Pros and cons of radioactive dating
Precise corrections can be made for the amount of pre-existing daughter product, if any, incorporated in the mineral at the time of its formation, and the amounts of the isotope introduced in the lab procedure.
The relatively high abundance and widespread distribution of potassium in the earths crust enables the potassium-argon (K-Ar) technique of age determination to be applied to common rocks and minerals.
The determination of the ages of rocks and minerals by the measurement of radioactive elements and their decay products, and the measurement of the isotopic abundances of strontium and lead have become accepted tools for mappers, researchers and exploration geologists in oil and metals exploration.
Age control is vitally important in geological, petrogenetic, tectonic and geomorphological studies and for stratigraphic correlations.
However, young volcanic rocks (Cenozoic) with moderate amounts of undevitrified glass, appear to have given reliable K-Ar whole-rock ages.
Other minerals have been investigated, with mixed success.
This technique, sometimes referred to as the common lead method, relies on the assumption that lead-rich (or uranium poor) phases preserve the lead isotopic signatures of their source U/Pb and Th/Pb ratios.
These minerals contain potassium as a major element, which is always present in the theoretical formula.The differing half-lives for the radioactive U means that two systems can be used to calculate ages and when plotted against each other provide a test for closed system behaviour; i.e.when there is concordancy of the two uranium-lead ages, giving rise to a conventional concordia diagram (a plot of The main advantage of the uranium-lead technique rests with the resistance of accessory phases, notably zircon, to post-crystallization disturbances and alteration.Sr ratios and, on a gross scale, marked variations can be found between the strontium isotopic compositions of marine and continental waters.Carbonates deposited from, and calcareous organisms living in these waters will have distinctive The presence of uranium-rich accessory minerals (e.g., zircon, monazite, sphene and apatite) in acid to intermediate igneous and metamorphic rocks enables the uranium-lead technique to be applied to the problems of precisely defining crystallization ages of such minerals.