Extensive debate has focussed on the nature and location of the Snowbird Tectonic Zone (STZ), the suture between the Rae and Hearne cratons. Geological mapping in the Baker Lake area revealed a similar to 7 km wide deformation zone associated with the Chesterfield Fault Zone (CFZ), a south-dipping, dextral strike-slip structure previously interpreted to represent the northern segment of the STZ. New geochronology across the CFZ indicates both the footwall and hangingwall are dominated by ca. 2.72 Ga tonalite gneisses and ca. 2.6 Ga porphyritic monzogranite, effectively ruling out the CFZ as the northern segment of the STZ. Geochronology, thermobarometry, and thermodynamic modelling from the hangingwall indicate three Paleoproterozoic metamorphic events (M1-M3) that outline a clockwise P-T-t path. Prograde metamorphism (M1) reaching peak conditions of 0.75 GPa and 700 degrees C is dated by early titanite growth at ca. 1.92 Ga, consistent with burial during southeast-verging folding and thrusting associated with collision of the Rae-Chesterfield and Hearne cratons. Peak conditions of similar to 1.0 GPa and 740 degrees C at ca. 1.87 Ga (M2; garnet Lu-Hf) are coeval with northwest-vergent folding and thrusting during early, intra-oceanic accretionary episodes associated with the Trans-Hudson Orogeny. Dextral strike-slip kinematics argue against the CFZ as the structure responsible for exhumation of ca. 1.9 Ga high-pressure rocks to the south. Instead, exhumation may have been accommodated along discrete, reverse-sense shear zones associated with the CFZ, or an alternate structure to the south. Together, these data highlight that crustal-scale shear zones can preserve tectonometamorphic information, critical for tectonic reconstructions and understanding orogenic processes, that is not recorded in the surrounding lithotectonic blocks.

Carbonatites are the primary source of rare earth elements (REE), but their distribution and controls on REE mineralization remain poorly constrained. Using a new compilation of global carbonatites and associated REE deposits, here we show that plate boundaries exert a first-order control on their distribution. This is best illustrated by the long-lived margin that developed along the southern margin of the Nuna and then Rodinia supercontinents, where many REE-bearing carbonatites and mineralization related to felsic magmatism are localized inboard of former convergent margins. Moreover, many deposits (and mineral provinces) underwent multiples stages of carbonatite emplacement and/or hydrothermal upgrading. The reoccurrence of carbonatites and REE mineralization are best illustrated by Bayan Obo, with REE being introduced by two stages of carbonatites dated at 1320 Ma and 430 Ma. Such repeated occurrences of carbonatites and related mineralization can be explained by melts extraction from low degree melting of fertilized mantle, with fertilization being achieved by subduction.

Canada's northern cratons record a complex poly-metamorphic evolution in response to multiple orogenic events. The Snowbird Tectonic Zone (STZ), the principal suture between the Archean Rae and Hearne cratons, is a highly debated structure; it is argued to have accommodated modern-style accretion in either the Neoarchean (2.6-2.5 Ga) or Palaeoproterozoic (ca. 1.9 Ga). To resolve this controversy, we use Lu-Hf garnet geochronology to date an eclogite collected from the East Athabasca mylonite triangle of the STZ. Garnet shows prograde trace-element zoning, and we obtained an age of 1914.5 +/- 3.4 Ma. The age is interpreted to date the timing of collision related to deep burial of crust along the STZ. This strongly supports Palaeoproterozoic terminal collision between the Rae and Hearne cratons, and that to constrain high-pressure metamorphism during supercontinent assembly, dating eclogite itself is key.

