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Slave Craton and Wopmay Orogen, NW Canada Canadian Journal of Earth Sciences Parentage of Archean basement within a Paleoproterozoic orogen and implications for on-craton diamond preservation: Slave craton and Wopmay orogen, NW Canada Journal: Canadian Journal of Earth Sciences Manuscript ID cjes-2016-0059.R1 Manuscript Type: Article Date Submitted by the Author: 01-Sep-2016 Complete List of Authors: Ootes, Luke; Northwest Territories Geological Survey; British Columbia Geological DraftSurvey; Arctic Institute of North America Jackson, Valerie; Northwest Territories Geological Survey; Arctic Institute of North America; 3126 Westridge Pl Davis, William; Geological Survey of Canada Bennett, Venessa; Geomantia Consulting Smar, Leanne; Desert Star Resources Cousens, Brian; Carleton University, Earth Sciences Wopmay orogen, Archean basement, rift-related thermal weakening, Slave Keyword: craton, diamond preservation https://mc06.manuscriptcentral.com/cjes-pubs Page 1 of 80 Canadian Journal of Earth Sciences 1 Parentage of Archean basement within a Paleoproterozoic orogen and implications for on- craton diamond preservation: Slave craton and Wopmay orogen, NW Canada Luke Ootes* and Valerie A. Jackson^ Northwest Territories Geological Survey, Box 1320, Yellowknife, NT, Canada X1A 2L9 and Arctic Institute of North America, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1N4 ^current address: * British Columbia Geological Survey, Box 9333 Stn Prov Govt, Victoria, BC, Canada V8W 9N3 corresponding author: [email protected] Ph. 250-387-2021 ^3126 Westridge Pl, Victoria, BC, Canada V9E 1C8 [email protected] William J. Davis Draft Geological Survey of Canada, 601 Booth Street, Ottawa, ON, Canada K1A 0E8 [email protected] Venessa Bennett Geomantia Consulting, 33 Roundel Road, Whitehorse, YT, Canada Y1A 3H4 [email protected] Leanne Smar Desert Star Resources, 717-1030 West Georgia St,, Vancouver, BC, Canada V6E 2Y3 [email protected] Brian L. Cousens Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada K1S 5B6 [email protected] https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 2 of 80 2 Abstract The Wopmay orogen is a Paleoproterozoic accretionary belt preserved to the west of the Archean Slave craton, NW Canada. Reworked Archean crystalline basement occurs in the orogen and new bedrock mapping, U-Pb geochronology, and Sm-Nd isotopic data further substantiate a Slave craton parentage for this basement. Detrital zircon results from unconformably overlying Paleoproterozoic supracrustal rocks also support a Slave craton provenance. Rifting of the Slave margin began at ca. 2.02 Ga with a second rift phase constrained between ca. 1.92 and 1.89 Ga, resulting in thermal weakening of the Archean basement and allowing subsequent penetrative deformation during the Calderian orogeny (ca. 1.88 to 1.85 Ga). The boundary between the western Slave craton and the reworked Archean basement in the southern Wopmay orogen is interpreted as the rifted cratonic margin, which later acted as a rigid backstop during compressional deformation. Age-isotopic characteristics of plutonic phases track the extent and evolution of these processes that left penetratively deformed Archean basement, Paleoproterozoic cover,Draft and plutons in the west, and ‘rigid’ Archean Slave craton to the east. Diamond-bearing kimberlite occurs across the central and eastern parts of the Slave craton, but kimberlite (diamond-bearing or not) has not been documented west of ~114 ⁰W. It is proposed that, while the crust of the western Slave craton escaped thermal weakening, the mantle did not and was moved out of the diamond stability field. The Paleoproterozoic extension- convergence cycle preserved in the Wopmay orogen provides a reasonable explanation as to why the western Slave craton appears to be diamond-sterile. Keywords: Wopmay orogen, internal metamorphic zone, Archean basement, rift-related thermal weakening, Slave craton, diamond preservation https://mc06.manuscriptcentral.com/cjes-pubs Page 3 of 80 Canadian Journal of Earth Sciences 3 INTRODUCTION The Slave craton, in northwest Canada, is a crustal block that formed and ‘cratonized’ during the Archean eon (Kusky 1989; Bleeker 2002; Davis et al. 2003a; Helmstaedt 2009; Heaman and Pearson 2010). Immediately west of the Slave craton is the Wopmay orogen, which contains Archean basement exposures and Paleoproterozoic supracrustal and plutonic rocks (St- Onge et al. 1983, 1991; Hoffman 1984; King 1987; Hildebrand et al. 1991, 2010; Jackson 2008; Hoffman et al. 2011; Jackson and Ootes 2012; Jackson et al. 2013). Collectively, these rocks underwent penetrative ductile deformation and associated metamorphism during the Paleoproterozoic (King 1987; St-Onge et al. 