New Sm-Nd Data from the Zemlak Domain: Testing the Model for Tectonically Amalgamated Taltson Complex and Proto-Rae Cratonic Blocks within the Rae Province of Northwestern

Ken Ashton 1, Robert A. Creaser 2 and Kathryn Bethune 3

Information from this publication may be used if credit is given. It is recommended that reference to this publication be made in the following form: Ashton, K., Creaser, R.A. and Bethune, K. (2016): New Sm-Nd data from the Zemlak Domain: testing the model for tectonically amalgamated Taltson basement complex and proto-Rae cratonic blocks within the Rae Province of northwestern Saskatchewan; in Summary of Investigations 2016, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2016-4.2, Paper A-7, 12p.

Abstract

Three of five new Sm-Nd analyses from the Zemlak Domain yield TDM ages in the 3.04 to 3.00 Ga range, similar to previously analyzed Zemlak samples, and slightly older than the 2.89 to 2.84 Ma range for rocks in the Nolan Domain. A 2.52 Ga gneissic granodiorite from a highly magnetic zone near the northern boundary of the Zemlak Domain yielded a TDM age of 2.96 Ga with a -6.9 ƐNd value calculated at 1900 Ma. A -0.7 ƐNd value calculated at its crystallization age, together with an unpublished arc-type geochemical signature, suggests that this rock is slightly contaminated by older crustal material and may have been emplaced above a subduction zone. A pink leucogranite, from south of the eastern end of Tazin Lake, yielded a similar TDM age of 3.01 Ga but a more evolved -11.3 ƐNd value (calculated at 1900 Ma), consistent with its inferred anatectic origin. In the southeastern zone of the Zemlak Domain, between the Black Bay and Island Bay faults, variably magnetic granodioritic orthogneisses are overlain by the Paleoproterozoic Murmac Bay group. A gneissic granodiorite from the LeBlanc Lake area of this southeastern zone yielded a 3.04 Ga TDM age and a -6.6 ƐNd value. A sample of the Cairns Island granite, also collected from this southeastern zone, yielded a similar 3.00 Ga TDM age but a -11.1 ƐNd value, indicative of a more evolved history and consistent with its derivation from crustal melting. The fifth sample, collected from variably mylonitic gneissic granodiorite in a zone central to the northern and southeastern Zemlak Domain, yielded a younger 2.87 Ga TDM age and a -6.9 ƐNd value, more similar to the ca. 2.6 Ga rocks of the Nolan and northwestern Beaverlodge domains. Keywords: Sm-Nd, Zemlak Domain, proto–Rae craton, Taltson basement complex

1. Introduction It was recently proposed that the Rae Province in northwestern Saskatchewan (Figure 1) could have resulted from the amalgamation of two cratonic blocks (Ashton et al., 2014; Bethune, 2014) during the ca. 2.5 to 2.3 Ga Arrowsmith (Berman et al., 2005, 2013). One block, termed the proto–Rae craton, was thought to include rocks of the Nolan Domain and parts of the central Beaverlodge Domain, and be dominated by ca. 2.68 to 2.58 Ma rocks (Figure 2; Van Schmus et al., 1986; Hartlaub et al., 2004, 2005; Ashton et al., 2007a; Bethune et al., 2013). The other block consisted of ca. 3.0, 2.5 and 2.3 Ga granitoid rocks (Persons, 1983; Hartlaub et al., 2004, 2007; Ashton et al., 2007a) of the ‘Taltson basement complex’ (Panӑ, 2010) that extend from northeastern and the southern eastward into Saskatchewan as the Zemlak and southwestern Beaverlodge domains. The basal Murmac Bay group was interpreted as a post-orogenic extensional response to this plate amalgamation and, together with the older rocks, was subsequently overprinted by the ca. 1.98 to 1.92 Ga Taltson orogeny (Ross et al., 1991; McDonough et al., 2000; Ross, 2002).

