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.