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Provenance and paleotectonic setting of North American Triassic strata in Yukon : the sedimentary record of pericratonic terrane accretion in the northern Canadian Cordillera Beranek, Luke P.

Abstract

Detrital mineral geochronology, trace element and Nd isotope geochemistry, and field studies provide constraints for the source and paleotectonic setting of Late Devonian to Late Triassic North American strata in the northern Cordillera. Late Devonian-Early Mississippian clastic wedge deposits in northern Yukon and Northwest Territories record the influx of northerly derived sediment from the Innuitian orogenic belt. Isotopic data suggest that Innuitian clastic material was consistently recycled into post-Late Devonian Cordilleran margin strata. Early to Late Triassic sedimentation in Yukon was related to Late Permian-Early Triassic collision of the pericratonic Yukon-Tanana terrane (YTT) with western North America. Permo-Triassic closure of a marginal back-arc basin, whose remnants comprise the Slide Mountain terrane (SMT), juxtaposed YTT against the ancestral North American margin. The age and nature of this collision is analogous to that of the Sonoman orogeny in the southwestern United States and argues for accretionary tectonism along much of the Cordilleran margin during final construction of the Pangean supercontinent. Three stages of basin evolution following Late Permian-Early Triassic tectonism are now recognized in the northern Cordillera: (1) Early(?) to Middle Triassic SMT-YTT overlap assemblage- Early(?) to Middle Triassic coarse sandstone and conglomerate underlain by SMT in southeastern Yukon have detrital mineral ages which suggest that these strata represent westerly derived, first-cycle deposits shed from YTT following collision. (2) Early(?) to Middle Triassic peripheral foreland basin - Ladinian (Middle Triassic) strata in southeastern Yukon contain detrital mineral ages which document the first known occurrences of sediment derived from allochthonous terranes to the west deposited on North America. These data call for pre-Ladinian peripheral foreland basin development along the former Cordilleran margin. This depocentre is now largely buried under younger Mesozoic allochthons; however, Early(?) to Middle Triassic rocks that comprise the YTT-SMT overlap may represent correlatives to these Ladinian strata. (3) Middle to Late Triassic overlap assemblage – Tectonic quiescence in Middle to Late Triassic time led to development of an overlap assemblage linking the YTT, SMT, and ancestral North American margin. These units comprise a geodynamic linkage between outboard pericratonic terranes and the North American plate.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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