A Detrital Zircon Test of Large-Scale Terrane Displacement Along the Arctic Margin of North America Timothy M

https://doi.org/10.1130/G48336.1

Manuscript received 28 August 2020 Revised manuscript received 13 October 2020 Manuscript accepted 27 October 2020

© 2021 Geological Society of America. For permission to copy, contact [email protected].

A detrital zircon test of large-scale terrane displacement along the Arctic margin of North America Timothy M. Gibson1,2, Karol Faehnrich1, James F. Busch1, William C. McClelland3, Mark D. Schmitz4 and Justin V. Strauss1 1Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA 2Department of Earth & Planetary Sciences, Yale University, New Haven, Connecticut 06511, USA 3Department of Earth & Environmental Sciences, University of Iowa, Iowa City, Iowa 52242, USA 4Department of Geosciences, Boise State University, Boise, Idaho 83725, USA

ABSTRACT the opening of the Canada Basin and evolution Detrital zircon U-Pb geochronology is one of the most common methods used to constrain of the circum-Arctic region (Fig. 1). Competing the provenance of ancient sedimentary systems. Yet, its efficacy for precisely constraining models posit that the North Slope subterrane was paleogeographic reconstructions is often complicated by geological, analytical, and statistical either displaced >1000 km along the northern uncertainties. To test the utility of this technique for reconstructing complex, margin-parallel (all directions are in modern coordinates) margin terrane displacements, we compiled new and previously published U-Pb detrital zircon data of Laurentia during the Paleozoic and/or Meso- (n = 7924; 70 samples) from Neoproterozoic–Cambrian marine sandstone-bearing units zoic (e.g., Sweeney, 1982; Strauss et al., 2013), across the Porcupine shear zone of northern Yukon and Alaska, which separates the North or it originated as an autochthonous continuation Slope subterrane of Arctic Alaska from northwestern Laurentia (Yukon block). Contrasting of the northwestern margin of Laurentia (e.g., tectonic models for the North Slope subterrane indicate it originated either near its current Lane and Gehrels, 2014; Lane et al., 2016). In position as an autochthonous continuation of the Yukon block or from a position adjacent to order to test these models and to explore the the northeastern Laurentian margin prior to >1000 km of Paleozoic–Mesozoic translation. utility of detrital zircon U-Pb geochronol- Our statistical results demonstrate that zircon U-Pb age distributions from the North Slope ogy for reconstructing terranes juxtaposed by subterrane are consistently distinct from the Yukon block, thereby supporting a model of complex tectonic boundaries more generally, continent-scale strike-slip displacement along the Arctic margin of North America. Further we compiled new (n = 3009; 22 samples) and examination of this dataset highlights important pitfalls associated with common method- previously published (n = 1317; 17 samples) ological approaches using small sample sizes and reveals challenges in relying solely on de- detrital zircon U-Pb ages from autochthonous trital zircon age spectra for testing models of terranes displaced along the same continental Neoproterozoic–Cambrian strata of the Yukon margin from which they originated. Nevertheless, large-n detrital zircon datasets interpreted block and Mackenzie platform in northwestern within a robust geologic framework can be effective for evaluating translation across complex Canada to compare with recently published age- tectonic boundaries. equivalent data (n = 3598; 31 samples) from the North Slope subterrane in northeastern Alaska INTRODUCTION in the number of grains analyzed per sample and northwestern Yukon (Fig. 1). This large-n Detrital zircon U-Pb geochronology has (e.g., Vermeesch, 2004), sampling and mineral dataset not only helps to constrain the tectonic become widespread for investigating ques- separation biases (e.g., Sláma and Košler, 2012), evolution of the Arctic margin of North America, tions in the fields of structural geology, tecton- age fractionation between different grain sizes but it also facilitates an examination of com- ics, sedimentary geology, and geomorphology in modern drainages (e.g., Ibañez-Mejia et al., mon data-treatment approaches in detrital zircon (Gehrels, 2014). A transition to more quantita- 2018), and nonunique age signatures from dis- U-Pb geochronology. tive approaches to data interpretation (e.g., Ver- parate source regions (e.g., Andersen, 2014). We meesch, 2004, 2018; Andersen, 2005; Saylor present a case study from the northern North GEOLOGICAL SETTING and Sundell, 2016; Sundell and Saylor, 2017), American Cordillera to test the efficacy of detri- Northwestern Laurentian Autochthon along with improved analytical methods that tal zircon U-Pb geochronology for deciphering The Yukon block, Selwyn basin, and Mack- allow for larger sample sizes (e.g., Pullen et al., tectonic relationships across complex terrane enzie platform of northwestern Laurentia span 2014), has increased the application of this tech- boundaries—in particular, those that juxtapose from east-central Alaska (USA) into the south- nique for elucidating sedimentary provenance crustal fragments displaced along the same con- western Northwest Territories (NWT, Canada), and disentangling cryptic tectonic boundaries. tinental margin from which they originated. and collectively reflect a broad zone of Neo- However, the application of detrital mineral Despite decades of debate, the tectonic evo- proterozoic–Paleozoic shallow- to deep-water geochronology as a precise paleogeographic lution of the circum-Arctic region remains con- ­sedimentation along the autochthonous north- indicator, as well as the growing use of statis- troversial. The displacement history of the North western margin of Laurentia (Fig. 1; Cecile tical dissimilarity measures on small-n datas- Slope subterrane of Arctic Alaska, which bor- et al., 1997). These depocenters are bounded to ets, has been challenged due to inconsistency ders the Arctic Ocean, played an integral role in the southwest by the Late Cretaceous–­Paleogene

