Northeastern Section (45th Annual) and Southeastern Section (59th Annual) Joint Meeting (13-16 March 2010)

Paper No. 4
Presentation Time: 9:05 AM


POTTER, Joanna, Department of Earth Sciences, The University of Western Ontario, London, ON N6A 5B7, Canada, LONGSTAFFE, Fred J., Department of Earth Sciences, The University of Western Ontario, 1151 Richmond Street, Biological and Geological Sciences Building, London, ON N6A 5B7, Canada, BARR, Sandra, Department of Geology, Acadia University, 12 University Avenue, Wolfville, NS B4P 2R6, Canada and HIBBARD, James, Marine, Earth, and Atmospheric Sciences, North Carolina State U, Box 8208, Raleigh, NC 27695,

The pre-accretion history of peri-Gondwanan terranes in the Appalachian orogen can control certain geochemical characteristics of individual terranes components. In the best case, these traits can be used to trace the relative positioning of individual terranes along the Gondwanan margin and to determine the timing of their rift-drift history and subsequent accretion to Laurentia. Ganderia, Avalonia and Carolinia form a sizeable fraction of the Appalachians and they share many gross similarities in their pre-Paleozoic magmatic histories; consequently they were initially interpreted to constitute a single, coherent Neoproterozoic microcontinent. More recent detailed fieldwork, precise radiometric dating and further geochemical analysis demonstrate that these terranes have distinctly different crust-building, rifting, and collisional histories.

We have used whole-rock and mineral oxygen-isotope compositions to obtain unique information on the source characteristics and regional hydrothermal processes that affected each of these terranes. Previous oxygen-isotope studies showed the Neoproterozoic rocks in West Avalonia to be significantly depleted of 18O (as low as –3‰). These δ18O results have been attributed to regional-scale hydrothermal meteoric alteration during late-Neoproterozoic rifting and extension (~590-550Ma). No signs of regional 18O-depletion have been observed in Ganderia. New oxygen-isotope data for Carolinia, however, reveal significant 18O-depletion in the 630-615 Ma Hyco magmatic arc (+0.4 to +5.4‰). That said, the lower δ18OWR values of the Hyco magmatic arc are succeeded by normal-high δ18OWR values in the younger ~545-540 Ma Albermarle magmatic arc (+8.6 to +11.4‰), a transition not observed in West Avalonia. Different processes must have been active in Carolinia at the time that West Avalonia underwent extensive rock-water interaction and alteration.