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Source-normalized α-dose: discrimination of first- and multi-cycle detrital zircon

Detrital zircon (DZ) U-Pb geochronology is widely applied in the geosciences to address a very wide range of questions. However, zircon is refractory and discrimination of first- versus multi-cycle origin is challenging which blurs source-to-sink relationships. We performed DZ U-Pb geochronology of modern sediments in fluvial and littoral environments on the Scott Coastal Plain in Western Australia. Principal age modes are at c. 730-500 Ma and c. 1100-880 Ma (Pinjarra Orogen), c. 1240-1120 Ma and c. 1700-1600 Ma (Albany-Fraser-Wilkes Orogen), and c. 2710-2580 Ma (Yilgarn Craton), corresponding to ultimate derivation from local crystalline basement rocks. The DZ U-Pb age spectra show a mismatch to the areal extent of source rocks in the catchment area. Here, we propose the application of a novel approach – source-normalized α-dose – to quantify active time of DZ grains in the sedimentary system and thus identify sedimentary recycling of DZ. This metric compares the α-dose (a measure of metamictization using U and Th content) of DZ and the values of crystals from their source crystalline basement. We show that source-normalized α-dose records the selective removal of labile (high α-dose) grains and is able to discriminate (i) first-cycle and (ii) multi-cycle DZ populations that experienced progressive sedimentary recycling and/or transport. Source-normalized α-dose provides an internal measure to address sedimentary recycling of DZ, i.e., it does not necessitate comparison with other mineral systems. Consequently, this tool aids in the identification of first- and multi-cycle DZ origin and ultimately strengthens source-to-sink correlations improving interpretation of DZ grain histories.


Maximilian Dröllner, Milo Barham, Christopher L. Kirkland
Timescales of Mineral Systems Group, School of Earth and Planetary Sciences, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
GeoKarlsruhe 2021