Radiometric dating of metamorphic rocks types
Direct isotopic dating of a sedimentary rock is only possible if it contains an authigenic mineral e. For each parent isotope that decays, a daughter isotope takes its place. If none of these are present, then the only alternative is to date whole rocks. For example, uranium-lead dating can be used to find the age of a uranium-containing mineral. These two uranium isotopes decay at different rates.
Elements like K, U, Th, and Rb occur in quantities large enough to release a substantial amount of heat through radioactive decay. Radiocarbon dates are obtained from such things as bones, teeth, charcoal, fossilized wood, and shells. This can reduce the problem of contamination. This temperature is what is known as closure temperature and represents the temperature below which the mineral is a closed system to isotopes. In the event that no metamorphism occurred, mineral ages will coincide with whole-rock ages and both will give the age of initial crystallization of the rock.
Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert. Like Rutherford's, Boltwood's attempt to apply the principle to the dating of rocks was technically flawed but a step forward. We can thus use these ratios of light isotopes to shed light on processes and temperatures of past events. Other Uses of Isotopes Radioactivity is an important heat source in the Earth. The Earth might, indeed, be much older than his calculations indicated.
The thing that makes this decay process so valuable for determining the age of an object is that each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life. In fact, this form of dating has been used to date the age of rocks brought back to Earth from the moon. This provides a built-in cross-check to more accurately determine the age of the sample. Luminescence dating Luminescence dating methods are not radiometric dating methods in that they do not rely on abundances of isotopes to calculate age.
Such trapped Ar is not problematical when the age of the rock is in hundreds of millions of years. At best, detrital minerals can only provide the ages of their original source rocks.
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