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Title Insights Into the Paleoproterozoic Paleogeography of the Superia Supercraton From Detrital Zircon Geochronology, Isotope Geochemistry, and Chemostratigraphy of Supracrustal Successions on the Southern Margin of the Wyoming Craton

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Author Mammone, Nicholas Michael

Publication Date 2021

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Insights Into the Paleoproterozoic Paleogeography of the Superia Supercraton From Detrital Zircon Geochronology, Isotope Geochemistry, and Chemostratigraphy of Supracrustal Successions on the Southern Margin of the Wyoming Craton

A Thesis submitted in partial satisfaction of the requirements for the degree of

Master of Science

Geological Sciences

Nicholas Michael Mammone

June 2021

Thesis Committee: Dr. Andrey Bekker, Chairperson Dr. Peter Sadler Dr. Heather Ford

The Thesis of Nicholas Michael Mammone is approved:

Committee Chairperson

University of California, Riverside

Table of Contents General Background ...... 1 Chapter 1: Insights into the early Paleoproterozoic paleogeography of the Superia supercraton from detrital zircon geochronology, and Sm-Nd and Pb-Pb isotope geochemistry of supracrustal successions on the southern margin of the Wyoming craton ...... 9 Abstract ...... 9 Introduction ...... 11 Regional Geology ...... 15 Paleoproterozoic stratigraphy of the Medicine Bow Mountains and Sierra Madre ...... 19 Methods ...... 25 Detrital Zircon Results ...... 31 Nd Model Ages for fine-grained metasediments of the Snowy Pass Supergroup, Medicine Bow Mountains ...... 34 Pb isotope composition of fine-grained metasediments from the Snowy Pass Supergroup, Medicine Bow Mountains ...... 35 Discussion ...... 38 1.1. Age of the Phantom Lake Group ...... 38 1.2. Correlation between the Paleoproterozoic successions in Sierra Madre and Medicine Bow Mountains ...... 38 1.3. Changes in provenance during deposition of Paleoproterozoic successions in Medicine Bow Mountains and Sierra Madre ...... 39 1.4. Age and correlation of the Nash Fork and Slaughterhouse formations ...... 40 1.5. Comparing Sm-Nd data for shales and U-Pb data for detrital zircons from sandstones ...... 42 2.1. Correlation between the Paleoproterozoic successions of Wyoming and the Huronian Supergroup on the Superior craton ...... 42 2.2. Lower Huronian Supergroup and Phantom Lake Group ...... 43 2.3. Comparing changes in provenance during deposition of Paleoproterozoic successions in the Snowy Pass and Huronian basins ...... 44 2.4. Detrital zircon patterns for the upper parts of the Huronian and Snowy Pass successions ...... 47 2.5. Sm-Nd data for the Snowy Pass and Huronian supergroups ...... 50 2.6. Events affecting the Pb isotope system ...... 53 3.1. Implications for the evolution of the early Paleoproterozoic Earth System ...... 56 3.2. Reconstruction of the Superia supercraton...... 57 3.3. Age constraints for the early Paleoproterozoic (Huronian) glaciations ...... 57 3.4. 2.3 Ga magmatic event and the proposed tectono-magmatic lull of the Paleoproterozoic ...... 58 3.5. Age constraints for C isotope variations in seawater in the early Paleoproterozoic ...... 60 Conclusion ...... 61

iv References ...... 65 Chapter 2: Reconstructing the paleogeography of the Superia supercraton using detrital zircon provenance of early Paleoproterozoic supracrustal successions from the southern margin of the Wyoming craton ...... 78 Abstract ...... 78 Introduction ...... 80 Results ...... 89 Detrital zircon U-Pb data ...... 89 Carbon and oxygen isotope values for carbonates ...... 92 Discussion ...... 96 1.1. Comparing records for the Red Creek Quartzite with other supracrustal successions on the southern margin of the Wyoming craton ...... 96 1.2. Provenance of the Red Creek Quartzite ...... 102 1.3. Tectonic model for early Paleoproterozoic tectonic evolution on the southern margin of the Wyoming craton ...... 103 1.4. Reconstruction of Superia by comparing potential provenances for early Paleoproterozoic supracrustal successions ...... 104 Conclusion ...... 114 References ...... 117 General Conclusions ...... 139

v List of Figures

Figure 1.1: Global changes in surface environments, mantle activity, and plate tectonics during the early Paleoproterozoic ...... 15

Figure 1.2: The Wyoming craton and its subprovinces...... 18

Figure 1.3: A - Map showing Archean cratons of North America B – Geologic map of the Medicine Bow Mountains and Sierra Madre ...... 23

Figure 1.4: A – Lithostratigraphic correlation between the Snowy Pass Supergroup of the Medicine Bow Mountains, WY, USA, the Snowy Pass Group of the Sierra Madre, WY, USA, and the Huronian Supergroup, Ontario, CA B – Stratigraphically ordered detrital zircon histograms for units of the Snowy Pass Supergroup of the Medicine Bow Mountains with correlative formations of the Snowy Pass Group of the Sierra Madre, and Huronian Supergroup...... 24

Figure 1.5: Nd data for the Snowy Pass Supergroup and Huronian Supergroup ...... 35

Figure 1.6: Plot of 206Pb/204Pb vs. 207Pb/204Pb for units from the SPS and HS ...... 37

Figure 1.7: Early Paleoproterozoic reconstruction of the Superior and Wyoming cratons ...... 50

Figure 1.8: Plot of 206Pb/204Pb vs. 208Pb/204Pb for units from the SPS and HS ...... 55

Figure 1.9: (232Th/238U) values for Archean and Paleoproterozoic shale suites through time ...... 56

Figure 1.10: Compilation of all concordant (<10%) detrital zircon data from this study ...... 60

Figure 2.1: The Wyoming craton with the placement and extent of subprovinces within and the location of the Uinta Mountains, NE Utah ...... 83

Figure 2.2: Study area in the Uinta Mountains showing the Red Creek Quartzite that was sampled for detrital zircon geochronologic analysis of quartzites and chemostratigraphic study of carbonates ...... 86

Figure 2.3: Detrital zircon histogram for quartzite samples from the Red Creek Quartzite and Owiyukuts Complex ...... 91

Figure 2.4: Plot of age vs. Th/U ratios for detrital zircons from the Owiyukuts Complex ...... 92

Figure 2.5: Plot of 18O vs. 13C for marble samples from the Red Creek Quartzite ...... 94

Figure 2.6: Detrital zircon age spectra comparisons for the Farmington zone, Red Creek Quartzite, Owiyukuts complex, and Phantom Lake Metamorphic Suit ...... 99

Figure 2.7: : Nd data for the Snowy Pass Supergroup, Red Creek Quartzite, and Owiyukuts Complex 100

Figure 2.8: Detrital zircon data comparisons for the Paleoproterozoic supracrustal successions on Archean cratons that were components of Superia ...... 110

Figure 2.9: Detrital zircon age data spectra from the Red Creek Quartzite and Owiyukuts Complex ... 111

Figure 2.10: Detrital zircon data comparisons for the Paleoproterozoic supracrustal successions on Archean cratons that were parts of the Superia supercraton ...... 112

Figure 2.11: Preferred reconstruction of Superia based on compiled detrital zircon data from Paleoproterozoic supracrustal successions on each craton ...... 113

vii List of Tables

Table 1.1: Summary table for detrital zircon results from the Medicine Bow Mountains and Sierra Madre describing data populations observed in the histogram charts of Figure 1.4B...... 29

Table 1.2: Summary table for Sm-Nd and Pb-Pb data from the Snowy Pass Supergroup of the Medicine Bow Mountains ...... 30

Table 2.1: 18O and 13C for sampled marbles from the Red Creek Quartzite ...... 95

Sample Locations and Descriptions: Table of sample locations and descriptions ...... 149

viii General Background

The reconstruction of the early Paleoproterozoic paleogeography of Archean cratons has the potential to significantly advance current understandings of the relationships between surficial conditions and geological events during this time period.

Specific globally important events include, but are not limited to: the onset and continuation of the Great Oxidation Episode (Bekker et al., 2004; Guo et al., 2009) that influenced the evolution of life on Earth, 4 major, potentially low-latitude glaciations

(Rasmussen et al., 2013), large-amplitude shifts in the biogeochemical carbon cycle (i.e., the Lomagundi Carbon Isotope Excursion in marine carbonates; Karhu & Holland, 1996;

Bekker & Eriksson, 2003; Bekker, 2014), and a quiescence in juvenile magmatism and collisional tectonics between ca. 2.3 – 2.2 Ga (Condie et al., 2009; Spencer et al., 2018).

The widespread emplacement of Large Igneous Provinces on cratonic margins, and the associated dike swarms radiating from their plume centers, during the early

Paleoproterozoic is linked to the protracted rifting and breakup of cratons (Ernst & Bleeker,

2010). Paleomagnetic data for dike swarms from the Wyoming and Superior cratons (both in North America) have strengthened Paleoproterozoic reconstruction models, supporting their adjacency between ca. 2.6 and 2.16 Ga (Kilian et al., 2015).

The Snowy Pass and Huronian supergroups, two supracrustal successions located on the southern margins of the Wyoming and Superior cratons, respectively, have pointed to this cratonic reconstruction for almost a century due to apparent similarities in their lithostratigraphies, potentially indicating deposition in a shared basin (Blackwelder, 1926;

Houston et al., 1992; Roscoe & Card, 1993; Bekker et al., 2003). Extensive study has been

1 conducted on the Huronian Supergroup in an effort to better chronicle and describe the early Paleoproterozoic Earth system. The upper and lower geochronological bounds on the succession are established and widely accepted at ca. 2.45 Ga and ca. 2.22 Ga (upper age limit: Krogh et al., 1984; Ketchum et al., 2013; Bleeker et al., 2015; lower age limit: Corfu

& Andrews, 1986; Noble & Lightfoot, 1992; Buchan et al., 1993; Bleeker et al., 2015).

Ash layers of the upper Huronian Supergroup are dated at ca. 2.31 Ga (Rasmussen et al.,

2013), and the uppermost sedimentary formations of the supergroup contain detrital zircon populations as young as ca. 2.3 Ga (Hill et al., 2018), placing tighter age constraints for deposition. Detrital zircon provenance studies from sedimentary units of the Huronian

Supergroup mostly include age modes likely derived from the southern part of the Superior craton (Craddock et al., 2013), however, the presence of age modes at ca. 2.3 Ga and ca.

2.55 Ga, which are uncommon on the Superior craton, in the uppermost formations requires input from an exotic provenance (Hill et al., 2018).

Geochronologic work for the Snowy Pass Supergroup is severely limited in comparison, with published data only including a minimal amount of zircon dates for the lowermost Magnolia Formation (establishing a maximum depositional age constraint on the supergroup at ca. 2.45 Ga) and for an intrusive gabbroic plug, which cross-cuts the lower-middle Cascade Quartzite (possibly establishing a minimum age constraint for the entire Deep Lake Group at ca. 2.1 Ga) (Premo & Van Schmus, 1989). The Nash Fork

Formation of the Libby Creek Group in the upper Snowy Pass Supergroup as well as the

Slaughterhouse Formation (part of the correlative Snowy Pass Group of the Sierra Madre about 60 km west of the Medicine Bow Mountains) record the Lomagundi Carbon Isotope

2 Excursion as well as its termination in the Medicine Bow Mountains (Bekker et al., 2003), suggesting that deposition of the Snowy Pass Supergroup continued at least to around 2.06

Ga; the time at which the end of the Lomagundi Event is currently constrained (Karhu &

Holland, 1996; Bekker & Holland, 2012; Bekker, 2014). Geochronologic data for the lower and upper Libby Creek groups are absent, and filling in the missing gaps in age constraints for the Snowy Pass Supergroup would dramatically enhance the study of the

Paleoproterozoic geological history of the Wyoming craton.

Detrital zircon analysis, paired with Sm-Nd and Pb-Pb isotope systematics, from the Snowy Pass Supergroup provides insight into the provenance of sedimentary material.

Detrital zircon age data (plotted as histograms) from sedimentary rock samples can present information towards the source of their constituents in the form of significant graphical age peaks. These peaks generally represent relatively large contributions of material

(containing zircon), from local and extensively exposed source rocks, that was eroded and eventually incorporated into the analyzed rock sample. Initial source rocks potentially extend to other Paleoproterozoic cratons (Hearne, Rae, Kola, and Karelia) which were components of the Archean Superia supercraton along with the Wyoming and Superior cratons (Bleeker & Ernst, 2006; Ernst & Bleeker, 2010; Bleeker et al., 2016; Gumsley et al., 2017; Davey et al., 2020). Detrital zircon data from surrounding cratons with contemporaneous supracrustal successions to the Snowy Pass Supergroup can be used to constrain zircon-producing events and help test proposed paleogeographic reconstructions for neighboring cratons with respect to the Wyoming craton.

3 The Red Creek Quartzite is a Paleoproterozoic sedimentary unit located along the southern margin of the Wyoming craton in NE Utah in the Uinta Mountains and has been correlated to the units of the upper Snowy Pass Supergroup in SE Wyoming based on similar quartzite and carbonate rock types reflecting similar depositional facies

(Blackwelder, 1926; Hansen, 1965; Graff et al., 1980). Detrital zircon as well as carbon isotope data from this unit, as well as the underlying, Paleoproterozoic Owiyukuts

Complex, is largely absent and has the potential to further improve these loose correlations and enable the Paleoproterozoic reconstruction of the SW margin of the Wyoming craton, thus permitting a robust set of zircon data to be compared with cratons that were potentially adjacent to the Wyoming craton in the early Paleoproterozoic.

Detrital zircon, Sm-Nd, and Pb-Pb data from the southeastern margin of the

Wyoming craton is presented in chapter 1, supporting the established connection between the Wyoming and Superior cratons in the Paleoproterozoic, and showcasing the shared provenances and comparable tectonic histories of the Snowy Pass and Huronian supergroups at their respective southern margins. Chapter 2 investigates supracrustal successions, of similar age to the successions in the Medicine Bow Mountains and Sierra

Madre, along the southwestern margin of the Wyoming craton to further describe provenance, detrital zircon age distributions, and the tectonic history of the craton’s southern margin. Proposed paleogeographic reconstructions of Superia are tested, and compiled detrital zircon data is used to provide insight into the configuration of its constituent cratons during the Paleoproterozoic.

4 References

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Bekker, A, Karhu, J. A., Eriksson, K. A., & Kaufman, A. J. (2003). Chemostratigraphy of Paleoproterozoic carbonate successions of the Wyoming Craton: tectonic forcing of biogeochemical change? Precambrian Research, 120, 279–325. Retrieved from papers3://publication/uuid/7D9A956F-5CD0-4F13-AFBA-D9E4999BE365

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5 Buchan, K. L., Mortensen, J. K., & Card, K. D. (1993). Northeast-trending early Proterozoic dykes of southern Superior Province: multiple episodes of emplacement recognized from integrated paleomagnetism and U-Pb geochronology. Canadian Journal of Earth Sciences, 30(6), 1286–1296. https://doi.org/10.1139/e93-110

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Kilian, T. M., Bleeker, W., Chamberlain, K. R., Evans, D. A. D., & Cousens, B. (2015). Palaeomagnetism , geochronology and geochemistry of the Palaeoproterozoic supercraton Superia. Geological Society, London, Special Publications, 424, 15–45. https://doi.org/10.1144/SP424.7

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7 Rasmussen, B., Bekker, A., & Fletcher, I. R. (2013). Correlation of Paleoproterozoic glaciations based on U-Pb zircon ages for tuff beds in the Transvaal and Huronian Supergroups. Earth and Planetary Science Letters, 382, 173–180. https://doi.org/10.1016/j.epsl.2013.08.037

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8 Chapter 1

Insights into the early Paleoproterozoic paleogeography of the Superia supercraton from detrital zircon geochronology, and Sm-Nd and Pb-Pb isotope geochemistry of supracrustal successions on the southern margin of the Wyoming craton

Mammone, N.1, Bekker, A.1,2, Chamberlain, K.3, Kuznetsov, A.4

1Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA 2Department of Geology, University of Johannesburg, Auckland Park, South Africa 3Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071 4Institute of Precambrian Geology and Geochronology (IPGG), Russian Academy of Sciences, Saint-Petersburg 199034, Russia

Keywords: Paleoproterozoic, Superia supercraton, detrital zircon geochronology, Sm-Nd isotope geochemistry, Medicine Bow Mountains, Sierra Madre, Lomagundi carbon isotope excursion

Abstract

Paleogeography is a critical component in providing a backdrop for environmental changes, yet the Paleoproterozoic configuration of Archean cratons still remains controversial. The Snowy Pass Supergroup (SPS), a Paleoproterozoic supracrustal succession on the SE Wyoming craton, has been historically correlated with the Huronian

Supergroup (HS) of the Superior craton based on similar lithostratigraphic patterns, suggesting deposition in the same basin between ca. 2.45 and 2.31 Ga, and indicating that these cratons were marginally adjoined in a Paleoproterozoic Superia supercraton. This study presents LA-ICP-MS and SHRIMP U-Pb detrital zircon age data for all units of the

Phantom Lake Metamorphic Suite, SPS, and Snowy Pass Group (SPG) of the Medicine

9 Bow Mountains (MBM) and Sierra Madre (SM) further constraining the paleogeographic position of these cratons. The Phantom Lake Metamorphic Suite contains statistically significant modes of ca. 2.45 Ga zircon ages in the basal Jack Creek Quartzite and Bridger

Peak Quartzite of the SM; zircons of this age also occur in one to two grain quantities in two additional units of the Phantom Lake Metamorphic suite in the MBM, indicating the early Paleoproterozoic age for this suite and allowing correlation with the basal HS units of the Superior craton. Zircon age spectra for lithostratigraphically correlative units on the southern Wyoming and Superior cratons demonstrate strikingly similar, primarily Archean patterns indicating similar provenance, whereas paleocurrent directions establish provenance of both cratons for the shared basin. Most units of the SPS and SPG have detrital zircon age peaks at ca. 2.85 and 2.7 Ga, ca. 2.3 and 2.55 Ga modes are common for the uppermost formations, and five units throughout both successions contain minor peaks at ca. 2.45 Ga. Sm-Nd and Pb-Pb data for fine-grained siliciclastic samples throughout the

SPS yield similar TDM Nd ages as well as and values to the literature data for the

HS, further supporting similar provenance for the two supergroups.

Correlation between the HS and SPS breaks down in the upper SPS at the Nash

Fork Formation, which bears unique modes at ca. 2.2 and 2.1 Ga, whereas deposition of the HS was terminated before ca. 2.22 Ga when the Nipissing dikes intruded and shortly after a ca. 2.31 Ga volcanic event recorded by tuffs and volcaniclastic sediments of the

Gordon Lake and Bar River formations. The matching, globally unique, ca. 2.3 Ga mode, first appearing in the Lookout Schist and steadily decreasing upsection through the upper

SPS, points to a similar, volcanic source. Maximum depositional ages for the uppermost

10 formations of the SPS and SPG, the purportedly correlative Nash Fork and Slaughterhouse formations, are at 2081 10 Ma and 2334 20 Ma, respectively. The Nash Fork Formation also has more positive C isotope values than the Slaughterhouse Formation. This might indicate that the latter unit is time equivalent to the Lookout Schist of the SPS and the

Gordon Lake Formation of the HS, which have similar carbon isotope values and a ca. 2.31

Ga zircon mode, or, alternatively, it might be pointing to differences in the provenance of the SPS and SPG. The maximum depositional age and the youngest (2066 9 Ma) concordant zircon age for the upper Nash Fork Formation, deposited in the immediate aftermath of the Lomagundi Carbon Isotope Excursion, further supports the current age constraints placed on the end of the excursion between ca. 2.11 – 2.06 Ga. This detrital zircon mode also corresponds to that of the basal Animikie basin units (Denham Formation of the Mille Lacs Group in MN and East Branch Arkose of the Dickinson Group, MI), dating rifting, breakup, and ultimate separation of the Wyoming and Superior cratons at ca. 2075 Ma.

