Abstract Mesoproterozoic orogenesis is well established on the western and southern flanks of Laurentia in the well-known Racklan–Forward and Mazatzal orogens, but its significance within the previously assembled interior of the supercontinent Nuna has not been established. We examine regional isotopic and structural evidence for Mesoproterozoic deformation in the c. 1.7–1.63 Ga Hornby Bay, Elu, Thelon and Athabasca intracontinental basins, and present evidence for Mesoproterozoic reactivation of Paleoproterozoic structures in the Wopmay and Trans-Hudson orogens. The Racklan–Forward Orogeny in the interior of north Laurentia comprises north–south-trending, high-angle, east-vergent folds and thrusts that occur across a region 1660 km wide and over 1000 km long, stretching from the Yukon to near Hudson Bay and from Banks Island to below the Western Canada Sedimentary Basin. The structures progress from ductile amphibolite and greenschist facies in the Racklan type area to sub-greenschist facies and ultimately brittle or brittle-ductile in the far foreland, showing a predominant thick-skinned style typical of many intracontinental orogens. We present compiled low-temperature thermochronological data, including ages of spatially associated uraninite mineralization, to characterize the scope of reactivation of basement structures in the Archean Rae craton in Nuna's interior. We compare the nature of widespread far-field reactivation in the Racklan–Forward Orogen with other orogens of Nuna's assembly to show it is unusual for Nuna's peripheral margin. We suggest that c. 1.6 Ga continent–continent collision of North Australia with NW Laurentia propagated stresses far into the interior as a result of combined favourable pre-existing structural grain and a weak subcontinental lithospheric mantle in the Rae craton due to repeated episodes of refertilization across 500 Ma of accretion and intrusion. Cratons that experience the complex, two-sided collision and protracted upper plate setting during supercontinent assembly noted herein may be particularly susceptible to extensive foreland propagation of peripheral orogens.

ABSTRACT It is debated whether plate tectonics (horizontal tectonics) or single-lid tectonics (vertical tectonics) dominated the Mesoproterozoic Era. Either rifting of the Nuna/Columbia supercontinent or a localized vertical subsidence and tectonism mechanism within a single tectonic plate is likely recorded in Mesoproterozoic basins. This study summarizes detrital zircon samples from the Mesoproterozoic Belt and Purcell Supergroups and Lemhi subbasin of the western United States and Canada and tests competing rift and intracratonic basin models. Rift models take the observed detrital zircon trends to mean that a non-Laurentian (ca. 1.6–1.5 Ga) detrital zircon component becomes completely absent higher in the section, signifying rifting of the Nuna/Columbia supercontinent at ca. 1.4 Ga. Intracratonic models acknowledge this observed shift in provenance but interpret a long-lived intracratonic setting for the basin following an earlier failed rifting event. The fundamental question is whether the Belt basin represents a failed or successful rift. We used statistical comparison of 72 detrital zircon signatures, reported in the literature and presented in this study, to test the rift model. Samples are not evenly distributed across the basin or its stratigraphy. Non-Laurentian grains are spatially restricted to the northwest part of the basin but are present in all groups, suggesting that the apparent loss of the non-Laurentian population is an artifact of sampling bias. Like stratigraphic boundaries and facies changes, mixing trends are gradual, not sharp or sudden, signifying progressive reworking of Proterozoic zircons and transport from all sides. Archean zircons are localized near the edges of Archean blocks, signifying local down-dropping along cratonic margins. The rift model is therefore rejected in favor of the intracratonic model for the Belt basin on the basis of variable mixing between non-Laurentian and Laurentian sources in both pre–Missoula Group and Missoula Group strata. Far away from plate margins, sediment incrementally filled topographic depressions created by densified and thinned Proterozoic crustal blocks, resulting in vertical down-dropping along preexisting sutures with neighboring Archean blocks. More systematic detrital zircon studies are needed in order to accurately quantify provenance trends in space and time. Continued investigation of the Belt basin may reveal underappreciated or unrecognized vertical tectonic processes that may explain Mesoproterozoic rocks more accurately.