CITATION: Gibson, T.M., et al., 2021, A detrital zircon test of large-scale terrane displacement along the Arctic margin of North America: Geology, v. 49, p. XXX–XXX, https://doi.org/10.1130/G48336.1

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Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/doi/10.1130/G48336.1/5213836/g48336.pdf by Dartmouth College , Timothy M. Gibson on 14 January 2021 Figure 1. Simplified ter- rane map of eastern Alaska and northwest- ern Canada, modified after Nelson et al. (2013), with inset map showing key elements discussed in text. New and previ- ously published sample locations from the Yukon block are shown in dif- ferent colors. SZ—shear zone; NWT—Northwest Territories; DZ—detrital zircon; Yb—Yukon block; Mp—Mackenzie plat- form; NSs—North Slope subterrane.

Tintina fault and to the northwest by the Paleo- the Windermere Supergroup, as well as vari- Although a Laurentian origin for the North Slope zoic–Eocene(?) Porcupine shear zone, the lat- ous ungrouped Cambrian units throughout the is undisputed, its pre-Mississippian position ter of which delineates a prominent tectonic Yukon block and Mackenzie platform (Fig. 1; along the ancestral continental margin remains boundary with the North Slope subterrane of see Supplemental Material). contentious, with some models emphasizing a Arctic Alaska (von Gosen et al., 2019). Protero- northwestern Laurentian origin (e.g., Lane and zoic strata of the Yukon block and Mackenzie North Slope Subterrane of Arctic Alaska Gehrels, 2014; Lane et al., 2016) and others pre- platform are exposed across central Yukon and The North American Cordillera terminates at ferring links to the northeastern (Franklinian) western NWT (Fig. 1; see the Supplemental its northernmost extent within the Arctic Alaska– margin of Ellesmere Island, Canada, and Green- Material1 and Figure S1 therein) and comprise Chukotka microplate, which is a composite ter- land (Fig. 1; e.g., Strauss et al., 2013, 2019a, three unconformity-bounded successions: the rane made up of Neoproterozoic–Devonian 2019b; Johnson et al., 2016; Colpron et al., ca. 1.7–1.2 Ga Wernecke Supergroup, the ca. crustal fragments with diverse tectonic affini- 2019). Both end-member models rely heavily on 1.2–0.8 Ga Mackenzie Mountains Supergroup, ties (Moore et al., 1994; Strauss et al., 2013; detrital zircon geochronology; however, attempts and the ca. 0.8–0.5 Ga Windermere Supergroup Hoiland et al., 2018; Miller et al., 2018). The to deconvolve the tectonic affinity of the North (Young et al., 1979). Lower Paleozoic carbon- Arctic Alaska terrane can be broadly subdivided Slope subterrane using detrital records have been ate, siliciclastic, and volcanic deposits overlie into two regions characterized by distinct­ pre- hampered by small-n datasets (e.g., McClelland these Proterozoic units and record a complex Mississippian geological histories—the North et al., 2015; Lane et al., 2016). history of passive-margin development (Cecile Slope and southwestern subterranes (e.g., Strauss et al., 1997; Beranek, 2017; Moynihan et al., et al., 2013; Hoiland et al., 2018). Whereas the METHODS 2019). Here, we focused on marine