EARLY PALEOZOIC ASSEMBLY OF THE NORTH SLOPE SUBTERRANE: EVIDENCE FROM AN ACCRETIONARY COMPLEX EXPOSED IN THE NORTHEASTERN BROOKS RANGE, ALASKA

Pre-Mississippian stratigraphy of Arctic Alaska’s North Slope subterrane is extensively exposed in the northeastern Brooks Range. Three major tectonostratigraphic units of Laurentian affinity are included: 1) a late Neoproterozoic to Early Cambrian siliciclastic-dominated passive margin succession; 2) a thick Neoproterozoic to Early Devonian carbonate platform; and 3) a Late Cambrian to Early Devonian(?) accretionary complex, herein named the Whale Mountain allochthon. Integrated geological, geochronological, and geochemical evidence is presented here to suggest that these tectonostratigraphic units were assembled in a long-lived accretionary episode that coincided with phases of Caledonian tectonism (~474 - 404 Ma). Structural and stratigraphic relationships, along with new major and trace element geochemical data from volcanic rocks, indicate that the Whale Mountain allochthon includes ocean-island basalt and deep-marine siliciclastic rocks that were deformed within an accretionary prism. The youngest U-Pb detrital zircon ages from siliciclastic rocks of the allochthon are coeval with 40Ar/39Ar metamorphic muscovite cooling ages, implying a syntectonic depositional setting. This, along with the geographic distribution of the 40Ar/39Ar ages, supports a hypothesis of episodic accretion and rapid exhumation of the accretionary complex, possibly in a south to north (current coordinates) progression above a southward dipping subduction zone. A reasonable plate reconstruction that fits these findings, positions the North Slope accretionary complex as an extension of the Maskell Inlet complex of the Pearya terrane at Ellesmere Island.