VizualAge: A Novel Approach to Laser Ablation ICP-MS U-Pb Geochronology Data Reduction

VizualAge, a new computer software tool for analysing U-Pb data obtained by laser ablation-inductively coupled plasma-mass spectrometry, was developed. It consists of a data reduction scheme (DRS) for Iolite (a general mass spectrometry data analysis tool) as well as visualisation routines. In addition to the U/Pb and Th/Pb ages calculated by Iolites U-Pb geochronology DRS, VizualAge also calculates 207Pb/206Pb ages and common Pb corrections for each time-slice of raw data. Importantly, VizualAge allows one to display a live concordia diagram for visualising data on such a diagram as an integration interval is being adjusted. This provides instantaneous feedback regarding discordance, uncertainty, error correlation and common Pb. Several zircon data sets were used to illustrate how the live concordia could be used as a powerful inspection tool, revealing a single analysis to consist of zones of concordance, metamict areas, as well as inherited cores or younger overgrowths. VizualAge also constructs histograms, conventional and Tera-Wasserburg type concordia diagrams, as well as 3D U-Th-Pb and total U-Pb concordia diagrams. The precision and accuracy of data reduced with VizualAge are demonstrated with examples of the Plesovice, Temora-2 and Penglai zircon reference materials. Data for zircon from the Long Lake Batholith (Wyoming craton) were used to illustrate how VizualAge calculated common Pb corrections and helped to expose as yet unexplained difficulties with accurately determining 204Pb.