Introduction

The early Paleoproterozoic was a significant transitional time period in Earth’s history, hosting 4 major, potentially low-latitude glaciations (Rasmussen et al., 2013), the onset and advance of the Great Oxidation Episode (GOE) (Bekker et al., 2004; Guo et al.,

2009), large-amplitude shifts in the carbon cycle as recorded by the Lomagundi carbon isotope excursion in marine carbonates between 2.22 – 2.06 Ga (Karhu & Holland, 1996;

Bekker & Eriksson, 2003; Bekker, 2014), the widespread emplacement of Large Igneous

Provinces (LIPs) (Ernst & Bleeker, 2010), and Superia supercraton breakup ca. 2.1 Ga

11 (Kilian et al., 2015) (Fig. 1.1). One of the most extensive sedimentary records of this time period, the Huronian Supergroup located in Ontario, Canada, contains an exceptionally well-preserved perspective into the run up to and the beginning of the GOE between ca.

2.5 and 2.32 Ga and has therefore prompted extensive regional study. The Snowy Pass

Supergroup (SPS), located in the Medicine Bow Mountains (MBM), and the proximal time-equivalent Snowy Pass Group (SPG) of the Sierra Madre (SM), both in Wyoming,

USA (Figs. 1.2 and 1.3), also host well-preserved records of the early Paleoproterozoic, while additionally documenting the Lomagundi positive carbon isotope excursion (and its termination in the MBM) in the primarily meta-dolomitic and potentially correlative

Slaughterhouse and Nash Fork formations of the upper SPG and SPS, respectively (Bekker et al., 2003). However, these two successions have been subject to much less attention due to the higher grade of metamorphism, lack of age constraints, more complex deformation history, and generally more mountainous topography over a smaller area. The Huronian and Snowy Pass supergroups are the most extensive early Paleoproterozoic successions in

North America and have been correlated lithostratigraphically for almost a century based on the presence of glacial diamictites, red beds, and post-glacial carbonates (Blackwelder,

1926; Houston et al., 1992; Roscoe & Card, 1993; Bekker et al., 2003) at similar stratigraphic levels, indicating that they were likely once deposited in the same depositional basin.

Despite apparent similarities in the stratigraphic makeup of these two successions, there are unexplained differences in their magmatic history. First, the HS has thick, extensive, and well-dated bi-modal volcanic and intrusive rocks in the basal Elliott Lake

12 Group (Fig. 1.4) constraining its upper depositional age limit to ca. 2.45 Ga, which are lacking in the Wyoming successions (Krogh et al., 1984; Ketchum et al., 2013; Bleeker et al., 2015). Secondly, extensive mafic dikes, sheets, and sills of the ca. 2220-2210 Ma

Nipissing Diabase that cuts the HS over the its entire areal extent do not find a time- equivalent match along the southern margin of the Wyoming craton (Corfu & Andrews,

1986; Noble & Lightfoot, 1992; Buchan et al., 1993; Bleeker et al., 2015). Finally, correlative volcanic deposits or igneous events to the ca. 2.31 Ga ash beds and volcaniclastic deposits of the Gordon Lake Formation, at the top of the HS (Rasmussen et al., 2013; Hill et al., 2018), have not been recognized on the Wyoming craton. This difference in magmatic history in otherwise correlative stratigraphic successions call for further investigation into their paleogeographic proximity.

Paleogeographic models based on paleomagnetic data from dike swarms developed on the Wyoming and surrounding cratons place the Wyoming craton in the center of the

Neoarchean Superia supercraton throughout the early Paleoproterozoic (Kilian et al., 2015;

Bleeker et al., 2016; Gumsley et al., 2017), enforcing the connection between the Wyoming and Superior cratons along their southern margins in present coordinates. The rifting of the

Wyoming craton from the southern margin of the Superior craton likely initiated at ca. 2.45

Ga as a result of the emplacement of a voluminous mantle plume recorded by the extensive

(>200,000 km2) Matachewan and Hearst dike swarms on the Superior craton (Heaman,

1997), but this event failed to separate the cratons, which eventually drifted apart between ca. 2.1 and 2.0 Ga (Kilian et al., 2015). The Wyoming craton then experienced a clockwise rotation of about 140 to its current position (Roscoe & Card, 1993).

13 Our study presents detrital zircon U-Pb geochronology, Sm-Nd model ages, and

Pb-Pb isotope data for all quartzite- and shale-bearing units of the SPS in the MBM and all quartzite units of the SPG of the SM for sedimentary provenance analysis of both felsic and mafic materials, respectively, and to constrain depositional ages to further test the correlation between the Snowy Pass and Huronian supergroups and their deposition in the same basin. Our data improves the currently limited geochronological constraints for the early Paleoproterozoic successions developed along the southern margin of the Wyoming craton. Current published data includes detrital and magmatic zircon U-Pb age constraints for the basal Magnolia Formation and gabbroic dikes intruding the Deep Lake Group of the lower SPS (Premo & Van Schmus, 1989) and limited Sm-Nd data for the fine-grained units of the upper SPS of the MBM and Phantom Lake Metamorphic Suite of the SM (Ball

& Farmer, 1991; Souders & Frost, 2006).

This study will additionally contribute to both the reconstruction and the breakup history of the Neoarchean Superia supercraton and provide some insight into a plate tectonic and magmatic lull proposed to have occurred between ca. 2.3 and 2.2 Ga, expressed as a global quiescence of magmatic activity and plate motion (Condie et al.,

2009; Spencer et al., 2018). This global plate tectonic quiescence has been challenged

(Partin et al., 2014; Pehrsson et al., 2014). The presence of ca. 2.31 Ga zircon in tuff beds and volcaniclastic sediments of the upper HS (Rasmussen et al., 2013; Hill et al., 2018), which were also found in the upper units of the SPS in this study, is not only useful for testing the correlation between the HS and SPS, but also bears on our understanding of this

14 period with relatively rare zircon crystallization ages in the global record (Condie et al.,

2009; Spencer et al., 2018).

Figure 1.1: Global changes in surface environments, mantle activity, and plate tectonics during the early Paleoproterozoic. Shown are four, major, low-latitude glaciations with blue vertical bars (Rasmussen et al., 2013), time series of mantle superplume events derived from adding gaussians defined by ages and errors of superplume proxies (minimum age errors are set to 5 million years, higher height indicates more accurate time constraints) (2.5 – 2.0 Ga section taken from Abbott & Isley, 2002), carbon isotope values of marine carbonates through time (modified from Bekker et al., 2006), timing and extent of the Great Oxidation Episode in yellow, and the Superia supercraton breakup in orange. Figure modified from Bekker & Holland, 2012.

Regional Geology

The Archean Wyoming craton consists of roughly 500,000 km2 of basement rocks encompassing a significant portion of the western United States and has had a complex

Archean and Paleoproterozoic tectonic history (Frost et al., 1998, 2000; Chamberlain et al.,

2003). The craton is separated into several tectonically distinct subprovinces (Fig. 1.2).

15 From north to south, the subprovinces include: (1) the Montana metasedimentary terrane

(MMT); (2) the Bighorn subprovince; (3) the Sweetwater subprovince; and (4) the southern accreted terranes (SAT).

The MMT contains one of the largest regions with preserved early to middle

Archean rocks that were unaffected by Late Archean deformation and magmatism. Its southeastern boundary is defined by the Late Archean (>2.55 Ga) shear zones that delineate the northern limit of significant 2.9 – 2.75 Ga magmatism that reworked the Bighorn subprovince to the south. The cessation of magmatism at 2.75 Ga is unique on the

Wyoming craton to the Bighorn subprovince, whereas the Sweetwater subprovince immediately to the south continued to be tectonically reworked until ca. 2.55 Ga. It is interpreted that the latter subprovince was formed at a long-lasting active continental margin based on recognized periods of shortening, deformation, and accretion of both juvenile and older continental crust (Frost et al., 2000; Frost et al., 1998; Kruckenberg et al., 2001; Fruchey, 2002). Both the MBM and SM are located on the SAT that is interpreted to have been accreted to the Wyoming craton after ca. 2.62 Ga. Pb isotope ratios for the basement rocks in the MBM and Nd isotope values for the Phantom Lake Metamorphic

Suite in the SM point to their derivation from sources not seen on the Wyoming craton

(Harper, 1997; Souders & Frost, 2006). The Oregon Trail - structural belt in south-central

Wyoming separates the isotopically distinct SAT, with low- ( = 238U/204Pb), thin

Neoarchean crust (<2.85 Ga), exhibiting isotopic similarities with the Superior craton, from the rest of the Wyoming craton to the north, where a relatively thick, high-, Mesoarchean crust (>3.2 Ga) developed. This, paired with their geological and geophysical attributes,

16 suggest that the SAT was torn from the Superior craton as a result of Paleoproterozoic rifting subsequent to ca. 2.65 Ga assembly of the Wyoming and Superior cratons

(Chamberlain et al., 2003, 2017).

The Archean Wyoming craton is surrounded by isolated Paleoproterozoic orogenic belts with only a few significant Paleoproterozoic exposures on the southeastern margin in the SM and MBM, and farther along to the east in the Black Hills of South Dakota. The exposures along the margin of the craton in the SM and MBM have been deformed to greenschist, biotite metamorphic grade during the Medicine Bow Orogeny at 1.78 – 1.74

Ga when island arcs were accreted to the southern margin along the Cheyenne Belt suture

(Karlstrom & Houston, 1984; Chamberlain, 1998; Dahl & Frei, 1998). To the south of the

Cheyenne Belt lies the 1.78 – 1.74 Ga island-arc assemblage of mainly hornblende and quartzofeldspathic gneisses with minor sillimanite gneisses and calc-silicates (Hills et al.,

1968; Hills & Houston, 1979; Chamberlain, 1998).

Figure 1.2: The Wyoming craton and its subprovinces (see text for discussion, modified from Chamberlain et al., 2003 and Chamberlain & Mueller, 2019). Age of supracrustal successions is shown in black text boxes. Intrusive rocks dated at ca. 2.45 Ga include: mafic intrusions in Tobacco Root Mountains (Roberts et al., 2002; Krogh et al., 2011), Beartooth Mountains – Elbow Creek Dikes (Rogers, 2017), and in the Tendoy Mountains (Kellogg et al., 2003), all in Montana, nephrite (jade) veins in Granite Mountains (Peterman & Hildreth, 1978; Sutherland, 2019), Baggot Rocks granite (Premo & Van Schmus, 1989), both in Wyoming, and in the Farmington Zone (labelled Selway terrane) in Utah (Mueller et al., 2011). GFTZ stands for the Great Falls Tectonic Zone, MMT for Montana Metasedimentary Terrane, and SAT for Southern Accreted Terranes.

Paleoproterozoic stratigraphy of the Medicine Bow Mountains and Sierra Madre

The SPS is a ~13 km thick metasedimentary succession located in the MBM, forming the northern fork of the frontal range of the southern Rocky Mountains in southeastern Wyoming that was uplifted and thrusted over Paleozoic and Mesozoic rocks during the Laramide Orogeny in the Late Cretaceous – Paleogene (Hills et al., 1968). The

MBM are a complex of Precambrian rocks that make up the core of a large asymmetric anticline bounded by west-dipping thrusts to the east (Houston & Karlstrom, 1992).

The SPS is located north of the border of two geologically and geochronologically distinct blocks: the Archean Wyoming craton and late Paleoproterozoic island arcs. The southern margin of the Wyoming craton hosts Archean gneisses unconformably overlain by the supposedly Late Archean Phantom Lake Metamorphic Suite and Paleoproterozoic

SPS and SPG in the SM and MBM, respectively. Geochronologic data for the basement rocks include dates of 2683 ± 6 Ma for a pink quartzofeldspathic orthogneiss and 2710 ±

10 Ma for the Spring Lake Granodiorite, which was interpreted to intrude the Phantom

Lake Metamorphic Suite in the central Sierra Madre (both are U-Pb TIMS zircon dates from Premo & Van Schmus, 1989). Contacts with the intrusions were not described by

Houston & Karlstrom (1992), but it was purported in the North Spring Creek Lake area of the Sierra Madre that the Spring Lake Granodiorite intrudes the basal Jack Creek Quartzite based on map relationships. Upper units of the Phantom Lake Metamorphic Suite are not in contact with this intrusion, but undated felsic igneous rocks considered correlative to the

Spring Lake Granodiorite intrude the upper Silver Lake Metavolcanics and Bridger Peak

Quartzite of the Phantom Lake Metamorphic Suite in the northwestern Sierra Madre, supporting the Archean depositional age for this suite (Houston et al., 1992).

The Phantom Lake Metamorphic Suite and SPG of the SM are located about 60 km west of the MBM and are time-equivalent successions with the Phantom Lake

Metamorphic Suite and SPS in the MBM with similar stratigraphic units that can be attributed to comparable depositional facies (Fig. 1.3). Lithologic and stratigraphic descriptions below largely follow Karlstrom et al., 1983 and Houston et al., 1992. The

Phantom Lake Metamorphic Suite of the SM and MBM consists of metamorphosed volcano-sedimentary rocks (Graff, 1979; Karlstrom, 1979; Karlstrom et al., 1983). The suite experienced amphibolite-facies metamorphism, relatively intense deformation, and shows rapid lithological changes along strike. Minor differences in stratigraphic units occur between the ranges, including the gradual thinning from an 8 km thick succession in the northwestern SM to the northeastern MBM where it eventually tapers out. Units within the

Phantom Lake Metamorphic Suite of both ranges contain conglomerates and quartzites in the lower part, metavolcanic units at similar levels, and upper quartzites. The Phantom

Lake Metamorphic Suite is interpreted to record a rift setting as made evident by syndepositional fluvial and volcanic rocks (Houston et al., 1992).

In the MBM, the unconformably overlying SPS is divided into three distinct units: the Deep Lake Group, the Lower Libby Creek Group, and the Upper Libby Creek Group.

The SPS and SPG of the MBM and SM, respectively, were deposited in deltaic, glacial, and marine settings. The Deep Lake Group is composed of quartz pebble-rich conglomerates, quartzites, and two glacial diamictite horizons within the Campbell Lake

and Vagner formations; additionally, there is a post-glacial cap carbonate within the latter formation. The Deep Lake Group is about 2.5 km thick in the MBM, whereas in the SM it is roughly 2 km thick (Karlstrom et al., 1983; Houston et al., 1992).

The Lower Libby Creek Group of the MBM is structurally separated from the Deep

Lake Group along the Reservoir Lake thrust fault. It is roughly a 4.5-km-thick succession of six units consisting of quartzites, phyllites, diamictite, and schist (Rock Knoll Formation

– Sugarloaf Quartzite), dominantly representing deltaic depositional facies in a deepening basin and including one prominent glaciomarine diamictite horizon within the

Headquarters Formation (Karlstrom et al., 1983). The Lower Libby Creek Group is correlated to the upper Bottle Creek Formation and Copperton Formation of the SM based on a similar sequence of lithologies (Fig. 1.4A; Houston et al., 1992).

The Upper Libby Creek Group of the MBM structurally overlies the Lower Libby

Creek Group along another thrust, the Lewis Lake fault. It consists of three units reflecting an open-marine depositional environment and is roughly 4 km thick. The predominantly stromatolitic carbonate platform (the Nash Fork Formation), overlain by submarine volcanic rocks of the Towner Greenstone and the black slates of the French Slate

(Karlstrom et al., 1983), introduces a suite of rock types that records a different pattern of sedimentation, which is absent from the underlying group (Karlstrom et al., 1983). The latter two units likely reflect deposition in a foreland basin related to the ca. 1.78 – 1.74 Ga

Medicine Bow Orogeny, while the Nash Fork Formation records the end of the global ca.

2.22 - 2.06 Ga Lomagundi Carbon Isotope Excursion (Bekker et al., 2003).

The SPG of the SM is separated into three distinct parts: the lower, middle, and upper. Units of the lower part are equivalent to those of the Deep Lake Group and the

Lower Libby Creek Group (up to the Heart Formation) of the SPS in the MBM, hosting diamictites, carbonate, and quartzites at similar stratigraphic positions (Fig. 1.4A). The lower part of the SPG is abutted by the Quartzite Peak Fault. The middle part of the SPG consists of the Copperton Formation, a quartzite-phyllite unit correlated to the Medicine

Peak Quartzite-Lookout Schist-Sugarloaf Quartzite of the MBM. The Copperton

Formation is truncated by another thrust, the Hidden Treasure Fault. The upper part of the

SPG consists of the Slaughterhouse Formation, a primarily meta-dolomite unit, which lithologically and geochemically closely resembles the Nash Fork Formation of the MBM

(Bekker et al., 2003). The Slaughterhouse Formation is bounded by the Mullen Creek –

Nash Fork Shear Zone (Fig. 1.3) that terminates the SPG in the SM and the SPS in the

MBM at the French Slate level. The Slaughterhouse Formation is significantly altered in much of the SM and continuous stratigraphic sections are rare due to thrusts slicing the formation from the east to the west (Graff, 1979; Houston et al., 1992).

The ca. 2.45 Ga, near-euhedral, detrital zircons of the basal Magnolia Formation of the SPG in the SM (Premo & Van Schmus, 1989) provide a maximum depositional age for the succession, however, a minimum age constraint for the SPS and SPG is largely missing, and the uppermost unit, the French Slate, is truncated by a thrust fault at the Cheyenne Belt suture.

Figure 1.3: A - Map showing Archean cratons of North America (from Hoffman, 1988; Bleeker & Hall, 2007). B – Geologic map of the Medicine Bow Mountains and Sierra Madre (modified from Karlstrom et al., 1983).

Figure 1.4: A – Lithostratigraphic correlation between the Snowy Pass Supergroup of the Medicine Bow Mountains, WY, USA, the Snowy Pass Group of the Sierra Madre, WY, USA, and the Huronian Supergroup, Ontario, CA based on 3 glacial horizons, post-glacial cap carbonate, mature quartz sandstones, and carbonates recording the Lomagundi carbon isotope excursion (modified from Bekker et al., 2005). B – Stratigraphically ordered detrital zircon histograms for units of the Snowy Pass Supergroup of the MBM with correlative formations of the Snowy Pass Group of the SM (black outlines), and Huronian Supergroup (HS) (shaded black is from Craddock et al., 2013; red outlines are from Hill et al., 2018). Zircon data filtered at 10% discordance.

