A brief introduction into the Greenland U-Pb Geochronology Database

Geochronology aims to establish the age of rocks, minerals, and geological events including fluid movement and mineralization, within a specific degree of uncertainty, using signatures inherent in the rocks themselves. Absolute dating is only accomplished through the use of naturally-occurring radioactive isotopes found within geological samples. The U–Th–Pb isotopic system is the benchmark for determining the ages of geological materials because, unlike other chronometers, it exploits three independent isotopic decay schemes for which the decay constants are well known: U to Pb, U to Pb, and Th to Pb. The ability to use more than one independent chronometer in the same sample allows open-system behaviour (i.e. radiogenic-Pb loss) to be detected. This helps to evaluate whether analyses represent the time of mineral growth or the time of a younger disturbance, and greatly enhances the reliability of age determinations. In principle any mineral that contains sufficient quantities of uranium can be dated. However, those minerals whose crystal structure expels lead are preferable because they will only (or to a great extent) contain radiogenic lead produced from insitu decay and thus will not be compromised with lead from outside the crystal that would contaminate the time signal. Zircon is by far the most commonly utilized mineral for U–Pb dating, monazite, apatite, xenotime, titanite, rutile, baddeleyite, allanite, and perovskite can also be dated using the U-Pb method. As each of these minerals will close to lead diffusion at different temperatures or have different susceptibilities to fluids they provide a broad range of geochronologic and thermochronologic applications. Such applications include not only directly dating igneous, metamorphic, hydrothermal, and epithermal processes but also potentially constraining the timing of exhumation.