UNLOCKING PROVENANCE SECRETS FROM SINGLE DETRITAL ZIRCONS BY U-PB AND TRACE-ELEMENT DEPTH-PROFILE LASER-ABLATION-SPLIT-STREAM ICP-MS ANALYSIS AND (U-TH)/HE DOUBLE DATING

Modern geo- and thermochronometric dating techniques such as combined U-Pb and (U-Th)/He dating has enabled a more holistic understanding of sediment provenance and hinterland tectonics. While Detrital Zircon (DZ) U-Pb dating has been widely used in detrital provenance studies, DZ U-Pb ages alone have been shown to have limitations due to sediment recycling, source ambiguity of U-Pb ages, or even the lack of variance of U-Pb ages in source terranes. DZ (U-Th)/He (ZHe) dating and double dating has added additional facets to reconstructing sedimentary provenance based on cooling/exhumation history of a sediment source region and also providing a record of hinterland exhumation through lag time analysis. The ultimate power and resolution, however, comes from combining geo- and thermochronometric data from single mineral grains with novel analytical means of teasing more comprehensive age information and additional geochemical fingerprints out of single accessory phases, such as zircon or rutile. This combination of tools could revolutionize provenance reconstruction based on multiple criteria of crystallization age, cooling age, and petrologic environment of source terranes. This study develops new analytical procedures to take advantage of this “double-dating plus” approach by employing laser-ablation split-stream (LASS)-ICP-MS depth profiling of unpolished tape-mounted detrital zircons. Time-resolved depth-profiling LASS-ICP-MS analysis has the ability to reveal different zircon U-Pb age components from a single zircon depth-profile and thus yielding a more complete picture of crystallization and zircon growth in the source terrane. Split-streaming of the ablated dry aerosol into two ICP-MS instrument permits measurement of U-Pb age at the same time as the corresponding REE and trace-element concentrations for the different zircon age zones, providing detailed provenance characteristics for individual zircons based on growth history, differentiation of magmatic and metamorphic origin, petrologic growth environment and crystallization temperatures. DZ depth-profile LASS-ICP-MS U-Pb and (U-Th)/He double dating can elucidate the potential sediment source region in much greater detail and reveal a more complete history of the journey of a single detrital zircon.