Abstract

A 734 ± 2 Ma U–Pb (zircon) age for the Economy River orthogneiss, Coboquid Highlands, Nova Scotia, is interpreted as being representative of a regionally extensive ca. 820–660 Ma event that is recorded in many parts of the Late Proterozoic – Early Cambrian Avalon Composite Terrane and the Gondwanan margin. The geochemistry of the gneiss is consistent with an arc environment. Although the gneiss may represent part of the sialic basement to the terrane, field relationships indicate that some of the basement is significantly older. The date may provide a minimum age for the platformal sedimentary rocks (Gamble Brook Formation) that the orthogneiss intruded and thus help constrain the Late Proterozoic paleogeographic position of Avalon relative to Gondwanaland.

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