Yankuang ceshi (Nov 2022)
A Review of Research Progress on the Analytical Method of Large-n Detrital Zircon U-Pb Geochronology
Abstract
BACKGROUND Detrital zircon U-Pb geochronology is an important tool for identifying sedimentary provenance and determining the maximum depositional age. The numbers of grains for detrital zircon provenance investigations using laser-ablation inductively coupled-plasma mass spectrometer (LA-ICP-MS) typically range from 60 to 120. In this range, age components are commonly not identified from the sample aliquot. In order to improve the reliability of provenance investigation, analysis of more grains (n≥300) or even the large-n aliquot with more than 1000 grains (n > 1000) are required. The emergence of large-n detrital zircon U-Pb geochronology is challenging the methods of data measurement, reduction and evaluation. OBJECTIVES To summarize the progress of measurement, data reduction and data evaluation of large-n detrital zircon U-Pb geochronology. METHODS By summarizing the method innovation of domestic and foreign literature. RESULTS Firstly, each measurement requires rapid acquisition of U and Pb isotope signals, which can be conducted by improving the transmission efficiency of aerosol. The "flat" signal acquisition time can be shortened or transformed to a "peak" signal mode for rapid measurement. Secondly, large-n data require efficient data reduction protocol or powerful software (e.g. iolite) to improve visualization and reduce the variability between inter-laboratory comparisons. For U-Pb data processing flow, several optimized methods are introduced for fractionation correction and propagating uncertainty. In addition, total integrated counts and linear regression correction are introduced to specially process "peak" signals. Thirdly, the new calculation method of U-Pb and Pb-Pb age discordance, such as using Aitchison concordia distance, makes data filtering more reasonable. Based on recent research progress, the future of automation and standardization of large-n detrital zircon U-Pb geochronology is discussed and advice on the selection of instruments and reduction software is provided. CONCLUSIONS In the future, the development of large-n detrital zircon U-Pb geochronology has great prospects, and will play a greater role in the study of provenance tracing and stratigraphic dating.
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