1 Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, 1000-2103 11th Avenue, Regina, SK S4P 3Z8 2 University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3 3 University of Regina, Department of Geology, 3737 Wascana Parkway, Regina, SK S4S 0A2 Although the Saskatchewan Ministry of the Economy has exercised all reasonable care in the compilation, interpretation and production of this product, it is not possible to ensure total accuracy, and all persons who rely on the information contained herein do so at their own risk. The Saskatchewan Ministry of the Economy and the Government of Saskatchewan do not accept liability for any errors, omissions or inaccuracies that may be included in, or derived from, this product.

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Figure 1 – Orogenic map of the western showing main tectonic elements both exposed and beneath Phanerozoic cover.

In order to test this tectonic model, it would be useful to learn more about the age and crustal history of each of the inferred plates. One way to do this is by analyzing rocks for their Sm-Nd isotopic composition. Previous work has shown that the temporally restricted 2.68 to 2.58 Ga (i.e., ca. 2.6 Ga) granitic rocks that make up the Nolan Domain and parts of the central Beaverlodge Domain have consistent depleted mantle (TDM) ages in the 2.92 to 2.84 Ga range and slightly positive ƐNd values calculated for the time of crystallization (Figure 3). Given the more temporally heterogeneous composition of the Taltson basement complex, which contains granitic rocks of ca. 3.0, 2.5 and 2.3 Ga ages, it is not surprising that corresponding TDM ages span a broader range, from 3.24 to 2.86 Ga (Figure 3). The ca. 3.0 Ga suite yields TDM ages older than 3.0 Ga and slightly positive ƐNd values (calculated for the time of crystallization), suggestive of minor influence from older rocks. The ca. 2.5 Ga suite yields TDM ages in the 2.96 to 2.86 Ga range and slightly negative ƐNd values (calculated for the time of crystallization), suggestive of a more significant influence from older rocks. In contrast, the two youngest of the five suites are crustal melts, which is inherent in their more evolved isotopic compositions. The ca. 2.3 Ga igneous suite yields TDM ages of 3.13 to 2.88 and ƐNd values of -1.9 to -6.7 (calculated for the time of crystallization). The single analyzed ca. 1.9 Ga rock yields a TDM age of 3.24 and ƐNd value of -13.6 (calculated for the time of crystallization).

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Figure 2 – Simplified geological map of the Rae Province in northwestern Saskatchewan (NTS 74N) showing locations and U-Pb crystallization ages of previously dated rocks, and locations and calculated TDM ages from pre-existing and new Sm-Nd isotopic analyses derived from all rocks that predate the Martin Group. Approximate inferred boundary between proto–Rae craton and Taltson basement complex shown as dot-dash lines. Inset shows lithotectonic domains in NTS 74N.

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Figure 3 – Nd evolution curve for the five known suites of granitoid rocks in the western Rae Province of northwestern Saskatchewan (see text for references). ƐNd values have been plotted at the crystallization age of each sample to show the degree of evolution of each igneous suite; coloured lines have been projected back to the depleted mantle curve and represent the maximum and minimum TDM ages for each suite. Abbreviations: CHUR, chondritic uniform reservoir; DM, depleted mantle.

Therefore, TDM ages at the upper end of the age range for the Taltson basement complex (i.e., ≥3.0 Ga) are useful for helping to define its extent. They can be generated directly from rocks of the ca. 3.0 Ga suite or from a younger crustal melt (i.e., the ca. 2.3 Ga or 1.9 Ga suite) incorporating variable proportions of Mesoarchean material. TDM ages at the lower limit of that range (i.e., ≤3.0 Ga) can be generated directly from the 2.5 Ga suite of the Taltson basement complex or from the 2.6 Ga suite of the proto–Rae craton, with only minimal input from Mesoarchean sources. Alternatively, TDM ages in the 2.8 to 3.0 Ga range can be derived from rocks of the more evolved 2.3 or 1.9 Ga suites by incorporating a smaller component of ancient material.

Assuming that the ranges of TDM ages and ƐNd values previously obtained for the five suites in the region are representative, the new Sm-Nd analyses, together with whole-rock geochemical analyses, may also provide constraints on the crystallization ages of the analyzed rocks. Therefore, to obtain better coverage of TDM ages in the Zemlak Domain and to potentially provide constraints on crystallization ages, five additional samples of granitic rocks from the eastern part of the domain were analyzed.

