Direct U–Pb dating of carbonates from micron-scale femtosecond laser ablation inductively coupled plasma mass spectrometry images using robust regression

Abstract. Uranium–lead (U–Pb) dating of carbonates by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) spot analysis is an increasingly used method in the field geosciences, as it brings very strong constraints over geological history basins, faults or reservoirs. Most ages currently published are based on measurement U and Pb ratios ablations, using nanosecond lasers to sector multi-collector ICP-MS. Here, we test a new strategy for U–Pb from 2D isotopic ratio maps, use robust regression approach data reduction workflow. The with minimum area 0.65 mm2 (∼ 1000 pixels 13×25 µm resolution), obtained 257 nm femtosecond system at high repetition rate (500 Hz) high-resolution maps commonly show significant variations isotope pixel scale, allowing plotting concordia isochron diagrams calculation ages. Due absence individual uncertainties, calculated MM-robust linear rather than more York-type regression. goodness fit assessed residual standard error (RSE) mean square weight deviates (MSWD) discretised data. Several examples provided that compare those other techniques (e.g. dilution, LA-ICP-MS analyses pixel-pooling approach). For most samples, characterised concentrations (> 1 ppm), allows uncertainties similar approaches. However, samples lower (< 0.5 up 10 % too young due ∕ acting leverage points We conclude tested here, although statistically robust, should be critically analysed before validation, especially low concentrations.