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TitleNew U-Pb and Ar/Ar isotopic age constraints on the timing of Eocene magmatism, Ford Fraser and Nechako River map areas, central British Columbia
AuthorGrainger, N C; Villeneuve, M E; Heaman, L M; Anderson, R G
SourceThe Nechako NATMAP project of the central Canadian Cordillera - Le projet NATMAP Nechako de la Cordillère canadienne centrale; by Struik, L C (ed.); MacIntyre, D G (ed.); Canadian Journal of Earth Sciences vol. 38, no. 4, 2001 p. 679-696, (Open Access)
Alt SeriesGeological Survey of Canada, Contribution Series 2000065
PublisherCanadian Science Publishing
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS93E; 93F; 93K; 93L
AreaFawnie Range; Nechako Plateau
Lat/Long WENS-128.0000 -124.0000 55.0000 53.0000
Subjectsgeochemistry; geochronology; igneous and metamorphic petrology; mineralogy; metallic minerals; regional geology; tectonics; uranium lead dates; uranium lead dating; potassium argon dates; potassium argon dating; magmatic arcs; mineralization; plutons; hypabyssal rocks; garnet; rhyolites; volcanic rocks; igneous rocks; andesites; magmatism; porphyry deposits; tectonic interpretations; gold; epithermal deposits; Cretaceous
Illustrationslocation maps; geological sketch maps; tables; graphs
ProgramNechako NATMAP Project
AbstractTwenty-three new, precise, Eocene U-Pb and 40Ar/39Ar age determinations for calc-alkaline volcanic rocks of the Ootsa Lake Group and associated intrusive rocks, widespread in the Nechako Plateau in central British Columbia, constrain the timing of the Eocene magmatism to 53.2-47.6 Ma, with a local duration of as little as 2-3 million years. The new dates show that magmatism in the study area is partly coeval with that responsible for the Babine Igneous Suite - Newman Volcanic Suite (53-50 Ma) to the north, and for the Endako Group (51-45 Ma), which overlies the Ootsa Lake Group; however, locally the three magmatic suites are distinct in age and (or) the strata record a magmatic hiatus of as much as 7.5 million years. The ages generally young from north to south (52-47 Ma) along the western portion of the study area. The Babine Igneous Suite - Newman Volcanic Suite represents the oldest member of this series. However, in the east, the Ootsa Lake Group volcanic rocks are generally older (53-51 Ma). The anomalously older ages may be related to the interaction of magmatism and formation of a nearby and coeval core complex, which ongoing studies show was uplifted at about the same time during the Eocene. Felsic plutonism associated with the Ootsa Lake Group occurred between 50.5 and 47.3 Ma. These plutons were emplaced in an extensional setting along north-northeast-trending faults. The new dates, stratigraphic relationships, and suggested correlations of Eocene strata in the study area with that to the west and north require a revision of the stratigraphic nomenclature for the Ootsa Lake and Endako groups.