2. Regional Geology and Sm-Nd Signatures of Previously Analyzed Rocks in the Tazin Lake Area The Nolan Domain (Figure 2) is dominated by weakly deformed and weakly to moderately magnetic (Ashton, 2009) 2.61 to 2.58 Ga granitic to granodioritic rocks (Van Schmus et al., 1986; Ashton et al., 2007a), with minor migmatitic to diatexitic psammopelitic rocks on its more highly metamorphosed eastern margin. Rocks of the adjacent Zemlak Domain are compositionally more heterogeneous, ranging from granite to diorite, and are much more intensely deformed. Rocks along the domain boundary are characterized by a southward-increasing strain and metamorphic gradient (Ashton et al., 2005). Based on outcrop appearance, bulk composition (Ashton et al., 2005) and similarities in Sm-Nd isotopic composition, it was suggested that some of the mylonitic rocks formerly assigned to the northwestern Zemlak Domain were actually mylonitized equivalents of the Nolan Domain , suggesting the need for revision of the domain boundary (Ashton et al., 2014). In contrast to those of the Nolan Domain, the variably mylonitized rocks of the adjacent Zemlak Domain include highly magnetic 2.52 Ga granodioritic to dioritic rocks (Ashton et al., 2014; Card, this volume) and 2.33 Ga granites in the north, and 2.71 and ca. 2.54 Ga granitic to granodioritic in the south (Ashton et al., 2007a, 2014). It is noteworthy that all of these Zemlak Domain ages are known from the Taltson basement complex to the west (Bostock and Loveridge, 1988; Villeneuve et al., 1993; van Breemen and Bostock, 1994; McNicoll et al., 2000) and/or its inferred extension to the south (Stern et al., 2003). The three existing depleted mantle model ages from Sm-Nd isotopic analysis of Nolan Domain granitoids, including one from the recently included southwestern area that was traditionally assigned to the Zemlak Domain, are consistent, ranging from 2.89 to 2.84 Ga (Figure 2; Hartlaub et al., 2005; Ashton et al., 2014). Although the number of analyses is small, the depleted mantle ages from the northern Zemlak Domain appear to extend over a broader

Saskatchewan Geological Survey 4 Summary of Investigations 2016, Volume 2 range than those from the Nolan Domain, from 3.13 to 2.83 Ga (Figure 2), consistent with an influence from older crust. Supracrustal rocks in all but the southeastern Zemlak Domain are dominated by psammopelitic compositions and are also highly strained. The only sample analyzed for detrital zircon geochronology contained a single population of ca. 2.6 Ga age, leaving their depositional age open to speculation (Ashton et al., 2013). In the western Beaverlodge Domain (i.e., the portion of it included in Figure 2), previous U-Pb dating shows a similar division of Nolan-like ca. 2.6 Ga ages in the northeast, and ca. 3.0 and 2.3 Ga granitoid ages more characteristic of the Taltson basement complex in the southwest (Hartlaub et al., 2004, 2005, 2007; Bethune et al., 2013). The Murmac Bay group unconformably overlies the ca. 3.0 and 2.3 Ga granitic rocks in the southwest, although its basal units are probably contemporaneous with emplacement of the 2.3 Ga granitic suite (Ashton et al., 2013). Eleven depleted mantle ages determined for igneous rocks in the southwestern Beaverlodge Domain range from 3.33 to 2.87 Ga, consistent with an influence from Mesoarchean crustal material. In the northeastern part of the Beaverlodge Domain shown on Figure 2, the relationship of the Murmac Bay group to the ca. 2.6 Ga suite is unclear, although previous workers have interpreted it as an unconformity (Hartlaub, 1999). The ca. 2.6 Ga granitic suite in the northeast has yielded TDM ages of 2.92 and 2.85. Rocks in the southeastern part of the Zemlak Domain, between the Black Bay and Island Bay faults (Figure 2), are less strained than elsewhere in the domain and may have more in common with those of the western Beaverlodge Domain. They mainly include granitic orthogneisses and the quartzite--psammopelite association that is characteristic of the Paleoproterozoic Murmac Bay group (Ashton et al., 2013). A 2.61 Ga U-Pb zircon age (Ashton et al., 2009) from a sample of the granitic orthogneiss suggests that this southeastern part of the Zemlak Domain may include rocks of the proto–Rae craton. The two previous depleted mantle ages obtained from igneous rocks in the southeastern Zemlak Domain are 3.08 and 2.86 Ga. Although the 2.86 Ga result is consistent with derivation from proto-Rae rocks similar to the one dated, the 3.08 Ga result suggests the presence of older crust and is more typical of rocks in the Taltson basement complex. Thus, rocks in the Nolan and northwestern Beaverlodge domains, which may represent a proto–Rae craton (Figure 2), appear temporally constrained to 2.68 to 2.58 Ga crystallization ages and TDM ages of 2.92 to 2.84 Ga (averaging 2.87 Ga; n=5). In contrast, ca. 2.6 Ga rocks have not been recognized in the northern Zemlak and southwestern Beaverlodge domains (Figure 2), which instead include the ca. 3.0, 2.7, 2.5 and 2.3 Ga suites that characterize the Taltson basement complex, and yield TDM ages of 3.33 to 2.83 Ga (averaging 3.06; n=15).

