Ordovician arc collision and foredeep evolution in the Gaspe Peninsula, Quebec: the Taconic Orogeny in Canada and its bearing on the Grampian Orogenyin Scotland

The Middle to Upper Ordovician Deslandes, Cloridorme and Garin Formations i n the eastern Gaspe Peninsula, Quebec, are some of the most extensively exp osed foredeep successions along the northern Appalachian portion of the Tac onic-Caledonian orogen. Their depositional and biostratigraphic frameworks (N. gracilis to C. spiniferus Zones, approximate correlatives to the N. gra cilis to D. clingani British Zones) indicate that foredeep evolution spanne d c. 10 Ma and was essentially synchronous with the convergence and accreti on of the Popelogan are to the Laurentian margin during the Caradoc (c. 458 -449 Ma). These results, when combined with metamorphic and radiometric age data synthesized from across the Laurentian segments of the northern Appal achian and northwestern Ireland Taconic-Caledonian orogen, further substant iate that orogenesis consisted of several short-lived (c. 10-20 Ma) deforma tional episodes confined to Arenig through Ashgill time (c. 485-440 Ma). Th is indicates that the total duration of orogeny, as recorded by are magmati sm, metamorphism and Laurentian foredeep development, spanned no more than c. 45 Ma. In that the Scottish Caledonides are a consanguineous part of thi s orogen, their tectonostratigraphic evolution, i.e., Grampian Orogeny, sho uld be similar. Accordingly, the results detailed above are geodynamically compatible with and thereby support tectonic models that definer the Grampi an Orogeny in Scotland as a mostly Early to Mid-Ordovician (c. 480-460 Ma) tectonic episode of short, rather than long duration.