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

Methodologies for the determination of depositional ages for elastic sedime ntary rocks by ion microprobe U-Pb analysis of their detrital zircon popula tions are described. Provided there has been no sample contamination or dis turbance of the U-Pb system, the youngest igneous crystallization dates obt ained on detrital zircons from a sedimentary rock sample will provide a max imum age for sediment deposition. Maximum depositional ages so obtained are comparable to minimum ages determined from the dating of cross-cutting dyk es, or of metamorphic or diagenetic minerals, but a significant advantage o f this approach is that detrital zircons are virtually ubiquitous in elasti c sedimentary rocks. The advantages and limitations of this approach are de monstrated in case studies of sedimentary rocks from the Archaean Yilgarn C raton, the Mesoproterozoic Albany-Fraser Orogen and the Neoproterozoic Offi cer Basin of Australia. These examples demonstrate that the probability tha t maximum deposition ages based on the dating of detrital zircons are close to the time of sediment deposition is influenced by the lithological chara cteristics of the sediment samples, with the best results obtained from lit hologies with the widest possible provenance range represented in their det rital zircon populations. Due to difficulties in matching wide provenance r anges to particular source areas, lithologies that are suited to maximum de positional age determinations are not necessarily suited to provenance stud ies. The approach will find applications particularly in studies of sedimen tary basins that lack volcanic or intrusive rocks amenable to radiometric d ating. (C) 2001 Elsevier Science B.V. All rights reserved.