Isoclock: a free and novel routine for common Pb correction in U–Th–Pb data reduction of LA-ICP-MS analysis

Abstract

Robust U–Pb dating of accessory minerals (e.g., apatite, titanite, wolframite, and cassiterite) by LA-ICP-MS is often impeded by variable contents of common Pb in matrix-matched reference material (RM). Therefore, common Pb needs to be corrected in these RMs analyses that are used as standards to calibrate isotope fractionation during data reduction. In this study, a novel stand-alone computer program (called Isoclock) focused on the deduction of common Pb from RM, and the corrected RM were used for isotope fractionation. A new common Pb correction method was introduced into the program that allows the deduction of common Pb not only in ²⁰⁶Pb and ²⁰⁷Pb, but also in ²⁰⁸Pb, so that both U/Pb and Th/Pb age calculations can be performed. The software contains several processing steps for the raw files of different mass spectrometers. The processing interface contains data import and view, background correction and filtering of outliers, calculation of common Pb for RMs, fractionation calibration, and age calculation. Isoclock is written using the free and open-source Python language and can either run the code directly or by using a graphical interface. Finally, we discuss the main advantages of this software and its geological application using six examples of apatite, cassiterite, titanite, monazite and wolframite U–Pb dating.