The position and nature of the Gander–Avalon boundary, southern New Brunswick, based on geochemical and isotopic data from granitoid rocks

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Whalen, Joseph B., Fyffe, Leslie R., Longstaffe, Frederick J., Jenner, George A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1996
• Subjects: Newfoundland
• Online Access: http://dx.doi.org/10.1139/e96-013; http://www.nrcresearchpress.com/doi/pdf/10.1139/e96-013

In southern New Brunswick, the Gander–Avalon boundary is obscured by boundary-parallel faults and various cover sequences. Siluro-Devonian granites, which intrude unequivocal Gander or Avalon rocks, display exclusively negative (−1.9 ± 1.0) and positive (+1.9 ± 0.7) ε Nd (T) signatures, respectively. Such contrasting Nd isotopic signatures, combined with other geochemical differences between plutons, are potentially valuable tools for terrane analysis. Nine small Devonian plutons intruding the boundary zone fall into contrasting geochemical groups with (La/Lu) N <4 and >4. The former are topaz-bearing granites, while the latter are volcanic-arc-type granites. Except for one pluton, with an ε Nd (T) signature of –2.0, ε Nd (T) values range from –0.4 to +0.7, spanning the gap between "type" Avalon and "type" Gander plutons. These results suggest the plutons sampled either (i) stratigraphically overlapping or tectonically interleaved Gander and Avalon basement rocks, or (ii) a distinct basement source beneath the boundary zone. Our results demonstrate that the Gander–Avalon boundary in southern New Brunswick is not a simple throughgoing crustal fault, and that the Gander and Avalon zones are underlain by different continental basement blocks. Comparison with results from Newfoundland and Nova Scotia suggests that these basement blocks are continuous throughout the Canadian Appalachians.