PROVENANCE, DETRITAL ZIRCON U-PB GEOCHRONOLOGY, AND TECTONIC SIGNIFICANCE OF MIDDLE CRETACEOUS SANDSTONES FROM THE ALBERTA FORELAND BASIN
Buechmann, Daniel Lee 1981-
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The Canadian-Alaskan Cordillera exhibits a severely overprinted amalgam of subduction zone, arc, back-arc, ocean basin, and continental margin assemblages that collectively represent more than 750 million years of tectonic activity. Sedimentary basins flanking the orogeny were filled with detritus from the adjacent uplifted fold-and-thrust belt and thus provide a detailed record of the source area that helps constrain the timing of paleogeographic reconstructions and tectonic evolution models. This study presents new U-Pb detrital zircon ages from Middle Cretaceous sandstones of the Alberta Foreland Basin that indicate a dramatic shift in provenance across the Albian-Cenomanian boundary and elucidate the extent of terrane emergence in the Cordillera between 101 and 96 Ma. The Albian Viking Formation yielded 221 U-Pb detrital zircon analyses with 206 grains (93%) providing Precambrian ages that are consistent with age spectra for Paleozoic and early Mesozoic miogeoclinal strata, indicating the foreland basin was being flooded by recycled passive margin detritus during the late Early Cretaceous. The Cenomanian Dunvegan Formation yielded 338 U-Pb detrital zircon analyses showing statistically significant Paleozoic age clusters at 358, 338, and 328 Ma that correspond with the Late Devonian to Early Mississippian Finlay and Late Mississipian Little Salmon magmatic cycles observed regionally throughout the large pericratonic Yukon-Tanana terrane. This correlation suggests the Yukon-Tanana terrane was entrained in the fold-and-thrust belt and exposed near the Dunvegan paleo-catchment area during the early Late Cretaceous, providing a minimum time constraint for the collision of the northern pericratonic terranes with western Laurentia.