U‐Pb Zircon Geochronology From the Northern Cordillera, Central Yukon, With Implications for Its Tectonic Assembly

The tectonic assembly of the Northern Cordillera is currently disputed and directly impacts Paleozoic‐to‐recent paleogeographic and plate tectonic reconstructions of North America. In this study, we present new U‐Pb zircon geochronology from the allochthonous Yukon‐Tanana terrane and the parautochthonous Cassiar terrane of the Northern Cordillera from south‐central Yukon, Canada. Our data provide new constraints for the assembly of the Northern Cordillera in this region. Metasedimentary samples from the Ingenika Group (Cassiar terrane) and the Snowcap and Finlayson assemblages (Yukon‐Tanana terrane) yielded detrital zircon age spectra that are comparable to known northwest Laurentia age spectra. One of our samples from the Snowcap assemblage yields a detrital zircon age spectrum that is anomalous for northwest Laurentia, but comparable to Early Paleozoic strata deposited in the Nevada‐Idaho‐Utah region. Zircon rim growth and Pb‐loss recorded by detrital zircon in the Snowcap assemblage and Ingenika Group samples record metamorphism at 370 ± 4 Ma and between 171 ± 5 and 135 ± 3 Ma. Late Devonian metamorphism and magmatism possibly corresponds to rifting of the Snowcap assemblage from the Laurentian margin. Middle Jurassic‐Early Cretaceous metamorphic zircon rim ages from the Cassiar terrane record metamorphism during collisions between the Intermontane superterrane (including the Yukon‐Tanana terrane) and Laurentia (Early to Middle Jurassic), and between the Insular superterrane and Laurentia (Middle to Late Jurassic). Our study suggests that collision between the Yukon‐Tanana terrane and the Laurentian margin began no earlier than ∼205 Ma.

nature of critical terrane relationships. Hence, a variety of contrasting tectonic models have been developed for the Northern Cordillera, which not only affect our general understanding of North American bedrock geology, but directly impact current models and understanding of Laurentian paleogeography, global tectonic plate networks, and the mantle record of subduction since the late Paleozoic (Clennett et al., 2020;Hildebrand, 2009;Johnston, 2008;Kemp et al., 2021;Monger & Gibson, 2019;Nelson et al., 2013;Pavlis et al., 2019;Sigloch & Mihalynuk, 2017; van Staal et al., 2018).
In this study, we present new zircon U-Pb geochronology and whole-rock geochemistry from the allochthonous, peri-Laurentian Yukon-Tanana terrane (Intermontane superterrane), and the parautochthonous Cassiar terrane (Laurentian margin) in the Dunite Peak region of central Yukon, Canada (Figures 1 and 2). Our results provide (a) new constraints for the detrital zircon provenance of (meta-)sedimentary units of the Yukon-Tanana and Cassiar terranes; and (b) new evidence for a Middle Jurassic-Early Cretaceous metamorphic event recorded by the Yukon-Tanana and Cassiar terranes in south-central Yukon. We interpret this Jurassic-Early Cretaceous metamorphic event as a record of sequential collisions of the Intermontane and Insular superterranes with the west Laurentian margin.

The Northern Cordillera of Yukon, British Columbia, and Eastern Alaska
In eastern Alaska, Yukon, western Northwest Territories, and British Columbia, autochthonous and parautochthonous units of the Northern Cordillera comprise a Neoproterozoic to early Paleozoic sedimentary and volcano-sedimentary stratigraphy deposited along the western passive margin of Laurentia. These stratigraphic units were subsequently deformed and displaced during multiple orogenic events and are now parautochthonous (Hadlari et al., 2012;Lane & Gehrels, 2014;Nelson et al., 2013;Tempelman-Kluit, 1976;Wheeler & McFeely, 1987). Basinal strata in Yukon, north British Columbia, and the Yukon-Tanana Upland in east Alaska were deposited in the Selwyn basin and Richardson and Kechika troughs; these basins were bound by regionally extensive platforms in north and south-central Yukon, western Northwest Territories, and northern British Columbia, including the Ogilvie, Mackenzie, Cassiar-McEvoy, and MacDonald platforms (e.g., Hadlari et al., 2012;Lane & Gehrels, 2014;Nelson et al., 2013). In south-central Yukon, parautochthonous platform strata of the Windermere Supergroup are assigned to the Cassiar terrane, which structurally underlies the Yukon-Tanana terrane (Figures 1  and 2; Colpron, Israel, Murphy, et al., 2016;Wheeler & McFeely, 1987).
The timing of accretion of the Yukon-Tanana terrane to Laurentia is poorly constrained; previous studies have proposed accretion during the Middle to Late Permian (Beranek & Mortensen, 2011;Colpron, Mortensen, et al., 2006;Mortensen, 1992b;Nelson et al., 2013), the latest Triassic-Early Jurassic (Evenchick et al., 2007;Gordey, 2002Gordey, , 2013Hansen & Dusel-Bacon, 1998;Nixon et al., 2020;Plint & Gordon, 1997;Stevens et al., 1996), or the Early Cretaceous (Hildebrand, 2009;Johnston, 2008). The identification of an Early to Middle Permian intra-oceanic arc within the Slide Mountain terrane led  and van Staal et al. (2018) to revise the history of terrane accretion in Yukon. Those authors proposed that the Middle Permian high-pressure collisional event recorded in the Yukon-Tanana terrane (the Klondike orogeny of Beranek & Mortensen, 2011) corresponded to its collision with the Dunite Peak intra-oceanic arc,  . Yellow dots show locations of samples analyzed in this study. Blue dots display previously published U-Pb zircon (with "z" notation) and monazite (with "m" notation) geochronology from de Keijzer et al. (1999), Gallagher (1999), and . Map location with respect to Yukon is shown in Figure 1.  The Dunite Peak region is located in the Big Salmon Range of central Yukon. We targeted this region because (a) it contains exposures of the Yukon-Tanana, Slide Mountain, and Cassiar terranes in close proximity; and (b) because the level of outcrop exposure and topographic relief provides a rare opportunity to observe large structural sections through these terranes and the structural and stratigraphic relationships within and between them (Figure 2;de Keijzer et al., 1999;Parsons et al., 2017Westberg, 2009;Westberg et al., 2009). From structural top to bottom, Dunite Peak is capped by the Dunite Peak ophiolite, which consists of variably serpentinized dunite, harzburgite and minor lherzolite structurally overlying a strongly sheared sequence of metamorphosed, mafic to intermediate plutonic, volcanic, and volcaniclastic rocks (Parsons et al., 2017. Whole-rock geochemical and Sm-Nd isotopic compositions of these rocks have juvenile, island arc tholeiite, and back-arc basin basalt signatures indicative of an intra-oceanic arc to back-arc setting . U-Pb zircon geochronology yielded ages of 265 ± 4 Ma from a gabbro sample  and 267 ± 10 Ma from a plagiogranite sample (de Keijzer et al., 2000; Figure 2), which are interpreted to reflect the timing of Dunite Peak arc magmatism.
The Dunite Peak ophiolite is structurally underlain by a sequence of variably deformed and mylonitized carbonaceous quartzite (metasedimentary protolith), marble, and shale, and rare pillow basalt and volcaniclastic rocks ( Figure 2). These units are assigned to the Devonian to Pennsylvanian Finlayson assemblage of the Yukon-Tanana terrane (Parsons et al., 2017. The Finlayson assemblage records continental and island arc magmatism and sedimentation after the Late Devonian rifting of Yukon-Tanana basement units from Laurentia (Colpron et al., 2007;Mortensen, 1992b;Tempelman-Kluit, 1976). The volcano-sedimentary rocks of the Finlayson assemblage are structurally underlain by marble with subordinate layers of garnet-amphibole calcareous schist and garnet-kyanite pelitic schist (Parsons et al., 2017;. These high-grade metasedimentary units are assigned to the pre-Late Devonian Snowcap assemblage of the Yukon-Tanana terrane (Figure 2), which comprises metamorphosed siliciclastic rocks that were deposited on the Laurentian margin prior to Late Devonian rifting from the margin (Colpron et al., 2007;Nelson et al., 2013). Approximately 15 km northwest of Dunite Peak, the Snowcap assemblage is intruded by augen orthogneiss of the Mississippian Simpson Range plutonic suite with a U-Pb zircon age of 331.5 ± 2 Ma (Figure 2; Colpron, Israel, & Friend, 2016;de Keijzer et al., 2000). Correlative Mississippian intrusions are also reported intruding the Snowcap Assemblage approximately 20 km south of Dunite Peak (Westberg, 2009;Westberg et al., 2009).

