216-9 Using discordance to date in situ geological events in the sedimentary record – a test from the Alta contact aureole

Session: Geochronology of Critical Mineral Deposits with Special Reference to U-Th-Pb Dating of Common-Pb-Rich Minerals

Presenting Author:

Jesse Reimink

Authors:

Reimink, Jesse R¹, Beckman, Renan², Schoonover, Erik Jeffery³, Lloyd, Max⁴, Garber, Joshua⁵, Davies, Joshua HFL⁶, Cerminaro, Alex P.⁷, Perrot, Morgann Gwenva⁸, Smye, Andrew⁹

(1) Geosciences, The Pennsylvania State University, University Park, Pennsylvania, USA, (2) Penn State, University Park, PA, USA, (3) Penn State, University Park, PA, USA, (4) The Pennsylvania State University, University Park, PA, USA, (5) The Pennsylvania State University, University Park, PA, USA, (6) UQAM, Quebec, Montreal, Canada, (7) Penn State, Berwick, PA, USA, (8) McGill University, Montréal, QC, Canada, (9) Penn State University, University Park, PA, USA,

Abstract:

The U-Pb system in zircon is perhaps the premier geochronometer and widely used to date Earth processes throughout much of geological time. Despite the relatively robust nature of zircon U-Pb dating, zircon grains can have their isotopic systems disturbed by a wide range of processes. These processes include high-temperature metamorphism, fluid ingress and leaching, and high-pressure crystal deformation. Such disturbance events are well known in the zircon record and typically induce ‘discordance’ of the paired U-Pb decay systems. While this discordance can be used to accurately and precisely date disturbance-inducing events, it requires analyses of several cogenetic mineral grains that have shared crystallization and disturbance histories.

Recently, there has been an increased focus on temporally constraining zircon alteration events, specifically in detrital zircon grain populations altered in situ within sedimentary rocks. Several suites of statistical modeling procedures have been developed to interrogate discordant zircon U-Pb data to gain geochronological information about the timing of the disturbance event(s) . These calculations share the goal of statistically assessing the timing of possible discordance inducing events to place temporal constraints on geological processes that are typically difficult to date such as the timing of fluid flow, and meteorite impacts.

In this presentation we will summarize the various approaches available for using discordant zircon U-Pb data to date geological alteration events and apply these to a new suite of zircon U-Pb-trace element data from detrital zircons extracted from Tintic formation sandstones within the Alta Stock metamorphic aureole. We will present a new approach – called Discordance Dating – that assesses the probability distribution of discordant U-Pb data populations and show that this method returns an accurate age for the timing of alteration of the Tintic formation zircon population of 24 +4/-8 Ma (Reimink et al., 2024).. We will also discuss the possible scenarios where discordance dating may be a valuable method for dating geological events, including mineral deposit systems and brine movement in basin systems.

 

Reimink, J. R., Beckman, R., Schoonover, E., Lloyd, M., Garber, J., Davies, J. H. F. L., Cerminaro, A., Perrot, M. G., and Smye, A. J.: Discordance Dating: A New Approach for Dating Sedimentary Alteration Events , Geochronology Discuss. [preprint], https://doi.org/10.5194/gchron-2024-27, in press, 2024.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9116

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