In this case, it is a big advantage to present the data in a form in which the abundance of both the parent and daughter isotopes are given with respect to the abundance of the initial background daughter.

what problems are encountered in dating metamorphic rocks-76what problems are encountered in dating metamorphic rocks-15

If minerals are used for dating, the necessary checks on the ages are achieved by analyzing samples from more than one location and by analyzing different grain sizes or mineral types that respond differently to disturbing events.

It can be said that minerals provide a high degree of sample integrity that can be predicted on the basis of experience gained through numerous investigations under a variety of geologic conditions.

Here, a single uranium–lead isotopic analysis can provide an age more precise than can be obtained by the whole rock isochron method involving many analyses.

When single minerals are analyzed, each grain can be studied under a microscope under intense side light so that alterations or imperfections can be revealed and excluded.

When a single body of liquid rock crystallizes, parent and daughter elements may separate so that, once solid, the isotopic data would define a series of points, such as those shown as open circles designated R.

With time each would then develop additional daughter abundances in proportion to the amount of parent present.

Certain rocks that cooled quickly at the surface were found to give precisely defined linear isochrons, but many others did not.

Some studies have shown that rubidium is very mobile both in fluids that migrate through the rock as it cools and in fluids that are present as the rock undergoes chemical weathering.

An ideal mineral is one that has sufficient parent and daughter isotopes to measure precisely, is chemically inert, contains little or no significant initial daughter isotopes, and retains daughter products at the highest possible temperatures.

A specific datable mineral like lead of mass 206 relative to that of mass 204 has changed from an initial value of about 10 present when the Earth was formed to an average value of about 19 in rocks at the terrestrial surface today.

In this case, the slope of the line in potassium–argon (K–Ar) dating, for example, because most minerals do not take argon into their structures initially.