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Cassiar terrane sedimentary rocks are exposed ∼10 km east of Dunite Peak. They comprise marble, shale and quartzite with subordinate foliation-parallel meta-igneous layers ( Figure 2). The structural boundary between the Yukon-Tanana and Cassiar terranes is not exposed in the Dunite Peak region, but has been inferred by previous studies to strike north-south along the base of the intervening valley between mapped outcrops (Figure 2; Colpron, Israel, Murphy, et al., 2016). Elsewhere, this boundary is mapped as the Inconnu thrust  and the Tummel fault zone (Colpron et al., 2005). Available constraints suggest that this terrane boundary records ductile deformation sometime between the Middle Triassic to Early Jurassic and brittle deformation after the Jurassic (Colpron et al., 2005;Murphy et al., 2006).

Note.
Complete dataset is presented in Data Set S1.

Table 1 Summary of Geochronology Results
Zircon with complex histories provide unique challenges for data interpretation. Outliers from a single population may be the result of mixing of different intra-grain age domains during analysis, Pb-loss, high common Pb due to metamictization or alteration, or analysis of inclusions (e.g., Gehrels, 2014). The potential for mixed domains and Pb loss in each measured volume is greatly increased in grains that have experienced either pre-depositional metamorphism (e.g., McClelland et al., 2016) or post-depositional metamorphism (e.g., Gilotti et al., 2017). A high degree of discordance in a detrital zircon population is a defining characteristic of metasedimentary rocks, which results in an increased probability of altering the observed age distribution. Comparison of plots generated Ellipses represent ratios corrected for common Pb using the measured 204 Pb and 1σ analytical errors. Concordia ages (Ludwig, 1998) are reported with 2σ systematic errors (bold ellipses) and MSWD values for concordance and equivalence. Gray ellipses are excluded from Concordia age calculations (see text for explanation). (c)-(h) Major and trace element geochemistry of igneous samples 17RAY-AP015A1 (red triangles) and 17RAY-AP016C1 (orange pentagons). Rare earth element and high field strength element concentrations in (c) are normalized against normal mid-ocean-ridge basalt (N-MORB; Sun & McDonough, 1989). N-MORB V and Sc concentrations are based on Klein (2003). Fields for I-, S-, and A-type granites in (e) and (g) are based on Frost et al. (2001). Abbreviations. Alk, Alkaline; ORG, ocean ridge granite; syn-COLG, syn-collisional granite; VAG, volcanic arc granite; WPG, within-plate granite.
for each sample using concordant data only versus the discordance filters cited above are provided in Supporting Information S1 ( Figure S2) to evaluate the potential impact of the Pb loss. Although the peaks produced by the "concordant-only" data (light blue line) have lower amplitudes due to the lower number of dates in the concordant-only data, the ages and shapes of the dominant age peaks remain relatively unchanged with respect to the "discordance-filtered" data (dark blue line). Discordance-filtered age peaks presented in Figure 6 can therefore be used to make robust inferences of sediment provenance.  Doughty & Chamberlain, 1996;Doughty et al., 1998;Evans et al., 2000;Jones et al., 2015;Lewis et al., 2007;Link et al., 2016;Ross & Villeneuve, 2003;Sears et al., 1998;Stewart et al., 2010) and Southwest Laurentia Yavapai-Mazatzal Province (light green fill; Amato et al., 2008;Daniel et al., 2013;Doe et al., 2012Doe et al., , 2013Jessup et al., 2005;Jones & Connelly, 2006;Jones et al., 2009Jones et al., , 2011Jones et al., , 2015. Histogram bin width is 75 Myr. (j) Cumulative frequency plot for all samples, and reference spectra. Colored vertical bars behind histogram and probability distribution plots define distinct zircon age sources, based on Ross and Villeneuve (2003)   Data that does not pass the discordance filter criteria is not used in our evaluation of provenance but is incorporated into our discussion and interpretation of the timing of metamorphism. In addition, textural observations and compositional data are is used to guide our analysis and interpretation of metamorphic rims or domains further. Dates interpreted to reflect zircon growth during metamorphism are evaluated and grouped on the basis of concordance and the degree of overlap exhibited by the results. Concordia ages (Ludwig, 1998) are calculated  (Taylor & McLennan, 1985), (c) and (d) post-Archean Australian shale (Taylor & McLennan, 1985), and (e) and (f) total crustal majors (Rudnick & Gao, 2003).

