2025/08/06 by Morgann Perrot, Morgann G. Perrot, John W.F. Waldron +6
Earth and Planetary Sciences · Computer Science · #Geological and Geochemical Analysis #Paleontology and Stratigraphy of Fossils #Geochemistry and Geologic Mapping
paper · pdf · doi:10.1130/b38057.1
Abstract In the northern Appalachian orogen, the timing and extent of Gondwanan terranes accreting to Laurentia during the Ordovician to Silurian Periods remain unclear, especially in the Gaspé Peninsula (Québec, Canada), where basement rocks are covered by the thick sedimentary sequence of the Gaspé Belt. In such context, detrital mineral analysis from syntectonic sedimentary basins can help to constrain this timing. A compilation of zircon U-Pb and εHf data from Laurentian and Ganderian sources shows distinct differences, with Ganderian rocks having a Cryogenian to Late Ordovician primitive εHf signature, while Laurentian zircon grains display variable but mostly negative εHf values at these times. To better constrain the timing of Ganderia's accretion, we tracked sedimentary provenance shifts along the Laurentian margin using U-Pb + Hf isotope data from detrital zircon grains in Ordovician to Devonian sediments in the Gaspé Peninsula deposited on the Laurentian margin and in the Connecticut Valley–Gaspé trough. These were compared with zircon grains from Ganderian exposures in the Bathurst Supergroup, Miramichi terrane. The detrital zircon U-Pb ages mainly indicate Laurentian sources, with abundant Mesoproterozoic grains and varying proportions of Ordovician to Devonian ages, plus a few Ediacaran zircons in post-Taconic sediments. While Ediacaran zircons potentially constrain the timing of Ganderian accretion, εHf data significantly enhance source differentiation, revealing a distinct Middle Ordovician primitive εHf signature in Upper Ordovician sediments, which we interpret as Ganderian. This signature aligns with compiled U-Pb and εHf data from Ganderia and the newly analyzed rhyolitic Hayden Lake Formation of the Miramichi terrane, suggesting Ganderia contributed to the Gaspé Belt sediments during the Late Ordovician and was near the Laurentian margin. Our data underscore the importance of multiproxy analysis in provenance studies for identifying sediment sources, especially when source regions have similar ages.