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Geochronology Advances in geochronological science
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https://doi.org/10.5194/gchron-2019-15
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gchron-2019-15
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 06 Nov 2019

Submitted as: research article | 06 Nov 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geochronology (GChron).

LA-ICP-MS U-Pb carbonate geochronology: strategies, progress, and application to fracture-fill calcite

Nick M. W. Roberts1, Kerstin Drost2, Matthew S. A. Horstwood1, Daniel J. Condon1, David Chew2, Henrik Drake3, Antoni E. Milodowski4, Noah M. McLean5, Andrew J. Smye6, Richard J. Walker7, Richard Haslam4, Keith Hodson8, Jonathan Imber9, and Nicolas Beaudoin10 Nick M. W. Roberts et al.
  • 1Geochronology and Tracers Facility, British Geological Survey, Environmental Science Centre, Nottingham, NG12 5GG, UK
  • 2Department of Geology, Trinity College Dublin, Dublin 2, Ireland
  • 3Department of Biology and Environmental Science, Linnaeus University, 39231 Kalmar, Sweden
  • 4British Geological Survey, Environmental Science Centre, Nottingham, NG12 5GG, UK
  • 5Department of Geology, University of Kansas, Lawrence, KS 66045, USA
  • 6Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA
  • 7School of Geography, Geology, and the Environment, University of Leicester, Leicester, LE1 7RH, UK
  • 8Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195, USA
  • 9Department of Earth Sciences, Durham University, Science Labs, Durham, UK
  • 10Laboratoire des Fluides Complexes et leurs Réservoirs-IPRA, E2SUPPA, Total, CNRS, Université de Pau et des Pays de l’Adour, UMR5150, Pau, France

Abstract. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb geochronology of carbonate minerals, calcite in particular, is rapidly gaining popularity as an absolute dating method. The technique has proven useful for dating fracture-fill calcite, which provides a powerful record of palaeohydrology, and within certain constraints, can be used to bracket the timing of brittle fracture and fault development. The high spatial resolution of LA-ICP-MS U-Pb carbonate geochronology is beneficial over traditional Isotope Dilution methods, particularly for diagenetic and hydrothermal calcite, because uranium and lead are heterogeneously distributed on the sub-mm scale. At the same time, this can provide limitations to the method, as locating zones of radiogenic lead can be time-consuming and ‘hit or miss’. Here, we present strategies for dating carbonates with in situ techniques, through imaging and petrographic techniques to data interpretation; we focus on examples of fracture-filling calcite, but most of our discussion is relevant to all carbonate applications. We demonstrate these strategies through a series of case studies. We review several limitations to the method, including open system behaviour, variable initial lead compositions, and U-daughter disequilibrium. We also discuss two approaches to data collection: traditional spot analyses guided by petrographic and elemental imaging, and image-based dating that utilises LA-ICP-MS elemental and isotopic map data.

Nick M. W. Roberts et al.
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Nick M. W. Roberts et al.
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Short summary
Here we review current progress in LA-ICP-MS U-Pb carbonate geochronology, and present strategies for acquisition and interpretation of carbonate U-Pb dates. We cover topics from imaging techniques and U and Pb incorporation into calcite, to potential limitations of the method – disequilibrium and isotope mobility. We demonstrate the incorporation of imaging and compositional data to help refine and interpret U-Pb dates. We expect this paper to become a ‘go-to’ reference paper for years to come.
Here we review current progress in LA-ICP-MS U-Pb carbonate geochronology, and present...
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