Methods

A total of nineteen quartzites were collected from the SPS and Phantom Lake

Metamorphic Suite of the MBM and ten quartzites were collected from the SPG and

Phantom Lake Metamorphic Suite of the SM for geochronological analysis (see supplementary sample locations and descriptions). Roughly 2 kg of each quartzite sample was collected, and weathered surfaces were removed in the field to minimize contamination in the lab. Samples were then run through a jaw crusher and refined into a fine sand using a disk mill. The fine material of each sample then first underwent density separation using either a Wilfley Shaker Table or a Gemeni Table. The dried heavy-mineral fraction was run through a Frantz magnetic separator to remove magnetically susceptible minerals. Heavy liquid density separation was then performed on the nonmagnetic splits using methyl iodide (specific gravity: 3.1 g/cm2) and a centrifuge. The remaining heavy splits were then cleaned, dried, and placed in petri dishes for hand-picking. About 150 hand-picked zircons were randomly chosen from each sample with the addition of 10-15 of the most euhedral grains in an effort to better constrain provenance and maximum depositional ages. Chosen zircons were mounted in epoxy pucks and polished down to expose equatorial sections.

Prior to U-Pb analysis, sample pucks were carbon coated and imaged using a cathodoluminescence (CL) detector on a FEI Quanta400f scanning electron microscope

(SEM). Images were used as a reference to compare with measured U-Pb isotope data.

Zircon U-Pb isotope ratios were measured using a 193 nm ArF excimer laser ablation (LA) system coupled to a Nu Plasma inductively coupled plasma mass-spectrometer (ICP-MS)

at the University of California, Santa Barbara. Data were calibrated using the zircon reference materials GJ1 (601.7 ± 1.3 Ma; Jackson et al., 2004), Plešovice (337.13 ± 0.37

Ma; Sláma et al., 2008), 91500 (1062.4 ± 0.4 Ma; Wiedenbeck et al., 1995), and Peixe (564

± 4 Ma; Dickinson & Gehrels, 2003). Data reduction was performed using Iolite software

(Paton et al., 2010, 2011), concordia plots were created using IsoplotR (Vermeesch, 2018), and histogram Kernel Density Estimation (KDE) plots were made using DensityPlotter

(Vermeesch, 2012). SHRIMP U-Pb isotope data for the Medicine Peak Quartzite,

Sugarloaf Quartzite, and Nash Fork Formation obtained at the University of Western

Australia are included in this study and were collected following the standard operating procedure outlined in Smith et al. (1998) using Sri Lankan zircon standard CZ3 (564 Ma,

Pidgeon et al.., 1994).

Sm-Nd isotope analyses were conducted using isotope dilution mass spectrometry on twenty-three shales, the matrixes of two diamictites, and the matrix of one conglomerate at the Institute of Precambrian Geology and Geochronology at the Russian Academy of

Sciences, St. Petersburg, Russia. Shale samples were prepared by cutting and polishing away altered sections. Diamictite and conglomerate samples were crushed by hand and visible rock clasts and areas of alteration were removed from the matrix. Samples were then cleaned and processed into a fine powder using an agate puck mill while cleaning with quartz sand between samples to prevent contamination. For isotope analysis, a mixed

150Nd-149Sm spike was added to each sample powder (~50 mg) and the samples were then dissolved in Savillex teflon beakers in two stages. First in a mixture of concentrated

HCl+HNO3+HF acids at a temperature of 110 - 120

dried and the residue was re-dissolved in a mixture of concentrated HCl+HNO3 acids for a day at the same temperature and dried again. After dissolution, the residue was re-dissolved a third time in concentrated HCl. REE were eluted from the ion-exchange column filled with Dowex AG50W×8 resin (200 – 400 mesh) using 5N HCl. Nd was separated from the rare-earth elements on Ln Resin (EiChrom) in 0.3 N HCl solution, and Sm was separated on the same resin in 0.7 N HCl solution (Gorokhov et al., 2007).

Isotope compositions of Sm and Nd were measured using a multi-collector Triton

TI thermal ionization mass-spectrometer in static collection mode using an Re filament.

The average 143Nd/144Nd value measured for the jNd-1 isotope standard during this study

DM were calculated using the following values for CHUR and DM, respectively: 143Nd/144Nd = 0.512638, 147Sm/144Nd = 0.1967 and 143Nd/144Nd = 0.513151, 147Sm/144Nd = 0.2136.

Analyses of Pb isotope composition in shales were performed using the procedure developed for the silicate component of carbonates at the same lab as for Sm-Nd isotope analysis (Ovchinnikova et al., 2007; 2012). Powdered samples (~50 mg in weight) were decomposed in Savillex teflon beakers using the HF+HNO3 mixture under T = 220ºC.

After dissolution, the sample was re-dissolved to the bromide solution. Pb was extracted by ion exchange with 1×8 Bio-Rad resin in bromide form. The Pb isotope composition was measured on a Finnigan MAT-261 multi-collector mass spectrometer in a static mode on

Re filaments with samples loaded on a silica-supported orthophosphoric acid. The measured Pb isotope ratios were corrected for instrumental mass fractionation (0.13% per

mass unit) determined with multiple measurements of Pb isotope composition of the NIST

SRM 982 standard. According to the processed blanks, the procedural blank during the course of this study never exceeded 0.2 ng for Pb.

Detrital Zircon Results

Detrital zircon geochronology for the SPS of the MBM and SPG of the SM are presented in Table 1.1 and are shown on Fig. 1.4B; dates were filtered to demonstrate 10% discordance. Errors are reported at 1.

General Trends

A dominant peak at ca. 2.7 Ga is observed throughout all the Paleoproterozoic metasedimentary units of the MBM and SM and represents the most abundant zircon mode in all units of the successions (except for two units of the upper SPS). Zircon age modes present in the lower and middle units of the MBM and SM terminate at ca. 2.45 Ga whereas younger modes appear in the younger formations. A prominent ca. 2.3 Ga mode emerges at the Lookout Schist level and diminishes in relative prominence upsection in the upper

Sugarloaf Quartzite and Nash Fork Formation. The Nash Fork Formation contains the youngest detrital zircon mode at ca. 2.2 - 2.1 Ga.

Phantom Lake Metamorphic Suite

The Phantom Lake Metamorphic Suite of the MBM (Stud Creek Volcaniclastics –

Conical Peak Quartzite) and the SM (Jack Creek Quartzite – Bridger Peak Quartzite) show similar zircon age spectra. The zircon age distributions of most of these units are generally unimodal with respect to the dominant ca. 2.7 Ga peak. Minor yet significant modes at ca.

2.45 Ga occur in the Jack Creek (4 dates) and Bridger Peak (5 dates) quartzites of the SM and are present in 1 to 2 grain quantities in the Conical Peak Quartzite, Bow quartzite, and

Colberg Metavolcanics of the MBM.

Snowy Pass Supergroup – Medicine Bow Mountains

The SPS of the MBM includes unique modes not found in underlying samples at the stratigraphic level of the Medicine Peak Quartzite where zircon grains younger than ca.

2.45 Ga become statistically significant for the first time; concordant grains are dated at

2359 10.3 Ma, 2359 17.6 Ma, 2422 14.3 Ma, and 2425 10.6 Ma and comprise a total of four grains younger than 2.43 Ga at this horizon. One grain in the underlying Heart

Formation produced a date at 2317 13.9 Ma; i.e. 300 million years younger than the next youngest mode of dates from the same sample. Additionally, two concordant grains of the

Heart Formation were dated at 1617 Ma and 1681 Ma, which are interpreted as sample contamination or analytical error and have been discarded as statistically insignificant. The next youngest mode occurs in the Lookout Schist overlying the Medicine Peak Quartzite where 42 grains make up the 2328 Ma peak. In addition, the first significant modal population of grains at 2530 Ma occurs in this formation and is composed of 27 dates spanning the 2447 – 2635 Ma range. The ca. 2.7 Ga detrital zircon mode diminishes significantly in the Lookout Schist and the overlying Sugarloaf Quartzite, but returns to dominance in the uppermost Nash Fork Formation. The Sugarloaf Quartzite exhibits its most prominent peak at 2533 Ga, and has the highest relative concentration of grains this age out of all samples. The 2.3 Ga peak is also prominent at this stratigraphic level, although smaller in relative proportion when compared to the underlying Lookout Schist.

The ca. 2.45 Ga detrital zircon mode is at its highest relative abundance in the Sugarloaf

Quartzite in comparison to other samples. The data for the Nash Fork Formation were treated separately for the lower and upper units in Table 1.1. The lower Nash Fork

Formation shows its youngest mode at ca. 2.45 Ga, but contains younger concordant zircon

(as young as 2056 18.1 Ma) with no modal significance. The upper Nash Fork Formation in contrast contains detrital zircon populations younger than ca. 2.45 Ga, centered at 2344

Ma and 2120 Ma. The 2120 Ma detrital zircon mode is the second most prominent in the

Nash Fork Formation (Fig. 1.4B). The youngest detrital zircon grain in the upper Nash

Fork Formation is dated at 2066 9.3 Ma, which is comparable to the youngest detrital zircon grain of the lower Nash Fork Formation dated at 2056 18.1 Ma. These 2 youngest ages of the Nash Fork Formation paired with another grain of the upper Nash Fork

Formation dated at 2067 24 Ma average out to a statistically significant population present at ca. 2062 Ma.

Snowy Pass Group – Sierra Madre

Detrital zircon spectra of the SPG in the SM contain similar modes to their correlative units in the MBM, however, there are instances where the ranges in dates are more limited through time. The Cascade Quartzite of the SM lacks the ca. 2.45 Ga mode observed in its counterpart in the MBM and its youngest grain is dated at 2657 18.5 Ma.

The Bottle Creek Formation includes the first appearance of Paleoproterozoic grains in the

SPG with two grains dated at 2460 17.3 Ma and 2487 17.3 Ma. The lower and upper

Copperton formations contain similar detrital zircon modes; the lower part exhibits a more unimodal age distribution centered on 2710 Ma, while the upper part has a slightly more diverse age distribution covering a longer range of ages centered on 2715 Ma with an additional minor mode present at 3032 Ma composed of 4 grains. The Slaughterhouse

Formation of the upper part of the SPG contains the youngest detrital zircon mode seen in

the SM at 2345 Ma (composed of 5 grains). A new detrital zircon mode to the SM appears at 2552 Ma and is the second most abundant mode for the Slaughterhouse Formation. The youngest dated zircon grain in this formation is 2332 17.6 Ma.

Nd Model Ages for fine-grained metasediments of the Snowy Pass Supergroup, Medicine Bow Mountains

Nd model ages are stratigraphically presented for shale units and for fine-grained matrix fractions of diamictite-bearing units of the SPS in the MBM (the Campbell Lake

Formation to the French Slate; Table 1.2). The depleted mantle curve from DePaolo, 1981 is used and average crustal ages are denoted with TDM. The depositional age is estimated for units based on available geochronologic and geological constraints; resultant variations in Nd(t) are shown on Fig 1.5. Generally, the Nd values do not demonstrate significant trends, and are fairly consistent across formations. TDM values range from 3.91 - 2.64 Ga with Nd values ranging from -0.04 to -10.15. Compared with the detrital zircon data, which include a significant contribution of ca. 2.7 Ga-aged material, the TDM ages of most of the sampled units point to an incorporation of more mature crustal sources responsible for the shift to older model ages. This shift towards older dates is most apparent for the Rock Knoll and Headquarters formations where TDM and Nd(2.3-2.35 Ga) values shift to 3.0+ Ga and less than -6.5, respectively. The Headquarters Formation also has one TDM age of 2.64 Ga, the second youngest in the sample set with an Nd(2.3 Ga) value of -0.04. This dramatic spread in values may indicate a mix of juvenile and mature sources. Another example where more mature sources may have been introduced is the uppermost French Slate where the range of TDM and Nd(1.8 Ga) values is 2.66 – 2.83 Ga and -4.94 to -8.99, respectively.

Figure 1.5: Nd data for the Snowy Pass Supergroup and Huronian Supergroup. Data taken from (1) Ball & Farmer, 1991, (2) Souders & Frost, 2006, and (3) McLennan et al., 2000. The envelope for the Superior craton is as in McLennan et al., 2000 and from Mcculloch & Wasserburg, 1978. Summary fields (grey fields) representing Nd evolution of the Wyoming craton are taken from Chamberlain & Mueller, 2019, Figure 29.4 (see data sources therein). BBMZ – Beartooth-Bighorn Magmatic Zone, MMP – Montana Metasedimentary Province, Neoarchean calc-alkaline magmatism from the Wind River Range is interpreted as continental-arc plutons (Frost et al., 1998).

Pb isotope composition of fine-grained metasediments from the Snowy Pass Supergroup, Medicine Bow Mountains

Pb isotope data can be a useful for interpreting provenance and post-depositional processes in sedimentary systems (Dickin et al., 1996; McLennan et al., 2000). Data for 14 shale samples from the SPS in the MBM (Table 1.2) cluster around an isochron with a date of 1785 87.9 Ma (95% conf.), based on an ordinary least-square regression, reflecting a metamorphic resetting age in the MBM (Fig 1.6).

Calculated 232Th/238U () ratios for all of the sampled units produce an average value of 2.35 (n = 14, range: 1.11 – 4.69) (Table 1.2). The lower SPS formations (Campbell

Lake – Heart formations) produce a slightly smaller averaged value of 2.13 (n = 10, range: 1.11 – 2.68) while the Lookout Schist and Nash Fork Formation exhibit a larger average value of 2.92 (n = 4, range: 1.44 – 4.69). 238U/204Pb () values were also calculated and range from 10.86 to 210.60 with an average of 62.77 (Table 1.2). The average for the Campbell Lake – Heart formations is 67.57 (n = 10, range: 12.87 –

210.60), while the Lookout Schist and Nash Fork Formation have lower average of 50.75

(n = 4, range: 10.86 – 154.00).

Figure 1.6: Plot of 206Pb/204Pb vs. 207Pb/204Pb for units from the SPS and HS. Shown for reference are a =8 growth curve, a 2.7 – 0.0 Ga reference line, which passes through unaltered igneous k-feldspars from the Archean Superior craton (Hemming et al., 1996; McLennan et al., 2000), a 2.2 – 0.0 Ga reference line, along which the data for the McKim – Mississagi formations of the HS are scattered, a ca. 1.79 – 0.0 Ga reference line, along which data for the SPS formations are scattered, and a ca. 1.7 – 0.0 Ga reference line, which fits the data for the Gowganda and Gordon Lake formations of the HS. The HS data is taken from McLennan et al., 2000.

Discussion

1.1. Age of the Phantom Lake Group

The presence of Proterozoic zircons with ages of ca. 2.45 Ga in the basal Jack Creek

Quartzite and the upper Bridger Peak Quartzite of the Phantom Lake Metamorphic Suite in the SM indicates that the Phantom Lake Metamorphic Suite is Paleoproterozoic in age

(Table 1.1 and Fig 4B). Paleoproterozoic zircons were not found in the correlative basal

Stud Creek Volcaniclastics of the MBM. They do occur, however, in minor quantities (one to two grains) in the Colberg Metavolcanics, Bow Quartzite, and Conical Peak Quartzite.

The 2.45 Ga detrital zircon dates obtained from the Magnolia Formation of the SPS in the

MBM originally constrained the maximum depositional age for the Deep Lake Group

(Premo & Van Schmus, 1989). The data from this study agrees with this age, but extends the same maximum depositional age (ca. 2.45 Ga) to the Phantom Lake Metamorphic

Suite.

1.2. Correlation between the Paleoproterozoic successions in Sierra Madre and Medicine Bow Mountains

U-Pb age spectra from units of the SPS and SPG show similar trends throughout their stratigraphy with some notable differences. The ca. 2.45 Ga zircon mode that is seen in the MBM, most prominently in the Cascade, Medicine Peak, and Sugarloaf quartzites, is not seen in the SPG, although it is expressed in the underlying Phantom Lake Group of the SM (see discussion above). Many units of the SPS and SPG exhibit similar Archean detrital zircon age populations; most Archean age modes that are present in the SPG generally occur in the SPS (although the range of ages is more diverse in the SPS),

indicating similar sources for these populations. For example, the ca. 2.7 Ga peak persists through all samples in both ranges as well as the less pronounced population at ca. 2.8 Ga

(Fig 1.4B). Differences between age spectra from the MBM and SM include the general lack of ages greater than 3.1 Ga in the SPG (except for in the Jack Creek Quartzite of the

Phantom Lake Metamorphic Suite and Bottle Creek Formation) and the overall lack of significant age peaks younger than ca. 2.45 Ga up to the upper Copperton Formation. These disparities are potentially related to differences in provenance of these successions. In summary, units from the MBM generally show older age modes (> 3.0 Ga) than their SM counterparts. The rarity of the ca. 3.5 – 3.0 Ga grains in the SM might indicate that zircons of this age are derived from sources in closer proximity to the MBM. With regards to the younger zircon modes in the ranges, the SM demonstrates a general cutoff in ages at ca.

2.4 Ga (with the exception of several younger grains with ca. 2.3 Ga dates in the

Slaughterhouse Formation), whereas the MBM contains populations that date to ca. 2.1

Ga.

1.3. Changes in provenance during deposition of Paleoproterozoic successions in Medicine Bow Mountains and Sierra Madre

Age spectra from all units of the Phantom Lake Metamorphic Suite and the Snowy

Pass Supergroup combined demonstrate a range in dates from ca. 3.5 to 2.1 Ga. The age range from the Phantom Lake Metamorphic Suite falls between ca. 3.5 and 2.45 Ga. The youngest detrital zircon populations generally do not extend beyond ca. 2.45 Ga for most of the middle stratigraphical units of the Paleoproterozoic SPS. The Lookout Schist of the

MBM demonstrates the first deviation from this pattern with a dramatic peak in zircon dates at ca. 2328 Ma. Zircons with ca. 2.3 Ga dates persist as the youngest mode through

the Sugarloaf Quartzite and Slaughterhouse Formation of the MBM and SM, respectively, but a significant shift in provenance occurred during deposition of the upper Nash Fork

Formation where ca. 2.2 – 2.1 Ga zircon grains emerge in abundance. Importantly, magmatism at ca. 2.2 Ga is not yet recognized on the southern margin of the Wyoming craton. Ages at 2010.9 1.2 Ma and 2051 9 Ma have been obtained for mafic intrusive rock units associated with rifting in the Laramie Mountains (Snyder et al., 1995; Cox et al.,

2000), and a 2092 9 Ma age was obtained for an intrusion located in the Cascade

Quartzite of the SM (Premo & Van Schmus, 1989). The upper Nash Fork Formation contains detrital zircon grains with ages between 2066 Ma and 2100 Ma that could potentially have been derived from the sources associated with these intrusive events, although no zircon grains with dates near the 2010 10 Ma age obtained for the Kennedy

Dike Swarm in the Laramie Mountains were found.

1.4. Age and correlation of the Nash Fork and Slaughterhouse formations

The Nash Fork Formation of the MBM and the Slaughterhouse Formation of the

SM have been considered correlative based on their stratigraphic position (Houston et al.,

1992) and highly positive C isotope values recorded by carbonates (Bekker et al., 2003).

Detrital zircons from the upper Nash Fork Formation and Slaughterhouse Formation provide the maximum depositional ages of 2081 10 Ma (MSWD = 0.22) and 2334 11

Ma (MSWD = 0.0073), respectively, based on the mean age of the 3 youngest grains with overlapping 2(Dickinson & Gehrels, 2009; Spencer et al., 2016). A more conservative approach to maximum depositional ages using the youngest statistical population by calculating the weighted average of the youngest mode of 2 or more grains

with an MSWD of about 1 (cf. Coutts et al., 2019; Herriott et al., 2019) has yielded maximum depositional ages for the upper Nash Fork and Slaughterhouse formations at

2118 2.4 Ma (MSWD = 0.97) and 2344 8.7 Ma (MSWD = 1.29), respectively.

