Multi-instrumental approach to better characterize zircon populations in the geological record

Session: Advances and Applications in Geochronology for Interpreting Stratigraphic and Basin Records (Posters)

Presenting Author:

Vicente Lopes

Authors:

Lopes, Vicente Lucio¹, Senger, Martin Hugo², Kroeger, Emma³, Dettman, Ari⁴, Campbell, Clay Franklin⁵, Foley, Michelle⁶, Pecha, Mark⁷, Pullen, Alexander⁸, Ketcham, Richard A.⁹, Ibanez-Mejia, Mauricio¹⁰

(1) Department of Geoscienes, Unversity of Arizona, Tucson, Arizona, USA, (2) Department of Geosciences, Unversity of Arizona, Tucson, AZ, USA, (3) Clemson University, Anderson, SC, USA, (4) University of Arizona, Tucson, Arizona, USA, (5) The University of Arizona, Tucson, Arizona, USA, (6) University of Arizona, Tucson, Arizona, USA, (7) University of Arizona, Tucson, Arizona, USA, (8) Clemson University, Anderson, SC, USA, (9) University of Texas, Austin, TX, USA, (10) University of Arizona, Geosciences, Tucson, AZ, USA,

Abstract:

    The number of studies involving detrital zircon (DZ) analyses has grown rapidly over the past two decades. For accurate interpretation of the sedimentary record, it is important to generate reliable and reproducible datasets, while also understanding and minimizing artificial sources of bias introduced during sample preparation, such that natural variations can be isolated. While DZ U-Pb age analyses have been widely adopted by researchers and many statistical tests have been used to interpret these datasets, emerging analytical methods may provide additional information to uncover natural as well as experimental sources of variations that have been overlooked in the past. 

We have developed a new workflow where large numbers of individual zircon crystals are first morphologically characterized in 3D using micro-XRCT (size, sphericity, etc.), then U-Pb dated using LA-ICP-MS, and finally analyzed for accumulated alpha-dose using Raman spectroscopy, all while tracking each feature throughout the process. Altogether, we achieve full integration of these multi-dimensional datasets, such that variables other than U-Pb ages alone can be considered to interrogate the detrital record and aid in data interpretation.     

As a test case, we used the well-characterized DZ reference sample CP-40 to evaluate the impact that barite removal during sample processing may have on DZ U-Pb results. Two aliquots of pure CP-40 zircon were mixed with fine-grained barite in ~1:10 proportions, and then subsequently treated using the traditional barite mechanical abrasion method (“Wig-L-Bug”) for one aliquot, and a chelation method using Diethylenetriaminepentaacetic acid (DTPA) for the second. These two aliquots, as well as a control CP-40 aliquot without added barite, were analyzed independently using the new method. Our results indicate that, while U-Pb age spectra are not significantly impacted by the different barite removal methods, the distribution of grain sizes and morphologies are severely modified by the mechanical abrasion approach, precluding recovery of accurate morphological information. We therefore conclude that mechanical abrasion methods for barite removal should be discontinued. Furthermore, we posit that the method described here will help clarify persistent statistical issues that affect the quantitative interpretation of the detrital zircon data.