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Two ages of magmatism have been determined from zircon in felsic flows and plutons in the Churchill Province of Manitoba. A rhyolite flow from the Lynn Lake metavolcanic belt has a U -Pb age of 1910?:8 Ma, and a rhyolite flow from the adjacent Rusty Lake metavolcanic belt has an age of 1878:: Ma. Tonalite and quartz diorite from two composite plutons emplaced into the volcanic rocks at Lynn Lake have ages of 1876:: and 1876:; Ma, indistinguishable from the age of the Rusty Lake belt rhyolite. The arcuate domain of metavolcanic rocks that includes the Rusty Lake belt in the southeast, the Lynn Lake belt in the north, and the La Ronge belt (Saskatchewan) in the southwest has previously been considered a single structural subprovince with similar ages throughout. Our results and published U-Pb ages from Saskatchewan indicate that an older magmatism is represented by volcanic rocks in the Lynn Lake belt; a younger magmatism, by volcanic rocks in the Rusty Lake and La Ronge belts and plutons in the Lynn Lake belt. At Lynn Lake the older magmatism (1910 Ma) produced mafic, intermediate, and felsic volcanic rocks and synvolcanic plutons. The volcanic rocks are geochemically similar to Cenozoic islandarc magmatic sequences. These rocks were isoclinally folded and subsequently intruded by the 1876 Ma plutons. The younger, dominantly subaerial, volcanism (1878 Ma) at Rusty Lake was predominantly felsic, and the coeval plutons were granitoid. The distribution of ages and the 8 km thickness of the younger volcanic sequence suggest that the older rock served as basement during the younger magmatism.Les Lges obtenus sur le zircon des coultes felsitiques et des plutons de la province de Churchill du Manitoba ont permis de reconnaitre deux Cpisodes de magmatisme. Une coulte de rhyolite dans la ceinture mttavolcanique de Lynn Lake fournit un bge U-Pb de 1910!:8 Ma et une coult de rhyolite dans la ceinture mCtavolcanique adjacente de Rusty Lake donne un Lge de 18784 Ma. Une tonalite et une diorite quartzique de deux plutons composites mis en place dans les roches volcaniques i Lynn Lake fournissent des Lges de 1876:: et 1876:; Ma, donc d'ige presqu'identique i celui de la rhyolite de la ceinture de Rusty Lake. Les roches mCtavolcaniques du domaine arqut incluant la ceinture de Rusty Lake dans le sud-est, la ceinture de Lynn Lake dans le n o d et la ceinture La Ronge (Saskatchewan) dans le sud-ouest ont Ct C considtkes antkrieurement comme formant une sous-province st~ucturale unique d'bges similaires en tous lieux. Nos dsultats et les bges U-Pb publiCs pour la Saskatchewan dvklent l'existence d'une activitC magmatique plus Lgte repksentte par les roches volcaniques de la ceinture de Lynn Lake et un Cpisode de magmatisme plus dcent coppondant aux roches volcaniques des ceintures de Rusty Lake et de La Ronge et par les plutons de la ceinture de Lynn Lake. A Lynn Lake, les roches volcaniques mafiques, intermkdiaires et felsitiques et les plutons synvolcaniques sont le produit de I'activitC magmatique la plus ancienne (1910 Ma); les r...

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