1991; Jackson et al. 2013). Two competing interpretations have been proposed for the parentage of the deformed Archean basement in Wopmay orogen: 1) it originated as part of the Slave craton, but underwent reworking in the Proterozoic (Jackson et al. 2013), or 2) it was part of an exotic micro-continent (Hottah terrane) and structurally emplaced over the western Slave craton and its margin, and is now preserved as a klippe (Hildebrand et al. 2010). Draft In this contribution we present results from bedrock mapping, U-Pb zircon geochronology, and whole-rock Nd isotopic fingerprinting of the Archean basement exposures in the Wopmay orogen. We also present detrital zircon U-Pb data from metasedimentary rocks that unconformably overly this Archean basement. The integration of these datasets further demonstrates that the Archean basement exposures and overlying sedimentary rocks have a Slave craton parentage/provenance and provide a revised understanding of the architecture of the rifted western cratonic margin. In turn, this has implications for the Slave craton’s lithospheric evolution and provides insights into the diamond fertility of its western region. For example, diamond-bearing kimberlites are prevalent across the central and eastern parts of the Slave craton, but after intense exploration efforts during the past two decades, no on-craton kimberlite has been discovered west of 114 ⁰W, or within the eastern parts of the Wopmay orogen. In northern Canada, diamond-bearing kimberlites have generally been discovered using dispersed diamond-indicator minerals in glacial till. Have no kimberlites been discovered because they do not contain diamonds and therefore the glacially dispersed till does not contain the appropriate diamond indicator minerals? On-craton studies have yet to provide a resolution of this paradox; however, the Archean basement in the adjacent Paleoproterozoic orogenic belt may contain the clues for resolving western Slave craton diamond enigma. https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 4 of 80 4 GEOLOGICAL BACKGROUND Slave Craton The Slave craton (Fig. 1) is a 4.02 to 2.55 Ga composite cratonic block (Kusky 1989; Bleeker 2002; Davis et al. 2003a, b; Snyder 2008; Helmstaedt 2009; Heaman and Pearson 2010). The west-central Slave craton contains bedrock older than ca. 2.85 Ga, preserved as gneissic basement complexes and a late Mesoarchean supracrustal cover sequence (Bleeker et al. 1999, 2000; Sircombe et al. 2001; Bleeker 2002; Ketchum et al. 2004; Reimink et al. 2014). Stratigraphically above the basement and cover are Neoarchean volcanic belts (>2.73 Ga to ca. 2.66 Ga; e.g., Bleeker 2002) and greywacke-mudstone successions (ca. 2.66 to 2.62 Ga; Ootes et al. 2009; Haugaard et al. 2016), as well as late polymictic conglomerates and sandstones (<2.6 Ga; Corcoran and Mueller 2002). The western Slave craton is dominated by ca. 2630 to 2580 Ma plutonic rocks (van Breemen et al. 1992; Davis and BleekerDraft 1999; Bennett et al. 2005), and the youngest identified is the Stagg granite, dated at 2565.4 ± 4.1 Ma (Bleeker et al. 2007). Metamorphic grade in the western Slave craton is variable, but generally characterized by high-temperature, low-pressure, greenschist to granulite-facies assemblages preserved in both volcanic and sedimentary rocks and spatially associated with granitic intrusions (Davis and Bleeker 1999; Pehrsson et al. 2000; Bennett et al. 2005; Ootes et al. 2005). Upper-amphibolite to granulite-facies assemblages are locally well-preserved and metamorphism occurred between ca. 2600 and 2580 Ma (e.g., Pehrsson et al. 2000; Bennett et al. 2005; Ootes et al. 2005; Jackson et al. 2006). Metamorphism in the deep crust continued to ca. 2550 Ma, as recorded by lower crustal xenoliths recovered from kimberlites (Davis et al. 2003a). The timing of penetrative ductile deformation in the Slave craton is best documented in the Duncan Lake Group greywacke-mudstone successions, where D1-D2 occurred between ca. 2650 and 2590 Ma, with a younger D 3 overprint (Bleeker and Beaumont-Smith 1995; Davis and Bleeker 1999; Bleeker 2002; Ootes et al. 2005). The Mesoarchean and older basement has a more complicated history of deformation (e.g., Bleeker et al. 1999; Ketchum et al. 2004), whereas plutonic rocks younger than ca. 2590 Ma do not contain penetrative deformation fabrics (Pehrsson 2002; Bennett et al. 2005; Jackson et al. 2006). The Slave craton does not contain post-Archean ductile deformation-related fabrics, nor metamorphic assemblages, with the possible exception of its eastern boundary with the Thelon orogen https://mc06.manuscriptcentral.com/cjes-pubs Page 5 of 80 Canadian Journal of Earth Sciences 5 (Culshaw 1991). The Slave craton was,
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