K-Ar dating of Precambrian Rocks

Abstract

Much of the early K-Ar dating was on Precambrian rocks because the concentration of radiogenic argon was so much greater than in younger rocks that analytical difficulties were minimized. A serious disadvantage to dating these rocks is the loss of radiogenic argon by diffusion or later orogenies. Time gaps are often a feature of deep-seated plutons, due to slow cooling. However, radiogenic argon is retained very well under sufficiently tranquil geologic conditions. The complexities introduced by the multiple metamorphic history of most Precambrian areas are too great to be unraveled by K-Ar measurements alone, and a combined K-Ar, Rb-Sr, and U-Pb, and geologic approach is needed.