Zircon as a provenance tracer: Coupling Raman spectroscopy and U[sbnd]Pb geochronology in source-to-sink studies

Abstract

UPb zircon geochronology is one of the most widely used techniques in sedimentary provenance analysis. Unfortunately, the ability of this method to identify sediment sources is often degraded by sediment recycling and mixing of detritus from different source rocks sharing similar age signatures. These processes create non-unique zircon UPb age signatures and thereby obscure the provenance signal. We here address this problem by combining detrital zircon UPb geochronology with Raman spectroscopy. The position and width of the Raman signal in zircon scales with its degree of metamictization, which in turn is sensitive to temperature. Thus, combined U-Pb + Raman datasets encode information about the crystallization history of detrital zircons as well as their thermal history. Using three borehole samples from Mozambique as part of a source-to-sink study of interest for hydrocarbon exploration, we show that zircon populations with similar UPb age distributions can exhibit different Raman signatures. The joint U-Pb + Raman analysis allowed us to identify three different annealing trends, which were linked to specific thermal events. Thus we were able to differentiate a dominant Pan-African UPb age peak into several sub-populations and highlight the major effect of Karoo tectono-magmatic events. In our case study, we used Raman also as a means to systematically identify all zircon grains in heavy-mineral mounts, resulting in considerable time savings. Raman spectroscopy is a non-destructive and cost-effective method that is easily integrated in the zircon UPb dating workflow to augment the resolution power of detrital zircon UPb geochronology.