Two of the three ca. 2.3 Ga grains used for the calculation of the maximum depositional age with the “3 youngest grains” method for the Slaughterhouse Formation are euhedral. The upper Gordon Lake Formation of the HS contains volcanoclastic sediments with a calculated depositional age of 2315 5 Ma based on the youngest grains

(Hill et al., 2018), and tuff beds of the Gordon Lake Formation produced a U-Pb SHRIMP zircon age of 2308 8 Ma (Rasmussen et al., 2013). Carbon isotopes from carbonates of the Slaughterhouse and Gordon Lake formation range between +5.9‰ and +16.6‰, and

+5.0‰ to +8.2‰, respectively (Bekker et al., 2003; Bekker et al., 2006). New geochronological constraints thus leaves us with a dilemma that either the Slaughterhouse and Nash Fork formations are correlative as earlier suggested, but their provenances were dramatically different with Paleoproterozoic sources not accessible in the SM area

(consistent with the provenance difference in general between the SM and MBM in terms of Paleoproterozoic sources) or that the Slaughterhouse Formation is not correlative with the Nash Fork Formation, but older and potentially correlative with the Lookout Schist of the SPS and the Gordon Lake Formation of the HS that contain zircons with similar ages and carbonates with similarly positive C isotope values (in the case of the Gordon Lake

Formation). Interestingly, Paleoproterozoic igneous rocks are exposed in the SM such as the ca. 2.45 Ga Baggot Rocks Granite and ca. 2.09 Ga metagabbro plug (Premo and Van

Schmus, 1989).

1.5. Comparing Sm-Nd data for shales and U-Pb data for detrital zircons from sandstones

Sm-Nd data from the SPS in the MBM exhibits Nd values ranging from -10.15 to

-0.04 and TDM ages spanning 3.91 to 2.64 Ga. These values are in agreement with the results from previous Sm-Nd studies of the SPS in the MBM and those for the Phantom

Lake Metamorphic Suite of the SM (Fig. 1.5; Ball & Farmer, 1991; Souders & Frost, 2006).

There is a significant disconnect between detrital zircon and TDM ages. Since the detrital zircon data are dominated by ca. 2.7 Ga ages, likely derived from juvenile greenstone belts, one would expect that the TDM ages would be tied more closely to this age. However, only 2 analyzed samples of the 26 total produced TDM ages younger than

2.7 Ga, and 8 samples produced TDM ages younger than 2.9 Ga. This disconnect might reflect that zircons are derived from later magmatic events that reworked continental crust, whereas Sm-Nd model ages reflect the time of magma extraction from the depleted mantle.

2.1. Correlation between the Paleoproterozoic successions of Wyoming and the Huronian Supergroup on the Superior craton

The HS and SPS have long been correlated with one another through lithostratigraphy and geochemistry, and paleomagnetic studies have contributed strong arguments for their correlation (Young, 1970, 1973; Karlstrom et al., 1983; Bekker et al.,

2003; Kilian et al., 2015). The detrital zircon data presented in this study demonstrates shared provenance at corelative stratigraphic levels with generally the same relative abundances (Fig 1.4B), confirming the proximal deposition of the HS and SPS. The HS age spectra of units at corresponding stratigraphic levels to the Magnolia Formation –

Sugarloaf Quartzite of the SPS demonstrate nearly identical zircon age modes and relative

abundances with the exception of younger zircon modes appearing in the SPS at the upper

Nash Fork Formation stratigraphic level at ca. 2.2 - 2.1 Ga, as deposition of the HS is terminated after deposition of the ca. 2.31 Ga Gordon Lake Formation and long before the emplacement of the ca. 2.2 Ga Nipissing Diabase (Corfu & Andrews, 1986; Noble &

Lightfoot, 1992; Buchan et al., 1993; Bleeker et al., 2015).

2.2. Lower Huronian Supergroup and Phantom Lake Group

The basal volcanic formations in the eastern part of the HS are dated at ca. 2.45 Ga

(Krogh et al., 1984; Ketchum et al., 2013; Bleeker et al., 2015), allowing correlation of volcanic and sedimentary rocks of the Elliott Lake Group of the HS to the Phantom Lake

Metamorphic Suite of the southern Wyoming craton. Lithologically, the Phantom Lake

Metamorphic Suite includes similar rock types to those of the Thessalon and Livingstone

Creek formations of the Elliott Lake Group in the western part of the Huronian basin. The basal Livingstone Creek Formation of the Elliot Lake Group starts with conglomerates and grades to sandstones, while the overlying Thessalon Formation hosts amygdaloidal basalts, some conglomerates (radioactive in some areas), and dacite-rhyodacite volcanic rocks

(Bennett et al., 1991; Ketchum et al., 2013). In the eastern part of the Huronian basin, the lower Huronian Supergroup units contain the Elsie Mountain, Stobie, and Copper Cliff formations in stratigraphically ascending order. The Elsie Mountain and Stobie formations are lithologically similar, differentiated by the prominent increase in intercalated sedimentary rocks in the upper formation. They both contain metamorphosed mafic lava flows with common pillow structures and include sections with rhyolitic flows (Bennett et al., 1991). The Copper Cliff Formation conformably overlies the Stobie Formation and is

characterized by intercalated felsic and mafic flows, and minor felsic pyroclastic and metasedimentary rocks (Innes, 1977; Bleeker et al., 2015). The Rock Mountain

Conglomerate and Deep Gulch Conglomerate Member of the Jack Creek Quartzite form the basal part of the Phantom Lake Metamorphic Suite in the MBM and SM, respectively, grade to the overlying sandstone units, and contain detrital U minerals similar to the base of the Thessalon Formation, while the overlying Colberg and Silver Lake metavolcanics contain a heterogenous package of similar volcanic and sedimentary rocks including amygdaloidal and pillow basalts, rhyolitic to basaltic fragmental rocks, conglomerates, and quartzites (Houston et al., 1992). The ages of detrital zircons in sandstones of the Phantom

Lake Metamorphic suite compared to the ages of the basal volcanics of the Huronian

Supergroup along with the lithological similarities observed in these basal and overlying groups provide evidence for the contemporaneous deposition of these basal units in the joint basin.

2.3. Comparing changes in provenance during deposition of Paleoproterozoic successions in the Snowy Pass and Huronian basins

Detrital zircon modes are nearly identical between the Snowy Pass and Huronian supergroups (Fig. 1.4B). Data for the HS is mainly from Craddock et al., 2013 with additional data for the Gordon Lake and Bar River formations of the upper HS from Hills et al., 2018. Paleocurrent analysis of the Paleoproterozoic units of the SPS and HS paired with craton reconstructions shows orientations towards the joint basin of the SPS and HS

(Long, 1995; Karlstrom et al., 1983).

A strong ca. 2.7 Ga peak is expressed in almost every unit of the MBM, SM, and

HS. Material of this age from the Superior craton could have been sourced from the

extensive ca. 2730 – 2670 Ma Wawa-Abitibi greenstone belt located just north and northwest of the Huronian Basin (Ayer & Dostal, 2000; Davis, 2002) as well as from the ca. 2.7 Ga rocks of SAT, Sweetwater, and Bighorn subprovinces of the Wyoming craton

(see Chamberlain et al., 2003, Table 1 and references therein). Minor peaks between ca.

2.9 and 2.8 Ga are also shared by the SPS and HS (especially prominent in the Rock Knoll

Formation and the Medicine Peak Quartzite), and igneous sources of this age in the central

Wyoming craton are located in the Bighorn, Granite, and Owl Creek mountains

(Chamberlain et al., 2003, Table 1 and references therein). The ca. 2.9 – 2.8 Ga igneous units on the Superior craton that could have contributed sediments to the SPS and HS joint basin occur in greenstone belts of the Marmion and Winnipeg River terranes west of the

Huronian Basin (Stone et al., 2002; Tomlinson et al., 2003).

Some minor differences are noticeable between the correlative Lindsey Quartzite and Matinenda Formation where the Lindsey Quartzite includes a broader range of detrital zircon dates. The Matinenda Formation detrital zircon age data occupy a narrow range between ca. 2.8 and 2.6 Ga, while the Lindsey Quartzite shows a range of ages between ca.

3.5 and 2.55 Ga. Farther upsection, the Cascade Quartzite and Mississagi Formation demonstrate very similar age spectra, although some minor differences occur in the older part of the spectrum between ca. 3.5 and 2.9 Ga where minor peaks do not exactly match between units. Slight differences in relative concentrations within zircon populations are observed in the Serpent and Lorraine formations with respect to their SPS correlatives. The

Serpent Formation contains a more prominent peak at ca. 2.9 – 2.8 Ga, which could reflect either larger contribution from source rocks of this age or a bias related to a smaller sample

size (n = 46), influencing true relative abundances (Vermeesch, 2004). The Lorraine

Formation of the HS shows different age spectra from the correlative Medicine Peak

Quartzite with a more limited distribution spanning ca. 2.95 – 2.6 Ga, whereas the latter formation contains a multi-modal population ranging between ca. 3.0 and 2.45 Ga. The emergence of ca. 2.3 Ga zircon modes in the Lookout Schist and Sugarloaf Quartzite of the SPS corresponds to similar peaks at the correlative levels of the Gordon Lake and Bar

River formations in the HS, respectively (Hill et al., 2018). The absence of a ca. 2.7 Ga mode in the Lookout Schist does not correspond with data from the Gordon Lake

Formation, although all other peaks in the spectra overlap, albeit at different relative ratios.

The ca. 2.55 and 2.3 Ga modes are much broader and larger in the Lookout Schist than in the Gordon Lake Formation, potentially implying closer proximity to these sources on the

Wyoming craton. Rocks dated at ca. 2.55 Ga on the Wyoming craton are preserved in the

Teton Range and the Beartooth Mountains (Mogk et al., 1988; Zartman & Reed, 1998;

Chamberlain et al., 2003). The Sugarloaf Quartzite of the SPS also carries a pronounced ca. 2.3 Ga peak, which is not as prominent as that of the Lookout Schist, and matches up to the ca. 2.3 Ga mode seen in the Bar River Formation based on data from Hills et al.,

2018. There is a similar mode at ca. 2.55 Ga and a significantly lower abundance of ca.

2.45 Ga zircon in the HS at this stratigraphic level. Older zircons with ca. 3.3 Ga ages present in this unit of the SPS are entirely lacking from the HS data.

Igneous units on the Wyoming craton with ages ranging from ca. 3.6 to 3.2 Ga are found in the northern Granite Mountains where ca. 3.6 – 3.3 Ga orthogneisses are preserved

(Kruckenberg et al., 2001; Fruchey, 2002; Grace et al., 2006; Chamberlain & Mueller,

2019), and metasupracrustal successions in the Hellroaring Plateau of the eastern Beartooth

Mountains contain detrital zircon population with the predominantly ca. 3.4 - 3.2 Ga age range, indicating proximal sources of this age during their deposition between 3.2 and 2.7

Ga (Mueller et al., 1992; Mueller et al., 1998; Chamberlain & Mueller, 2019). Ca. 3.5 - 3.2

Ga quartzofeldspathic gneisses are also found in the Montana Metasedimentary Province tectonically interleaved with metasedimentary sequences and contributing to their detrital zircon populations (Mogk et al., 1992, 2004; Mueller et al., 1993; Mueller et al., 2014). In contrast, ca. 3.5 – 3.0 Ga zircons present in the HS have been attributed to sources in the

Watersmeet and Minnesota River Valley gneiss terranes of WI and MN, west of the

Huronian Basin on the Superior craton (Bickford et al., 2006; Schmitz et al., 2006;

Craddock et al., 2013).

2.4. Detrital zircon patterns for the upper parts of the Huronian and Snowy Pass successions

Since deposition of the HS terminated before intrusion of the ca. 2220 - 2210 Ga

Nipissing Diabase dikes (Corfu & Andrews, 1986; Noble & Lightfoot, 1992; Buchan et al., 1993; Bleeker et al., 2015), younger detrital zircon modes from the upper SPS are not expected to have a match in the HS. The first appearance of a detrital zircon modes unique to the SPS occur in the upper Nash Fork Formation. This ca. 2.2 – 2.1 Ga mode is not observed either in the lower Nash Fork Formation, although 1 grain at was dated at 2056

18 Ma, or in the Slaughterhouse Formation of the SM. Similar ages of hydrothermal xenotime are observed in the Chocolay Group of the Chocolay Basin, which is constrained to be younger than ca. 2.3 Ga, based on detrital zircon ages (Vallini et al., 2006). The

Chocolay Basin has been proposed to constitute the primary depocenter on the southern

Superior Craton around 2.2 Ga as the western Huronian Basin was uplifted in association with the Marathon LIP hotspot and subsidence shifted to the west (Craddock et al., 2013).

The Chocolay Group has been lithologically correlated to the upper HS based on matching glacial diamictite, clean, mature quartzite, and stromatolitic dolostone sequences as well as the presence of ca. 2.3 Ga detrital zircon populations similar to the detrital and volcanic zircons in the Gordon Lake and Bar River formations of the HS (Vallini et al., 2006;

Craddock et al., 2013; Rasmussen et al., 2013; Hill et al., 2018), ultimately correlating it to the middle part of the SPS. Alternatively, the Chocolay Group diamictite might correspond to the fourth early Paleoproterozoic glaciation, recorded so far only by the

Reitfontein Member of the Timeball Hill Formation, Pretoria Group in South Africa

(Coetzee et al., 2006; Rasmussen et al., 2013) and the overlying Kona Dolomite might record the early part of the Lomagundi carbon isotope excursion (Bekker et al., 2003), negating their correlation with the upper HS. Similar to the Nash Fork Formation in the

MBM, a mode at ca. 2.1 Ga is seen in the East Branch Arkose of the Dickinson Group and the Denham Formation of the Mille Lacs Group (Craddock et al., 2013), which likely correspond to rifting, breakup, and separation of the Superior and Wyoming cratons. The ca. 2125 – 2100 Ma Marathon and 2075 Ma Fort Frances dike swarms are centered on the southern margin of the Superior craton and dikes of similar age are observed in radial arrangement on the Wyoming craton (Ernst & Bleeker, 2010) (Fig. 1.7). The Bear

Mountain dikes from the Granite Mountains in central Wyoming yield a U-Pb TIMs zircon age of 2113 15 Ma and the dated unit strikes towards the inferred plume center of the

Marathon dike swarm on a paleogeographic reconstruction of the Wyoming and Superior

cratons before their breakup (Bowers & Chamberlain, 2006; Ernst & Bleeker, 2010). The

2170 8 Ma Wind River dikes in the Wind River Range are subparallel to the coeval

Biscotasing dikes of the eastern Superior craton, although only one Wyoming dike was used in this reconstruction (Harlan et al., 2003; Ernst & Bleeker, 2010). The 2060 6 Ma metamorphosed mafic dikes and sills of the Tobacco Root Mountains of the northwest

Wyoming craton are also an approximate age match to the ca. 2075 Ma Fort Frances dikes on the Superior craton (Brady et al., 2004; Mueller et al., 2004; Ernst & Bleeker, 2010) and could be radiating from the Fort Frances plume center. Further, these events broadly correspond to the age of the youngest concordant detrital zircons in the upper Nash Fork

Formation (2081 10 Ma; MSWD = 0.22) based on the mean age of 3 youngest grains with overlapping 2 9 Ma.

The 2092 9 Ma metagabbro plug in the SM (Premo & Van Schmus, 1989) adds to the record of the widespread LIP magmatism at this time. Since LIP magmas do not produce much zircon, zircons of this age might be attributed to the widespread, contemporaneous siliceous LIP (SLIP) that may have been emplaced throughout the Wyoming and Superior cratons.

Figure 1.7: Early Paleoproterozoic reconstruction of the Superior and Wyoming cratons (modified from Ernst & Bleeker, 2010). Fort Frances, Marathon, and Biscotasing dikes with plume centers on the margin of the Superior craton demonstrate radial agreement with coeval intrusive units on the Wyoming craton. Abbreviations are as follows: Snowy Pass Supergroup (SPS), Huronian Supergroup (HS), Animikie Basin (AB), Bear Mountain dikes (BM), Wind River dikes (WR), metamorphosed mafic dikes and sills of the Tobacco Root Mountains (MM). 2092 9 Ma metagabbro intrusion of the SM (Premo & Van Schmus, 1989) is shown with a red circle. See text for further discussion.

2.5. Sm-Nd data for the Snowy Pass and Huronian supergroups

Units of the HS that have been analyzed for Sm-Nd isotopic composition demonstrate a smaller range of TDM ages and Nd(2.3 Ga) values (excluding the Gordon

Lake Formation), ranging from 3.0 to 2.84 Ga and -4.97 to -2.47, respectively (McLennan et al., 2000), in comparison to the data for the early Paleoproterozoic supracrustal successions from the southern margin of the Wyoming craton. However, there is striking overlap between these values from the southern Superior Province and values for the

correlative units of the Snowy Pass Supergroup. A field representing the evolution of

Archean material derived from the Superior craton is shown in Fig. 1.5 (McCulloch &

Wasserburg, 1978; McLennan et al., 2000). Since much of the data for the HS falls within this field, it is interpreted that its provenance was on the Superior craton, which is further supported by geochemical, petrological, and paleocurrent data (e.g. Young, 1983;

McLennan et al., 2000). Many of the Paleoproterozoic units of southern Wyoming are also within the field corresponding to the provenance from the Superior craton. The Campbell

Lake, Vagner, and Heart formations, Lookout Schist, and French Slate of the MBM fall entirely into this field, while most datapoints for other formations spread between this field and the fields representing provenance of the Wyoming craton.

Nd datapoints from the Rock Knoll, Headquarters, and Nash Fork formations have values, which fall much lower than the Superior craton evolution field into the Beartooth-

Bighorn magmatic zone (BBMZ) and Sacawee block gneiss fields. These lower Nd values might be due to sediment contribution from ancient rocks of the Wyoming craton core.

Metamorphic and igneous rocks with ages at ca. 2.85 Ga are common in the BBMZ and ca. 3.3 – 3.1 Ga zircon ages are known in the Sacawee block (Mogk et al., 1992; Grace et al., 2006). A small peak in detrital zircon ages at ca. 2.85 Ga is shown by the Rock Knoll

Formation dataset and 3 detrital zircon grains from this unit fall into the ca. 3.3 – 3.2 Ga range; the correlative Bottle Creek Formation in the SM contains 2 detrital zircon grains at ca. 2.85 Ga and 3 grains between ca. 3.3 and 3.2 Ga. The Headquarters Formation also has a small group of zircons with ages at ca. 2.85 Ga and 1 older grain at ca. 3.1 Ga. The Nash

Fork Formation produced a significant amount of datapoints corresponding to the age of the BBMZ and Sacawee block gneisses.

The Gordon Lake Formation of the upper Huronian Supergroup plots above the

Superior craton provenance, having Nd(2.3 Ga) and TDM values ranging between -1.04 and +1.06 and 2.55 and 2.76 Ga, respectively, and has been interpreted to have a provenance with a significant contribution of juvenile material (McLennan et al., 2000).

