3‐D Characterization of Detrital Zircon Grains and its Implications for Fluvial Transport, Mixing, and Preservation Bias

Abstract

Detrital zircon studies can suffer from selective loss of provenance information due to U‐Pb age discordance, metamictization, metamorphic overprinting and fluviatile transport processes. The relationship between isotopic composition and zircon grain shape, and how grain shape is modified during transport, is largely unknown. We combine X‐ray tomography with U‐Pb geochronology to quantify how fluvial transport affects 3‐D zircon shape, detrital age signature, and grain density along the Murchison River, whose catchment comprises Eoarchean to Early Paleozoic source rocks in Western Australia. We acquired tomographic volumes and isotopic data from 373 detrital zircons to document changes in size, shape and density in transport direction, and explore how grain shape, age spectra and the proportion of discordant material vary along the channel. Results show that shape characteristics are sensitive to transport distance, stream gradient, proximity to source material, and whether the source consists of primary or recycled zircons. With increasing transport distance, grain lengths decrease more than their widths. Furthermore, the loss of metamict grains occurs at a near constant rate, resulting in a linear increase of mean calculated zircon density by ca. 0.03 g/cm3 per 100 km transport distance. 3‐D grain shape is therefore strongly linked to detrital age signature, and mean grain density is a function of the absolute transport distance. 3‐D shape characteristics provide valuable information on detrital zircon populations, including the interaction between source materials with fluvial transport processes, which significantly affects preservation bias and, by inference, the representativeness of the sampled data.

Use and abuse of detrital zircon U-Pb geochronology—A case from the Río Orinoco delta, eastern Venezuela

“…(3) Regardless of n, further documenting (and quantifying) morphological information for crystals dated in detrital zircon studies will continue to illuminate the systematic relationships between physico-mechanical and age biasing that are prevalent in different sedimentary environments (e.g., Finzel, 2017;Markwitz et al, 2017).…”

Reduce or recycle? Revealing source to sink links through integrated zircon–feldspar provenance fingerprinting

“…Spencer et al, 2018). The K erosion factor assesses the relative representation of a certain source within a catchment and compares this to the relative abundances of the erosive products of the sources in a sediment (Dhuime et al, 2011;Markwitz et al, 2017;Spencer et al, 2018); (iii) integrated provenance fingerprinting on single mineral phases (for example, trace elements, Hf-isotopes, thermochronology and geochronology in zircon) is capable of more uniquely identifying source regions that might otherwise be indistinguishable on one character alone, while also tracking a broader range of geological processes of interest (Campbell et al, 2005;Reiners et al, 2005;Xu et al, 2017;Kirkland et al, 2020); and (iv) measuring extremely large grain populations to ensure full characterization of minor components and applying statistics to understand the limitations of what fraction of any population has been represented (Vermeesch, 2004;Andersen, 2005;Pullen et al, 2014). Despite this progress, the well-known, but poorly quantified potential of sediment recycling remains extremely relevant for sediment system understanding (Andersen et al, 2018).…”

Tectonic controls on sediment provenance evolution in rift basins: Detrital zircon U–Pb and Hf isotope analysis from the Perth Basin, Western Australia

“…We implicitly assume that comminution and abrasion are minimal when utilizing zircon isotope systematics, but this may not necessarily be true. For example, granites with high U-bearing zircons may be more prone to metamictization and chemical alteration, which consequently reduces their ability to be transported across long distances (Markwitz et al, 2017b). Another issue that is not addressed is the homogeneity of zircon fertility of each of the basement terranes throughout their erosion and transport into the Perth Basin (Spencer et al, in press).…”