The Geo-mapping for Energy and Minerals (GEM) program was funded between 2008 and 2020 with the aim of advancing geological knowledge of the North to reduce risk for mineral exploration and inform land-use decisions and future management of the North. Twenty-one regional activities were undertaken across Canada's northern shield, spanning northern Prairie Provinces, northern Quebec, Labrador, along with much of Nunavut and Northwest Territories. A further five activities were thematic in nature. Bulletin 612 presents results from 12 of these endeavours, including integrated regional bedrock geoscience studies, geophysical surveys, and basin analyses, as well as thematic thermochronology, geochemistry and large igneous province syntheses. The results highlight that GEM has contributed to new era of understanding of the northern Canadian Shield, expanding its framework substantially and developing an increasingly complex model of Archean cratons, Archean/Proterozoic microcontinents, and juvenile Paleoproterozoic crust that highlights the existence of a dozen new pericratonic to exotic ribbon microcontinents within a mosaic once considered as mostly large cratonic masses welded by Paleoproterozoic orogens. This emerging picture brings additional questions for future northern studies - particularly in the granularity of subdivision of the largest blocks, the impact of enigmatic earliest Paleoproterozoic orogens, and dynamics of assembly of exotic and little-known terranes.

The Geo-mapping for Energy and Minerals (GEM) program was funded between 2008 and 2020 with the aim of advancing geological knowledge of the North to reduce risk for mineral exploration and inform land-use decisions and future management of the North. Twenty-one regional activities were undertaken across Canada's northern shield, spanning northern Prairie Provinces, northern Quebec, Labrador, along with much of Nunavut and Northwest Territories. A further five activities were thematic in nature. Bulletin 612 presents results from 12 of these endeavours, including integrated regional bedrock geoscience studies, geophysical surveys, and basin analyses, as well as thematic thermochronology, geochemistry and large igneous province syntheses. The results highlight that GEM has contributed to new era of understanding of the northern Canadian Shield, expanding its framework substantially and developing an increasingly complex model of Archean cratons, Archean/Proterozoic microcontinents, and juvenile Paleoproterozoic crust that highlights the existence of a dozen new pericratonic to exotic ribbon microcontinents within a mosaic once considered as mostly large cratonic masses welded by Paleoproterozoic orogens. This emerging picture brings additional questions for future northern studies - particularly in the granularity of subdivision of the largest blocks, the impact of enigmatic earliest Paleoproterozoic orogens, and dynamics of assembly of exotic and little-known terranes.

The package PbIso is a free and open R toolbox for commonly used calculations and plots of Pb–Pb isotope data and for generating Pb evolution models. In this paper, we review Pb isotope systematics and the calculations that are commonly used, such as model age, model source μ (238U/204Pb), time-integrated κ (232Th/238U), and initial Pb isotope ratios. These equations are implemented into R functions in the package PbIso. In addition, functions are provided for generating Pb evolution models, paleoisochrons, and isochrons. This allows users to apply calculations to their data in a straightforward way while providing transparency and flexibility of the calculations used. We have implemented some basic features of the PbIso package into an online shiny R application (see https://shereearmistead.github.io/software/pbiso), which makes it easy for users without any R experience to use these calculations with their own data and to generate plots. We have provided a case study from the Superior Province in Canada, showing how different Pb evolution models can be generated in PbIso and compared to Pb isotope data.

Between 2.62 and 2.58 Ga, Rae Province was intruded from Lake Athabasca to Melville Peninsula (more than 1700 km) by mafic to felsic plutons (Snow Island Suite), and overlain by volcanic rocks that are now mostly preserved beneath Paleoproterozoic basins. The Snow Island Suite was preceded by offshore arc volcanism and possible back-arc basin activity, with a U-Pb age peak at 2.635 Ga (Marjorie peak). About 50% of the Snow Island Suite is an infracrustal granitoid with K-enriched and tonalitic subtypes; the remainder lies on a sanukitoid spectrum. The sanukitoidal rocks are dominantly orthopyroxene-bearing magnesian diorite and monzodiorite with Mesoarchean Nd model ages. Some isotopically juvenile Snow Island Suite and Marjorie peak mafic rocks also have strong sanukitoid or adakite trace-element signatures. Four important features in the data are: 1) Marjorie peak mafic assemblages are prominent on the southeastern edge of Rae Province. Related nickel showings are present in south Rae Province Marjorie peak and early Snow Island Suite rocks; 2) U-Pb ages in the Snow Island Suite young toward the west edge of the province; 3) the Committee Bay Block (north-central Rae Province) is distinctively rich in infracrustal Snow Island Suite migmatite and poor in Snow Island Suite sanukitoid rocks and in tonalite of any age; and 4) there is a marked shift from tonalite-rich infracrustal sources in south Rae Province to more tonalite-poor sources in central Rae Province. The data are consistent with the Snow Island Suite, representing a continental magmatic arc segment, verging westward, with ponding of mafic magmas, inducing melting in the lower lithosphere to generate intermediate melts that ascended and induced additional melting in the middle to upper crust to generate granite.