Facies B -Late Neoproterozoic-Cambrian
from metamorphic rim data using IsoplotR (Vermeesch, 2018). Outlier rim dates with high common Pb, high uncertainty, or discordance are also considered (but not included in Concordia ages), where metamorphism may be responsible for those outliers.
Figures 3a, 3b, 4, 5,and 6 were plotted using Isoplot 4.1 (Ludwig, 2012), IsoplotR (Vermeesch, 2018), and Age-CalcML 1.42 (Sundell et al., 2021). Results and key interpretations are summarized in Table 1. CL-images of zircon are presented in Figure 5 and Supporting Information S1 ( Figure S1). Analytical procedures for SIMS, LA-ICPMS, and whole-rock geochemical analyses are described in Supporting Information S1. The complete SIMS, LA-ICPMS, and whole-rock geochemical datasets are presented in Data Set S1. Sample 17RAY-AP015A1 yielded subhedral to euhedral zircon texturally ranging from well-developed oscillatory zoning to low-U core and high-U rim textures. Spot analyses were conducted on 12 zircon grains. A single measurement of a CL-bright, low U (66 ppm) core (spot 12.1) gave a 206 Pb/ 238 U date of 1,110 ± 20 Ma (1σ analytical error) that is interpreted to reflect the age of an inherited component in the sample. The remaining analyses targeted CL-dark domains and gave 206 Pb/ 238 U dates of 137 ± 2-110 ± 3 Ma (1σ analytical error). The oldest date in this range (spot 12.1, 137 ± 2 Ma) was from measurement of an inner rim that overgrows a CL-bright core and surrounded by a CL-dark rim. This date is a clear outlier from the younger population and is interpreted as a mixed age or older metamorphic rim on a xenocryst based on the lower U (239 ppm), low Th/U (0.004), and lighter CL response. The remaining dates (123 ± 4-110 ± 3 Ma), with higher U (786-2,562 ppm) and low Th/U (0.01-0.10) are interpreted to record igneous zircon growth and define a Concordia age of 116 ± 2 Ma (2σ systematic error; MSWD = 1.9 for concordance and equivalence; n = 10) which we interpret as the magmatic crystallization age of the undeformed biotite-monzogranite sample 17RAY-AP015A1 ( Figure 3a).

17RAY-AP016C1
Sample 17RAY-AP016C1 is a foliated, feldspar augen-muscovite-biotite-schist ( Figure 3b) collected from a ∼5 m thick layer within a foliated marble (sample 17RAY-AP016A2, see below). At this outcrop (Figure 2), compositional layering and foliation are parallel. The outcrop is mapped as part of the Ingenika Group (Cassiar terrane, Figure 2; Colpron, Israel, Murphy, et al., 2016). The sample of augen schist is enriched in light rare earth elements (LREEs) and light HFSEs by an order of magnitude relative to heavy rare earth element (HREEs) and heavy HFSEs (Figure 3c). HREE and heavy HFSE concentrations are slightly elevated with respect to N-MORB concentrations ( Figure 3c). Based on sample lithology and whole rock geochemistry, combined with its unimodal population of zircon dates, and presence of recrystallized feldspar augen, we interpret sample 17RAY-AP016C1 as a metamorphosed monzogranite. Relative concentrations of FeO, MgO, and alkaline content, and depletion in Eu, Ti, V, and Sc are indicative of a peraluminous, calc-alkaline, and S-type granite (Figures 3d-3h).
Sample 17RAY-AP016C1 yielded subhedral to euhedral zircon with well-developed oscillatory zoning in entire grains or in rims that overgrow cores. Spot analyses targeting the oscillatory zoned domains were conducted on 11 zircon grains. Ten measurements produce a cluster of 206 Pb/ 238 U dates ranging between 392 ± 5 and 356 ± 7 Ma (1σ analytical error; Figure 3b). These 10 measurements define a Concordia age of 372 ± 5 Ma (2σ systematic error; MSWD = 2.8 for concordance and equivalence, n = 10) and have U concentrations and Th/U ratios of 144-772 ppm and 0.06-0.40, respectively. Spot 3.1 gave a young 206 Pb/ 238 U date (267 ± 2 Ma; 1σ analytical error) that combined with high U (1,830 ppm) and significant common Pb correction suggests the analysis is an outlier from the main population due to real age variation, Pb-loss, or presence of inclusions. We interpret the Concordia age as the magmatic crystallization age, which provides a minimum depositional age for the surrounding marble layers (sample 17RAY-AP016A2).

16RAY-AP077B1
Sample 16RAY-AP077B1 (Figures 4e and 4f) is a strongly foliated, garnet-biotite-schist with rare kyanite grains, collected from a 0.5 m thick bed within marble; this outcrop is currently assigned to the Snowcap assemblage of the Yukon-Tanana terrane ( Figure 2). The zircon population recovered from this sample includes subhedral, equant to elongate grains, and subrounded grain fragments (Figure 5a). Most grains exhibit clear core rim relationships with oscillatory-zoned cores overgrown by 1-20 μm thick CL-bright rims (Figure 5a). Spot analyses were conducted on 348 zircon grains: 310 analyses targeted homogeneous core domains and 38 analyses attempted to target CL-bright rim domains. A total of 208 measurements (60%) do not pass the discordance and uncertainty filters for detrital ages (Figures 4e and 4f (Figures 4e and 4f). On the basis of CL-textures, Th/U and evidence to isotopic disturbance, we interpret a relatively young (Mesozoic) post-depositional metamorphic history for this sample.

