IMPROVED DETRITAL ZIRCON U-PB PROVENANCE BY LA-ICP-MS DEPTH PROFILE ANALYSIS

Provenance studies have long been used to investigate source-to-sink dynamics, the linkages between hinterland erosion and sediment supply, controlled by tectonics, climate, and intrinsic factors inherent to the local geology, sediment transport and dispersal, sediment storage and recycling from intermediate sinks, as well as deposition in the terminal sink. Detrital zircon U-Pb geochronology has become a very widely used method for isotopic provenance studies of modern rivers to ancient drainage systems. While this rapidly proliferating technique has revolutionized provenance studies, it has its limitations due to inherent ambiguities related to single or multiple recycling events or monotonous or homogenized signatures of U-Pb crystallization ages in the drainage basin. U-Pb depth-profile analysis of tape-mounted, unpolished zircon allows for the recovery of multiple growth ages from individual zircons to constrain detrital provenance more precisely. For example, zircons from magmatic provinces, such as continent arcs, can exhibit cores reflecting the underlying basement, or plutonic or magmatic zircon growth might affect rocks in otherwise monotonous basement domains. For example in the Gulf of Mexico, Grenville zircons are ubiquitous in Cenozoic sandstones as the Grenville hinterland spans from Maritime Canada to southern Mexico. However, Permian zircon overgrowth due to arc magmatism is only evident in zircons from central and southern Mexico and is completely absent in Laurentia. Similarly, Late Cretaceous magmatic rocks are present in the Cordilleran hinterland both in the USA and in Mexico. Recovery of core ages from such Late Cretaceous zircons through depth profiling has shown the ability to more precisely locate the source terrane as they contain very different Proterozoic aged cores and can be related to the basement underlying these Cretaceous plutons. Lastly, depth profile U-Pb also reliably and effectively recovers the youngest zircon growth mode from detrital zircon populations that can be interpreted as the maximum deposition age (MDA) that commonly places tight constraints on the chronostratigraphic age of a unit – critical for stratigraphic correlations and the establishment of a chronostratigraphic framework for source-to-sink or sequence stratigraphic studies.