3. Sm-Nd Results Sm-Nd analytical work was carried out at the University of Alberta. Analytical procedures for Sm-Nd analyses followed those outlined by Creaser et al. (1997), Unterschutz et al. (2002) and Schmidberger et al. (2007). All ƐNd values have been calculated at the same time to facilitate a comparison of the data from the five samples: 1900 Ma was chosen, as it is thought to approximate the crystallization age of one of the samples and the age of the last high- grade metamorphic event to affect the others.

a) 4701-0531 – LeBlanc Lake Gneissic Granodiorite (Eastern Zemlak Domain) In the area between the Black Bay and Island Bay faults (Figure 2), there appears to be a basement-cover relationship between variably magnetic orthogneisses and the quartzite-amphibolite-psammopelite supracrustal association characteristic of the highly metamorphosed Murmac Bay group (Ashton et al., 2001). The sampled orthogneiss is about 3 km southeast of Leblanc Lake (Figure 2) and comprises approximately equal proportions of intermediate to and layers. The former are grey, fine to medium grained, magnetic, and contain about 20% and 15% , with centimetre-scale layers of pink leucosome (Figure 4A). The felsic component is a homogeneous, pink, medium-grained granite containing inclusions of the more mafic material. It is not internally layered and contains 5 to 10% hornblende and 10 to 15% biotite in lenses up to 3 x 10 mm in size, suggesting that it was originally coarse grained. The intermediate to mafic component was analyzed and yielded a TDM age of 3.04 Ga and an ƐNd value at 1900 Ma of -6.6 (Table 1, Figure 5).

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Figure 4 – Photos of analyzed samples: A) 4701- 0531 – LeBlanc Lake gneissic granodiorite from eastern Zemlak Domain; B) 4701-0305 – Cairns Island granite; C) 4705-0353 – gneissic granodiorite from south of Thluicho Lake; D) 4705-0263 – gneissic granodiorite from south shore of Tazin Lake.