sandstone southwestern subterranes have peri-Baltican We present 3009 new U-Pb detrital zircon samples from the Neoproterozoic Mount Harper, or Siberian affinities (Patrick and McClelland, ages (3590 before filtering) from 22 samples Rapitan, Hay Creek, and Rackla Groups of 1995; Dumoulin et al., 2002; Amato et al., 2009; of Tonian–Cambrian fine- to coarse-grained Miller et al., 2011; Hoiland et al., 2018), the stra- marine sandstone units from the Yukon block tigraphy, sedimentary provenance, paleobiogeo- of northwestern Canada (Fig. 1; Figs. S1 and S2; 1Supplemental Material. Supplemental methods, graphic affinity, and magmatic history of the Tables S1 and S2). Following standard mineral sample descriptions, and U-Pb results, as well as North Slope subterrane all indicate a peri-Lau- separation techniques, zircons were analyzed via Figures S1 and S2 and Tables S1–S3. Please visit https://doi​.org/10.1130/GEOL.S.13377206 to access rentian origin (e.g., Moore et al., 1994; Strauss laser ablation–inductively coupled plasma–mass the supplemental material, and contact editing@ et al., 2013, 2019a, 2019b; McClelland et al., spectrometry (LA-ICP-MS) at the University geosociety.org with any questions. 2015; Johnson et al., 2016; Colpron et al., 2019). of Arizona (Tucson, Arizona), University of

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Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/doi/10.1130/G48336.1/5213836/g48336.pdf by Dartmouth College , Timothy M. Gibson on 14 January 2021 TABLE 1. STATISTICAL RESULTS COMPARING DETRITAL ZIRCON AGE POPULATIONS BETWEEN STRATA FROM THE NORTHWESTERN LAURENTIAN AUTOCHTHON VERSUS THE NORTH SLOPE SUBTERRANE Same parent Different parent Tonian–Cryogenian Ediacaran Cambrian Combined Cross-correlation coefficient >0.75 <0.5 0.18 0.16 0.55 0.28 Likeness coefficient >0.8 <0.8 0.51 0.46 0.69 0.56 Similarity coefficient >0.95 <0.95 0.84 0.82 0.94 0.89 K-S test D statistic <0.1 >0.1 0.44 0.55 0.32 0.45 Kuiper test V statistic <0.1 >0.1 0.49 0.55 0.32 0.45 Northwest Laurentia sample size – – 2209 664 1453 4326 North Slope sample size – – 552 862 2184 3598 Note: K-S—Kolmogorov-Smirnov. Values for determining whether populations were derived from the same versus different parents were approximated from Saylor and Sundell (2016) for n ∼500. Shading relates to statistics, where lighter is more similar, and darker is more dissimilar.

A

B

C

Figure 2. (A) Probability density plots (solid lines), histograms, and kernel density estimates (dashed lines), and (B) cumulative probability plot showing new and compiled U-Pb data binned by age from the North Slope subterrane and the northwest Laurentian autochthon (Yukon block and Mackenzie platform). Plotted using AgeCalcML (Sundell et al., 2020) with a kernel bandwidth of 10 m.y. and a bin size of 30 m.y. (C) Statistical parameters (Table 1) comparing detrital zircon U-Pb age populations between the North Slope subterrane and northwest Laurentian autochthon. Significance thresholds for determining whether populations were derived from the same versus different parents were approximated from Saylor and Sundell (2016) for n = 500. K-S—Kolmogorov-Smirnov.