Considering that there are abundant tuffs and volcaniclastic sediments in the Gordon Lake

Formation (e.g. Rasmussen et al., 2013; Hill et al., 2018), they might have been a source of the more juvenile component for the Gordon Lake Formation. Some samples from the

Headquarters and Nash Fork formations, along with those from the French Slate, include similar TDM ages, ranging between 2.89 and 2.64 Ga, and show more positive Nd values relative to other samples, indicating that the juvenile provenance inferred for the Gordon

Lake Formation is also observed in the MBM. The French Slate was likely deposited in the foreland basin when an island arc collided with the southern margin of the Wyoming craton so the juvenile material was likely derived from this arc. The Nash Fork Formation was deposited shortly after the ultimate rifting, breakup, and separation of the Wyoming and

Superior cratons, and juvenile material might correspond to contribution from the associated emplacement of LIPs and rift volcanics. The change in provenance reflected by the range of Nd values for the Headquarters Formation is harder to explain, although long- distance transport during glacial intervals could have delivered material from distant sources to the Wyoming craton.

2.6. Events affecting the Pb isotope system

The regression age obtained for samples of the SPS at ca. 1.8 Ga is similar to that based on the Pb isotope data for the Gowganda and Gordon Lake formations of the upper

HS (Fig 1.6). The datapoints from several SPS formations are comparable to the high

206Pb/204Pb values (>40) of the Gowganda and Gordon Lake formations, which have been attributed to post-depositional disturbance (McLennan et al., 2000). A reference line, corresponding to the undisturbed evolution of the U-Pb isotope system through time since ca. 2.7 Ga and based on Pb isotope composition of K-feldspar from unaltered plutonic rocks of the Superior craton is shown in Fig. 1.6 (data from Hemming et al., 1996), highlighting the shift seen in disturbed HS and SPS metasediments. The resetting event recorded by the Huronian data may coincide with the SPS Pb isotope disturbance.

The potentially associated metamorphic event on the southern margin of the

Wyoming craton is the 1.78 – 1.74 Ga Medicine Bow Orogeny, which occurred when the

Wyoming craton collided with an island-arc terrane to the south along the Cheyenne Belt, and is in direct contact with units of the uppermost SPS (Chamberlain, 1998; Frost et al.,

2000). This orogenic event may have led to Pb isotope re-equilibration. The Yavapai orogeny, which could have triggered the similar Pb-Pb isotope system resetting in upper units of the HS on the southern Superior craton (cf. McLennan et al., 2000), is recorded by: 1) ca. 1.75 – 1.70 Ga felsic intrusions and metamorphic monazite U-Th-total Pb dates in the southern portion of the Huronian Basin (Davidson et al., 1992; Piercey et al., 2007);

2) similar-age (1.77 – 1.76 Ga), staurolite-grade metamorphism in the Penokean Orogen of Minnesota (Holm et al., 1998, 2005, 2007; Van Schmus et al., 2007), and 3) 39Ar/40Ar

whole rock dates of sedimentary rocks from the McKim, Gowganda, and Gordon Lake formations, which show evidence for disturbance at 1.76 – 1.70 Ga (Hu et al., 1998).

The 232Th/238U () ratios calculated for the HS sediments are largely between 2 and

4 (Fig 1.8), with the average at 2.45 (full range: 0.88 – 3.58) (data from McLennan et al.,

2000), which is comparable to the average upper crustal value of 3.8 (Taylor & McLennan,

1985; McLennan et al., 2000). The values for the SPS metasediments are similarly between 2 and 4, with the average at 2.35 (full range: 1.11 – 4.69), indicating oxic, terrestrial, chemical weathering decoupling Th and U with resultant high values in organic-lean sediments and low values in organic-rich sediments deposited from an oxic water column (cf. Pollack et al., 2009). Pb isotope data for various Archean and

Paleoproterozoic shale suites further demonstrate this decoupling effect through Earth’s atmospheric evolution (Fig. 1.9). The 238U/204Pb () values for the correlative Lookout

Schist and Nash Fork Formation of the SPS and the Gowganda and Gordon Lake formations of the HS yield similar average values of 50.75 (full range: 10.86 – 154.00) and

54.51 (full range: 18.87 – 193.86), respectively. The similar high values and age of resetting of U-Pb isotope system likely reflect either Pb-loss or U-gain in association with a high-temperature event. Lower units of the SPS yielded similar values to the upper SPS, with the total average of 62.77 (full range: 10.86 – 210.60) (Table 1.2). In contrast, lower formations of the HS have lower values; samples from the McKim to Mississagi formations have an average of 23.47 (full range: 9.01 – 86.91), which might be related to an older resetting event recorded by their Pb isotope system at ca. 2.2 Ga in association

with emplacement of the Nipissing diabase dikes and sills (Dickin et al., 1996; McLennan et al., 2000).

Figure 1.8: Plot of 206Pb/204Pb vs. 208Pb/204Pb for units from the SPS and HS. The origin for the 232Th/238U ( value) evolution lines is the isotope composition of unaltered igneous K-feldspars from the Superior craton with lines representing isotopic evolution at = 1 through 4 (Hemming et al., 1996; McLennan et al., 2000). Most values fall between = 2 and 4, which is different from the typical upper crustal value of ~3.8 (Taylor & McLennan, 1985). The HS data is taken from McLennan et al., 2000.

Figure 1.9: (232Th/238U) values for Archean and Paleoproterozoic shale suites through time. Data ranges represent the (1) ca. 3.8 Ga Isua Belt, Greenland (Rosing & Frei, 2004), (2) ca. 3.05 Ga Buhwa shales, Buhwa greenstone belt, Zimbabwe (Krogstad et al., 2004), (3) ca. 2.3 Ga Huronian Supergroup, Ontario, Canada (McLennan et al., 2000), (4) ca. 2.15 Ga Sengoma Argillite Formation, Botswana (Pollack et al., 2009), (5) ca. 2.1 Ga Snowy Pass Supergroup, (6) ca. 1.8 Ga Hondo Group, southwestern USA (McLennan et al., 1995), and (7) modern turbiditic muds (Hemming & McLennan, 2001). The value for the average marine shale (light grey field, =3.2, Turekian & Wedepohl, 1961) and for average upper continental crust (dark grey, =3.8, Taylor & McLennan, 1985), as well as the timing of the Great Oxidation Episode (GOE) are included for reference. Data for each suite displayed as mean values with 1 constraints. Archean data shows little variation, however decoupling of U and Th is made apparent during the progress of the GOE as reflected by increased spread of , likely due to the initiation of oxidative continental weathering. Modified from Pollack et al., 2009.

3.1. Implications for the evolution of the early Paleoproterozoic Earth System

The HS has been extensively studied to understand the evolution of the early

Paleoproterozoic global Earth system. The rise of atmospheric oxygen during the GOE, the onset and termination of the Lomagundi carbon isotope excursion, and 4 global low- latitude glaciations occurred during the early Paleoproterozoic (Karhu & Holland, 1996;

Bekker & Eriksson, 2003; Bekker et al., 2004; Bekker et al., 2005; Guo et al., 2009;

Rasmussen et al., 2013; Bekker, 2014). Detrital zircon data from the SPS paired with those for the HS further enable the constraint of the timing of these events across the Wyoming and Superior cratons.

3.2. Reconstruction of the Superia supercraton

The Wyoming and Superior cratons have been interpreted to have assembled during the ca. 2.65 Ga Oregon Trail Orogeny along the Oregon Trail Structural Belt and separated between ca. 2.1 – 2.0 Ga based on paleomagnetic data from dike swarms (Chamberlain et al., 2003; Kilian et al., 2015; Chamberlain et al., 2017). The detrital zircon data from this study and for the HS (Craddock et al., 2013; Hills et al., 2018) demonstrate a consistently shared depositional history in the same basin for all but the uppermost units of the SPS, which postdate the termination of the HS deposition between ca. 2.31 and 2.22 Ga (Corfu

& Andrews, 1986; Noble & Lightfoot, 1992; Buchan et al., 1993; Rasmussen et al., 2013;

Bleeker et al., 2015), thus providing further support to the Wyoming-Superior cratonic link, which persisted through much of the early Paleoproterozoic.

3.3. Age constraints for the early Paleoproterozoic (Huronian) glaciations

Glacial diamictite units of the SPS, which occur in the Campbell Lake, Vagner, and

Headquarters formations are respectively correlated with the Ramsay Lake, Bruce, and

Gowganda formations of the HS based on lithostratigraphic similarities (Blackwelder,

1926; Houston et al., 1992; Roscoe & Card, 1993; Bekker et al., 2003). The glacial units of the HS are constrained in age between ca. 2450 and 2308 Ma (Krogh et al., 1984;

Ketchum et al., 2013; Rasmussen et al., 2013; Bleeker et al., 2015). The oldest Huronian

glaciation is constrained in age between ca. 2.44 and 2.43 Ga in South Africa, West

Australia, and Fennoscandia (Brasier et al., 2013; Gumsley et al., 2017; Bekker et al., 2020;

Warke et al., 2020). The middle and upper Huronian glaciations do not have separate age constraints and are together bracketed in age between 2.43 and 2.31 Ga in South Africa and in the HS (Rasmussen et al., 2013; Gumsley et al., 2017), whereas the fourth early

Paleoproterozoic glaciation is between 2.26 and 2.22 Ga in age (Rasmussen et al., 2013).

Detrital zircon dates less than ca. 2.6 Ga are not present in the Campbell Lake and Vagner formations and detrital zircon dates from the Headquarters Formation are not younger than ca. 2.4 Ga. However, the data from the SPS agrees with the above age constraints as the three diamictite-bearing formations are bracketed in age between ca. 2450 and 2300 Ma based on detrital zircon maximum depositional ages for the Phantom Lake Metamorphic

Suite and the upper formations of the SPS.

3.4. 2.3 Ga magmatic event and the proposed tectono-magmatic lull of the Paleoproterozoic

A unique mode in the global record of detrital zircon ages at ca. 2.3 Ga is found in the upper units of the SPS; a time period when plate tectonics supposedly experienced tectonic shutdown or slowdown between ca. 2.45 and 2.2 Ga (Condie et al., 2009) or ca.

2.3 - 2.2 Ga (Spencer et al., 2018), based partially on a general scarcity of subduction- related granitoid magmatism and paucity of detrital zircon of this age in the global record.

Alternative views have emerged with studies that went on to demonstrate the presence of magmatism during this time period globally (Partin et al., 2014; Pehrsson et al., 2014).

Although records do show the presence of igneous and metamorphic units of this age as well as detrital zircon, global magmatism and orogenic activity as well as the number of

passive continental margins are significantly decreased between 2.3 – 2.2 Ga (Spencer et al., 2018). The presence of ca. 2.3 - 2.2 Ga detrital zircon in the SPS contributes to this ongoing debate. The Lookout Schist includes the ca. 2.3 Ga detrital zircon mode in high relative abundance and zircons of this age are also present, albeit less abundantly, in the upper Sugarloaf Quartzite and Nash Fork Formation. Grains dated to ca. 2.3 Ga occur with a similar relative abundance in tuff beds and volcaniclastic sandstones of the Gordon Lake and Bar River formations in the HS (Rasmussen et al., 2013; Hill et al., 2018), further supporting correlation between these two supergroups at this stratigraphic level.

Preservation of long, prismatic zircon grains of this age in the Gordon Lake Formation

(euhedral grains of this age are also observed in the Slaughterhouse Formation of the SPG) provides an indication that these zircons were locally derived and thus have not been much abraded during transport (cf. Hill et al., 2018). Although zircons with dates between ca. 2.3

- 2.2 Ga are present in the SPS, a compilation of all concordant dates in our study demonstrates a general paucity of detrital zircons with this age (Fig 1.10). Indeed, out of the 3000+ concordant grains from the early Paleoproterozoic units of the MBM and SM, only 14 zircons produced dates within this range, lending further support to the proposed slowdown of zircon-forming events during this period. In conclusion, although detrital zircon geochronology of the upper SPS demonstrates some magmatic activity on or next to the Wyoming and Superior cratons during this time period (see also Raharimahefa et al.,

2014), the notion of relative magmatic and tectonic quiescence during this period is supported by our Wyoming data.

Figure 1.10: Compilation of all concordant (10%) detrital zircon data from this study. 3.5. Age constraints for C isotope variations in seawater in the early Paleoproterozoic

The Nash Fork Formation records the end of the Lomagundi carbon isotope excursion, which is still poorly constrained in age between ca. 2.22 and 2.06 Ga (Karhu &

Holland, 1996; Bekker & Holland, 2012; Bekker, 2014). Detrital zircon populations from the upper Nash Fork Formation that were deposited after the end of the Lomagundi carbon isotope excursion provide a maximum depositional ages of 2118 2.4 Ma (MSWD = 0.97),

using the youngest statistical population method (Coutts et al., 2019; Herriott et al., 2019),

2081 10 Ma (MSWD = 0.22), based on the mean age of the 3 youngest grains with overlapping 2(Dickinson & Gehrels, 2009; Spencer et al., 2016), and 2066

9 Ma for the youngest concordant zircon grain; all these values are in agreement with the previously established range for the end of the Lomagundi carbon isotope excursion.

Conclusion

Detrital zircon data from the SPS and SPG further constrain the depositional age of the Phantom Lake Metamorphic suite to the Paleoproterozoic Era given the presence of statistically significant ca. 2.45 Ga dates in the Jack Creek and Bridger Peak quartzites of the SM, as well as a few zircon grains with Paleoproterozoic age in the Bow and Conical

Peak quartzites of the MBM. Maximum depositional age of the youngest units of the early

Paleoproterozoic supracrustal successions in the MBM and SM have been calculated at

2118 2.4 Ma (MSWD = 0.97) and 2344 8.7 Ma (MSWD = 1.29), using the youngest statistical population method (Coutts et al., 2019; Herriott et al., 2019), and 2081 10 Ma

(MSWD = 0.22) and 2334 11 Ma (MSWD = 0.0073), respectively, based on the mean age of the 3 youngest grains with overlapping 2(Dickinson & Gehrels, 2009;

Spencer et al., 2016). These dates provide new constraints on the depositional age of the

SPS and SPG in southern Wyoming.

Previous proposals supporting the contemporaneous and proximal deposition of the

SPS and HS based on similar lithostratigraphy and paleomagnetic data are further strengthened with the incorporation of detrital zircon and Sm-Nd data. Detrital zircon age spectra demonstrate similar modes for correlative units, most strikingly at ca. 2.7 Ga for

all units, ca. 2.8 Ga for the lower and middle units, and ca. 2.55 and ca. 2.3 Ga for the upper units, indicating incorporation of sediments from the similar-age provenance into both supergroups. Potential Archean and Paleoproterozoic source rocks are present on both cratons. The shared ca. 2.3 Ga detrital zircon age mode in the upper SPS and HS further strengthens the depositional link between these two successions as this age is rare in the detrital zircon record and was likely derived locally as prismatic ca. 2.3 Ga zircon is observed in tuff beds of the Gordon Lake Formation (Rasmussen et al., 2013), euhedral ca.

2.3 Ga zircon grains are present in metasediments of the Slaughterhouse Formation, and a high relative abundance of ca. 2.3 Ga zircons is noted in the Lookout Schist.

Trends in TDM and Nd values displayed by correlative shale-bearing units of the

SPS and HS also support their shared provenance. Many Nd datapoints from units of the

SPS fall into the field set by the material sourced from the Superior craton (McCulloch &

Wasserburg, 1978; McLennan et al., 2000), whereas more mature crustal sources potentially derived from the Wyoming craton are suggested by several SPS units with lower Nd values. Fine-grained sediments in both supergroups were likely derived from similar sources on both cratons (Fig. 1.5). Higher Nd values attributed to incorporation of more juvenile material into the Gordon Lake Formation are also displayed by the

Headquarters and Nash Fork formations, as well as the French Slate of the SPS.

Surprisingly, Pb isotope data between both supergroups demonstrate similar trends in post depositional, oxic chemical weathering and suggest resetting events at ca. 1.78 Ga despite the Wyoming and Superior cratons being separated by that time. The ca. 1.78 –

1.74 Ga Medicine Bow Orogeny was attributed to a collision between the southern margin

of the Wyoming craton and Proterozoic arcs to the south (Chamberlain, 1998) and this event likely disturbed the U-Pb isotope system in fine-grained sediments of the SPS in the

MBM. The Yavapai orogeny that may have reset the HS U-Pb isotope system is strongly expressed in the southern province of the Superior craton and Penokean orogen (Davidson et al., 1992; Holm et al., 1998, 2005, 2007; Hu et al., 1998; Piercey et al., 2007; Van

Schmus et al., 2007).

As deposition of the HS is terminated between ca. 2.31 and 2.22 Ga, a new correlation scheme between the early Paleoproterozoic units deposited on the southern

Wyoming and Superior cratons after ca. 2.31 Ga is needed. The Chocolay Group of the southern Superior craton to the west of the Huronian Basin has been lithostratigraphically correlated to the upper HS based on similar diamictite, quartzite, and stromatolitic dolostone sequences (Craddock et al., 2013), which might be further supported by the presence of ca. 2.3 Ga volcanic and detrital zircon populations in these successions (Vallini et al., 2006; Rasmussen et al., 2013; Hill et al., 2018), ultimately correlating them to the middle part of the SPS. Alternatively, the Chocolay Group diamictite might correspond to the fourth early Paleoproterozoic glaciation, breaking up this correlation with the upper

HS. The upper SPS is uniquely characterized by peaks in zircon dates at ca. 2.2 - 2.1 Ga, which are lacking in the HS and Chocolay Group. Similar to the upper Nash Fork

Formation in the MBM, a mode at ca. 2.1 Ga is seen in the East Branch Arkose of the

Dickinson Group in MI and the Denham Formation of the Mille Lacs Group in MN, both forming the basal part of the Animikie basin (Craddock et al., 2013), which likely correspond to rifting, breakup, and separation of the Superior and Wyoming cratons.

The detrital zircon data generated in this study provides insight to global events, which occurred during the early Paleoproterozoic. Firstly, a tectono-magmatic lull, which supposedly occurred between ca. 2.45 and 2.2 Ga (Condie et al., 2009), or ca. 2.3 and 2.2

Ga (Spencer et al., 2018), has been inferred to setback zircon production on a global scale.

The compilation of all concordant dates from the SPS and SPG is consistent with the lull between ca. 2.3 and 2.2 Ga as there are only 14 grains within this age-range out of the

3000+ analyses. Secondly, the detrital zircon age spectra for units of the MBM and SM bracket the age of the glacially derived diamictites of the Campbell Lake, Vagner, and

Headquarters formations between ca. 2.45 and 2.3 Ga, which is fully consistent with the age constraints for the HS glacial diamictites. Finally, as the Nash Fork Formation records the termination of the Lomagundi carbon isotope excursion in marine carbonates, the maximum depositional age at ca. 2080 Ma and the youngest grain at 2066 9 Ma provide additional confirmation to the established constraints placed on the end of this event between ca. 2.11 and 2.06 Ga (Karhu & Holland, 1996; Bekker & Holland, 2012; Martin et al., 2013; Bekker, 2014).

