U-PB GEOCHRONOLOGY: ITS DEVELOPMENT AND IMPORTANCE IN CANADA

This article presents a history of the development of U-Pb geochronology with emphasis on the role of Canadian researchers and some of its applications to Canadian geology. Modern U-Pb dating is the result of work by many individuals over the past 60 years, but the most important was Tom Krogh, who established methods that allowed determination of precise ages (<0.1% errors) on zircon using isotope dilution thermal ionization mass spectrometry (ID-TIMS). This was followed by the introduction of new analytical approaches by others, notably secondary ion mass spectrometry (SIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) that allow intra-crystal domains to be dated. U-Pb geochronology is now an indispensable tool for understanding the Earth. In collaboration with field mapping it has vastly improved our understanding of the geological history of Canada as well as understanding important geological events such as mass extinctions, secular changes in geological processes and the birth of the solar system.