COLLISION INVESTIGATION: TERRANE FORENSICS IN THE NORTHERN APPALACHIANS AND CALEDONIDES

Numerous detrital zircon data sets have been assembled from the Canadian Appalachians and their transatlantic correlatives in the British Caledonides over the past 10 years. Most analyses of these data sets rely on visual comparisons of probability density plots. In examples from the Southern Uplands of Scotland, the English Lake District, SE Ireland, North Wales, Nova Scotia and New Brunswick, these allow relatively clear distinction between Laurentian sources, with a dominant peak at ~ 1 Ga, and peri-Gondwanan sources, dominated by a Neoproterozoic peaks from 540 - 650 Ma, and often containing a secondary peak from 1.95 - 2.2 Ga. Based on these distinctions it is possible to qualitatively track the progressive arrival of Laurentian detritus in peri-Gondwanan terranes as they were accreted to Laurentia in the Ordovician and Silurian. Some significant contrasts between the British Caledonides and the Canadian Appalachians emerge. Whereas the first influx of Laurentian detritus above definite peri-Gondwanan crust in Britain and Ireland does not appear until the mid-Silurian, in Atlantic Canada some peri-Gondwanan fragments were clearly in contact with Laurentia by the Late Ordovician; others did not arrive until mid-Silurian. This suggests that the paleogeography of continental fragments in the northern Appalachian segment of Iapetus was much more complex than in the Caledonides.

These distinctions have previously been based entirely on relatively clear qualitative distinctions between detrital zircon samples. The data provide an opportunity to evaluate the Kolmogorov-Smirnov test and other proposed quantitative measures of similarity between detrital zircon data sets, and to apply those tests to seek more subtle differences between samples that may provide additional insights into paleogeography and tectonics.