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Chapter 2

Reconstructing the paleogeography of the Superia supercraton using detrital zircon provenance of early Paleoproterozoic supracrustal successions from the southern margin of the Wyoming craton

Mammone, N.1, Bekker, A.1,2, Chamberlain, K.3

Keywords: Paleoproterozoic, Superia supercraton, detrital zircon geochronology, Uinta Mountains, Medicine Bow Mountains, Sierra Madre Range, Lomagundi carbon isotope excursion

Abstract

The early Paleoproterozoic connection between the Archean Wyoming and

Superior cratons, along their southern margins, is indicated by paleomagnetic data for similarly aged dike swarms on both cratons. Reconstructions of the early Paleoproterozoic paleogeography have placed the Wyoming craton in the center of the Superia supercraton, which also included the Hearne, Rae, Kola, and Karelia cratons. The southeastern margin of the Wyoming craton hosts the early Paleoproterozoic Snowy Pass Supergroup and

Snowy Pass Group in Medicine Bow Mountains and Sierra Madre Range, respectively, which record surface processes from the early Paleoproterozoic (ca. 2.45 Ga) up to ca. 2.1

- 2.0 Ga when episodic rifting eventually succeeded with the breakup of Superia. The

Snowy Pass Supergroup and Group exhibit similar detrital zircon age modes to the

Huronian Supergroup, indicating coeval deposition in a shared basin developed on the

adjoined southern margins of these cratons. Extension of the southern margin of the

Wyoming craton to the west, beyond the Sierra Madre, has been debated as outcrops of

Archean and early Paleoproterozoic units are limited in this area, have high metamorphic grade, and are generally poorly dated. The Red Creek Quartzite and underlying Owiyukuts

Complex from the Uinta Mountains of Northeast Utah yield detrital zircon age spectra demonstrating Archean and Paleoproterozoic provenance, which are comparable to age data from marginal successions on the southeast margin of the Wyoming craton, the

Farmington zone, and the Grouse Creek block. The Red Creek Quartzite hosts marbles, which have high 13C values (up to +12.5‰) indicative of the Lomagundi carbon isotope excursion in marine carbonates. Combined detrital zircon geochronology and chemostratigraphy suggest deposition of the Red Creek Quartzite on the southern margin of the Wyoming craton and support correlation with the upper formations of the Snowy

Pass Supergroup. The comparison of compiled detrital zircon data from the early

Paleoproterozoic supracrustal successions in southeastern Wyoming, paired with the data for the Red Creek Quartzite, to those from similar-age sedimentary successions on potentially adjacent cratons provides new insight into their relative position within Superia as certain zircon-forming, igneous and metamorphic events, especially at uncommon or rare periods (e.g., ca. 2.55 – 2.50 Ga and ca. 2.3 Ga), can help to test craton proximity during these time intervals. The early Paleoproterozoic sedimentary successions from the

Hearne and Rae cratons include similar detrital zircon age patterns to the Wyoming craton

(which include uncommon and rare zircon age peaks), supporting their proximity within the Superia supercraton. In contrast, similarly aged sedimentary successions from the Kola

and Karelia cratons do not show as significant matches in zircon modes with the Wyoming craton, arguing for their paleogeographical position further away from the craton’s southern margin within Superia.

Introduction

Early Paleoproterozoic sedimentary successions have been used extensively to identify and document critical events in the early Earth system: the rise of atmospheric oxygen starting at ca. 2.43 Ga and environmental oxygen trajectory through the early

Paleoproterozoic (Bekker et al., 2004, 2020; Guo et al., 2009), four global, low-latitude glaciations (Rasmussen et al., 2013), large-amplitude carbon isotope shifts in composition of the atmosphere and oceans, reflecting significant biogeochemical changes from ca. 2.31 to 2.06 Ga (Karhu & Holland, 1996; Bekker & Eriksson, 2003; Bekker, 2014), the widespread and episodic emplacement of Large Igneous Provinces (LIPs) (Ernst &

Bleeker, 2010), and Superia supercraton breakup between ca. 2.1 and 2.0 Ga (Kilian et al.,

2015) (Fig. 1.1). Paleogeographic and tectonic reconstruction, providing a backdrop for these environmental changes, is highly uncertain, and the arrangement of Archean cratons within the Superia supercraton is debated. Paleomagnetic data for similar-age, early

Paleoproterozoic dike swarms developed on both the Wyoming and Superior cratons have undeniably connected these two cratons together between ca. 2.6 and 2.16 Ga (Kilian et al., 2015). Geochemical and geological features as well as LIP magmatic events paired with dike swarm orientations have been used to position the Hearne and Kola-Karelia cratons as neighbors to the Wyoming and Superior craton from 2.5 to 2.1 Ga (Vuollo et al.,

1995; Ernst & Bleeker, 2010; Salminen et al., 2014; Gumsley et al., 2017; Davey et al.,

2020), however arguments continue regarding their relative position within Superia. For example, while Ernst & Bleeker (2010) and Gumsley et al. (2017) positioned the Hearne craton next to the western margin of the Wyoming craton and the Kola-Karelia craton along the eastern margin of the Superior craton (all references are to the present geography),

Davey et al. (2020) place the Kola-Karelia craton against the western margin of the

Wyoming craton. Detrital zircon U-Pb analyses for quartzites from the Snowy Pass

Supergroup and Snowy Pass Group of the respective Medicine Bow Mountains and Sierra

Madre Range, on the southern margin of the Wyoming craton and Sm-Nd and Pb-Pb data for shales from the supergroup compare well with data for the Huronian Supergroup on the southern margin of the Superior craton, providing independent support to the Wyoming and Superior craton connection and shared provenance for these successions (Chapter 1).

The Wyoming craton margins are well defined to the north in Idaho and Montana by the Great Falls Tectonic Zone (O’Neill & Lopez, 1985; Mueller et al., 2002, 2005;

Harms et al., 2004; Gifford et al., 2014; Chamberlain & Mueller, 2019) and to the east where a Proterozoic orogen abuts the Wyoming craton in eastern Wyoming (Fig. 2.1,

Dakotan orogen; Dahl et al., 1999; McCombs et al., 2004; Worthington et al., 2016;

Chamberlain & Mueller, 2019). The southern margin is bounded by the Cheyenne Belt, which extends through Wyoming, but remains unrecognized in northeast Utah (Karlstrom

& Houston, 1984; Chamberlain, 1998; Chamberlain & Mueller, 2019). The Cheyenne

Belt’s westward extension has been disputed with the boundary between the Archean

Wyoming craton and the Proterozoic Mojavia terrane to the south within the Great Basin of the western United States being drawn either trending southwest through northeast Utah

or directly west through Wyoming (along its southern border), based on Nd model ages and geophysical data (Bennett & DePaolo, 1987; Karlstrom et al., 2002; Crosswhite &

Humphreys, 2003; Yuan & Dueker, 2005; Nelson et al., 2002, 2011; Mueller et al., 2011).

The Red Creek Quartzite, exposed in the Uinta Mountains of northeast Utah either sits along the Wyoming craton’s southern margin or within the Mojave terrane. It is a roughly 6 km thick succession of quartzite, amphibolite, mica schist, and marble, which is has a thrust contact with the underlying Owiyukuts complex (a high-grade gneiss; Hansen,

1965; Sears et al., 1982). Two 40Ar-39Ar dates derived from hornblende in the amphibolite sections of the Red Creak Quartzite are ca. 1650 Ma (probably reflecting the time of peak metamorphism in the region) and concordant U-Pb ages from detrital zircons in the

Owiyukuts complex produced dates ranging from ca. 2750 to 1740 Ma (Nelson et al.,

2011).

Data from this study provide evidence for the placement of the southwestern margin of the Wyoming craton through the Uinta Mountains of northeast Utah based on the presence of Paleoproterozoic detrital zircons in quartzites and the positive Lomagundi carbon isotope excursion in marbles of the Red Creek Quartzite. Detrital zircon data from this study and literature also provide insight towards the positioning of the Hearne, Rae, and Kola-Karelia cratons within Superia.

Figure 2.1: The Wyoming craton with the placement and extent of subprovinces within (see text for discussion, MMT – Montana Metasedimentary Terrane, GFTZ – Great Falls Tectonic Zone; modified from Chamberlain et al., 2003; Chamberlain & Mueller, 2019). The inset shows Archean cratons and Paleoproterozoic orogens of North America. S – Slave craton, R – Rae craton, H – Hearne craton, W – Wyoming craton, GC – Grouse Creek block, Y – Yavapai province, M – Mazatzal province, THO – Trans Hudson Orogen, DO – Dakota Orogen, PO – Penokean orogen, FZ – Farmington zone, and SP – Superior craton. The Uinta Mountains (boxed in red) hosts the Red Creek Quartzite. A closer view of the study area is shown in Figure 2.2.

Geological Setting The Uinta Mountains of northeast Utah are an east-west trending chain of mountains, which were uplifted during the Laramide Orogeny in the late Cretaceous –

Paleogene (Hansen, 1965; Sears et al., 1982). Precambrian units are separated from

younger units to the north by a major thrust, the Uinta Fault, that extends through many of the areas with Precambrian exposure, and to the east where successively younger units are truncated by the fault (Hansen, 1965). Precambrian rocks are separated into three units, the basal Owiyukuts complex, the middle Red Creek Quartzite, and the upper Uinta Mountain

Group (Fig. 2.2). The Owiyukuts complex is composed of gneiss, which has been subjected to high-grade regional metamorphism and demonstrates extreme structural complexity, feldspathization, migmatization, and pegmatization; the complex unconformably underlies the Red Creek Quartzite (Hansen, 1965; Sears et al., 1982). The Red Creek Quartzite is a roughly 6 km thick succession primarily composed of quartzite, with smaller amounts of amphibolite, marble, and mica schist (Hansen, 1965). Following deposition of the Red

Creek Quartzite and prior to deposition of the unconformably overlying Uinta Mountain

Group, the area was subjected to multiple deformation events, regional, amphibolite-facies metamorphism, and was deeply eroded (Hansen, 1965). A composite section of the Uinta

Mountains indicates that the Red Creek Quartzite was thrusted northward on the

Owiyukuts Complex along a ductile décollement zone, similar to the emplacement of the

Libby Creek Group of the Snowy Pass Supergroup in the Medicine Bow Mountains of southeastern Wyoming (Houston & Karlstrom, 1979; Sears et al., 1982). The Red Creek

Quartzite crops out in several localities of generally east-west alignment within a roughly

40 km2 area, each locality is surrounded by the younger Uinta Mountain Group (Hansen,

1965). Limited published detrital zircon age data show age distributions from ca. 2917 ±

16 Ma to 2275 ± 12 Ma (30 grains analyzed, 21 grains are less than 10% discordant) and

Sm-Nd data provides TDM ages of 3.5 to 2.6 Ga and Nd(0) ranging from -31.6 to -11.2 for

the Red Creek Quartzite (Mueller et al., 2011). Hornblende from the amphibolite of the

Red Creek Quartzite produced two 40Ar-39Ar dates at ca. 1650 Ma, deemed to correspond to peak metamorphism (Nelson et al., 2011). Overgrowths on zircon from the Owiyukuts complex and Red Creek Quartzite with Th/U ratios below 0.1 and concordance 10% generated dates at ca. 1674 Ma, which was been interpreted to correspond to juvenile terrane accretion with subduction occurring to the south (Mueller et al., 2011). The Uinta

Mountain Group is a thick, relatively unmetamorphosed Neoproterozoic succession unconformably overlying the Red Creek Quartzite and is composed of crossbedded sandstone, siltstone, shale, and conglomerate (Sears et al., 1982; Dehler et al., 2010).

The Wyoming craton’s southern margin has been traced through the Uinta

Mountains based on geophysical data (Karlstrom et al., 2002; Crosswhite & Humphreys,

2003; Yuan & Dueker, 2005), and has been demonstrated with geochemical studies to run through northern Utah, albeit with low confidence (Bennett & DePaolo, 1987; Nelson et al., 2011). Rocks from the Red Creek Quartzite include depositional facies similar to nearshore marine and carbonate bank settings, which have been correlated lithologically to the upper units of the Snowy Pass Supergroup in the Medicine Bow Mountains of southeastern Wyoming (Graff et al., 1980). The quartzite, mica schist, and marble of the

Red Creek Quartzite are similar to marginal settings and might be a continuation of marginal deposits on the southwestern boundary of the Archean Wyoming craton.

Methods Three quartzites were collected for geochronological analysis, two from the Red

Creek Quartzite and one from the Owiyukuts Complex (see supplementary sample locations and descriptions; Fig. 2.2). Roughly 2 kg of each quartzite sample were collected and weathered surfaces were removed in the field to minimize contamination in the laboratory. Samples were run through a jaw crusher and refined into a fine sand using a disk mill. The fine material of each sample then first underwent a density separation using either a Wilfley Shaker Table or a Gemeni Table. The dried heavy-mineral fraction was run through a Frantz magnetic separator to remove magnetically susceptible minerals.

Heavy liquid density separation was then performed on the non-magnetic splits using methyl iodide (with specific gravity of 3.1 g/cm2) and a centrifuge. The remaining heavy splits were then cleaned, dried, and placed in petri dishes for hand-picking. About 150 hand-picked zircons were randomly chosen from each sample with the addition of 10-15

of the most euhedral grains in an effort to constrain provenance and maximum depositional ages. Chosen zircons were mounted in epoxy pucks and abraded down to expose equatorial sections.

Prior to U-Pb analysis, sample pucks were carbon coated and imaged using a cathodoluminescence (CL) detector on a FEI Quanta400f scanning electron microscope

(SEM). Images were used as a reference to compare with measured U-Pb isotope data.

Zircon U-Pb isotope ratios were measured using a 193 nm ArF excimer laser ablation (LA) system coupled to a Nu Plasma inductively coupled plasma mass-spectrometer (ICP-MS) at the University of California, Santa Barbara. Data was calibrated using the zircon reference materials GJ1 (601.7 ± 1.3 Ma, Jackson et al., 2004), Plešovice (337.13 ± 0.37

Ma, Sláma et al., 2008), 91500 (1062.4 ± 0.4 Ma, Wiedenbeck et al., 1995), and Peixe (564

± 4 Ma, Dickinson & Gehrels, 2003). Data reduction was performed using Iolite software

(Paton et al., 2010, 2011), concordia plots were created using IsoplotR (Vermeesch, 2018), and histogram Kernel Density Estimation (KDE) plots were prepared using DensityPlotter

(Vermeesch, 2012).

Eleven marble samples were collected from the Red Creek Quartzite. Samples were cut and polished, and the visually determined, least altered, fine-grained portions were micro-drilled with a 1 mm-diameter diamond drill-bit. Some marble samples were separated into splits and powder was collected from visually distinct areas of polished

13 18 surfaces, bringing the total number of individual analyses to 15. Ccarb Ocarb

weighed out into vials and flushed with Airgas ultra-high purity He in a heating block. Sample powders were acidified with 100%

phosphoric acid (McCrea, 1950) and held at 50°C in the heating block for 24 hours to allow for complete dissolution of carbonate minerals. The isotopic composition of carbonate C and O were measured using a Thermo Finnigan Delta V Advantage isotope-ratio mass spectrometer in a continuous-flow mode on phosphoric acid-liberated CO2 gas and

Vienna-Pee Dee Belemnite (VPDB) standard. Data results are reported with an analytical

that was better than 0.1 ‰ for carbon and 0.2 ‰ for oxygen isotope data. Data was calibrated against international and internal laboratory standards. International

13C = -18O = -13C = 1.95

18O = -1318O

= -13C = -18O = -17.95 ‰), M-13C = -8.76

18O = -1318O = - 7.59 ‰), and Tytiri dolomite

13C = 0.718O = -7.07 ‰). A calibration line was calculated by least squares linear regression using the known UC Davis calcite and NBS 18 measured isotope values of the standards. To check the quality of analysis, one calibrated international calcite standard

(NBS 19) and one calibrated internal dolomite standard (Tytiri) were analyzed together with unknown samples (Turner & Bekker, 2015)13C

18O = -13C = 0.73 ± 0.01

18O = -5.74 ± 0.16 ‰ (n = 24).

Carbonate mineral identification for the analyzed samples was caried out following a three-step staining method (Dickson, 1965), using 1.5% hydrochloric acid, alizarine red

S, and potassium ferricyanide. Based on the results of staining, oxygen isotope data was

corrected using known oxygen isotope values for calcite standard (NBS 19) and Tytiri dolomite.

Results

Detrital zircon U-Pb data

Detrital zircon U-Pb isotope data for the Red Creek Quartzite is presented in Fig.

2.3; dates are filtered to demonstrate 10% discordance. Concordant zircon dates (n = 102) span a range from 3438 – 1593 Ma. Fourteen concordant Paleoproterozoic dates were obtained (not including two dates younger than 1.9 Ga); the youngest is at 2352 13.1 Ma.

The next youngest grain is dated at 2411 17.1 Ma, and the remaining Paleoproterozoic zircons gave ages between 2498 – 2461 Ma. The largest population of grains is present between 2616 – 2461 Ma (55 dates). The most prominent modal peak within this range is at 2512 Ma (26 dates: 2525 – 2461 Ma). A secondary peak of similar prominence within this range is at 2561 Ma (29 dates: 2616 – 2531 Ma). Older, less prominent peaks are present at 2685 Ma (7 dates: 2724 – 2681 Ma) and 2654 Ma (7 dates: 2665 – 2638 Ma). A small, yet significant range of zircon dates is between 3148 – 2967 Ma. Two peaks at similar levels are present at 3110 Ma (7 dates: 3148 – 3083 Ma) and 3030 Ma (6 dates:

3042 – 2994 Ma). Minor peaks of 5 grains are at 3339 Ma (5 dates: 3361 – 3295 Ma) and

2771 Ma (4 dates: 2784 – 2762 Ma). Two grains were dated at 1890.8 30.1 Ma and

1593.8 19.8 Ma, and Th/U ratios for these dates are around and below .1 (Th/U = 0.112 and Th/U = 0.006), indicating that they are likely related to zircon overgrowth due to a metamorphic event.

The Owiyukuts complex produces concordant detrital zircon age spectra (n = 100) ranging from 3535 to 1641 Ma (Fig. 2.3). The dominant peak in the sample is at 2700 Ma with 55 zircon dates ranging from 2792 to 2600 Ma. The next prominent peak is at 2829

Ma (14 datapoints, 2875 – 2806 Ma). Two minor populations are on both sides of the 2.7

Ga peak and include populations centered at 2931 Ma (8 dates; 2994 – 2906 Ma) and 2492

Ma (5 dates; 2518 – 2467 Ma). The youngest grouping of ages is at 1698 Ma, and includes

3 grains at 1747.8 18.4 Ma, 1706 18.7 Ma, and 1641.4 19.1 Ma. Older age modes are scattered between 3535 and 3046 Ma and produce no significant peaks.

The analyzed Owiyukuts Complex quartzite includes a population of relatively young dates (n = 5) between ca. 1.6 and 2.1 Ga. Similar dates obtained for this unit in the past have been used to argue for a maximum depositional age of ca. 1.74 Ga (Nelson et al.,

2011). The Th/U ratios for these grains however are the lowest within the sample set, dates at 1747.8 18.4 Ma and 1706 18.7 Ma have corresponding Th/U ratios of 0.019 and

0.106, respectively. Although not all dates younger than 2.1 Ga have Th/U ratios less than

0.1, similar dates between ca. 2.1 and 1.6 Ga obtained for the Owiyukuts Complex by

Mueller et al., 2011 (Fig. 2.4) have Th/U ratios trending to low values and have been attributed to zircon overgrowth as a result of metamorphism.

Figure 2.3: Detrital zircon histogram for quartzite samples from the Red Creek Quartzite and Owiyukuts Complex. Not shown are metamorphic dates for the Red Creek Quartzite at 1593.8 19.8 Ma and 1890.8 30.1 Ma, and for the Owiyukuts Complex at 1747.8 18.4 Ma, 1706 18.7 Ma, and 1641.4 19.1 Ma.

