Preprints
https://doi.org/10.5194/gchron-2024-27
https://doi.org/10.5194/gchron-2024-27
28 Oct 2024
 | 28 Oct 2024
Status: this preprint is currently under review for the journal GChron.

Discordance Dating: A New Approach for Dating Sedimentary Alteration Events  

Jesse R. Reimink, Renan Beckman, Erik Schoonover, Max Lloyd, Joshua Garber, Joshua H. F. L. Davies, Alexander Cerminaro, Morgann G. Perrot, and Andrew J. Smye

Abstract. Zircon is the premier geochronometer used to date igneous and metamorphic processes, constrain sediment provenance, and monitor key events in Earth history such as the growth of continents and the evolution of the biosphere. Zircon U-Pb systematics can be perturbed by the loss or gain of uranium and/or lead, which can result in disagreement between the apparent radiometric ages of the two U-Pb decay systems – a phenomenon that is commonly termed ‘discordance’. Discordance in zircon can be difficult to reliably interpret and therefore discordant data are traditionally culled from U-Pb isotopic datasets, particularly detrital zircon datasets. Here we provide a data reduction scheme that extracts reliable age information from discordant zircon U-Pb data found in detrital zircon suites, tracing such processes as fluid flow or contact metamorphism. We provide the template for data reduction and interpretation, a suite of sensitivity tests using synthetic data, and ground-truth this method by analyzing zircons from the well-studied Alta Stock metamorphic aureole. Our results show accurate quantification of a ~23 Ma in situ zircon alteration event that affected 1.0–2.0 Ga detrital zircons in the Tintic quartzite. The ‘discordance dating’ method outlined here may be widely applicable to a variety of detrital zircon suites where pervasive fluid alteration or metamorphic recrystallization has occurred, even in the absence of concordant U-Pb data.

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Jesse R. Reimink, Renan Beckman, Erik Schoonover, Max Lloyd, Joshua Garber, Joshua H. F. L. Davies, Alexander Cerminaro, Morgann G. Perrot, and Andrew J. Smye

Status: open (until 09 Dec 2024)

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Jesse R. Reimink, Renan Beckman, Erik Schoonover, Max Lloyd, Joshua Garber, Joshua H. F. L. Davies, Alexander Cerminaro, Morgann G. Perrot, and Andrew J. Smye

Data sets

Reference Material and Sample Zircon U-Pb-TE datasets Jesse R. Reimink, Renan Beckman, Erik Schoonover, Max Lloyd, Joshua Garber, Joshua H. F. L. Davies, Alexander Cerminaro, Morgann G. Perrot, and Andrew J. Smye https://doi.org/10.5281/zenodo.13972611

Model code and software

Modeling code for discordance dating Jesse R. Reimink, Renan Beckman, Erik Schoonover, Max Lloyd, Joshua Garber, Joshua H. F. L. Davies, Alexander Cerminaro, Morgann G. Perrot, and Andrew J. Smye https://doi.org/10.5281/zenodo.13972611

Jesse R. Reimink, Renan Beckman, Erik Schoonover, Max Lloyd, Joshua Garber, Joshua H. F. L. Davies, Alexander Cerminaro, Morgann G. Perrot, and Andrew J. Smye

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Short summary
This manuscript presents a new method to date geological events affecting sedimentary rocks. This method relies on the potential for the zircon U-Pb system to be disturbed during fluid-flow, alteration, and metamorphic events in sedimentary rocks. This manuscript presents synthetic datasets for testing the accuracy and precision of the discordance dating method, as well as data from detrital zircons found in the contact metamorphic aureole surround the Alta Stock.