Uranium dating zircon
In uranium–lead (U–Pb) dating of zircon, the zircon is found to exclude initial lead almost completely.Minerals, too, are predictable chemical compounds that can be shown to form at...
The half-life is the amount of time it takes for one half of the initial amount of the parent, radioactive isotope, to decay to the daughter isotope.Finally, with few predictable exceptions, zircon grows or regrows only in liquid rock or in solid rock reheated to approach its melting point.Combining all of these attributes, it is often possible to measure both the time of crystallization and the time of second melting in different parts of the same grain or in different selected grains from the same rock.Of course, such a high blocking temperature can have its disadvantages.Inherited cores may give a mixed false age when the age of crystallization is sought.U–Pb Decay System and Age Calculations The accumulation of Pb in U-bearing minerals according to known decay rates of radioactive parent isotopes of U and Th forms the basis of this dating method.
One measures the amount of radiogenic (i.e., produced from radioactive decay) Pb relative to the amount of radioactive parent isotope.
Definition Uranium–Lead dating is the geological age-determination method that uses the radioactive decay of uranium (U) isotopes (238U, 235U, and also in this entry 232Th) into stable isotopes of lead (Pb) (206Pb, 207Pb, and 208Pb, respectively).
U–Pb geochronology is the science of both the methodology but also the application of these methods to geological problems.
To see how we actually use this information to date rocks, consider the following: Usually, we know the amount, N, of an isotope present today, and the amount of a daughter element produced by decay, D*.
By definition, D* = N-1) (2) Now we can calculate the age if we know the number of daughter atoms produced by decay, D* and the number of parent atoms now present, N.
As there are three radioactive isotopes (238U, 235U, and 232Th) that decay into stable “daughter” isotopes of Pb, one can calculate three ages in this manner, two of which have the same (i.e., U and Pb) elements forming parent and daughter.