New U-Pb geochronology evidence for 2.3 Ga detrital zircon grains in the youngest Huronian Supergroup formations, Canada

Detrital zircon U-Pb ages from one sandstone and one claystone unit in the upper Huronian Supergroup, near Flack Lake, Ontario, Canada, provide new evidence for the maximum depositional age of the two youngest formations and reinterpretation of the depositional history of the upper Huronian Supergroup. The average age of the youngest zircon grains constrains the age of deposition to sometime after 2315 ± 5 Ma, but prior to intrusion of gabbro (Nipissing) dykes approximately 95 m.y. later. Clusters of late Archean age zircon are prominent in both samples, but a considerable addition from post-Archean sources is also present. The sample from the Bar River Formation contains a greater proportion of post-Archean material, which may be a result of grain-size bias. Our results are similar to U-Pb zircon ages determined from stratigraphically lower purported tuff beds in the Gordon Lake Formation, however our field and Scanning Electron Microscope (SEM) analyses demonstrate that the samples in the present study were not part of tuff units.