b) 4701-0305 – Cairns Island Granite (Western Black Bay, Lake Athabasca) The Cairns Island granite extends for about 1 km from the mainland southeastward onto two islands northeast of Cairns Island in Black Bay, Lake Athabasca (Figure 2; Ashton et al., 2001). It was distinguished from the orthogneisses making up most of the area between the Black Bay and Island Bay faults on the basis of its homogeneous nature and salmon pink colour. The sampled outcrop comprised 70% pink, medium-grained granite, 25% medium- to coarse-grained granitic leucosome and 5% inclusions derived from mafic dykes. The sample was collected from the dominant rock type, which locally contained coarse-grained feldspar augen and was non-magnetic (Figure 4B). The rock was variably strained, ranging from foliated to gneissic where shearing was intense. It contains about 5% chloritized biotite and/or hornblende. The pink colour results from hematite dusting preferentially developed in . This salmon pink colour, together with the indication of an originally coarse grain size and homogeneous composition, suggest that the Cairns Lake granite is part of the ca. 2.3 Ga granite suite. Unpublished geochemical data cannot confirm this correlation, but are consistent with it. The Cairns Island granite sample yielded a TDM age of 3.00 Ga (Table 1, Figure 5). Calculated at 1900 Ma, the ƐNd value for the rock is -11.1; assuming a 2300 Ma crystallization age, the ƐNd value is -5.7.

c) 4705-0353 – Thluicho Lake Gneissic Granodiorite West of the Island Bay fault, the rocks north of the northern shore of Lake Athabasca are dominated by intensely mylonitized gneissic granodiorite, gneissic to diatexitic psammopelite, and the unconformably overlying Thluicho Lake group (Figure 2), consisting of facies, continental clastic rocks (Hunter et al., 2010). Since quartzite and amphibolite, which are diagnostic of the Murmac Bay group east of the Island Bay fault, are not associated with the gneissic to diatexitic psammopelitic, the latter rocks may not be correlative. Therefore, the associated gneissic granodioritic rocks were also considered to be disparate from the orthogneisses to the east (Ashton and Hunter, 2004). The gneissic granodiorite weathers pink and grey due to a large component of in situ pink leucosome, and contains 10 to 25% variably chloritized biotite and minor hornblende. A mylonitized sample of this unit was analyzed using isotope dilution thermal ionization mass spectrometry (ID-TIMS) and, subsequently, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to determine its crystallization age, but the results were ambiguous. Two peaks of 207Pb/206Pb ages were determined in the LA-ICP-MS study at ca. 2490 and ca. 2540 Ma, either of which could broadly represent the crystallization age (Ashton et al., 2014). The authors favoured the older age, but

Saskatchewan Geological Survey 6 Summary of Investigations 2016, Volume 2 the ambiguity in the result, together with 207Pb/206Pb ages as old as 2570 Ma, make it difficult to say with certainty that this rock is younger than those of the 2605 to 2581 Ma suite characterizing the Nolan Domain. The sample analyzed for Sm-Nd was collected about 7 km northeast of the sample dated for U-Pb, but was thought to represent a better-preserved candidate from the same suite. It came from the area immediately south of Thluicho Lake, where it forms part of the basement to the Thluicho Lake group (Figure 2). It is a pink and grey, coarse-grained granodiorite with feldspar augen up to 1 cm, in a matrix containing 20% biotite (Figure 4C). It is intruded by 20% sheets of pink leucogranite with a colour index of about 0. The Thluicho Lake gneissic granodiorite yielded a TDM age of 2.87 Ga and an ƐNd value of -7.1 calculated at 1900 Ma (Table 1, Figure 5).

d) 4705-0263 – South Tazin Gneissic Granodiorite The boundary between ca. 2.6 Ga granitoids of the Nolan Domain and magnetic orthogneisses of the Zemlak Domain runs through southern Tazin Lake (Figure 2; Ashton et al., 2014). A unit of gneissic granodiorite from about 3 km south of the boundary, on the southern shore of Tazin Lake, previously yielded a U-Pb sensitive high-resolution ion microprobe (SHRIMP) age of 2517 ±4 Ma (Ashton et al., 2014). In order to learn more about the crustal history of rocks with this atypical age, a sample from the dated rock was analyzed using Sm-Nd techniques. A detailed description of the rock can be found in Ashton et al. (2014). In summary, it is grey, medium grained, and contains about 15% variably chloritized hornblende and biotite (Figure 4D). This dated granodioritic component contains centimetre-scale layers of fine-grained amphibolite and was intruded by 1- to 30-cm-thick sheets of pink, medium- grained to pegmatitic leucogranite, which exhibits ptygmatic folding about northeast-trending axes (F4 in the scheme of Ashton et al., 2005). The gneissic granodiorite yielded a TDM age of 2.96 Ga with ƐNd values of -6.9 calculated at 1900 Ma, and -0.7 at its 2517 Ma crystallization age (Table 1, Figure 5).