17RAY-AP014A2
Sample 17RAY-AP014A2 (Figures 4c and 4d) is a foliated, biotite-schist with rare sillimanite collected from an outcrop presently mapped as the Ingenika Group (Cassiar terrane, Figure 2). Sample 17RAY-AP014A2 yielded rounded equant to elongate zircon with oscillatory to patchy zoning and thin (1-10 μm) CL-bright rims. Oscillatory zoning in equant grains is commonly truncated at the grain boundary which is overgrown by a CL-bright rim. Spot analyses on 320 zircon grains (including 20 dates measured via SIMS) generated a strongly discordant array of data; 184 of the measurements (58%) do not pass the discordance and uncertainty filters for detrital ages (Figures 4c and 4d) Figure 6b). The youngest detrital zircon core age of 568 ± 10 Ma (2σ systematic error) is interpreted as the maximum depositional age of this sample, while recognizing the potential effects of the pronounced degree of Pb loss observed in the detrital zircon population and the relatively high uncertainty (13%, 2σ analytical error) of the measured 207 Pb/ 206 Pb ratio for this analysis.
Spot analyses specifically targeting CL-bright zircon rims (n = 12) produced concordant and discordant results with most 206 Pb/ 238 U dates ranging from Late Silurian to Early Cretaceous and U and Th/U values of 72-3,066 ppm and 0.002-3.3, respectively. Four additional SIMS analyses targeting CL rim domains produced older discordant data that is interpreted to reflect analysis of mixed domains or Pb loss. A group of four concordant ages with low Th/U (0.01-0.1) define a Concordia age of 370 ± 4 Ma (2σ systematic error; MSWD = 2.5 for concordance and equivalence; Figure 5d). A single concordant SIMS rim analysis with a very low Th/U (0.003) yielded a 206 Pb/ 238 U age of 134 ± 5 Ma (2σ systematic error; Figure 5d) that when combined with two slightly discordant, low Th/U (0.002-0.003) LAICPMS analyses yields a 206 Pb/ 238 U weighted mean age of 130 ± 4 Ma (2σ systematic error; MSWD = 3.0). Discordant zircon in this sample produce arrays with poorly defined lower intercepts that converge upon the Late Devonian to Early Cretaceous rim ages (Figures 4c and 4d). On the basis of textural evidence for rim growth and low Th/U ratios we interpret these concordant and discordant rim dates as a record of zircon rim growth and Pb-loss during Late Devonian and Early Cretaceous metamorphism.

17RAY-AP016A2
Sample 17RAY-AP016A2 (Figures 4a and 4b) is a weakly foliated marble with minor grains of quartz and mica collected from an outcrop of marble with sub-meter thick beds of muscovite-biotite schist (e.g., sample 17RAY-AP016C1), which is mapped as the Ingenika Group (Cassiar terrane; Figure 2). Sample 17RAY-AP016A2 zircon are subrounded, subhedral, equant to elongate grains Most grains have well-defined core-rim relationships with oscillatory zoned cores overgrown by 1-30 μm thick CL-bright rims (Figure 5b). Spot analyses of 313 zircon grains produced 177 analyses (57%) that do not pass the discordance and uncertainty filters for detrital ages (Figures 4a and 4b). The remaining 135 grains yielded interpreted detrital zircon ages ranging between the Mesoarchean to early Paleoproterozoic, middle to late Paleoproterozoic, early Mesoproterozoic, and early to late Neoproterozoic (Figure 6a). Precambrian zircon have concentrations of U ranging between 37 and 983 ppm and show no correlation with age. Ratios of Th/U range between 0.31 and 1.52 for Mesoarchean to Siderian zircon and 0.10-1.62 for latest Rhyacian to Ediacaran zircon. The probability distribution of Precambrian detrital zircon ages produces statistically significant clusters of Neoarchean to Siderian, and Orosirian to Statherian ages, with age-peaks of 2,664 Ma (n = 10), 2,567 Ma (n = 6), 2,506 Ma (n = 6), 1,850 Ma (n = 18), 1,765 Ma (n = 36), and 1,688 Ma (n = 8; Figure 6a). We interpret the 616 ± 21 Ma (2σ systematic error) detrital zircon age as a maximum depositional age for sample 17RAY-AP016A2, whereas the igneous crystallization age of 372 ± 5 Ma (2σ systematic error) from sample 17RAY-AP016C1 provides a minimum depositional age.
Analyses that targeted CL-bright rims and domains within grains yielded Middle Jurassic to Early Cretaceous dates (n = 19) accompanied by U concentrations of 19-699 ppm and Th/U ratios of <0.009, except for three outliers with Th/U ratios of 0.01-0.42. None of the rim dates pass the discordance and uncertainty filters applied for provenance analysis of detrital ages, but are interpreted here instead to record metamorphic rim growth on the basis of their CL response showing clear core/rim textures, low U concentrations, and low Th/U. Nine of the rim dates are concordant and the remaining 10 discordant dates define an array consistent with the combined effects of analysis of mixed metamorphic and igneous domains, Pb loss, and common Pb (Figure 5e). The concordant dates produce a spread of 206 Pb/ 238 U ages between 171 ± 5 and 135 ± 3 Ma (2σ analytical error; Figure 5e). The five concordant Jurassic ages define a Concordia age of 166 ± 2 Ma (2σ systematic error; MSWD = 4.6 for concordance and equivalence). The four concordant Cretaceous grains define a Concordia 206 Pb/ 238 U age of 139 ± 2 Ma (2σ systematic error; MSWD = 3.2 for concordance and equivalence). Discordant dates from the detrital population in this sample produce arrays with lower intercepts that converge upon these Jurassic-Early Cretaceous Concordia ages (Figures 4a and 4b). We interpret the Jurassic and Early Cretaceous rim ages to represent either one or two phases of post-depositional metamorphism (Figure 5e).

17RAY-AP017A1
Sample 17RAY-AP017A1 ( Figure 4h) is a foliated white quartzite collected from metasedimentary unit MMS2, structurally below the Dunite Peak ophiolite (Figure 2). This unit was assigned to the Finlayson assemblage of the Yukon-Tanana terrane by Parsons et al. (2017) and . The sample yielded a population of rounded, spherical to ellipsoidal zircon. CL images show zircon with bright cores and thin dark rims, plus cross-cutting CL-dark bands following fractures (Figure 5c). Well-developed oscillatory zoning is common and can be traced crossing from bright cores, through thin dark rims, to the boundaries of round grains (Figure 5c). Based on the continuity of zonation from core to rim and grain boundary, we interpret the dark rims and internal domains along cracks as a record of post-deposition fluid-mediated element diffusion, which occurred without significant metamorphic rim growth.
Spot analyses were conducted on 314 zircon grains; 44 of these measurements (14%) do not pass the discordance and uncertainty filters for detrital ages (Figures 4h and 6e). The remaining 270 grains yielded interpreted detrital zircon ages ranging between the latest Mesoarchean to early Paleoproterozoic, middle Paleoproterozoic to early Mesoproterozoic, and middle Mesoproterozoic to earliest Neoproterozoic (Figure 6e). Zircon accepted for provenance evaluation have concentrations of U and Th/U ratios of 13-991 ppm and 0.01-1.9, respectively, and show no correlation with age; four outliers have Th/U ratios of 2.0-3.6.
Age distributions show clusters of latest Mesoarchean to Neoarchean, latest Siderian to earliest Rhyacian, late Rhyacian, Orosirian to Statherian, and late Stenian to earliest Tonian ages, with age peaks of 2,821 Ma (n = 4), 2,697 Ma (n = 9), 2,642 Ma (n = 11), 2,585 Ma (n = 4), 2,541 (n = 10), 2,285 Ma (n = 6), 2,067 Ma (n = 19), 1,913 Ma (n = 24), 1,828 Ma (n = 117), 1,720 Ma (n = 5), 1,651 Ma (n = 7), and 1,023 Ma (n = 5; Figure 6e). We interpret all of these zircon to be of detrital origin and use the youngest single grain age of 988 ± 18 Ma (2σ systematic error) as the maximum depositional age of this sample. Discordant zircon produce a poorly defined lower intercept of <200 Ma (Figure 4h).  (Figure 7). Specifically, sample 17RAY-AP017A1 is characterized by very high SiO 2 , very low Al 2 O 3 , and high Zr concentrations suggesting that the parent sediment was largely composed of quartz with abundant zircon (Figure 7). This may be indicative of rogeny transport, or reworking of rogeny sediments. Sample 16RAY-AP077B1 is characterized by high Zr/Sc and Th/Sc ratios indicative of weathering and sorting processes, however it has low SiO 2 and high MgO, FeO, Ni, and V (Figure 7). This sample may be a mixture of reworked continentally derived sediment and sediment derived primarily from one or more mafic volcanic sources.

