DETRITAL ZIRCON U-PB GEOCHRONOLOGICAL AND HF ISOTOPIC CONSTRAINTS ON THE GEOLOGICAL EVOLUTION OF NORTH YUKON

North Yukon lies at the juncture of two major tectonic domains that define the western and northern edges of the North American continent – the northern Cordilleran mountain belt and the Arctic Ocean. Both tectonic provinces share a long and complicated history dating back to the Neoproterozoic breakup of Rodinia and subsequent development of the western (Cordilleran) and northern (Franklinian) continental margins of Laurentia. In the middle Paleozoic, passive margin deposition was interrupted along the Franklinian margin by compressional and strike-slip tectonism, culminating in the Late Devonian-Early Mississippian Ellesmerian orogeny, while western Laurentia witnessed onset of subduction and development of a convergent margin. These tectonic events are inferred to relate geodynamically with large-scale terrane displacements from the Arctic realm into northeast Panthalassa in the Paleozoic. The subsequent Mesozoic construction of the Cordilleran accretionary orogen is closely linked with Cretaceous opening of the Canada Basin; and the Tertiary onset of the Aleutian trench and development of the modern transform margin of northwestern North America coincide with opening of the North Atlantic and Eurasian basins.

To help refine understanding of the geological evolution of the region, we present detrital zircon U-Pb and Hf isotopic data for 19 sandstone and conglomerate samples from Neoproterozoic to Tertiary strata collected across North Yukon, between ~69°15’N and 67°10’N. Neoproterozoic-Cambrian strata exhibit distinct Precambrian sources, with dominance of Paleoproterozoic zircons (peak at 1.8-1.7 Ga) in northern samples and abundant Mesoproterozoic grains (1.5-1.0 Ga) in the south; signals that compare well with coeval strata along the Franklinian margin.

Precambrian zircons from Carboniferous and younger strata reflect mostly recycling of local older strata. Carboniferous conglomerates all show Late Devonian peaks (378-365 Ma) consistent with erosion of nearby granites. Triassic to Paleocene samples yielded a range of Neoproterozoic-Paleozoic zircons recycled from nearby Devonian flysch. Most significantly, these samples also yielded juvenile zircons that are close to depositional age, but for which arc sources are only known in southern Yukon and Alaska, more than 700 km away.