e) 4705-0189 – Taz Bay Pink Leucogranite Pink leucogranite is a relatively common rock type in the Zemlak, Nolan and Beaverlodge domains. Crosscutting field relationships with Zemlak orthogneisses, Nolan Domain granitoids, and Murmac Bay group rocks generally suggest that they were emplaced late in the geological history. Two attempts to date such rocks in the Uranium City and southern Black Bay areas have yielded a scatter of inherited zircon with little evidence for zircon growth at the time of crystallization (Hartlaub et al., 2005). However, a mylonitic pink leucogranite from an island about 1.5 km north of the Zemlak/Nolan domain boundary, which was thought to have intruded granite based on field relationships, yielded only ca. 2.6 Ga zircon, leading to its tentative reinterpretation as a mylonitized equivalent of the Archean granite (Ashton et al., 2007a). Some pink leucogranite in the southwestern Beaverlodge Domain has a geochemical signature remarkably similar to that of the ca. 2.3 Ga suite, but most of the pink leucogranite in the Zemlak Domain clearly intrudes the widespread orthogneisses and is thought to have formed by partial melting during a ca. 1.9 Ga metamorphic event. The sample analyzed in this study was collected from a relatively large body of pink leucogranite south of Taz Bay at the eastern extent of Tazin Lake (Figure 2). Rocks within this unit are generally salmon pink with a colour index of close to 0. The best-preserved zones appear massive and locally contain feldspar relicts up to 5 mm long, but the vast majority is fine to medium grained due to intense shearing and mylonitization. This ductile deformation locally produces feldspar beading, ribboning and sugary quartzofeldspathic textures. A gneissic appearance is also locally developed due to shearing, which produces centimetre-scale grey-green layers due to the development of sericite and minor chlorite. A strong cataclastic overprint imparts a hackly appearance to most outcrops, with chlorite commonly lining fracture planes. The pink leucogranite occurs as intrusive sheets in the magnetic granodioritic (sample 4705-0263 described above) that yielded the 2517 ±4 Ma U-Pb age, the 2.96 Ga TDM age and the -6.9 ƐNd value (calculated at 1900 Ma) about 5 km to the west (Ashton et al., 2014). This intrusive relationship was seen both at the site where the dated granodioritic gneiss was sampled and within the large body south of eastern Tazin Lake, where the granodioritic gneiss occurs as a decametre-scale inclusion in the pink leucogranite. Minor fine- grained amphibolite also occurs rarely in the leucogranite unit, generally as centimetre-scale layers. In one such case, the amphibolite is intruded by the pink leucogranite, which has a white colouration adjacent to the amphibolite. The sampled mylonitic pink leucogranite yielded a TDM age of 3.01 Ma (Table 1). Its ƐNd value at 1900 Ma is -11.3 (Figure 5).

Saskatchewan Geological Survey 7 Summary of Investigations 2016, Volume 2 Table 1 – Sm-Nd isotopic data for Zemlak Domain samples analyzed in 2015. CHUR @ Sample Rock UTM_E1 UTM_N Sm Nd 147Sm/144Nd 143Nd/144Nd0 uncert. ƐNd0 143Nd/144NdT TDM ~T TMa ƐNdT ppm ppm (2 SE ±) Ga Ma LeBlanc Lake gneissic 4701-0531 granodiorite 633324 6614810 10.28 48.5 0.1281 0.511442 0.000007 -23.3 0.509840 3.04 1900 0.510179 -6.6 4701-0305 Cairns Island granite 614090 6597780 10.3 66.9 0.0935 0.510783 0.000008 -36.2 0.509614 3.00 1900 0.510179 -11.1 Thluicho Lake gneissic 4705-0353 granodiorite 597269 6613971 8.95 49.4 0.1097 0.511189 0.000006 -28.3 0.509818 2.87 1900 0.510179 -7.1 South Tazin gneissic 4705-0263 granodiorite 611678 6623348 7.11 35.8 0.1201 0.511330 0.000010 -25.5 0.509829 2.96 1900 0.510179 -6.9 Taz Bay pink leucogranite; 4705-0189 mylonitic 627611 6621966 2.06 13.4 0.0931 0.510768 0.000008 -36.5 0.509604 3.01 1900 0.510179 -11.3