Igneous Samples
17RAY-AP015A1 is an undeformed biotite-monzogranite intruded within the Ingenika Group of the Cassiar terrane; it has a crystallization age of 116 ± 2 Ma (2σ systematic error; Figure 3a), and a peraluminous geochemical composition (Figures 3c-3h). This sample is comparable in age and composition to local intrusions within the Cassiar and Yukon-Tanana terranes including the d'Abbadie pluton, Last Peak granite (Figure 2), Dycer Creek Stock, and the Big Salmon Batholith (Colpron, Israel, & Friend,2016;Colpron, Israel, Murphy, et al., 2016;de Keijzer et al., 2000;Gallagher, 1999;Westberg et al., 2009). Plutonic rocks of this age and composition are common across south-central Yukon, and are assigned to the Cassiar magmatic suite (117-104 Ma, Colpron, Israel, & Friend, 2016). These and other Early to Late Cretaceous intrusions are typically associated with crustal thickening and subsequent collapse of the Cordilleran rogeny in Alaska, Yukon and northern British Columbia (e.g., Hart et al., 2004;Mair et al., 2006). This is consistent with the low Th/U ratios, high U concentrations and abundant xenocrysts reported from this sample, which may be explained by zircon growth during incongruent crustal anatexis.
17RAY-AP016C1 is a foliated and metamorphosed monzogranite within the Ingenika Group of the Cassiar terrane; it has a crystallization age of 372 ± 5 Ma (2σ systematic error; Figure 3b) and a peraluminous geochemical composition (Figures 3c-3h). Volcanic and plutonic rocks of similar age to 17RAY-AP016C1 are reported elsewhere in south-central Yukon from the Seagull group, which is associated with continental rifting and intra-plate magmatism (Beranek et al., 2016;Tempelman-Kluit, 2012), and the Earn Group, which is associated with backarc rifting and subduction (Campbell, 1967;Cobbett et al., 2020). The peraluminous composition of sample 17RAY-AP016C1 (Figures 3c-3h) is compatible with both of those settings.

Mesozoic Metamorphism
Detrital zircon in samples 16RAY-077B1 (Yukon-Tanana terrane), 17RAY-AP016A2, and 17RAY-AP014A2 (Cassiar terrane) record evidence of metamorphism during the Late Devonian and the Middle Jurassic to Early Cretaceous. In sample 17RAY-AP014A2, CL-bright zircon rims with low Th/U ratios yielded a Concordia age of 370 ± 4 Ma (2σ systematic error; MSWD = 2.5; n = 4; Figure 5d), which we interpret as a record of metamorphism which accompanied monzogranite emplacement (17RAY-AP016C1). A single concordant date from a metamorphic rim with a very low Th/U ratio yielded a 206 Pb/ 238 U age of 134 ± 5 Ma (Figure 5d), which is comparable to Early Cretaceous metamorphic zircon rim ages reported from 17RAY-AP016A2 (Figure 8b). Discordant zircon in sample 17RAY-AP014A2 produce arrays with poorly defined lower intercepts that converge upon the Late Devonian to Early Cretaceous metamorphic ages (Figures 4c and 4d).
Our record of Middle Jurassic-Early Cretaceous metamorphism recorded by the Cassiar and Yukon-Tanana terranes in the Dunite Peak region (Figure 8b) is comparable to preliminary U-Pb monazite dates reported from the Yukon-Tanana terrane in the Mendocina Creek area, ∼10 km south of Dunite Peak (Figure 8b; Westberg, 2010). Westberg (2010) analyzed two samples of Snowcap assemblage from the Mendocina Creek area that yielded U-Pb monazite singe-grain dates of 192 ± 26, 179 ± 9, 152 ± 18, and 143 ± 8-106 ± 8 Ma (n = 18; Figure 8b). The mid-Cretaceous monazite dates may indicate that metamorphism continued after our youngest metamorphic zircon age (135 ± 3 Ma; 2σ systematic error) at conditions not conducive to metamorphic zircon growth. We note that these younger monazite dates are consistent with two CL-bright zircon rim dates from sample 16RAY-077B1 that give 206 Pb/ 238 U dates of 95 ± 2 and 119 ± 2 Ma (2σ systematic error), and low Th/U. However, high common Pb and very large uncertainty in measured 207 Pb/ 206 Pb ratios from these two zircon dates means that we cannot be certain of their origin.
Collectively these data indicate a regionally significant period of metamorphism of the parautochthonous Laurentian margin and Yukon-Tanana terrane in Yukon from the Middle Jurassic to Early Cretaceous (e.g., Staples et al., 2016). We explore the regional tectonic significance of this metamorphic event in our discussion below (Section 6.2).  Saylor et al., 2018). Statistical similarity between datasets is proportional to relative distances between data points. Solid-and dashedlined arrows point to closest and second-closest neighbors, respectively (i.e., lowest D values). A Sheperd plot showing the goodness of fit is presented in Supporting Information S1 ( Figure S3). Similarity matrices for D and the cross-correlation coefficient, R 2 , are presented in Data Set S1. (b) U-Pb zircon metamorphic rim dates from samples 17RAY-AP016A2 (Cassiar-blue), 17RAY-AP014A2 (Cassiar-red), and 16RAY-AP077B1 (Yukon-Tananayellow), with Concordia ages of 166 ± 2 and 139 ± 2 Ma (2σ systematic error) calculated from concordant ages in 17RAY-AP016A2. Large data points are interpreted as robust records of zircon growth during Middle Jurassic-Early Cretaceous metamorphism. Small data points are consistent with zircon growth during Middle Jurassic-Early Cretaceous metamorphism, but other explanations for these data are also possible (e.g., Pb loss or high common Pb). U-Pb monazite dates of Westberg (2010)

Metamorphic dates and interpreted ages (a) (b)
In contrast to the metamorphic overprint recorded by the Snowcap assemblage in the Dunite Peak region and neighboring areas, detrital zircon from our Finlayson assemblage sample 17RAY-AP017A1 are mostly concordant (86% of measurements), and show only minor evidence for Mesozoic Pb-loss, as indicated by CL-dark domains along cracks and grain boundaries, and a poorly defined lower intercept of <200 Ma (Figure 4h). Zircon in this sample show no textural evidence of post-depositional growth or recrystallization (Figure 5c). These differences may indicate that in the Dunite Peak region, a metamorphic discontinuity separates the Finlayson assemblage from the structurally underlying Snowcap assemblage.

