TIMING AND EMPLACEMENT OF THE WHALE MOUNTAIN ALLOCHTHON IN THE NORTHEAST BROOKS RANGE, ALASKA; A POTENTIAL LINK BETWEEN DEVONIAN TECTONISM ALONG THE CORDILLERAN AND ARCTIC MARGINS OF NORTH AMERICA

Despite the widespread recognition of Devonian-aged tectonism along the margins of the Canadian Arctic (Ellesmerian orogeny) and the North American Cordillera (Antler orogeny), there is no direct evidence that links these events to one another. In this research, whole-rock geochemistry, detrital zircon geochronology, and mapped structural relationships from rocks exposed in the northeast Brooks Range of Alaska are integrated to suggest emplacement of the Whale Mountain Allochthon, an Ordovician to Early Devonian subduction complex, along the northwest margin Laurentia. The allochthon includes mafic volcanic rocks (many of which have undergone greenschist metamorphism), radiolarian chert, deep-marine clastics, and mud-rich limestone containing fragmented trilobite fossils. Major and trace elemental analysis suggest that the volcanic rocks of the allochthon were erupted on an ocean floor, in the form of seamounts, and emplaced as ophiolitic slivers within an accretionary prism. Samples of the trench filling turbidites that fed the prism are characterized by 360-480, 580-900, 1000-1300, 1600-2000, and 2500-2800 Ma detrital zircon age distributions, witch indicate derivation from Caledonide, Laurentian, and possibly Timanide rock assemblages. These data are consistent with a paleography that involves an island arc offshore northwest Laurentia, while its accretionary prism developed inside a marginal ocean basin, simultaneously receiving sediment from Laurentia and the arc. By the Early Devonian, arc accreted to the Laurentian margin, and the allochthon was structurally juxtaposed against miogeoclinal rocks of the Franklinian sequence. The exact paleogeogrpahic position of this accretionary event remains in question, but these findings present possible linkages between accretionary events in the northern Cordillera (Kootenay arc, Yukon-Tanana) and in the northern Canadian Arctic (Pearya).