All samples relative to La Jolla 143Nd/144Nd = 0.511850

Uncertainty is 2 standard errors (2 S.E.) on 143Nd/144Nd

TDM age uses the linear Model of Goldstein et al., 1984

1 UTM coordinates are in Zone 12, NAD83

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Figure 5 – 143Nd evolution plot for analyzed samples from the eastern Zemlak Domain. ƐNd values have been plotted at the 1900 Ma approximate peak metamorphic age and are based on the evolution model of Goldstein et al. (1984). The ƐNd value of sample 4705-0263, the gneissic granodiorite from the southern shore of Tazin Lake, has also been plotted at its known 2517 Ma crystallization age. Abbreviations: CHUR, chondritic uniform reservoir; DM, depleted mantle.

4. Discussion

The three new results with TDM ages ≥3.0 Ga (samples 4701-0531, 4701-0305 and 4705-0189) are similar to a pre- existing 3.08 Ga result from the Feil Lake granite 6 km northeast of 4701-0305 (Ashton et al., 2007b; the latter sample also yielded an independent 3.18 Ga result reported in Hartlaub et al., 2005; Figure 2), and are consistent with the inference of Mesoarchean crustal involvement (Figure 3). They are significantly older than the other pre- existing 2.86 Ga TDM age from that area (Figures 2, 3), obtained from a sheared pink leucogranite (Hartlaub et al., 2005). Taken together with the presence of a 2.61 Ga crystallization age obtained from granitic orthogneiss 6 km east of sample 4701-0305 (Figure 2), this result suggests that the area is underlain by a heterogeneous mix of temporally distinct rocks. The crystallization age of the LeBlanc Lake gneissic granodiorite (sample 4701-0531) is unclear. Based on comparison of its 3.04 Ga TDM age and evolution curve (Figure 5) to those of the dated suites of rocks in the area (Figure 3), it could be a juvenile member of the ca. 3.0 Ga suite, a slightly evolved member of the ca. 2.6 Ga or 2.5 Ga suite, or a more evolved member of the ca. 2.3 Ga suite. The Cairns Lake granite (sample 4701-0305) on the other hand, is more evolved based on its ƐNd value (Figure 5), which, together with its pink coarse-grained appearance, is consistent with the suggestion that it is part of the 2.3 Ga granite suite. Since the pink leucogranite collected south of Taz Bay (sample 4705-0189) is known to intrude the granodiorite- quartz diorite suite that yielded the 2517 ±4 Ma age from the south Tazin gneissic granodiorite, its crystallization age must be younger. Based on its general lack of ferromagnesian minerals and its sheet-like mode of emplacement, it is thought to have formed during the 1.94 to 1.92 Ga high-grade metamorphic event associated with the Taltson orogeny (Ashton et al., 2005). Its TDM age of 3.01 Ga (Figure 3) indicates a significant component of Mesoarchean source material, consistent with emplacement in the Taltson basement complex, and its strongly negative ƐNd value (Figure 5) and relatively late time of emplacement further suggest that it is part of the ca. 1.9 Ga suite of anatectic granites. Since the 2517 ±4 Ma crystallization age of the gneissic granodiorite from the southern shore of Tazin Lake (sample 4705-0263) is known (Ashton et al., 2014), the purpose of obtaining an Sm-Nd analysis was to better characterize this newly recognized suite of rocks. The sampled rock was intercalated within a unit of granodioritic to dioritic rocks, and exhibits arc-type geochemical affinities (based on unpublished data). Its TDM age of 2.96 Ga and ƐNd value of -0.7 (calculated at its crystallization age) suggests minor contamination by older crust (Figures 2, 5), but are consistent with emplacement in a continental arc setting.

