THE BEGINNING OF THE STORY – EARLY TO MID-PALEOZOIC TRANSLATION OF TERRANES FROM THE ARCTIC REALM INTO EASTERN PANTHALASSA

The distinct geological histories, faunal affinities and detrital zircon signatures of some terranes in the North American Cordillera suggest Neoproterozoic to early Paleozoic origins in the Arctic realm – in proximity to Baltica, Siberia, and the northern Caledonides. In order to explain the ultimate juxtaposition of these Arctic terranes along the Cordilleran margin of western Laurentia, we hypothesized their mid-Paleozoic translation along the northern Laurentian margin at the favor of a Scotia-style subduction system termed the Northwest Passage. Since our initial proposal, substantial new observations both reaffirm the Arctic connections and refine our understanding of these terranes. The Pearya terrane of northern Ellesmere Island has stratigraphic affinities with Svalbard and contains Silurian-Devonian sinistral shear zones interpreted to record extrusion of terranes from the Caledonides and translation along the Laurentian Arctic margin. In north Yukon, the Porcupine shear zone also records pre-Late Devonian sinistral strike-slip displacement inferred to have accommodated translation of the Arctic Alaska terrane. Arctic Alaska comprises at least three pre-Carboniferous elements with distinct paleogeographic affinities. The North Slope subterrane is of northern Laurentian affinity and was likely translated along the Arctic margin in the mid-Paleozoic; other parts of Arctic Alaska (Seward, Hammond) are clearly of Baltican or Caledonian origin. The Alexander terrane also comprises three distinct elements with Baltican and Caledonian affinities that were successively juxtaposed in the Devonian and Permian. The Farewell and Kilbuk terranes of central and southwest Alaska have faunal and detrital zircon evidence that point to Siberian origins, but recent studies suggest it also comprises multiple early Paleozoic elements that were likely juxtaposed in the Early Permian. Detrital zircons from the Mystic subterrane of Farewell further suggest proximity to the Alexander and Wrangellia terranes in the Mississippian-Permian. Similar characteristics in the Northern Sierra and Eastern Klamath terranes of the western US also highlight potential Arctic origins.