U–Pb detrital ages and Hf isotopes from the Iapetan rift succession in the Québec Appalachian Orogen: the discovery of a Cryogenian–Ediacaran source and insights into Rodinia breakup

Detrital mineral grains preserve a critical record of the magmatic history associated with Rodinia breakup. Here, we present U-Pb geochronology and Hf isotope data from igneous and detrital zircon and detrital monazite in late Neoproterozoic to early Cambrian Iapetan rift successions of the Oak Hill and Saint-Roch Groups, along the Laurentian margin in the southern Québec Appalachians. While all sedimentary rocks contain dominant Mesoproterozoic detrital populations, the basal Pinnacle Formation sandstone yields Cryogenian-Ediacaran (710–625 Ma) detrital zircon grains that document a previously poorly constrained magmatic episode, likely associated with Rodinia breakup. These Neoproterozoic detrital grains display chondritic to positive εHf values, similar to igneous zircon included in the underlying alkaline Ediacaran Tibbit Hill Formation volcanic rocks. The Hf isotopic signatures from both formations are consistent with derivation from a similar mantle-derived source. We suggest that the sources of these rare 710–625 Ma detrital zircon grains may be concealed within Laurentian basement beneath the Northern Appalachians, though further work is needed to constrain the magmatic history of Iapetan rifting in this region.