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

Nd isotopic data are presented for rock units in four terranes within the t raditional Avalon Zone of southern New Brunswick. Initial epsilon(Nd) value s for igneous rocks within the Caledonia terrane range from -1.6 to +4.6, w hereas values for sedimentary rocks range from -8.4 to +3.6. A granite with in the Kingston terrane has epsilon(Nd)(438 Ma) = +4.0. Nd isotopic composi tions for the Kingston and Caledonia terranes are similar to those of the M ira 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. In itial epsilon(Nd) 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 epsilon(Nd) value of -12.1 and a depleted mantle model age of 1 .3 Ga, similar to Mesoproterozoic anorthosites in Laurentia. Clastic sedime ntary rocks in the Green Head Group have epsilon(Nd)(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 epsilon(Nd) 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 an d 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 te rrane (Bras d'Oria).