The peri-Gondwanan realm in Cape Breton Island and southern New Brunswick.

The current division of the peri-Gondwanan realm of the northern Appalachian orogen into Avalonian and Ganderian components resolves some of the long-standing problems in reconciling terrane models in New Brunswick and Cape Breton Island with those in New England and Newfoundland. The similarity in Neoproterozoic history between Ganderia and Avalonia makes resolution of those components particularly challenging, especially because the Neoproterozoic components of Ganderia are so little exposed in Newfoundland and Maine. Complexity within each of Ganderia and Avalonia also contributes to the problem, as both consist of multiple Neoproterozoic terranes. The previously well-documented geological contrasts between Ganderia and Avalonia are supported further by recognition that Avalonia experienced systematic and pervasive 18O-depletion that did not affect Ganderia. This depletion may have been linked to hydrothermal alteration during rifting at ca. 560-550 Ma as Avalonia separated from Gondwana. U-Pb dating has shown that Neoproterozoic rocks are more widespread in both western Cape Breton Island and in the New River belt of southern New Brunswick than was previously recognized. From mainland southern New Brunswick, they appear to be offset to Grand Manan Island and the central Gulf of Maine. These Neoproterozoic Ganderian belts are separated from the also Neoproterozoic Ganderian Brookville-Bras d'Or terrane of southern New Brunswick and Cape Breton Island by the Silurian Kingston-Aspy arc. Geophysical studies suggest that the basements are different under these Ganderian Neoproterozoic belts, although all these areas produced granitoid rocks with negative epsilon Nd values, in contrast to the positive values characteristic of Avalonia. The original positions of Ganderia and Avalonia around Gondwana, the nature of their pre-Neoproterozoic basements, and their relationship to the now-adjacent Meguma remain major uncertainties. Geochemical, isotopic, and detrital zircon data from sedimentary and metasedimentary sequences in Avalonia suggest that older stratigraphic units of Avalonia had different and more continental and mature sources than the Upper Neoproterozoic and Lower Paleozoic cover. Those sources were not identical to those which provided similarly continental and mature sediment to Ganderia. Links between sources and basements in Ganderia and Meguma seem more likely than links between those areas and Avalonia. [ABSTRACT FROM AUTHOR]