More Than Just An Age: Quantitative Analysis of Geochronological Data and Uncertainty

The resolving power of geochronological data in the earth sciences is dependent on the precision and accuracy of many numerical isotopic measurements and corrections. Recent advances in U-Pb geochronology have reinvigorated its application to problems such as precise timescale calibration, processes of crustal evolution, and early solar system dynamics. However, as factors that have dominated age uncertainty are resolved, other sources of error must be recognized and propagated accurately to determine overall uncertainty. At present, no common data reduction protocol exists, which limits interpretation of precise geochronology and makes inter-laboratory comparison difficult.

U-Pb_Redux and Tripoli—new, freely available software packages developed as part of the EARTHTIME project—enable the user to reduce and interpret U-Pb geochronological data on several levels. Tripoli is a graphical interface that allows the user to interact with raw mass spectrometer data to eliminate spurious data based on statistical models, correct time-dependent fractionation cycle-by-cycle for double-spiked U and Pb analyses, and to monitor changes in U oxide composition. U-Pb_Redux then implements transparent data reduction and error propagation algorithms that depend on the tracer type used, the real-time corrections to measured data employed, and the corrections applied for blank, common Pb, and initial daughter-product disequilibrium. Each of the >30 inputs used to calculate an age is assigned a value and uncertainty by the user, which can be tracked through these algorithms.

U-Pb_Redux provides graphical tools to explore reduced datasets and identify the most important components of the total age uncertainty, which will be important tools for experienced researchers as well as students of geochronology. These interactive plots also facilitate calculation of sample statistics with analytical and systematic errors on the fly. We expect Tripoli and Redux to become important tools for cutting-edge geochronology, and we invite suggestions and comments for their improvement.