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Geochronology Advances in geochronological science
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Preprints
https://doi.org/10.5194/gchron-2020-10
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gchron-2020-10
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 14 Apr 2020

Submitted as: research article | 14 Apr 2020

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This preprint is currently under review for the journal GChron.

Direct U-Pb dating of carbonates from micron scale fsLA-ICPMS images using robust regression

Guilhem Hoareau1, Fanny Claverie2, Christophe Pecheyran2, Christian Paroissin3, Pierre-Alexandre Grignard1, Geoffrey Motte1, Olivier Chailan4, and Jean-Pierre Girard4 Guilhem Hoareau et al.
  • 1Universite de Pau et des Pays de l'Adour, E2S UPPA, CNRS, TOTAL, LFCR, UMR5150, 64000 Pau, France
  • 2Universite de Pau et des Pays de l'Adour, E2S UPPA, CNRS, IPREM, UMR5254, 64000 Pau, France
  • 3Universite de Pau et des Pays de l'Adour, E2S UPPA, CNRS, LMAP, UMR5142, 64000 Pau, France
  • 4TOTAL, CSTJF, 64018 Pau Cedex, France

Abstract. U-Pb dating of carbonates by LA-ICPMS spot analysis is an increasingly used method in the field of geosciences, as it brings very strong constraints over the geological history of basins, faults or reservoirs. Most ages currently published are based on the measurement of U and Pb ratios on spot ablations, using nanosecond lasers coupled to sector-field or multi-collector ICPMS. Here, we present a new strategy for the U-Pb dating of carbonates from 2D isotopic ratio maps, based on the use of a robust regression approach in the data reduction workflow. The isotopic maps, having minimum area of 0.65 mm2 (∼ 1000 pixels of 13 x 25 µm resolution), are obtained using a 257 nm femtosecond laser ablation system at high repetition rate (500 Hz) coupled to a High Resolution ICPMS. The maps commonly show significant variations in isotope ratios at the pixel scale, allowing the plotting of pixel U-Pb ratios in concordia or isochron diagrams and the calculation of U-Pb ages. Due to the absence of individual ratio uncertainties, the ages are calculated by using MM-robust linear regression rather than the more commonly used York-type regression. Provided examples demonstrate that this strategy allows calculating ages and uncertainties similar to those obtained for samples already dated by more traditional techniques (isotope dilution or LA-ICPMS spot analyses). The goodness-of-fit to the data is assessed by the calculation of the residual standard error of the regression (RSE), and by the calculation of a MSWD on discretized data. The regression method proposed is a statistically robust, alternative approach to that proposed by Drost et al. (2018), that can be easily applied to U-Pb age determination from isotopic maps.

Guilhem Hoareau et al.

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Guilhem Hoareau et al.

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Latest update: 02 Jun 2020
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Short summary
A new methodology for the micron-scale uranium-lead dating of carbonate minerals is proposed. It is based on the extraction of ages directly from the pixels images (< 1 mm2) obtained by laser ablation coupled to a mass spectrometer. The ages are calculated with a robust linear regression through the pixel values, which is an efficient and simple approach to that can be easily applied to mineral dating.
A new methodology for the micron-scale uranium-lead dating of carbonate minerals is proposed. It...
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