USING SYNDEPOSITIONAL ZIRCONS AS A TRACER OF TERRANE (DIS-)PLACEMENT IN THE CANADIAN CORDILLERA

The Canadian Cordillera provides an important locality to test the impact of terrane accretion and potential terrane translation on adjoining foreland basins within an active orogen. The Alberta Foreland Basin stores the erosional record of fold-thrust belt propagation in the eastern cordillera and the potentially evolving igneous sources synchronous to terrane displacement in the western cordillera. We present new detrital zircon U-Pb geochronologic and Lu-Hf isotopic results from the Jurassic Fernie Formation through the Paleocene Paskapoo Formation in the Calgary region to evaluate evolving sediment sources throughout Alberta foreland basin development. Samples show variability, with prominent age modes at ca. 1.8 Ga, 1.1 Ga, and 250-65 Ma. The ca. 1.8 and 1.1 Ga grains, originally sourced from the Trans-Hudson and Grenville orogenies, are abundant within the deformed passive margin sequence of the Rocky Mountain fold-thrust belt, suggesting a local source. In many of the detrital samples, the 250-65 Ma age modes include isotopic ages that overlap with biostratigraphic depositional ages, suggesting the presence of roughly syndepositional zircons. Contemporaneous magmatic activity occurred in the inboard Omineca belt, distal outboard Coast Mountain Batholith, and southerly regions, including the Idaho and Boulder batholiths and associated volcanic centers. We use Lu-Hf isotopes on the near syndepositional grains to evaluate their most likely magmatic source and provide constraints on the paleogeographic configuration of the terranes through time.