Abstract

Cape Breton Island has been interpreted as consisting of four zones of pre-Carboniferous rocks, but the relationships among them are controversial. To help resolve the controversy, we have dated detrital zircons from a conglomerate (part of the Cheticamp Lake Gneiss) in the Aspy terrane in the northeastern Cape Breton Highlands using the U–Pb method. The following ages were obtained: 462 ± 2 Ma (Middle Ordovician); ~492–488 Ma (6 ages; Early Ordovician); 552 ± 3 Ma (latest Precambrian–Early Cambrian); 620 ± 13 and 687 ± 4 Ma (Cadomian); and 809 ± 17, 1423 ± 10, 1462 ± 12, 1605 ± 14, 1644 ± 4, and 1911 ± 5 Ma (Proterozoic). The Middle Ordovician age sets a maximum age limit for deposition of the conglomerate, and supports an Ordovician–Silurian age for the Cheticamp Lake Gneiss. The Early Ordovician, latest Precambrian–Early Cambrian, and Cadomian ages match published ages from the Bras d'Or terrane (and its correlatives) and the Mira terrane (and its correlatives), and indicate provenance of the conglomerate from both terranes. They also indicate that the Bras d'Or and Mira terranes had been connected by the time of deposition of the conglomerate. The combination of the Cadomian and the Proterozoic ages is typical of parts of South America, supporting a suggestion that the Avalon Composite Terrane was derived from South America.

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