Detrital zircon U-Pb geochronological and Hf isotopic constraints on the geological evolution of North Yukon

Abstract

North Yukon lies at the intersection 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. The pre-Carboniferous geology in North Yukon includes the Neoproterozoic−lower Paleozoic North Slope subterrane of the Arctic Alaska terrane and, south of the Porcupine shear zone, Mesoproterozoic−Paleozoic rocks of the Yukon stable block. The North Slope subterrane was deformed prior to deposition of Carboniferous and younger strata, and its paleogeographic origins are debated. North Yukon was deformed again during Cretaceous−Cenozoic development of the northern Cordilleran−Brookian orogen. To help refine understanding of the geological evolution of the region, we present detrital zircon U-Pb and Hf isotopic data for 21 sandstone and conglomerate samples from Neoproterozoic to Cenozoic strata collected across North Yukon, between ~69°15′N and 67°11′N. Neoproterozoic−Cambrian strata in the British Mountains are characterized by a dominance of Paleoproterozoic zircons (peak at 1.7–1.8 Ga), whereas samples from the Barn Mountains to the south have abundant Mesoproterozoic grains (1.0–1.5 Ga), suggesting these rocks may have been deposited along different segments of the northern Laurentian margin. Regional geophysics suggest these domains could be separated by a fault. Northeastern Laurentian origins are indicated by distinct early Neoproterozoic and Ordovician−Silurian zircons in Upper Silurian−Lower Devonian immature sandstone and conglomerate of the Clarence River Group and provide the most compelling evidence for large-scale translation along northern Laurentia. Precambrian detrital zircons in Carboniferous and younger strata reflect mostly recycling of local older strata. Carboniferous conglomerates all show Late Devonian peaks (365–378 Ma) consistent with erosion of nearby granitoid plutons. 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. These source regions are distinct from NE Russian sources inferred for early Brookian (Early Cretaceous) foreland deposits in Alaska.

’Taters versus Sliders: Evidence for a Long-Lived History of Strike-Slip Displacement along the Canadian Arctic Transform System (CATS)

“…Autochthonous strata of the Laurentian margin in northern Yukon are juxtaposed with peri-Laurentian platform and basinal strata of the North Slope subterrane of Arctic Alaska (Macdonald et al, 2009;Strauss et al, 2019aStrauss et al, , 2019bColpron et al, 2019) on a nearvertical fault zone broadly referred to as the Porcupine shear zone (Fig. 1; von Gosen et al, 2019).…”

“…The CATS model that accommodates large-magnitude translational motion of terranes suggests the source may have varied through time. Colpron et al, 2019). Insets show simplified (1) rotation and (2) translation models (from Patrick and McClelland, 1995).…”

Paleotectonic and paleogeographic history of the Arctic region

“…Miller et al (2017) considered these events to be related to Devonian plate reorganization. In contrast, others (Strauss et al 2018a, b;Colpron et al 2018;Nelson et al 2018) propose a more protracted orogenic history in which the Romanzof orogeny is interpreted as an Early to Middle Devonian event, probably representing the assembly of the peri-Laurentian North Slope subterrane with other elements of AACM. The final assembly of AACM was not complete until Early Mississippian, when the final docking of AACM occurred in the Canadian Arctic.…”

“…As the Ural Ocean closed and Siberia transformed with left-lateral motion along the affinities, probably originating off Greenland or the Canadian Arctic (Fig. 4), whereas most other terranes have Baltic affinities (Nelson et al 2013;Colpron et al 2018;Nelson et al 2018;Strauss et al 2018a, b).…”

“…The model followed in Figures 4-6 follows the Northwest Passage hypothesis Nelson 2009, 2011;Nelson et al 2013;Colpron et al 2018;Nelson et al 2018). The following concepts have evolved over the dozen or so years since the hypothesis was first conceived.…”