EVIDENCE FOR A PALEOZOIC STRIKE-SLIP OROGEN ON THE NORTH AMERICAN ARCTIC MARGIN

A growing set of observations requires or is permissive of Paleozoic terrane translation along the North American Arctic margin. The Pearya terrane on northernmost Ellesmere Island is a crustal fragment with well-documented ties to Svalbard and an allochthonous position on the Laurentian Arctic margin. Shear zones within the terrane preserve evidence of Silurian to Devonian sinistral displacement. These structures are interpreted to record the extrusion of fragments from the Caledonian orogen and translation along the Arctic margin during continued convergence and ultrahigh-pressure metamorphism on the northeastern Laurentian margin (North East Greenland). Paleomagnetic and faunal evidence suggest the Alexander terrane was located near the Laurentian Arctic margin in Early Devonian time; a fragment of the Alexander terrane basement might reside in the northernmost Pearya terrane. Other Ordovician–Silurian arc-related fragments associated with the Arctic Alaska terrane of northern Alaska likely have a similar displacement history. Stratigraphic, faunal and detrital zircon data from portions of the North Slope subterrane of Arctic Alaska are consistent with a northeastern Laurentian origin whereas other components are clearly allochthonous, suggesting that Arctic Alaska contains terranes of Laurentian and exotic origin juxtaposed by major shear zones and displaced along the Arctic margin. The Arctic Alaska terrane is separated from northwest Laurentia by the Porcupine shear zone. Tectonite fabrics documented along the shear zone indicate that Paleozoic and older units are deformed in a broad sinistral strike-slip system: there are currently no more precise timing constraints on the Porcupine shear zone, but these data are consistent with large magnitude Paleozoic strike-slip displacement of Arctic Alaska on the Laurentian Arctic margin concurrent with sinistral motion of Svalbard and the Pearya terrane. Paleozoic strike-slip structures along the North American Arctic margin have been reactivated and overprinted during Mesozoic and younger evolution of the Arctic margin and Canada basin. Due to structural overprinting, poor exposure, and difficult access, the Paleozoic North American Arctic margin remains one of the most poorly known and underappreciated strike-slip orogens in the world.