Nd isotopic characteristics of terranes within the Avalon Zone, southern New Brunswick

Abstract

Nd isotopic data are presented for rock units in four terranes within the traditional Avalon Zone of southern New Brunswick. Initial εNd values for igneous rocks within the Caledonia terrane range from -1.6 to +4.6, whereas values for sedimentary rocks range from -8.4 to +3.6. A granite within the Kingston terrane has εNd(438 Ma) = +4.0. Nd isotopic compositions for the Kingston and Caledonia terranes are similar to those of the Mira terrane in Cape Breton Island, the Antigonish Highlands of Nova Scotia, and plutonic rocks of eastern Newfoundland. Each of these regions may be a dismembered part of a single terrane, the Avalon terrane sensu stricto. Initial εNd values for rocks from the Brookville terrane range from -1.3 to +2.8. The Coverdale anorthosite within the Brookville terrane has a present day εNd value of -12.1 and a depleted mantle model age of 1.3 Ga, similar to Mesoproterozoic anorthosites in Laurentia. Clastic sedimentary rocks in the Green Head Group have εNd(750 Ma) values of -2.0 and -10.9. Viewed as a whole, the Brookville terrane is isotopically more evolved than the Caledonia terrane. Initial εNd values for rocks in the New River terrane range from -2.9 to 0.0. The Nd isotopic composition of the Brookville and New River terranes are thus similar to one another and have isotopic character similar to that of the Bras d'Or terrane of Cape Breton Island. It is suggested that all three regions belong to a single terrane (Bras d'Oria).