Detrital Zircon Geochronology of the Windermere Supergroup and the Tectonic Assembly of the Southern Canadian Cordillera

According to two recently proposed tectonic models for the accretionary history of the southern Canadian Cordillera, the Omineca Belt (the hinterland to the fold-and-thrust belt) is a composite suspect terrane assembled outboard of North America and subsequently sutured to it during the Late Cretaceous as part of a composite microcontinental terrane referred to as Cordilleria or Baja B.C. These models suggest displacement of Omineca Belt rocks with respect to North America of 1500 to 2500 km, respectively. To test these models, we analyzed U and Pb isotopes in both single crystal and multigrain detrital zircon populations from Late Proterozoic Windermere Supergroup metasedimentary rocks of inferred suspect origin and compared them to the ages of crystalline basement of western North America. Our data are consistent with a western Canadian provenance for these metasediments and thus call into question tectonic models that propose large latitudinal displacements of the Omineca Belt during assembly of the southern Canadian Cordillera.