Evaluating U-Pb zircon data using a 3-dimensional concordia

Abstract

When assessing zircon U-Pb data, Wendt’s (1984; 1989) 3-dimensional projection for calculating concordia intercept ages has a fundamental advantage over other methods: the best-fit plane in three dimensions defines a sample’s age without requiring any advance knowledge about the isotopic composition of the non-radiogenic Pb. However, until now the general validity of this approach has never been investigated using data sets measured on terrestrial samples. Best-fit plane calculations were made for three terrestrial zircon samples. The t1 and t2 concordia intercept ages of these samples were found to be statistically equivalent to the ages calculated by other means. However, the 3-dimensional calculations gave detectable differences in ages and precision estimates as compared to the mean207Pb/206Pb and line regression techniques; such differences could be important at moderate to high precision level. It was also found that the 3-dimensional concordia provides useful information for discerning which analyses should or should not be included within the final data set.