THE NORTHERN CORDILLERAN PERI-LAURENTIAN TERRANES AND THEIR INTERACTIONS THROUGH TIME

In the 25 years since the first application of the terrane concept to the North American Cordillera, a pattern of inter-terrane stratigraphic and intrusive linkages and shared isotopic and faunal elements has emerged. Far from being restricted to late, post-amalgamation overlaps, these linkages can be as old as the oldest rocks in one of the terranes. They give a coherent sense to Canadian Cordilleran terranes, which otherwise might appear to be a collection of isolated and unrelated fragments. They include: 1) Cambrian stratigraphic linkages between Kootenay terrane and ancestral North America; 2) the onlap of Slide Mountain terrane onto the Kootenay terrane in southern B.C.; 3) Early Permian depositional ties and stratigraphic overlap between Yukon-Tanana and Slide Mountain terranes in Yukon; 4) Yukon-Tanana terrane as basement to Quesnellia; 5) late Paleozoic and Triassic ties between Stikinia and Yukon-Tanana terrane; and 6) an Early Jurassic plutonic suite shared by Stikinia, Yukon-Tanana and Quesnellia. Such observed linkages effectively eliminate some of the paleogeographic uncertainties that were previously inferred between adjacent terranes (although not necessarily with respect to the Laurentian continent) and highlight their common history. In view of these relationships, it is now possible to interpret terranes in terms of shared geodynamic scenarios, such as repeated arc superposition on older arcs and/or basement, and co-existing arc system components. A primary result of this analysis is that the Intermontane terranes represent one inter-related set of arcs, marginal seas and continental fragments, that once formed a Paleozoic to early Mesozoic fringe to North America: the peri-Laurentian realm. By contrast, the Insular terranes, along with the Farewell and Arctic-Alaska terranes, include crustal fragments that probably originated from separate sites within the Arctic realm in Paleozoic time.