Compilation of age and endowment data for deposits that commonly occur on convergent margins (volcanichosted massive sulfide, porphyry copper, orogenic gold, granite-related rare metal and pegmatite deposits: over 1000 deposits from 21 mineral provinces) indicate that metallogenic patterns have changed over time. For much of Earth's history, metallogenesis along convergent margins is marked by a relatively systematic temporal progression of deposits succeeding one-another, which we refer to as the convergent margin metallogenic cycle (CMMC): volcanic-hosted massive sulfide (VHMS) and/or calc-alkalic porphyry copper -* orogenic gold -* alkalic porphyry copper, granite-related rare metals and/or pegmatite. Typically individual CMMCs last for 60-160 Myr, and the progression appears to be related to the convergent margin tectonic cycle. Prior to ca. 3000 Ma, however, CMMCs are not recognized. Rather, these old mineral provinces are characterized by long metallogenic histories (370-500 Myr) with no discernible pattern of deposit types. The Mesoarchean to Paleoproterozoic is characterized mostly by mineral provinces with relatively short (60-155 Myr) metallogenic histories and a single CMMC. Between 1950 Ma and 1700 Ma some convergent margin mineral provinces (e.g. Trans-Hudson and Svecofennian) are characterized by multiple CMMCs, with metallogenic histories that last up to 160 Myr. Between 1250 Ma and 750 Ma, longer-lived yet relatively poorly-constrained metallogenic histories (up to 320 Myr) appear, and after ca. 750 Ma, convergent margins are mostly long-lived (290-450 Myr) and are characterized by multiple CMMCs with complex metallogenic histories. These four periods in the metallogenesis of convergent margins appear to reflect secular changes in tectonic processes. Prior to ca. 3200-3000 Ma, stagnant lid tectonics, which did not involve modern-style subduction, dominated, resulting in non-cyclical mineralization. After the initiation of some early form of subduction between ca. 3200 Ma and ca. 3000 Ma, the metallogenic style changed. The dominance of provinces from 3000 to 1700 Ma with a single CMMC, and a relatively short metallogenic history suggests that convergent margins were shorter-lived. This is consistent with models of shallow-break-off subduction whereby the subducting slab breaks off at shallow levels due to lower plate strength beginning in the later Archean. We suggest that between ca. 3000 and ca. 1700 Ma a propensity for slab break-off could shut down individual subduction systems and produce short-lived metallogenic histories with a single CMMC. The change to longer metallogenic histories and dominant multiple CMMCs begins with Rodinia assembly: the length and complexity of metallogenesis systematically increases thereafter. The lengthening of convergent margin metallogenesis resulted from more stable convergence as continuous ridge push and the stronger density contrasts of the subducting slab causing re-initiation of subduction outboard rather than complete termination of subduction when the convergent margin was perturbed. As consequence of these driving factors, the metallogenic history of young convergent margins involves multiple CMMCs and/or complex temporal interleaving of deposit types.

