A Late Neoproterozoic age for a tonalite dyke in the Boisdale Hills, Cape Breton Island, Nova Scotia

A tonalite dyke in the Benacadie Brook Formation in the Boisdale Hills of c entral Cape Breton Island yielded a U-Pb (zircon) age of 564.5 +/- 5.1 Ma, interpreted to be the age of intrusion. The age is identical within error t o the U-Pb (zircon) age of 564 +3/-2 Ma previously reported for a granodior ite sample from the nearby Shunacadie Pluton. Based on geographic proximity and identical age, as well as petrological similarities, the tonalite dyke is interpreted to be comagmatic with the granodiorite. Although the new da te does not provide further constraint on the age of the Benacadie Brook Fo rmation, it affirms the importance of ca. 560 Ma plutonism in the Bras d'Or terrane of Cape Breton Island.