Figure 2.4: Plot of age vs. Th/U ratios for detrital zircons from the Owiyukuts Complex. The youngest ages produce significantly low Th/U indicating metamorphic resetting of the U-Pb system, likely near the dates recorded at ca. 1.7 Ga. Black diamonds are from this study, orange triangles are data from Mueller et al., 2011. Carbon and oxygen isotope values for carbonates

Carbon isotope data for the Red Creek Quartzite is presented in Table 2.1 and Fig.

2.5. 13C data for 15 analysis on 11 samples produced highly positive values ranging from

+4.7 to +12.5‰ V-PDB with an averaged value of +8.3‰. Oxygen isotope data for the carbonate samples yields values ranging between -18.1 and -11.8‰ V-PDB with an average of -14.3‰. Some samples appear to have undergone more advanced post- depositional alteration (i.e., silicification) than others; specimens with lower carbonate content generally produce lower 13C values.

Secondary geological processes (i.e. diagenesis and metamorphism) that can alter carbon isotope values in sedimentary carbonate are only known to reduce 13C (Valley,

1986; Baumgartner & Valley, 2001), indicating that the highly positive 13C measured in the Red Creek Quartzite is a primary feature set during deposition. Low temperature diagenetic alteration of carbonates can cause negative shifts in 18O values, however 13C values are generally undisturbed in comparison during the first stages of fluid interaction.

Initial alteration of the system, as a result of meteoric water introduction in small quantities

(low water to rock ratio, W/R), usually affects only 18O isotopes as O is a major component of the fluid while C is present in trace amounts and readily buffered by the plentiful C in the carbonate minerals themselves (Veizer et al., 1990). As the W/R ratio increases, meteoric water will continue to lower 13C, bringing it closer to meteoric values

(Lohmann, 1988; Sharp, 2017). The high 13C ratios of samples from the Red Creek

Quartzite demonstrate a minimal diagenetic effect on the primary 13C signal, and alteration in samples reported to include more silica is slightly more apparent. Some post depositional alteration is made evident by the widely negative range in 18O.

Figure 2.5: Plot of 18O vs. 13C for marble samples from the Red Creek Quartzite. 13C and 18O values for samples containing lower percentages of calcite are lower than those with higher percentages, demonstrating the effects of post-depositional alteration on the C and O isotope systems.

Table 2.1: Data table for sampled marbles from the Red Creek Quartzite.

Discussion

1.1. Comparing records for the Red Creek Quartzite with other supracrustal successions on the southern margin of the Wyoming craton

Detrital zircon U-Pb data from Mueller et al. (2011) are incorporated into our datasets for discussion, adding 20 concordant (non-metamorphic) zircon dates for the Red

Creek Quartzite and 6 concordant (non-metamorphic) dates for the Owiyukuts Complex.

Maximum depositional ages for the Red Creek Quartzite are 2362.1 ± 12.4 (MSWD = .11) and 2378.62 ± 6.73 (MSWD = 1.25) based on the mean age of the 3 youngest grains with overlapping 2(Dickinson & Gehrels, 2009; Spencer et al., 2016) and using the more conservative “youngest statistical population” method (Coutts et al., 2019;

Herriott et al., 2019), respectively. Maximum depositional ages for the Owiyukuts

Complex are 2478.5 ± 23.0 (MSWD = .060) and 2514.8 ± 14.1(MSWD = .93) following the same respective methods. The youngest zircon grains for the Red Creek Quartzite and

Owiyukuts Complex in these combined datasets are present at 2275 12 Ma and 2385

18.1 Ma.

The Mojave and Yavapai provinces that are adjacent to the Wyoming craton to the south contain units ranging in age from 2.5 to 1.6 Ga and 1.9 to 1.7 Ga, respectively

(Condie, 1992; Foster et al., 2006; references therein). Since the Red Creek Quartzite detrital zircon age spectrum does not show ages younger than ca. 2.3 Ga, it was most likely derived from the Archean Wyoming craton before the accretion of island arcs and the

Mojave province to the southern margin of the craton.

Detrital zircon age data from the Uinta Mountains exhibit similarities with zircon age data from the Farmington Zone, a separate terrane connected to the western limits of the Wyoming craton. Although the number of concordant ages is limited (n = 38), detrital zircon dates obtained from rocks in the Farmington Canyon and Little Willow complexes of the Farmington zone (data from Mueller et al., 2011) plot very similarly to the data from the Owiyukuts Complex, suggesting coeval deposition and shared provenance from the

Archean Wyoming craton (Fig. 2.6A). Comparable zircon age abundances are located from ca. 2.4 – 2.7 Ga, with a similar major age-peak at ca. 2.7 Ga.

The Owiyukuts and Farmington zone complexes are roughly time equivalent to the

Phantom Lake Metamorphic Suite in the Sierra Madre and Medicine Bow Mountains of southeast Wyoming, and include very similar detrital zircon age spectra, suggesting similar provenance (Fig. 2.6B). The Phantom Lake Metamorphic Suite has an abundance of detrital zircon dates (n = 1118, Chapter 1, Results) resulting in ages younger than the dominating ca. 2.7 Ga mode to appear relatively subordinate. Contrarily, smaller datasets from the Owiyukuts Complex (n = 106), and the Farmington Canyon and Little Willow (n

= 38) complexes contain modes that are exaggerated by relatively small abundances of zircon grains (the youngest Farmington canyon modes at ca. 2.4 and 2.5 Ga consist of 1 to

2 grains). Despite the graphical disagreement as a result of varying dataset sizes, zircon ages ca. 2.45 Ga that are present in the Phantom Lake Metamorphic Suite, Owiyukuts

Complex, and Farmington zone overlap and may permit correlation. Additionally,

Farmington Canyon Complex Nd(2.4) data (recalculated to time of deposition) ranging from -4.53 to -2.48 with TDM ages from 2.9 to 3.1 Ga (data from Mueller et al., 2011)

further demonstrate similar patterns when compared with fine grained sediments from the

Medicine Bow Mountains, strengthening the likelihood of their correlation (Fig. 2.7).

The stratigraphic lithology of the Owiyukuts and Red Creek Quartzite include basement gneisses of granitic origin, siliciclastic and carbonate deposits, and intrusions of thick amphibolite dikes (Hansen, 1965). Similarly, the Farmington Canyon Complex is composed of metasupracrustal gneisses, quartzites, and schists (Mueller et al., 2011). Mafic intrusions have also been described as intruding the entire terrane prior to regional deformation at ca. 1.8 Ga (Bryant, 1988). The detrital zircon spectra similarities indicating shared provenance and the lithologic correlation of rock sequences suggest that the

Wyoming craton’s western limit extended to and included the Farmington zone, a terrane not currently recognized as part of the Wyoming craton.

Figure 2.6: Detrital zircon age spectra comparisons for the Farmington zone, Red Creek Quartzite, Owiyukuts complex, and Phantom Lake Metamorphic Suite. Data for the Farmington zone and additional zircon dates for the Red Creek Quartzite and Owiyukuts Complex taken from Mueller et al., 2011.

Figure 2.7: Nd data for the Snowy Pass Supergroup, Red Creek Quartzite, and Owiyukuts Complex. Data taken from (1) Ball & Farmer, 1991, (2) Souders & Frost, 2006, and (3) Mueller et al., 2011. Summary fields (grey fields) representing Nd evolution of the Wyoming craton are taken from Chamberlain & Mueller, 2019, Figure 29.4 (see data sources therein). BBMZ – Beartooth-Bighorn Magmatic Zone, MMP – Montana Metasedimentary Province, Neoarchean calc-alkaline magmatism from the Wind River Range is interpreted as continental -arc plutons (Frost et al., 1998). Depleted mantle models from Depaolo, 1981 and Goldstein et al., 1984.

The presence of highly positive 13C values, with an average value of +8.3‰, for marbles of the Red Creek Quartzite indicates that the unit was deposited on a relatively shallow continental shelf during the Lomagundi carbon isotope excursion between ca. 2.31 and 2.06 Ga (Karhu & Holland, 1996; Bekker et al., 2003; Bekker, 2014). Carbonates recording the Lomagundi carbon isotope excursion on the southern margin of the Wyoming craton are also located in the supracrustal successions of the Medicine Bow Mountains and

Sierra Madre in southeast Wyoming. The Nash Fork Formation of the upper Snowy Pass

Supergroup in the Medicine Bow Mountains and the Slaughterhouse Formation of the

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upper Snowy Pass Group in the Sierra Madre have highly positive 13C isotope values and record the excursion’s termination in the Medicine Bow Mountains (Bekker et al., 2003).

Nd(2.3) data (recalculated to time of deposition) ranging from -3.14 to -1.53 and TDM ages of 3.5 to 2.6 Ga for the Red Creek Quartzite (Mueller et al., 2011) show similar ranges to fine grained units of the Medicine Bow Mountains (Fig. 2.7). Rock units of the upper

Snowy Pass Supergroup have been lithostratigraphically correlated to the Red Creek

Quartzite (Hansen, 1965; Graff et al., 1980); similar carbon isotope values, Nd data, and previous geophysical studies placing the margin of the craton through the Uinta Mountains of northeast Utah provide further support for this correlation (Karlstrom et al., 2002;

Crosswhite & Humphreys, 2003; Yuan & Dueker, 2005).

The youngest ca. 2.3 Ga detrital zircon dates obtained for the Red Creek Quartzite are similar to the youngest detrital zircon populations which first emerge in the Sugarloaf

Quartzite (as well as the lower Nash Fork Formation) of the Snowy Pass Supergroup in the

Medicine Bow Mountains and the Slaughterhouse Formation of the Sierra Madre (Fig 1.4B and Table 1.1). The prominent ca. 2.55 – 2.50 Ga peak in detrital zircon dates from the Red

Creek Quartzite is also seen in the Sugarloaf Quartzite and the Slaughterhouse Formation in southeastern Wyoming. The Sugarloaf Quartzite is the only unit of all early

Paleoproterozoic units in the Medicine Bow Mountains and Sierra Madre that contains its most abundant population of zircons at ca. 2.5 Ga (Fig 1.4B), potentially indicating that the Red Creek Quartzite is broadly time-correlative with the Sugarloaf Quartzite and

Slaughterhouse Formation.

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1.2. Provenance of the Red Creek Quartzite

On the Wyoming craton, rocks dated at ca. 2.55 – 2.50 Ga are preserved in the

Teton Range and the Beartooth Mountains (Mogk et al., 1988; Zartman & Reed, 1998;

Chamberlain et al., 2003). Metamorphic events in the Madison Range of SW Montana and the Granite Mountains of central Wyoming occurred at ca. 2.55 Ga as determined by monazite U-Pb, epidote U-Pb, and nephrite Ar-Ar dates (Loehn, 2009; Sutherland, 2019).

These events were likely capable of producing zircon-forming magmas. Rocks of this age were possibly exposed and eroded from the Wyoming craton during deposition of the Red

Creek Quartzite as this age mode is prevalent in this unit and in those from the upper formations of the Snowy Pass Supergroup on the southeastern margin of the craton.

A detrital zircon age mode between ca. 2.7 and 2.6 Ga is most prominent in the

Owiyukuts sample and it appears as a minor mode in the Red Creek Quartzite. Rocks of this age are found within the Southern Accreted Terranes, Sweetwater, and Bighorn subprovinces of the central-southern Wyoming craton (see Chamberlain et al., 2003, Table

1 and references therein). The peak in dates at ca. 2.8 Ga in both units could be derived from ca. 2.8 – 2.7 Ga granitoids exposed in the Beartooth Mountains (see Chamberlain et al., 2003, Table 1 and references therein). Sources for zircon age modes at ca. 3.1 and 3.03

Ga are not common on the Wyoming craton, although some rocks seem to have ages within the outer limits of these age modes; tonalitic gneisses in the Montana Metasedimentary

Terrane and Bighorn province have ages between ca. 3.5 and 3.1 Ga (Mueller et al., 1993;

1996) and the Beartooth-Bighorn Magmatic Zone is predominantly composed of granitoid rocks with 3.0 – 2.8 Ga ages (Wooden & Mueller, 1988; Frost & Fanning, 2006; Frost et

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al., 2006; Mueller & Frost, 2006). Rocks dated at ca. 3.35 Ga are located in the central

Granite Mountains of the Wyoming craton and might be the source for the minor detrital zircon mode centered at this date in the Red Creek Quartzite (Langstaff, 1995).

1.3. Tectonic model for early Paleoproterozoic tectonic evolution on the southern margin of the Wyoming craton

The tectonic history for Archean and Paleoproterozoic terranes in North America is largely unconstrained in regards to their Paleoproterozoic evolution alongside the

Wyoming craton. Distinct provinces of interest for this study include the Archean Grouse

Creek block and the Paleoproterozoic Farmington zone. Detrital zircon and Sm-Nd data from the Farmington Canyon and Little Willow complexes indicate provenance on the

Wyoming craton, suggesting that they may have been located at its western margin in the early Paleoproterozoic. The Grouse Creek block is a Neoarchean province to the west of the Farmington zone and contains gneissic units overlain by metasedimentary rock types including quartzite, conglomerate, and schist as well as ca. 2.5 – 2.6 Ga leucogranite intrusions in the Albion, Raft River, and Grouse Creek mountains (Strickland et al., 2011a,

2011b). Ca. 2.45 – 2.55 Ga ages have been obtained from the Angel Lake Gneiss Complex of the East Humboldt Range in northeastern Nevada, offering additional instances of

Paleoproterozoic magmatism in the Grouse Creek block (McGrew, 2011; Premo et al.,

2014). These rock types and ages are similar to those from the Farmington zone complexes,

Owiyukuts Complex, and Red Creek Quartzite, possibly suggesting further correlation and implications towards modeling the Archean and Paleoproterozoic tectonic evolution of these terranes.

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The onset of rifting at ca. 2.45 Ga is recorded by the widespread, radiating

Matechewan and Hearst dikes on the Superior craton which were the result of a large mantle plume (Heaman, 1997; Roscoe & Card, 1993). The presence of ca. 2.45 Ga intrusive units all over the Wyoming craton hints at the widespread impact this plume event could have had on the paleogeography (Fig. 1.2). The presence of ca. 2.45 - 2.50 Ga aged zircon and comparable lithologies in the Farmington zone, Grouse Creek block, and the southwestern Wyoming craton potentially record a rift event resulting in the failed separation of the Grouse Creek block and the Wyoming craton, leaving the Farmington zone as a rift basin between them. Reactivation at ca. 2.3 Ga could have occurred upon deposition of the marine carbonates of the ca. 2.3 Ga Red Creek Quartzite.

A collisional event at ca. 1.67 Ga is observed in the Uinta Mountains (Red Creek

Quartzite and Owiyukuts Complex) as well as the Wasatch Range (Farmington Canyon and Little Willow complexes) based on zircon overgrowths with low Th/U ratios (<.1)

(Mueller et al., 2011). This is near the time of deformation at ca. 1.78 Ga observed in fine grained Paleoproterozoic sediments of the Medicine Bow Mountains of southeastern

Wyoming, which have been attributed to a collision between the Wyoming craton with an island arc to the south during the Medicine Bow Orogeny (Chamberlain, 1998; Frost et al.,

2000) (Fig. 1.6).

1.4. Reconstruction of Superia by comparing potential provenances for early Paleoproterozoic supracrustal successions

Paleomagnetic dike swarm data places the Wyoming and Superior cratons together between ca. 2.6 and 2.16 Ga (Kilian et al., 2015). Detrital zircon U-Pb data from the

Paleoproterozoic Snowy Pass Supergroup on the southeastern margin of the Wyoming

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craton demonstrates prominent similarities with the Huronian Supergroup on the southern margin of the Superior craton, providing additional support for this reconstruction (Fig.

1.4B). Comparing detrital zircon data from similar-aged early Paleoproterozoic supracrustal successions with a focus on relatively rare age modes may offer insight into the paleogeography of cratons within Superia. In essence, if cratons experienced similarly aged magmatic events, especially at periods not globally recognized in the detrital zircon record, then it can be speculated that they were in relatively close proximity.

Paleogeographic reconstructions of a Neoarchean supercraton, Superia, demonstrate controversy in the placement of the Hearne, Rae, Kola, and Karelia cratons based on paleomagnetic data from dike swarms (Bleeker & Ernst, 2006; Ernst & Bleeker,

2010; Gumsley et al., 2017; Davey et al., 2020). Compiled detrital zircon data from

Paleoproterozoic supracrustal successions on these cratons provide insight into magmatic events expressed on these landmasses, offering hints towards their relative geographic placement. Key zircon age modes expressed in southern Wyoming are at ca. 2.55 – 2.50

Ga and ca. 2.3 Ga as these time periods represent unusual events of magma generation

(Fig. 1.10). The ca. 2.55 – 2.50 Ga detrital zircon age mode is observed in uppermost correlative formations of the Snowy Pass and Huronian supergroups (Hills et al., 2018)

(Fig. 1.4B), and is relatively uncommon on the Superior craton. It is known to occur in the non-extensive 2557 15 Ma McGrath Gneiss in the Minnesota River Valley terrane at its southern margin (Schmitz et al., 2006). The ca. 2.3 Ga zircon mode is also rare on the global scale as this time period in Earth’s history is associated with a significant decrease in tectono-magmatic processes (Condie et al., 2009; Spencer et al., 2018).

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The Hearne craton has been inferred to be the Wyoming craton’s eastern neighbor within Superia (Bleeker & Ernst, 2006; Ernst & Bleeker, 2010; Gumsley et al., 2017), and since the Rae and Hearne cratons have been interpreted to be connected along the Snowbird

Tectonic Zone during the early Paleoproterozoic based on similar lithostratigraphy of early

Paleoproterozoic supracrustal successions as well as detrital zircon U-Pb and Hf isotope compositions (Rainbird et al., 2010; Regan et al., 2017), the Rae craton can be also included into this model. The ca. 2.56 – 2.50 Ga MacQuoid orogeny is a widespread event recognized on the Hearne craton’s northwest margin (Davis et al., 2006) and might have been a potential source for detrital zircon of this age in the early Paleoproterozoic supracrustal successions of the Wyoming craton. The Arrowsmith orogeny on the western margin of the Rae craton, which is clustered into two intervals between ca. 2.56 and 2.4

Ga, and ca. 2.35 and 2.28 Ga (Berman et al., 2013; Pehrsson et al., 2013) provides another match with the detrital zircon age peaks of the Wyoming craton supracrustal successions.

These two laterally extensive orogenic events occurred at unusual time intervals and therefore could be particularly useful for paleogeographic reconstructions.

Concordant ( 10% discordance) detrital zircon age data for the Paleoproterozoic successions in the Medicine Bow Mountains and Sierra Madre of southeastern Wyoming

(n = 3266) are characterized by strong peaks at ca. 2.7 Ga, 2.55 Ga, 2.3 Ga, and 2.1 Ga

(Fig. 1.10). Concordant detrital zircon age data for the Hurwitz Group of the central Hearne craton ( 10% discordance, n = 153; Davis et al., 2005) demonstrate very similar patterns with modes at ca. 2.7 Ga, 2.55 – 2.60 Ga, 2.3 Ga, and 2.1 Ga (Fig. 2.8); indicating shared magmatic histories between these two cratons and suggesting relatively close proximity in

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the early Paleoproterozoic. Detrital zircon age data for the early Paleoproterozoic Amer and Ketyet River groups in the central Rae craton ( 10% discordance, n = 435, Rainbird et al., 2010) show an even better match to the Wyoming sediments than the Hurwitz Group data, likely due to the closer proximity between the Rae and Wyoming cratons at that time.

