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New U/Pb and [sup 40] Ar/[sup 39] Ar isotopic dating in the Babine porphyry copper district of central British Columbia documents three distinct magmatic events at 107–104, 85–78, and 54–50 Ma. The earliest event involved emplacement of rhyolite domes into submarine volcanic rocks of the Rocky Ridge Formation. The rhyolite domes and related dacitic to basaltic volcanic rocks gave a U–Pb age of 107.9 ± 0.2 Ma and an [sup 40] Ar/[sup 39] Ar age of 104.8 ± 1.2 Ma. The rhyolites, which were previously mapped as Eocene, are reinterpreted to be part of a previously unrecognized mid-Cretaceous cauldron subsidence complex. The regionally extensive Late Cretaceous magmatic event is also recognized in the Babine district and is represented by [sup 40] Ar/[sup 39] Ar ages of 85.2 ± 2.8 and 78.3 ± 0.8 Ma on two Bulkley intrusions, one of which has associated porphyry copper mineralization. The final magmatic event is the most widespread and involved emplacement of the Babine intrusions and formation of numerous porphyry copper deposits including the Bell and Granisle past producers. Twenty-one new [sup 40] Ar/[sup 39] Ar isotopic ages for these intrusions and coeval andesites of the Newman Formation have a narrow range from 53.6 ± 0.9 to 49.9 ± 0.6 Ma, whereas previous K–Ar isotopic dating had a possible range of 15 Ma. The mid-Cretaceous, Late Cretaceous, and Eocene magmatic suites in the Babine district are interpreted to be part of a long-lived volcano-plutonic complex that was the site of periodic magmatism and porphyry copper mineralization over a 60 Ma time period. This complex may have evolved within a zone of extension (pull-apart basins) situated between dextral strike-slip faults that were active during periods of rapid oblique plate convergence.De nouvelles datations U–Pb et isotopiques [sup 40] Ar/[sup 39] Ar dans le district de cuivre porphyrique Babine, du centre de la Colombie-Britannique, documentent trois événements magmatiques distincts à 107–104 Ma, 85–78 Ma et 54–50 Ma. L'événement le plus précoce impliquait la mise en place de dômes de rhyolite dans les roches volcaniques sous-marines de la Formation de Rocky Ridge. Les dômes de rhyolite et les roches volcaniques apparentées dacitiques à basaltiques ont donné un âge U–Pb de 107,9 ± 0,2 Ma et un âge [sup 40] Ar/[sup 39] Ar de 104,8 ± 1,2 Ma. Les rhyolites, antérieurement cartographiées comme datant de l'Éocène, sont réinterprétées comme faisant partie d'un complexe de cuvettes d'effondrement auparavant non reconnues et qui dateraient du Crétacé moyen. Le magmatisme extensif régional du Crétacé tardif est aussi reconnu dans le district de Babine et il est représenté par des âges [sup 40] Ar/[sup 39] Ar de 85,2 ± 2,8 et 78,3 ± 0,8 Ma sur deux intrusions Bulkley, dont l'une présente une minéralisation associée de cuivre porphyrique. L'événement magmatique final est le plus répandu et il comprend la mise en place des intrusions Babine et la formation de nombreux gisements de cuivre porphyrique incluant les anciens gisements productifs de Bell et de Granisle. Vingt et un nouveaux âges [sup 40] Ar/[sup 39] Ar pour ces intrusions et des andésites contemporaines de la Formation Newman ont une plage étroite de 53,6 ± 0,9 à 49,9 ± 0,6 alors que des datations antérieures d'isotopes K–Ar avaient une plage de 15 Ma. Les suites magmatiques du Crétacé moyen, du Crétacé tardif et de l'Éocène dans le district de Babine sont interprétées comme faisant partie d'un complexe volcano-plutonique de longue durée où s'est produit du magmatisme périodique et de la minéralisation en cuivre porphyrique durant une période de 60 Ma. Ce complexe peut avoir évolué à l'intérieur d'une zone d'extension (basins d'extension) située entre des failles dextres à décrochement horizontal qui étaient actives durant les périodes de convergence rapide et oblique des plaques.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)