Detrital Zircon Provenance
In this section, we consider the provenance of our detrital zircon samples through comparison with regionally distinct pre-Mesozoic detrital zircon signatures reported from north Laurentia (Figures 6f and 6g; Hadlari et al., 2012Hadlari et al., , 2015, and west to southwest Laurentia (Jones et al., 2015;Matthews et al., 2018;Figures 6h and 6i). This includes a visual statistical comparison of datasets using multi-dimensional scaling of the Kolmogorov-Smirnov (K-S) statistic, D (Figure 8a), which describes the maximum difference between the cumulative distribution functions of two samples (D = 0-1, increasing with dissimilarity; e.g., Saylor & Sundell, 2016). Statistical comparison using the cross-correlation coefficient, R 2 (e.g., Saylor & Sundell, 2016), which describes the similarity in amplitude and shape of normalized probability age peaks of two samples (R 2 = 0-1, increasing with similarity), was also conducted, and shows similar results to the K-S statistic (D; note that D and R 2 have an approximately inverse relationship). Values of D and R 2 are quoted below and presented in similarity matrices in Data Set S1 (calculated using Dzstats2.30; Saylor & Sundell, 2016).

Sample 17RAY-AP017A1 (North Laurentia Type 1 Spectrum)
The detrital zircon signature of Finlayson assemblage sample 17RAY-AP017A1 (Figure 6e) is typical of published detrital zircon datasets from the Yukon-Tanana terrane (Cleven et al., 2019). Statistically, it is most comparable to the North Laurentia Type 1 spectrum (D = 0.24, R 2 = 0.63; Figure 8a), owing to its large peak of 1.8-9 Ga ages and lack of Mesoproterozoic or younger age peaks (Figures 6e and 6g). The tectonostratigraphic framework for the Yukon-Tanana terrane  assumes that the Finlayson assemblage was deposited after the Yukon-Tanana terrane rifted from northwest Laurentian. The North Laurentia Type 1 spectrum of sample 17RAY-AP017A1 is therefore explained as reworked peri-Laurentian sedimentary basement rocks of the Snowcap assemblage. However, differences between our detrital zircon samples suggest that Finlayson assemblage sample 17RAY-AP017A1 was not sourced from the structurally underlying section of Snowcap assemblage represented by sample 16RAY-AP077B1 (D = 0.65, R 2 = 0.11). This is consistent with differences in the metamorphic assembalges and whole-rock geochemistry of all these samples.

Sample 17RAY-AP016A2 (Ambiguous Provenance)
The detrital zircon signature of Cassiar terrane sample 17RAY-AP016A2 is characterized by 1.65-1.9 and 2.3-2.7 Ga zircon ages (Figure 6a). Whereas this spread of ages is comparable to the North Laurentia Type 1 spectrum, the age peaks differ; sample 17RAY-AP016A2 has a maximum peak at 1.75-1.80 Ga (Figure 6a), whereas the Type 1 spectrum has a maximum peak at 1.80-1.95 Ga (Figure 6g). Additionally, sample 17RAY-AP016A2 has a lack of detrital zircon ages between ∼2.0 and 2.3 Ga, which are observed in the North Laurentia Type 1 spectrum, and samples 17RAY-AP012B1, 17RAY-AP014A2, and 17RAY-AP017A1. Likewise, a small peak of 1.3-1.4 Ga zircon and absence of 1.0-1.3 Ga zircon in sample 17RAY-AP016A2 is anomalous with respect to the North Laurentia spectra, but typical of the Yavapai region. Two Neoproterozoic zircon ages are of comparable age to igneous assemblages found in the Windermere Supergroup and elsewhere across western and northern Laurentia (e.g., Cox et al., 2018;Gordey, 2013;Macdonald et al., 2018;Pigage & Mortensen, 2004;Sandeman et al., 2014;Yonkee et al., 2014).

Sample 16RAY-AP077B1 (West Laurentia spectrum)
Snowcap assemblage sample 16RAY-AP077B1 (Figure 6c) has a detrital zircon age spectrum that is distinct from other samples reported here, and previously, from the Yukon-Tanana or Cassiar terranes (Figure 8a Fanning & Link, 2004;Gaschnig et al., 2013;Keeley et al., 2013;Linde et al., 2017;Lund et al., 2003Lund et al., , 2010Schmitz, 2011;Yonkee et al., 2014). As such, we argue that the detrital zircon spectrum in sample 16RAY-AP077B1 is most easily explained by sediment sourced from the Nevada-Idaho-Utah region. Piercey and Colpron (2009) proposed that the siliciclastic stratigraphic units of the Snowcap assemblage represent a continental fragment rifted from northwest Laurentia. If this were correct for the whole of the Snowcap assemblage, then the detrital zircon spectrum of sample 16RAY-AP077B1 would require a long-range drainage system that transported sediment ∼1,500 to 2,500 km northwards from the Nevada-Idaho-Utah region to NW Laurentia, without being contaminated by more local sediment sources. This is at odds with the lack of other sedimentary units with equivalent detrital zircon spectra reported from northwest Laurentia (e.g., Cleven et al., 2019;Matthews et al., 2018;McMechan et al., 2017).