Prominent modes at ca. 2.7 Ga, 2.5 Ga, 2.3 Ga, and 2.1 Ga are present in both datasets (Fig.

2.8). The Red Creek Quartzite and Owiyukuts Complex on the southwestern margin of the

Wyoming craton also include strong modal peaks at ca. 2.55 – 2.50 and 2.3 Ga; these can potentially be attributed to the extensive MacQuoid and Arrowsmith orogens located on the northwest margins of the Hearne and Rae cratons, respectively, as this mode is strongly pronounced in the Rae craton supracrustal successions. Potential provenance from the

Hearne and Rae cratons could include the Queen Maud Block, where a flare up in ca. 2.50

– 2.45 Ga granitoid magmatism occurred (Schultz et al., 2007; Tsermette et al., 2011;

Pehrsson et al., 2013). The Grouse Creek Block, which is considered to be either a separate craton or the western extension of the Wyoming craton (Foster et al., 2006), shows similar age modes (ca. 2.55 and 2.45 Ga) for migmatites, schists, and gneisses (Wright & Snoke,

1993; McGrew & Snoke, 2010; Premo et al., 2010; Strickland et al., 2011a, 2011b). Detrital zircon age modes of the Red Creek Quartzite and Owiyukuts Complex (as well as those from the early Paleoproterozoic supracrustal successions from the Medicine Bow

Mountains and Sierra Madre) between ca. 3.1 and 3.0 Ga are also found in the supracrustal successions of the Rae craton (Rainbird et al., 2010; Ashton et al., 2013). Comparison between age spectra from the southwestern Wyoming craton successions and the Rae craton show similar patterns (Fig. 2.9).

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Comparisons of detrital zircon data from the Wyoming craton and the Kola and

Karelia cratons, in contrast, do not include significant Paleoproterozoic overlap (Fig. 2.8).

Detrital zircon data ( 10% discordant, n = 859; Köykkä et al., 2019) from the

Paleoproterozoic (> 1.9 Ga) supracrustal successions of the central Lapland, Peräpohja, and Kuusamo greenstone belts of the Karelia craton in Finland lack the prominent ca. 2.55

Ga peak seen in the Wyoming, Hearne, and Rae craton datasets. Age modes between ca.

2.6 and 2.9 Ga included in the Wyoming and Karelia cratons are generally in agreement.

The relatively unpronounced, broad range of dates from ca. 2.5 to 2.2 Ga corresponds with age data from the Wyoming craton, but the prominent peak at 2.3 Ga is largely absent.

Peaks in zircon ages reappear at ca. 2.0 to 2.15 Ga in the Karelian dataset, and overlap with the Snowy Pass Supergroup.

Data from the Karelian Supergroup on the Kola craton (10% discordant, n = 604;

Gärtner et al., 2014) includes a very broad range of dates between ca. 2.6 and 2.9 Ga, with a major peak in ages at ca. 2.8 Ga, and a minor mode at ca. 2.7 Ga. Much of the zircon data from this dataset overlaps with the Wyoming craton data from ca. 2.3 Ga and older, but individual peak agreements are not apparent. A secondary peak in the Karelian Supergroup is present at ca. 2.45 Ga, which overlaps with a minor mode in the Snowy Pass Supergroup, but the critical age peaks at ca. 2.55 and 2.3 Ga are missing, suggesting that they may have been further apart in the early Paleoproterozoic.

The Kola and Karelia cratons lack the significant degree of similarity to the

Wyoming craton that is observed in the Rae and Hearne cratons. Craton comparisons with the compiled Huronian supergroup data from the southern Superior craton reveal a similar

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outcome (Fig. 2.10). The Huronian Supergroup exhibits an overlap in zircon dates with the

Karelia craton sediments from ca. 2.6 to 3.1 Ga. Correlation between the two datasets breaks down at ca. 2.55 Ga as this mode is prominently expressed on the southern Superior craton and is absent in the Karelia craton. Overlap at ca. 2.3 Ga occurs between both datasets, but a peak in ages is only expressed in the Huronian sediments. Reconstructions of Superia have placed the Kola and Karelia cratons on the southeastern margin of the

Superior craton (Bleeker & Ernst, 2006; Ernst & Bleeker, 2010; Gumsley et al., 2017), and similar Archean histories expressed by their detrital zircons (also seen on the Wyoming craton) may reflect this. Comparisons between the detrital zircon patterns of the Kola and

Karelia cratons include similar zircon age abundances up to ca. 2.6 Ga, but break down in correlation after this until similar peaks are expressed at ca. 2.1 Ga (Fig. 2.10).

The Kola and Karelia cratons’ early Paleoproterozoic detrital zircon age data does not exhibit as high of a degree of similarity to the supracrustal successions of the Wyoming and Superior cratons as those from the Hearne and Rae cratons do, arguing for the paleogeographic position of the Hearne and Rae cratons next to the Wyoming craton’s western margin in its present orientation. It is further suggested that the Kola and Karelia cratons were positioned further away from the Wyoming craton, possibly along the southeastern margin of the Superior craton (in its present orientation) consistent with previous reconstruction models (Fig. 2.11) (Bleeker & Ernst, 2006; Ernst & Bleeker, 2010;

Gumsley et al., 2017)

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Figure 2.8: Detrital zircon data for the Paleoproterozoic supracrustal successions on Archean cratons that were components of Superia. Data sourced from: Hearne craton - Davis et al., 2005; Rae craton - Rainbird et al., 2010; Karelia craton - Köykkä et al., 2019; Kola craton - Gärtner et al., 2014.

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Figure 2.9: Detrital zircon age data spectra from the Red Creek Quartzite and Owiyukuts Complex (data from Mueller et al., 2011 included) of the Uinta Mountains, Northeastern Utah and the Amer and Ketyet River groups of the Rae craton (Rainbird et al., 2010).

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Figure 2.10: Detrital zircon data for the Paleoproterozoic supracrustal successions on Archean cratons that were parts of the Superia supercraton. Data sourced from: Superior craton – Craddock et al., 2013 and Hill et al., 2018; Karelia craton - Köykkä et al., 2019; Kola craton - Gärtner et al., 2014.

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Figure 2.11: Preferred reconstruction of Superia based on compiled detrital zircon data from Paleoproterozoic supracrustal successions on each craton. Modified after Bleeker et al., 2016 and Gumsley et al., 2017.

Conclusion

Detrital zircon U-Pb data for the Red Creek Quartzite in the Uinta Mountains of northeast Utah includes Paleoproterozoic ages as young as ca. 2.3 Ga, and this, paired with

C isotope data for marbles recording the Lomagundi carbon isotope excursion, indicates that this unit was deposited in a shallow-marine setting along the southwestern margin of the Wyoming craton. Provenance of the Red Creek Quartzite and Owiyukuts Complex is potentially from the Wyoming craton, which contains magmatic and metamorphic units corresponding in age to the prominent detrital zircon age modes at ca. 2.8 - 2.7 Ga, 2.65

Ga, and 2.55 – 2.50 Ga. The Red Creek Quartzite is likely time-equivalent with the upper units of the Snowy Pass Supergroup in the Medicine Bow Mountains (Sugarloaf Quartzite and lower Nash Fork Formation) and the Snowy Pass Group in the Sierra Madre

(Slaughterhouse Formation) in southeast Wyoming based on similar marginal depositional facies, lithologies, detrital zircon age spectra, and high 13C values. Detrital zircon data from the Owiyukuts Complex suggests nearly time-equivalent deposition with the Phantom

Lake Metamorphic Suite that underlies the Snowy Pass Supergroup.

Similarities in zircon age data from the Grouse Creek block, Farmington zone, and marginal successions from the Wyoming craton suggest shared provenance likely derived from the Archean Wyoming craton, which is further supported by Nd data from the

Farmington Canyon Complex, Red Creek Quartzite, and Snowy Pass Supergroup. These data and the presence of comparable lithologies, potentially indicative of a rift setting, provide some hints towards their Paleoproterozoic tectonic evolution. The separation between these terranes may coincide with a failed rift event at ca. 2.45 Ga between the

114

Grouse Creek block and the Wyoming craton, leaving the Farmington zone as a rift basin.

Separation could have finally occurred at ca. 2.3 Ga during deposition of the Red Creek

Quartzite which hosts marine carbonates.

Since similar detrital zircon data between the Huronian and Snowy Pass supergroups have supported the connection between the southern margins of the Superior and Wyoming cratons through the early Paleoproterozoic, a similar approach using detrital zircon data from similarly aged successions farther along the Wyoming craton’s margin might be a viable strategy to identify other potentially adjacent cratons in the Superia supercraton configuration. The Superior, Wyoming, Hearne, Rae, Kola, and Karelia cratons have all been considered to be neighbors in the early Paleoproterozoic. Key age intervals at ca. 2.55 – 2.50 Ga and 2.3 Ga were chosen as critical matching points since zircons with these ages are uncommon on the Superior craton and rare in the global record.

The Hurwitz Group of the Hearne craton (Davis et al., 2005) and the Amer and Ketyet

River groups of the Rae craton (Rainbird et al., 2010) show nearly identical detrital zircon age spectra, suggesting the connection between these cratons in the early Paleoproterozoic.

Detrital zircon age data for the early Paleoproterozoic supracrustal successions of the

Wyoming, Hearne, and Rae cratons also closely match, indicating that the latter two cratons were attached to the Wyoming craton’s western margin (in its present orientation) within Superia. Importantly, the Red Creek Quartzite and Owiyukuts Complex of the southwest Wyoming craton demonstrate a close match with detrital zircon data from the

Rae craton, further supporting the connection between the two landmasses at their margins.

The MacQuoid and Arrowsmith orogens on the northwest margins of the respective Hearne

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and Rae cratons could have been sources for the ca. 2.55 – 2.50 Ga and 2.3 Ga detrital zircon age peaks seen in the successions of the southern Wyoming craton. The detrital zircon age data for the similarly aged supracrustal successions of the Kola and Karelia cratons do not demonstrate significant overlap with Paleoproterozoic Wyoming craton detrital zircon data and either lack or poorly express the ca. 2.55 – 2.50 Ga and 2.3 Ga age modes; arguing for the paleogeographic positioning of the Kola and Karelia cratons farther away from the Wyoming craton in Superia. Archean zircon data from the Kola and Karelia cratons show overlap with the Snowy Pass and Huronian supergroups, possibly suggesting placement at the Superior craton’s southeastern margin at this time.

116

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General Conclusions

The connection between the Wyoming and Superior cratons at their southern margins throughout the Paleoproterozoic is further confirmed with detrital zircon, Sm-Nd, and Pb-Pb data from the lithostratigraphically correlated supracrustal Snowy Pass and

Huronian supergroups (Blackwelder, 1926; Houston et al., 1992; Roscoe & Card, 1993;

Bekker et al., 2003). The presence of nearly identical zircon age modes throughout these paleomagnetically connected supergroups suggests provenance from both the Wyoming and Superior cratons and supports their deposition into a shared basin. Potential sources with age equivalencies have been identified on both cratons (Chapter 1, discussion). The presence of statistically significant zircon age populations at ca. 2.45 Ga in formations of the Phantom Lake Metamorphic Suite in the Medicine Bow Mountains and Sierra Madre of southeast Wyoming redefine the previously Archean group as Paleoproterozoic in age.

These ca. 2.45 Ga zircon dates are equivalent to the accepted ages of the basal Huronian volcanics which give the Huronian Supergroup its lower age constraint (Krogh et al., 1984;

Ketchum et al., 2013; Bleeker et al., 2015), and the presence of similar lithologies between these two lower groups suggest comparable and likely correlated geological histories.

Nd isotopes from shale and diamictite bearing units of the Snowy Pass Supergroup in the Medicine Bow Mountains are comparable with units of the Huronian Supergroup, indicating similar mafic provenance sources. Depleted mantle model ages from several units of the Medicine Bow Mountains are significantly older than those obtained from the

Huronian supergroup (>3.0 Ga), and likely represent sediment contribution from the

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ancient Wyoming craton core. Pb isotope data from the Snowy Pass and Huronian supergroups additionally demonstrate similar patterns and reflect a disturbance to the Pb-

Pb system between ca. 1.7 – 1.8 Ga, likely attributed to orogenic activity and accretionary processes along both craton margins. The ca. 1.78 – 1.74 Ga Medicine Bow Orogeny is the most likely cause for the disturbance in the Snowy Pass Supergroup, as it involved a collisional event between the southern margin of the craton with Proterozoic arcs to the south, resulting in the formation of a shear zone which terminates the uppermost units in southern Wyoming (Chamberlain, 1998). Pb isotopic system resetting events for the upper

Huronian sediments have been broadly attributed to plutonism and metamorphism during the Yavapai orogeny (cf. McLennan et al., 2000).

The southwestern margin of the Wyoming craton is preferentially oriented through the Uinta Mountains of northeast Utah as a result of the presence of Paleoproterozoic detrital zircon populations in quartzite and a Lomagundi Carbon Isotope Excursion signature in marbles of the Red Creek Quartzite, indicating shallow marine continental shelf deposition. The Red Creek Quartzite is correlated to the Sugarloaf Quartzite, lower

Nash Fork Formation, and Slaughterhouse Formation of the Medicine Bow Mountains and

Sierra Madre based on similar lithologies, detrital zircon age spectra, and the presence of

C isotopes reflecting the Lomagundi Event, further suggesting marginal deposition.

Zircon data from the Phantom Lake Metamorphic Suite of the Sierra Madre and

Medicine Bow Mountains, the Owiyukuts Complex of the Uinta Mountains (additional data included from Mueller et al., 2011), the Farmington Canyon and Little Willow complexes of the Farmington zone (Mueller et al., 2011), and various ranges from the

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Grouse Creek block (Wright & Snoke, 1993; McGrew & Snoke, 2010; Premo et al., 2010;

Strickland et al., 2011a, 2011b) indicate roughly time equivalent depositional ages and similar age distributions at ca. 2.45 Ga and older suggesting shared provenance. Significant overlap in zircon ages suggests similar provenance from the Wyoming craton, which is further supported by comparable Nd data from the Farmington zone, Uinta Mountains, and southeastern Wyoming craton. Lithological similarities between these provinces may hint at the occurrence of a failed rift event between the Grouse Creek block and southwest

Wyoming craton which likely initiated during an extensive ca. 2.45 Ga LIP event centered on the southern margin of Superior craton (Heaman, 1997; Roscoe & Card, 1993; Foster et al., 2006). Reactivation and successful separation potentially occurred at ca. 2.3 Ga with deposition of the Red Creek Quartzite. A metamorphic event at ca. 1.67 Ga is recorded by zircon overgrowth dates with low Th/U ratios from the Owiyukuts Complex and Red Creek

Quartzite of the Uinta Mountains, and the Farmington and Little Willow complexes of the

Wasatch Range (Mueller et al., 2011). This deformation event is close in age to the ca. 1.78

Ga metamorphic event recorded in the Pb-Pb system of fine grained sediments from the

Snowy Pass Supergroup.

Detrital zircon data from the supracrustal successions of the Medicine Bow

Mountains, Sierra Madre, and Uinta Mountains may support previously suggested paleogeographic reconstructions of the Paleoproterozoic supercraton, Superia (Ernst &

Bleeker, 2010; Bleeker et al., 2016; Gumsley et al., 2017; Davey et al., 2020), based on the comparison of compiled detrital zircon data from similar-age supracrustal successions on cratons modeled as neighboring one another. If cratons record similar magmatic events

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through time, relatively close proximity may be indicated. Key detrital zircon age modes at ca. 2.55 – 2.50 Ga and ca. 2.3 Ga were selected as critical matching points due to the uncommonness of the ca. 2.55 Ga mode on the Superior craton and the overall rarity of the ca. 2.3 Ga mode in the global detrital zircon record (Condie et al., 2009; Spencer et al.,

2018). The Hurwitz Group (Davis et al., 2005), and the Amer and Ketyet River groups

(Rainbird et al., 2010) (all Paleoproterozoic supracrustal successions) on the respective

Hearne and Rae cratons exhibit the best matches with compiled zircon data from the

Medicine Bow Mountains and Sierra Madre, especially at the previously defined critical matching points. Detrital zircon from Paleoproterozoic units from the Uinta Mountains also demonstrate significant similarity with the Rae and Hearne successions. These strong comparisons indicate similarly aged zircon forming events through time and suggest that the Rae, Hearne, and Wyoming cratons were connected in Superia throughout the early

Paleoproterozoic. These uncommon or rare age modes seen in the Wyoming craton marginal successions have been identified as possibly being partially derived from the laterally extensive Arrowsmith (ca. 2.56 – 2.4 Ga and ca. 2.35 – 2.28 Ga) and MacQuoid

(2.56 – 2.50 Ga) orogens on the NW margins of the respective Rae and Hearne cratons

(Davis et al., 2006; Berman et al., 2013), and the Red Creek Quartzite’s dominating zircon peak at ca. 2.55 – 2.50 Ga could be a result of its relatively closer proximity to the Rae craton margin than the Snowy Pass Supergroup.

The Kola and Karelia cratons do not demonstrate as much comparability to the detrital zircon spectra from the Medicine Bow Mountains and Sierra Madre as the Rae and

Hearne cratons. Compiled detrital zircon data from supracrustal metasedimentary

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formations of the central Lapland, Perapohja, and Kuusamo belts of northern Fennoscandia on the Karelian craton (Köykkä et al., 2019) lack the key pronounced age peaks at ca. 2.3 and 2.55 – 2.50 Ga. The Karelian Supergroup on the Kola craton (Gärtner et al., 2014) also demonstrates this lack of significant overlap at these time periods further supporting the positioning of the Rae and Hearne cratons next to the Wyoming craton’s southwestern margin in Superia. Detrital zircon data from the Kola and Karelia cratons produce similar

Archean detrital zircon spectra to the Snowy Pass and Huronian supergroups (which break down in correlation during the Late Archean), which could support reconstruction models placing the Kola and Karelia cratons against the Superior craton’s southeastern margin

(Bleeker & Ernst, 2006; Ernst & Bleeker, 2010; Bleeker et al., 2016; Gumsley et al., 2017), at least in the Archean.

Detrital zircon data from this study additionally contributes to a few other current research questions pertaining to the Paleoproterozoic Earth system. Secondary conclusions obtained from the data include:

1.) Detrital zircon age data (n=3266) from the Medicine Bow Mountains and Sierra

Madre supports the inferred occurrence of a tectonic slowdown resulting in the

reduction of magma generation from ca. 2.3 – 2.2 Ga (Condie et al., 2009;

Spencer et al., 2018) as there were only 14 ages obtained in this interval out of

a total of 3266 ages.

2.) The Lomagundi Carbon Isotope Excursion’s current durational constraint

between ca. 2.22 - 2.06 Ga (Karhu & Holland, 1996; Bekker & Holland, 2012;

Bekker, 2014) is supported by detrital zircon data from the upper Nash Fork

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Formation as the maximum depositional age is calculated at 2081 10 Ma

(MSWD = 0.22) (3 youngest ages within 2 error) with the youngest grain

dated at 2066 9 Ma.

3.) Age constraints for the 3 glacial diamictite units in the Snowy Pass Supergroup

are set between ca. 2.45 – 2.30 Ga, which is in agreement with the current age

limits on the 3 Huronian glaciations between 2450 – 2308 Ma (Krogh et al.,

1984; Ketchum et al., 2013; Rasmussen et al., 2013; Bleeker et al., 2015).

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Sample Locations and Descriptions

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