<p>Isotopic proxies such as Hf, Nd and Pb are widely used to understand the evolution of Earth’s crust and mantle. Of these, Pb isotopes are particularly sensitive to crustal influences, and the extraction of mantle melts. We present a global compilation of Pb isotope data from syngenetic Volcanogenic Massive Sulphide (VMS) deposits, which allow us to track the evolution of Pb isotopes in deposits that are associated with dominantly back-arc and extensional oceanic settings through time.</p> <p>Unradiogenic Pb isotope signatures, specifically low model source µ (<sup>238</sup>U/<sup>204</sup>Pb) values, in some Archean cratons have long been recognised, yet their origin remains elusive. For example, sulphides from the c. 2.7 Ga Abitibi Belt in the Superior Province of Canada require long-lived (> 500 my) evolution of a source component to generate the Pb isotope signatures observed. Other isotope systems, such as Lu-Hf and Sm-Nd, show relatively juvenile signatures for the Abitibi Belt, suggesting decoupling of the different systems. Low µ values are evident in ore deposits and rocks from the Archean to modern settings but are most prominent in Archean settings because of their associated low <sup>207</sup>Pb/<sup>204</sup>Pb values, unlike for younger times.</p> <p>Pb isotope data at a global and broad temporal scale show that periods with distinct low µ values have a marked cyclicity that coincides with the supercontinent cycle. We propose that during supercontinent assembly, portions of older unradiogenic, Pb-rich mantle are tapped and incorporated into VMS deposits. Pb, possibly enriched in sulphides, can explain the apparent decoupling of Pb from silicate-controlled isotope systems like Hf and Nd. We suggest that the source of this unradiogenic mantle component formed during the previous supercontinent cycle when large volumes are extracted from the mantle to form (radiogenic) crust and an unradiogenic residue, which most likely resides in the lithospheric mantle although some may also be present as discrete ‘pods’ in the circulating mantle. This process provides a mechanism to explain isolation of source regions for several hundred million years, as required to generate the low µ values, until later tapping during a subsequent supercontinent amalgamation cycle.</p> <p>The low µ values in the c. 2.7 Ga Abitibi Belt represent the best-known Archean occurrence of this signature, indicating that their unradiogenic source relates to a major mantle extraction event that would have occurred at least 500 my earlier, i.e. at about 3.2 Ga.</p>

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.

This study characterizes the polyphase tectonometamorphic history of a major shear system in the Rae craton, the Howard Lake shear zone (HLsz), which exhumed high-grade rocks in the distant hinterland of the Paleoproterozoic Trans-Hudson Orogen. Prior work established a Mesoarchean mantle model-age discrepancy in basement rocks across the HLsz, which we interpret to have contributed a fundamental lithospheric rheology contrast that allowed for HLsz localization. Our work shows that the HLsz has a long-lived history starting in the early Paleoproterozoic as it abruptly separates 2.36 Ga granulite-facies metamorphic units to the east from 2.4 Ga greenschist-facies metamorphic basement rocks to the west. Subsequent reactivation during Trans-Hudson Orogen time between 1.86 and 1.82 Ga accommodated re-burial and re-exhumation of high-grade rocks in its footwall coeval with Sask craton collision. Strong penetrative overprinting deformation in metaigneous rocks and a newly discovered < 2.04 Ga schist preserve evidence for right-lateral transpression within the HLsz at ca. 1.82 Ga, which is coincident with the terminal collision of the Superior craton. Our work demonstrates that the HLsz is one of several major crustal-scale anisotropies in the south Rae craton and it is broadly analogous to major detachment fault systems documented in numerous Phanerozoic orogenic systems. Furthermore, the polycyclic deformation history of the HLsz, along which regional burial and exhumation was strongly localized, demonstrates the considerable influence crustal scale anisotropies can have on the evolution of craton architecture such as that presently found in the south Rae craton of the Canadian Shield.

Several different Neoarchean–Paleoproterozoic supercontinents or supercratons have been proposed, including Kenorland, Protopangea, Vaalbara, Superia, Supervaalbara, Sclavia, and Nunavutia. We used high-quality paleomagnetic data and an updated magmatic record to test these various cratonic reconstructions. Based on these analyses, we suggest that a Vaalbara configuration might be possible through at least part of the Neoarchean–Paleoproterozoic transition, contradicting recent suggestions. We also propose a modified Superia reconstruction with a looser fit of the Karelia–Kola and Superior cratons than the original Superia configuration. Disagreement between the paleomagnetic poles, different drift velocities, and the latitudinal positions of Superia and Kaapvaal at 2.7–2.2 Ga and Superia and Nunavutia at 2.4–2.2 Ga indicate that these supercratons were separate, negating a single Neoarchean–Paleoproterozoic supercontinent and the proposed Supervaalbara configuration, and thus also arguing against the existence of a full-fledged Kenorland landmass during that interval of time. This also argues against stagnant-lid tectonics during the Archean–Paleoproterozoic transition. In addition, drift velocities at 2.4–2.2 Ga that are in the range of current plate motions contradict the proposed tectono-magmatic shutdown or a tectono-magmatic lull in the Paleoproterozoic.