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Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/doi/10.1130/G48336.1/5213836/g48336.pdf by Dartmouth College , Timothy M. Gibson on 14 January 2021 Adelaide (Australia), or Boise State University All filtered new and compiled data were three datasets were analyzed using the same suite (Boise, Idaho) (see the Supplemental Material). grouped by stratigraphic age into Tonian–Cryo- of statistical analyses to test the null hypothe- We then compiled 3598 previously published genian, Ediacaran, and Cambrian bins to facili- sis that detrital zircon age spectra were indis- U-Pb detrital zircon ages for 31 samples from tate age-equivalent comparisons. We computed tinguishable regardless of selected cutoff date the North Slope subterrane and an additional common statistical metrics (cross-correlation, (Fig. 3). Statistical values used to assess whether 1317 ages for 17 samples from the Yukon likeness, and similarity coefficients and Kol- to accept or reject these null hypotheses were block and Mackenzie platform (Fig. 1; Fig. S1, mogorov-Smirnov and Kuiper tests on sample a function of sample size (Saylor and Sundell, Tables S1 and S3). These previously published probability density plots) using DZstats (Saylor 2016); they should not be regarded as strict cut- Tonian–Cambrian marine sandstone samples and Sundell, 2016) to test the null hypothesis offs, but rather guidelines for assessing the rela- each provided >40 individual zircon analyses that Neoproterozoic–Cambrian samples from tive probability that age populations were drawn and were of similar composition, grain size, and the North Slope subterrane and northwestern from the same or different parent population, or depositional setting to the new data presented Laurentia were derived from a common source cannot be determined and remain ambiguous. herein. New and previously published data were region (Table 1; Fig. 2). A 1500 Ma “best age” filtered using error propagation on discordance cutoff was used for these statistical comparisons. DISCUSSION to exclude analyses where the 2σ uncertainty for Then, to assess the effects of using different Competing tectonic models for the evolu- either the 206Pb/238U or 207Pb/206Pb isotopic date cutoffs for selecting the 206Pb/238U or 207Pb/206Pb tion of the Canada Basin of the Arctic Ocean was >10% or where discordance was >10% or isotopic date as the “best age,” we applied 900, provide testable hypotheses regarding the prov- reverse discordance was >5% within 2σ uncer- 1200, and 1500 Ma cutoffs to all individual and enance and tectonic affinity of the North Slope tainty (see the Supplemental Material). binned data in our compilation. The resulting subterrane. Previous detrital zircon investigations

A B

Figure 3. (A) Statistical results comparing the effects of applying 900 Ma versus 1500 Ma 206Pb/238U or 207Pb/206Pb “best age” cutoffs to individ- ual samples from the northwest Laurentian autochthon. Thresholds for the same (blue dashed line) versus different (red dashed line) parent populations were estimated from Saylor and Sundell (2016), and colored data points refer to individual samples for which data are presented in B. Note that some low-n (<100) samples appear to be derived from different parents when variable “best age” cutoffs are applied. K-S— Kolmogorov-Smirnov. (B) Normalized probability density plots (PDPs) and kernel density estimates (KDEs) comparing the effects of applying 900, 1200, and 1500 Ma “best age” cutoffs to individual samples with small sample sizes. Note that individual PDPs and KDEs overlap in some areas. All plots were made using AgeCalcML (Sundell et al., 2020) with a kernel bandwidth of 20 m.y.