Implications of West Laurentia Zircon Spectra in the Yukon-Tanana Terrane
Alternatively, sample 16RAY-AP077B1 may represent a portion of Snowcap assemblage that was deposited in or close to the Nevada-Idaho-Utah region. This is consistent with the low SiO 2 and high MgO, FeO, Ni, and V geochemical composition of sample 16RAY-AP077B1, which is suggestive of a sediment component sourced from a local mafic igneous source (e.g., the Yavapai province and Windermere Supergroup). This hypothesis, which is similar to the interpretations of Wernicke and Klepacki (1988), implies that at least some parts of the Yukon-Tanana terrane derived from the west Laurentian margin, adjacent to the Nevada-Idaho-Utah region. We note that the large volume of carbonate sedimentary units mapped across the Dunite Peak region (see also Westberg et al., 2009) is atypical for the Snowcap assemblage and may highlight a distinct subterrane that is allochthonous with respect to the rest of the Yukon-Tanana terrane peri-Laurentian basement (e.g., Ryan et al., 2014;van Staal et al., 2018).
Lastly, we note that prior to our study, the presence of 1.3-1.8 Ga zircon in Cretaceous strata of southern Alaska and British Columbia, led some authors to propose that those units were deposited on the southwest Laurentian margin, before being structurally translated northwards to their present-day location (e.g., Garver & Davidson, 2015;Matthews et al., 2017). Our new data imply that the basement strata of Yukon-Tanana terrane may have acted as a previously unrecognized source of 1.3-1.8 Ga zircon to NW Laurentia, following its accretion to Laurentia in the Mesozoic. At present, the significance of this source for the post-Paleozoic zircon provenance of Laurentia is unclear due to the scarcity of other Yukon-Tanana terrane samples with high concentrations of 1.3-1.8 Ga zircon.

Metamorphic Events During the Tectonic Evolution of the Northern Cordillera
Our new constraints from the Dunite Peak region provide evidence for a Late Devonian metamorphic and magmatic event recorded by the Cassiar terrane (17RAY-AP014A2 and 17RAY-AP016C1; Figures 3b and 5d), and a Middle Jurassic-Early Cretaceous metamorphic event (Figures 5e and 8b) recorded by both the Cassiar terrane (17RAY-AP014A2 and 17RAY-AP016A1) and Yukon-Tanana terrane (16RAY-AP077B1). We interpret the significance of these results for the tectonic evolution of the Northern Cordillera as follows:
After Late Devonian-Early Mississippian rifting, an episode of deformation, high-pressure metamorphism, and magmatism was recorded by the Yukon-Tanana terrane during the Middle to Late Permian (Beranek & Mortensen, 2011;Berman et al., 2007;Erdmer et al., 1998;Gilotti et al., 2017;Mortensen, 1992b). Previous models interpreted this event as a record of Middle to Late Permian collision between the Yukon-Tanana terrane and Laurentia (Beranek & Mortensen, 2011;Mortensen, 1992b;Nelson et al., 2013). However, as noted by , van Staal et al. (2018), , and Zagorevski and , (a) there is no corresponding record of Permian collision in northwest Laurentian units that can be matched with the observations from the Yukon-Tanana terrane; (b) geochemical signatures of Middle to Late Permian magmatism on the Yukon-Tanana terrane (Klondike assemblage) are best explained by lithospheric extension, rather than arc magmatism; and (c) the arrangement of Permian suprasubduction ophiolites in the Slide Mountain terrane places the Yukon-Tanan terrane in a lower plate position during Permian collision. Consequently, those authors interpreted the Middle to Late Permian event as a record of collision between the Yukon-Tanana terrane and the Dunite Peak intra-oceanic arc van Staal et al., 2018). We have implemented the interpretations of  and van Staal et al. (2018) for pre-Jurassic events into our tectonic synthesis (Figure 9a), as they are most consistent with our independently constrained model for the Jurassic-Early Cretaceous evolution of the Northern Cordillera.
The 10-20 Myr gap between the earliest records of collision reported from the Yukon-Tanana terrane and the parautochthonous Laurentian units can be explained by two alternative models (Figures 9b-9d): In Model I, metamorphism and deformation of the Yukon-Tanana terrane between ∼205 and 180 Ma signifies the onset of collision with the leading edge of the Laurentian margin (Model I- Figure 9b), now located in the subsurface, several 100 km west of the eastern edge of the Yukon-Tanana terrane (e.g., Calvert et al., 2017;Cook et al., 2004). In this model, records of collision recorded by parautochthonous Laurentian margin units between ∼205 and 180 Ma must remain buried in the subsurface, west of the present-day contact between the Yukon-Tanana terrane and the Laurentian margin ("C"-Figures 9b-9e).
Furthermore, investigation of Models I and II is required in order to precisely constrain the timing of collision between the Yukon-Tanana terrane and the Laurentian margin. This is hindered by a lack of definitive evidence from the sedimentary and accretionary records, needed to constrain the timing of this collision. For example, the Slide Mountain terrane was originally interpreted as the accretionary record of Permian collision between the Yukon-Tanana terrane and Laurentia (e.g., Mortensen, 1992aMortensen, , 1992b. However, recent studies demonstrated that the Slide Mountain terrane includes Permian upper plate, intra-oceanic arc assemblages, and must comprise rocks from two or more oceanic basins van Staal et al., 2018;. Similarly, the Early to Late Triassic Jones Lake Formation has been interpreted as an overlap assemblage deposited on, and post-dating collision between, Slide Mountain terrane and Parautochthonous Laurentia (Beranek et al., 2010;Beranek & Mortensen, 2011). However,  highlighted significant differences in the detrital zircon content of Triassic samples over the Slide Mountain terrane (e.g., unimodal Mesozoic or bimodal Paleozoic and Mesozoic zircon age populations), verses Triassic samples overlying Parautochthonous Laurentia (e.g., Archean to Mesozoic zircon populations). Furthermore,  argued that the detrital signatures of Triassic strata on the Laurentia margin may be explained by a dominantly Laurentian sedimentary source with minor contributions from the Stikine/Quesnel arc and are at best, consistent with, but not definitive evidence for, Late Triassic collision between the Intermontane superterrane and Laurentia. These issues remain unresolved and require further assessment. Given the present-day thrust-slice structure of the Northern Cordillera, the original suture zone and accretionary record of the Intermontane-Laurentia collision may remain buried beneath the Intermontane or Insular superterranes ("C" -Figures 9b-9e).