The Nonacho Group comprises six formations of continental elastic rocks that were deposited between 1.91 and 1.83 Ga. The Nonacho Group is part of a broader assemblage of conglomerate and sandstone that was deposited atop the Rae craton in response to the amalgamation of Laurentia and supercontinent Nuna, but the details of its tectonic setting are contentious. This paper documents an outlier of Nonacho Group rocks similar to 50 km east of the main Nonacho basin. Field observations and LA-ICPMS (laser ablation inductively coupled plasma mass spectrometry) U-Pb detrital zircon geochronology are integrated with previous studies of the main basin to better understand the group's depositional history, provenance and tectonic setting. The lithology and detrital zircon age spectra of the outlier allow for its correlation to the upper two formations of the Nonacho Group. CA-ID-TIMS (chemical abrasion isotope dilution thermal ionization mass spectrometry) analyses of two fragments of the youngest detrital zircon provide a maximum depositional age of 1901.0 +/- 0.9 Ma. A felsic volcanic cobble dated at ca. 2.38 Ga provides evidence of volcanism during the Arrowsmith orogeny. Detrital zircon dates recovered from the outlier (ca. 3.4-3.0, 2.7, 2.5-2.3 and 2.0-1.9 Ga) are consistent with derivation from topography of the Taltson and/or Thelon orogens on the western margin of the Rae craton. Taltson-Thelon (2.0 to 1.9 Ga) aged detritus is only abundant in the upper two formations of the Nonacho Group, marking a change in provenance from the lower formations. This change in provenance may have coincided with a period of renewed uplift and the unroofing of Taltson-Thelon plutons. The detrital zircon provenance and depositional age of the Nonacho Group is consistent with models that link its deposition to the Taltson and/or Thelon orogens. However, tectonism associated with the 1.9 to 1.8 Ga Snowbird and Trans-Hudson orogens to the east could also have affected basin formation or the change in provenance from the lower to upper Nonacho Group. This study highlights the importance of CA-ID-TIMS in establishing accurate and precise maximum depositional ages for sedimentary successions.

New mineral deposit discoveries are required to meet the forecasted demand for some critical raw materials. Governments are responding to that challenge by investing in mineral systems research and by by making government geoscience datasets freely available to the public and explorers. However, translating conceptual mineral system models to mappable geological, geochemical, and geophysical proxies is difficult with incomplete data of variable quality from modern and legacy surveys. Herein we address those knowledge gaps and propose a new open source workflow in R for prospectivity modelling using public geoscience datasets. We focus on the largest footprints of magmatic Ni (+/- Cu) sulphide mineral systems and their critical raw materials (+/- Co +/- PGE). Multiple prospectivity models are presented, including data-driven methods (e.g., weights of evidence, gradient boosting machines) that use the features of known mineral occurrences as a training set and a hybrid method that also incorporates conceptual mineral system criteria. All models are validated using data from northern Canada (i.e., north of 60 degrees latitude) as a test set. Statistical analysis of the prospectivity results suggests that rock types and geological ages are two of the most important predictive datasets, which correspond to the sources and drivers within the mineral system framework, respectively. Variable importance plots further suggest that geological boundaries (e.g., horizontal gradient magnitude of the gravity data and multi-scale edges) and the close spatial association between areas of high mineral potential and the edges of thick continental crust represent prospective ore-forming pathways. Model performance and the best combination of predictors and hyperparameters for each model are based on the receiver operating characteristics (ROC) plots, which yield a range of area under the curve (AUC) from 0.846 to 0.923 for the spatially independent test set. Most Canadian geological provinces, possibly with the exception of the Grenville orogen for the hybrid and weights of evidence methods (AUC = 0.716-0.726), yield comparable model performance, suggesting that the heterogeneous spatial distribution of different mineral system sub-types (e.g., komatiite-associated, rift-related, Alaskan-type, and hydrothermal awaruite) have a relatively minor impact on the prospectivity results. Monte Carlo-type simulations further suggest that the expert weightings used in the hybrid method (AUC = 0.843) are only slightly better than an average model constructed from random combinations of weightings (AUC = 0.809). The general agreement between different methods and multiple iterations of the same model demonstrate that public geoscience datasets can effectively reduce the search space to support mineral exploration targeting (i.e., less than 8% of map pixels contain more than 80% of the known Ni mineralization). However, vast segments of the Canadian landmass have not undergone systematic geological surveying or data acquisition. Prospectivity modelling can thus also be used by governments and academia to prioritize areas for future targeted geoscience research.

