Preprints
https://doi.org/10.5194/gchron-2024-8
https://doi.org/10.5194/gchron-2024-8
29 Feb 2024
 | 29 Feb 2024
Status: a revised version of this preprint is currently under review for the journal GChron.

U and Th zonation in apatite observed by synchrotron X–ray fluorescence tomography and implications for the (U–Th)/He system

Francis J. Sousa, Stephen E. Cox, E. Troy Rasbury, Sidney R. Hemming, Antonio Lanzirotti, and Matthew Newville

Abstract. Synchrotron X–ray fluorescence microtomography can non-destructively image the three-dimensional distribution of several trace elements in whole apatite crystals at the scale of one µm3. This allows for precise determination of the physical geometry of a crystal and the quantification of the relative abundance of the radioactive parent nuclides uranium and thorium, with high fidelity. We use this data to develop a more precise alpha ejection correction for (U–Th)/He thermochronology and high-resolution models of apatite crystals that are the foundation for a new generation of three-dimensional diffusion modeling. The application of synchrotron radiation to non-destructive imaging of minerals used for geochronology sheds light on causes of longstanding unresolved problems in the field that are rooted in previously unmeasurable parent nuclide zonation, especially the pervasive overdispersion of single crystal ages.

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Francis J. Sousa, Stephen E. Cox, E. Troy Rasbury, Sidney R. Hemming, Antonio Lanzirotti, and Matthew Newville

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gchron-2024-8', Anonymous Referee #1, 13 Mar 2024
    • AC1: 'Reply on RC1', Francis Sousa, 26 May 2024
  • RC2: 'Comment on gchron-2024-8', Anonymous Referee #2, 22 Mar 2024
    • AC2: 'Reply on RC2', Francis Sousa, 26 May 2024
  • RC3: 'Comment on gchron-2024-8', Michael W.M. Jones, 17 Apr 2024
    • AC3: 'Reply on RC3', Francis Sousa, 26 May 2024
Francis J. Sousa, Stephen E. Cox, E. Troy Rasbury, Sidney R. Hemming, Antonio Lanzirotti, and Matthew Newville
Francis J. Sousa, Stephen E. Cox, E. Troy Rasbury, Sidney R. Hemming, Antonio Lanzirotti, and Matthew Newville

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Short summary
We have discovered a new way of measuring the three-dimensional distribution of radioactive elements in individual crystals by shining a very bright light on apatite crystals at the Advanced Photon Source at Argonne National Laboratory. This allows us to learn about the rates and timing of geologic processes, and to help resolve problems that previously were unsolvable because we had no way to make this type of measurement.