Conclusions
This study presents new zircon U-Pb geochronology from the allochthonous Yukon-Tanana terrane and the parautochthonous Cassiar terrane from the Dunite Peak region of south-central Yukon. The key findings from our results are as follows: 1. An undeformed, peraluminous, calc-alkaline biotite-monzogranite intruded within the Cassiar terrane (sample 17RAY-AP015A1), yielded a crystallization age of 116 ± 2 Ma (2σ systematic error). We correlate this intrusion with the Cassiar magmatic suite (117-104 Ma), which is commonly observed intruding both the Yukon-Tanana and Cassiar terranes in Yukon, and probably corresponds to a late-orogenic phase of extension, recorded across the Northern Cordillera. 2. A foliated, peraluminous, calc-alkaline monzogranite schist within the Cassiar terrane (sample 17RAY-AP016C1) yielded a crystallization age of 372 ± 5 Ma (2σ systematic error). Based on similarities in age and composition, this metaigneous rock correlates with igneous assemblages from either the Earn Group or the Seagull group, and was probably emplaced during rifting of siliciclastic basement units of the Yukon-Tanana terrane from the Laurentian margin. 3. Detrital zircon spectra from Finlayson assemblage sample 17RAY-AP017A1, Snowcap assemblage sample 17RAY-AP012B1 (Yukon Tanana terrane), and Igenika Group sample 17RAY-AP014A2 (Cassiar terrane) are typical of northwest Laurentia. Sample 17RAY-AP017A1 is comparable to the North Laurentia Type 1 spectrum of Hadlari et al. (2012;equivalent to Lineage A of Lane & Gehrels, 2014), whereas samples 17RAY-AP012B1 and 17RAY-AP014A2 are comparable to the North Laurentia mixed Type 1 and Type 2 spectrum of Hadlari et al. (2012; (equivalent to the "hybrid lineage" of Lane & Gehrels, 2014) Ingenika Group sample 17RAY-AP016A2 (Cassiar terrane) has an ambiguous detrital zircon spectrum, with similarities to both north and west Laurentian reference spectra. Potential source regions include the Swift Current anorogenic province and Trans-Hudson orogen, the Belt-Purcell Basin, and the Yavapai province. The detrital zircon spectrum from Snowcap assemblage sample 16RAY-AP077B1 (Yukon Tanana terrane) is anomalous to northwest Laurentia. Zircon ages in this sample are indicative of a sediment sourced from the Nevada-Idaho-Utah region, implying either (a) long range transport of sediment from Nevada-Idaho-Utah to northwest Laurentia, without contamination from more locally sourced sediment; or (b) sample 16RAY-AP077B1 and its outcrop of Snowcap assemblage in the Dunite Peak region were deposited in or close to the Nevada-Idaho-Utah region before rifting from the west Laurentian margin during the Devonian. The latter hypothesis implies that the Yukon-Tanana terrane comprises distinct sub-terranes with different paleogeographic origins that should be investigated further. Additionally, our data imply that the Yukon-Tanana terrane provided a previously unrecognized and potentially important source of Mesoproterozoic zircon to Mesozoic and younger units of NW Laurentia. 4. Discordant zircon and concordant metamorphic zircon rims in Ingenika Group sample 17RAY-AP014A2 (Cassiar terrane) records Pb-loss and zircon recrystallization during Late Devonian metamorphism. Four measurements produce a Concordia age of 370 ± 4 Ma (2σ systematic error), which overlaps with magmatic age of our monzogranite sample 17RAY-AP016C1 (372 ± 5 Ma; 2σ systematic error) from the Cassiar terrane. We interpret this magmatic and metamorphic event as a record of rifting of Snowcap assemblage units (Yukon-Tanana terrane) from the Laurentian margin. 5. Discordant zircon and concordant metamorphic zircon rims in Snowcap assemblage sample 16RAY-AP077B1 (Yukon-Tanana terrane) and Ingenika Group samples 17RAY-AP014A2 and 17RAY-AP016A2 (Cassiar terrane) record Pb-loss and zircon recrystallization during metamorphism between 171 ± 5 and 135 ± 3 Ma. These data produce Concordia ages of 166 ± 2 and 139 ± 2 Ma (2σ systematic error). Combined with similar ages of metamorphism reported elsewhere in Yukon, eastern and southern Alaska, and British Columbia, these data highlight a regionally significant period of metamorphism of the parautochthonous Laurentian margin from the Middle Jurassic to Early Cretaceous. We interpret this metamorphism as a combined record of: (a) Early to Middle Jurassic collision between Laurentia and the Intermontane superterrane (including the Yukon-Tanana terrane), which began no earlier than ∼205 Ma; and (b) Middle or Late Jurassic to Early Cretaceous collision between Laurentia and the Insular superterrane. Sample 17RAY-AP017A1 (Finlayson assemblage) shows only minor evidence for a Mesozoic Pb-loss event (<200 Ma), with no evidence of zircon recrystallization, suggesting that a metamorphic discontinuity separates this unit from the underlying Snowcap assemblage. This discontinuity may indicate the presence of an extensional detachment responsible for the exhumation of the Cassiar terrane, which is consistent with the record of Early Cretaceous retrograde metamorphism, exhumation, and crustal melting reported elsewhere in Yukon, eastern and southern Alaska, and British Columbia Finally, we note that consideration of the 3D geometry of collisions between Laurentia, the Intermontane, and Insular superterranes adds a significant degree of complexity that is beyond the interpretation of constraints presented in this study. Determination of the 3D geometries of these collisional events depends crucially on a robust framework of terrane definitions. Mounting evidence for the presence of subterranes, suture zones, and other structural or paleogeographic discontinuities within terranes of the Northern Cordillera (particularly within the Intermontane terranes), demonstrate critically, that the current terrane framework must be revised before the 3D structural assembly of the North Cordillera can be robustly interpreted (e.g., George et al., 2021;Golding, 2018Golding, , 2020McGoldrick et al., 2017;Milidragovic & Grundy, 2019;Pecha et al., 2016;Ryan et al., 2014Ryan et al., , 2021van Staal et al., 2018;Zagorevski, 2019;Zagorevski et al., 2017.

Data Availability Statement
Data presented in this study, including geochronology and geochemistry datasets are freely available at the University of Plymouth data repository, PEARL (Plymouth Electronic Archive and Research Library): Parsons, (2021).

Acknowledgments
Data presented in this research are available for use in the Supporting Information S1 and in the Supporting Data Set S1 (Parsons, 2021). This research is a contribution to the Geological Survey of Canada, GEM-II Cordillera project. Additional analytical support was provided by United States National Science Foundation EAR grants awarded to McClelland (162413) and the Arizona LaserChron Facility (1649254). We thank Ken Ridgway and William Matthews for providing constructive reviews and Associate Editor Robinson Cecil for efficient handling of the manuscript. We thank Mitch Mihalynuk for helpful discussion during initial write up of this manuscript. Jamey Jones is thanked for helping us compile the published detrital zircon data from the Belt-Purcell Supergroup and Yavapai-Mazatzal province. Luke Beranek is thanked for bringing the Seagull Group to our attention. We thank Capital Helicopters, Inc., and the Yukon Geological Survey for logistical support during fieldwork.