An assessment of the determination of depositional ages for precambrian clastic sedimentary rocks by U–Pb dating of detrital zircons

Abstract

Methodologies for the determination of depositional ages for clastic sedimentary rocks by ion microprobe U–Pb analysis of their detrital zircon populations are described. Provided there has been no sample contamination or disturbance of the U–Pb system, the youngest igneous crystallization dates obtained on detrital zircons from a sedimentary rock sample will provide a maximum age for sediment deposition. Maximum depositional ages so obtained are comparable to minimum ages determined from the dating of cross-cutting dykes, or of metamorphic or diagenetic minerals, but a significant advantage of this approach is that detrital zircons are virtually ubiquitous in clastic sedimentary rocks. The advantages and limitations of this approach are demonstrated in case studies of sedimentary rocks from the Archaean Yilgarn Craton, the Mesoproterozoic Albany–Fraser Orogen and the Neoproterozoic Officer Basin of Australia. These examples demonstrate that the probability that maximum deposition ages based on the dating of detrital zircons are close to the time of sediment deposition is influenced by the lithological characteristics of the sediment samples, with the best results obtained from lithologies with the widest possible provenance range represented in their detrital zircon populations. Due to difficulties in matching wide provenance ranges to particular source areas, lithologies that are suited to maximum depositional age determinations are not necessarily suited to provenance studies. The approach will find applications particularly in studies of sedimentary basins that lack volcanic or intrusive rocks amenable to radiometric dating.