Detrital zircon geochronology of Neoproterozoic to Permian miogeoclinal strata in British Columbia and Alberta

U-Pb ages have been determined on 250 detrital zircon grains from Neoproter ozoic through Permian miogeoclinal strata in British Columbia and Alberta. Most of the grains in these strata are >1.75 Ga and are interpreted to have been derived from nearby basement provinces (although most grains were pro bably cycled though one or more sedimentary units prior to final deposition ). Important exceptions are Ordovician sandstones that contain grains deriv ed from the Peace River arch, and upper Paleozoic strata with detrital zirc ons derived from the Franklinian orogen, Salmon River arch (northwestern U. S.A.), and (or) Grenville orogen. These provenance changes resulted in aver age detrital zircon ages that become progressively younger with time, and m ay also be reflected by previously reported shifts in the Nd isotopic signa ture of miogeoclinal strata. In addition to the grains that have identifiab le sources, grains of similar to 1030, similar to 1053, 1750-1774, and 2344 -2464 Ma are common in our samples, but igneous rocks of these ages have no t been recognized in the western Canadian Shield. We speculate that unrecog nized plutons of these ages may be present beneath strata of the western Ca nada sedimentary basin. Collectively, our data provide a record of the ages of detrital zircons that accumulated along the Canadian Cordilleran margin during much of Paleozoic time. Comparisons between this reference and the ages of detrital zircons in strata of potentially displaced outboard terran es may help reconstruct the paleogeography and accretionary history of the Cordilleran orogen.