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Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/doi/10.1130/G48336.1/5213836/g48336.pdf by Dartmouth College , Timothy M. Gibson on 14 January 2021 of pre-Mississippian strata of the North Slope changes to critical age populations upon which Precambrian Research, v. 244, p. 279–287, subterrane had insufficient sample sizes to defini- key interpretations hinge. https://doi.org/10.1016/​ j.precamres.2013.10.013​ . tively constrain these models (e.g., McClelland Beranek, L.P., 2017, A magma-poor rift model for the Cordilleran margin of western North Amer- et al., 2015; Lane et al., 2016). In contrast, all CONCLUSIONS ica: Geology, v. 45, p. 1115–1118, https://doi​ statistical metrics applied to the large-n detrital Statistical analyses of a large compilation .org/10.1130/G39265.1. zircon data set presented herein demonstrate that of new and previously published detrital zir- Cecile, M.P., Morrow, D.W., and Williams, G.K., age spectra of Neoproterozoic–Cambrian strata con U-Pb data from Tonian–Cambrian marine 1997, Early Paleozoic (Cambrian to Early Devonian) tectonic framework, Canadian Cor- from the North Slope subterrane and northwest- strata within autochthonous northwestern dillera: Bulletin of Canadian Petroleum Geol- ern Laurentian autochthon are distinct from one Laurentia and the North Slope subterrane of ogy, v. 45, p. 54–74. another—i.e., they consistently plot in fields that Arctic Alaska support tectonic models for Colpron, M., and Nelson, J.L., 2009, A Palaeozoic suggest different parent populations (Table 1; large-scale Paleozoic and/or younger strike- Northwest Passage: Incursion of Caledonian, Bal- Fig. 2). Our compilation displays a subtle secular slip displacement along the Arctic margin tican and Siberian terranes into eastern Panthal- assa, and the early evolution of the North Ameri- increase in statistical similarity in detrital zircon of North America. This case study from the can Cordillera, in Cawood, P.A., and Kröner, A., age populations of Cambrian strata relative to northern Cordillera also facilitates examina- eds., Earth Accretionary Systems in Space and the older age bins. However, these results do not tion of essential data treatment strategies in Time: Geological Society [London] Special Pub- meet the criteria to indicate they were derived detrital zircon U-Pb geochronology. In particu- lication 318, p. 273–307, https://doi.org/10.1144/​ SP318.10. from a common parent (Table 1, Fig. 2). This lar, these results highlight the importance of Colpron, M., Strauss, J.V., and McClelland, W.C., prolonged difference in provenance between age- choosing consistent and informed 206Pb/238U or 2019, Detrital zircon U-Pb geochronological equivalent marine sandstone samples of broadly 207Pb/206Pb “best age” cutoffs and reinforce the and Hf isotopic constraints on the geological similar maturity, grain size, and depositional set- pitfalls of statistical similarity metrics applied evolution of north Yukon, in Piepjohn, K., et al., ting is inconsistent with models in which strata to small-n datasets. However, when integrated eds., Circum-Arctic Structural Events: Tectonic Evolution of the Arctic Margins and Trans-Arctic from the North Slope subterrane were deposited with relevant geological context, such as struc- Links with Adjacent Orogens: Geological Society near their current position adjacent to the Yukon tural and sedimentological/stratigraphic data, of America Special Papers, v. 541, p. 397–437, block. Rather, these statistical results are bet- large-n detrital zircon U-Pb geochronology https://doi​.org/10.1130/2018.2541(19). ter resolved with an origin for the North Slope may be one of the best tools for reconstructing Døssing, A., Gaina, C., Jackson, H.R., and Andersen, O.B., 2020, Cretaceous ocean formation in the subterrane independent from autochthonous cryptic margin-parallel displacements, espe- High Arctic: Earth and Planetary Science Let- northwestern