Recent discoveries of basement-hosted uranium deposits in the Patterson Lake corridor in the southwestern Athabasca Basin of Canada have brought vigorous exploration interest to the region. New lithostratigraphic constraints, geochronology and airborne geophysical surveys have dramatically improved the understanding of the host basement geology, warranting a re-examination of the remote predictive mapping and geophysical responses of the buried basement rocks. This study took a two-step approach to examine the regional basement geology and architecture. First, a mosaic of the long-wavelength response of potential field (gravity and magnetic) datasets was examined to divide the basement into regional domains based on bulk physical property variations. The interpretive geological model was then refined using textural and lineament analysis of new airborne gravity and magnetic datasets, geological drill hole logs and magnetic susceptibility measurements. The new basement map identifies and updates major features including a crustal-scale structure that separates the southern Tantato Domain from the newly defined eastern Taltson Domain. This structure may have played a role in localizing fluid flow in the Patterson Lake corridor, defining the spatial extents of structurally controlled buried felsic intrusions, and redefines the boundaries of the Taltson, Clearwater and Tantato Domains. In addition, the potential field enhancements delineated significant regional faults that controlled the geometry of Paleoproterozoic cover sequences and have implications for understanding the crustal architecture of the southern Rae Province. These new interpretations shed light on the tectonic history of the region to support on-going exploration activities and delineate regionally prospective areas in this understudied area of the Canadian Shield. Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

The synoptic analysis of coeval orogens and sedimentary basins is crucial to our understanding of Earth's crustal and surface processes. The Nonacho Group (Northwest Territories, Canada) is a major and yet enigmatic clastic sedimentary unit part of a basin system preserved over >2300 km along its original continental-sloping direction. This basin system records crustal sagging, relaxation, and flexure at similar to 2.3-1.9 Ga in the Rae Craton, one of the main building blocks of ancestral North America. Correlations between the Nonacho Group and coeval supracrustal assemblages in the Rae Craton has posed challenges. The group has been hitherto related to continental deposition at similar to 1.9 Ga, in a regime of sinistral strike-slip linked to the collision of the Rae and adjoining Slave cratons. We reappraise the Nonacho Group by means of facies analysis, stratigraphic logging, and palaeocurrentdata collection at key sites. Record of marine deposition is inferred based on the cumulative thickness of shoreface strata, an inference corroborated by sedimentological indicators such as wave- and bimodal-ripple, hummocky-cross, and flaser stratification. The alluvial to marine stratigraphy of the lower and middle parts of the Nonacho Group records basin inception and expansion in a regime of crustal relaxation. Topographic rejuvenation and deposition of younger alluvial to marine strata floored by an unconformity (upper Nonacho Group) followed in a regime of crustal flexure and renewed extension. These stratigraphic trends are tentatively related to broadly contemporaneous tectono-depositional events in the Rae Craton, including crustal thickening and ensuing extensional collapse of the bounding Thelon-Taltson and Snowbird orogens. By these means, we provide new testable hypotheses of a pan-continental tectono-sedimentary system developed during the Palaeoproterozoic amalgamation of the Canadian Shield.