Late Cretaceous to Paleocene Tectonometamorphic Evolution of the Blanchard River Assemblage, Southwest Yukon: New Insight into the Terminal Accretion of Insular Terranes in the Northern Cordillera

Peer reviewed: 
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Faculty/Staff
Final version published as: 

Vice, L., Gibson, H. D., & Israel, S. (2020). Late Cretaceous to Paleocene Tectonometamorphic Evolution of the Blanchard River Assemblage, Southwest Yukon: New Insight into the Terminal Accretion of Insular Terranes in the Northern Cordillera. Lithosphere, 2020(1), 1–22. https://doi.org/10.2113/2020/2298288

Date created: 
2020-09-21
Identifier: 
DOI: 10.2113/2020/2298288
Keywords: 
Absolute age
Amphibolite facies
Burial
Canada
Canadian Cordillera
Cenozoic
Contact metamorphism
Cretaceous
Dates
Exhumation
Facies
Intermontane Belt
Lithosphere
Mesozoic
Metamorphic rocks
Metamorphism
Monazite
North America
North American Cordillera
Paleocene
Paleogene
Petrography
Phosphates
Tectonics
Tertiary
Trace elements
U/Th/Pb
Upper Cretaceous
Western Canada
Yukon Territory
Southwestern Yukon Territory
Insular Belt
Coast Mountains Batholith
Ruby Range Suite
Blanchard River Assemblage
Abstract: 

The Intermontane-Insular terrane boundary stretches over 2000 kilometers from British Columbia to Alaska in the western Cordillera. Juxtaposed between these terranes is a series of Jura-Cretaceous basinal and arc assemblages that record a complicated and contested tectonic evolution related to the Mesozoic-Paleocene accretionary history of northwestern North America. In southwest Yukon, west-verging thrust faults facilitated structural stacking of the Yukon-Tanana terrane over these basinal assemblages, including the Early Cretaceous Blanchard River assemblage. These previously undated compressional structures are thought to be related to the final collapse of the Jura-Cretaceous basins and the tectonic burial of the Blanchard River assemblage resulting in amphibolite facies metamorphism. New in situ U-Th-Pb monazite ages record at least three tectonic events: (1) the tectonic burial of the Blanchard River assemblage to amphibolite facies conditions between 83 and 76 Ma; (2) peak burial was followed by regional exhumation at ca. 70-68 Ma; and (3) intense heating and ca. 63-61 Ma low-pressure contact metamorphism attributed to the intrusion of the voluminous Ruby Range suite, which is part of the northern Coast Mountains batholith. The tectonometamorphic evolution recorded in the Blanchard River assemblage can be correlated to tectonism within southwest Yukon and along the length of the Insular-Intermontane boundary from western British Columbia through southwestern Yukon and Alaska. In southwest Yukon, these results suggest an asymmetric final collapse of Jura-Cretaceous basins during the Late Cretaceous, which relates to the terminal accretion of the Insular terranes as they moved northward.

Language: 
English
Document type: 
Article
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