Laurentia, consistent with models cially where crustal-scale fault zones between ters, v. 551, p. 116552, https://doi​.org/10.1016/​ that evoke large-scale Paleozoic and/or younger (para)autochthonous terranes have not been j.epsl.2020.116552. strike-slip displacement along the northern mar- recognized or fully appreciated. Dumoulin, J.A., Harris, A.G., Gagiev, M., Bradley, gin of Laurentia (e.g., Sweeney, 1982; Colpron D.C., Repetski, J.E., Miller, E.L., Grantz, A., and Klemperer, S.L., 2002, Lithostratigraphic, ACKNOWLEDGMENTS and Nelson, 2009; Strauss et al., 2013; Døssing conodont, and other faunal links between This work was funded by U.S. National Sci- et al., 2020). Lower Paleozoic strata in northern and central ence Foundation (NSF) Tectonics Division grants Alaska and northeastern Russia, in Miller, E.L., We also leveraged this large-n dataset to EAR-1624131/-1947074 awarded to Strauss and et al., eds., Tectonic Evolution of the Bering examine some common techniques in data EAR-1624132/-1947075 to McClelland. Gibson Shelf–Chukchi Sea–Artic Margin and Adjacent acknowledges support from the Agouron Geobiol- treatment and associated assumptions in detri- Landmasses: Geological Society of America ogy Fellowship. We thank the Tr’ondëk Hwech’in tal zircon­ U-Pb geochronology. When individual Special Papers, v. 360, p. 291–312, https://doi​ and Na-Cho Nyäk Dun First Nations for permission 206 238 .org/10.1130/0-8137-2360-4.291. samples were assessed using different Pb/ U to conduct field work on their traditional lands. Par- 207 206 Gehrels, G.E., 2014, Detrital zircon U-Pb geochronol- or Pb/ Pb cutoffs for determining the “best tial support for field work was provided by the Yukon ogy applied to tectonics: Annual Review of Earth age” of each zircon and then compared to them- Geological Survey (Canada) and Bundesanstalt für and Planetary Sciences, v. 42, p. 127–149, https:// Geowissenschaften und Rohstoffe (BGR, Germany). selves, most samples appeared to be derived doi​.org/10.1146/annurev-earth-050212-124012. The Arizona LaserChron Center was supported by from the same parent population (Fig. 3A; Hoiland, C.W., Miller, E.L., Pease, V., and Hourigan, NSF grant EAR-1649254. We acknowledge G. Halv- J.K., 2018, Detrital zircon U-Pb geochronology Table S3). However, for some samples with erson and F. Macdonald for contributing unpublished and Hf isotope geochemistry of metasedimen- <100 grains, age distributions that result from data; G. Cox, M. Kunzmann, L. Nelson, E. Sperling, tary strata in the southern Brooks Range: Con- and W. Ward for aid in sampling; M. Pecha, N. Geisler, applying a 900 Ma versus 1500 Ma cutoff do not straints on Neoproterozoic–Cretaceous evolu- J. Crowley, D. Pierce, and T. Allen for laboratory assis- appear to be drawn from the same parent popula- tion of Arctic Alaska, in Pease, V., and Coakley, tance; and G. Gehrels, M. Colpron, B. Johnson, and B., eds, Circum-Arctic Lithosphere Evolution: tion; i.e., they plot in “ambiguous” or “different D. Moynihan for discussion. Elizabeth Miller and an Geological Society [London] Special Publica- parent” fields Fig. 3A( ). These differences also anonymous reviewer provided suggestions that greatly tion 460, p. 121–158, https://doi​.org/10.1144/ manifest as changes in the position and magni- improved this manuscript. SP460.16. tude of individual U-Pb age peaks (Fig. 3B) and Ibañez-Mejia, M., Pullen, A., Pepper, M., Urbani, F., are greatest in samples with prominent popula- REFERENCES CITED Ghoshal, G., and Ibañez-Mejia, J.C., 2018, Use tions near the “best age” cutoff. This is an impor- Amato, J.M., Toro, J., Miller, E.L., Gehrels, G.E., and abuse of detrital zircon U-Pb geochronol- Farmer, G.L., Gottlieb, E.S., and Till, A.B., tant and underappreciated factor when consider- ogy—A case from the Río Orinoco delta, eastern 2009, Late Proterozoic–Paleozoic evolution of Venezuela: Geology, v. 46, p. 1019–1022, https:// ing which cutoff to apply. 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