and Thrust Belt.
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.
Therefore when the rock first forms, some of the minerals in it will have more potassium in and some less, but all the minerals will have the same initial ratio of But what is J?
J is a factor which depends on the nature of the neutron bombardment.