The TDM age of 2.87 Ga determined for the gneissic granodiorite from south of Thluicho Lake (sample 4705-0353; Table 1, Figure 2) indicates that it was not significantly affected by Mesoarchean crustal material, and is similar to the

Saskatchewan Geological Survey 9 Summary of Investigations 2016, Volume 2 TDM ages derived for the ca. 2.5 and 2.3 Ga rocks of the Taltson basement complex and the 2.6 Ga rocks of the proto–Rae craton (Figure 3). This is the sample that previously yielded an ambiguous U-Pb age that could be interpreted as ca. 2.49 Ga, 2.54 Ga, or older (Ashton et al., 2014). This TDM age is not compatible with inclusion of the gneissic granodiorite in the ca. 3.0 Ga suite, and its ƐNd value is less evolved than that of the Taz Bay pink leucogranite (sample 4705-0189) and the known sample from the dated 1.9 Ga rock (Figure 3), suggesting that it is not part of that suite. Correlation with the ca. 2.5 Ga suite found to the north seems unlikely, based on its pink colour and the absence of more intermediate granodioritic to dioritic rocks. Therefore, it is likely that the Thluicho Lake gneissic granodiorite is part of the ca. 2.6 Ga or ca. 2.3 Ga suites. If it is part of the former suite, it would increase the proportion of ca. 2.6 Ga rocks in the Zemlak Domain, further suggesting that rocks of this age are not unique to the Nolan and northwestern Beaverlodge domains, or that rocks of the inferred proto–Rae craton are structurally intercalated with the Taltson basement complex in the Zemlak Domain.

5. Summary

Three of the five new TDM ages reported from the Zemlak Domain are ≥3.0 Ga, suggesting interaction with Mesoarchean material, which is common in rocks of the Taltson basement complex, but has yet to be recognized in the inferred proto–Rae craton. TDM ages from the other two samples yielded ambiguous results that could have been derived from rocks in either tectonic plate. The presence of a gneissic granite of known 2.61 Ga age in the southeastern Zemlak Domain has already inferred that either rocks of this age are present in the Taltson basement complex or that rocks of the two tectonic plates are structurally intercalated in this area. Therefore, the new results are broadly consistent with the model of plate amalgamation during Arrowsmith time. The Sm-Nd results support the interpretations of the Taz Bay pink leucogranite being derived by anatexis at about 1.9 Ga, and the Cairns Island granite belonging to the suite of ca. 2.3 Ga granites, as was suspected from field characteristics. The crystallization ages of the LeBlanc Lake and the Thluicho Lake gneissic granodiorites remain unclear. Further work directed towards testing the tectonic amalgamation model is ongoing at the University of Regina in the form of two M.Sc. thesis projects under the supervision of K. Bethune.

6. References Ashton, K.E. (2009): Compilation bedrock geology, Tazin Lake, NTS area 74N; Saskatchewan Ministry of Energy and Resources, Map 246A, scale 1:250 000. Ashton, K.E., Boivin, D. and Heggie, G. (2001): Geology of the southern Black Bay Belt, west of Uranium City, Rae Province; in Summary of Investigations 2001, Volume 2, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report 2001-4.2, Section A: Northern Mapping, p.50-63. Ashton, K.E., Card, C.D., Davis, W., and Heaman, L.M. (2007a): New U-Pb zircon age dates from the Tazin Lake map area (NTS 74N); in Summary of Investigations 2007, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of Energy and Resources, Miscellaneous Report 2007-4.2, Paper A-11, 8p. Ashton, K.E., Card, C. and Modeland, S. (2005): Geological reconnaissance of the northern Tazin Lake map area (NTS 74N), including parts of the Ena, Nolan, Zemlak, and Taltson domains, Rae Province; in Summary of Investigations 2005, Volume 2, Saskatchewan Geological Survey, Saskatchewan Industry and Resources, Miscellaneous Report 2005-4.2, Paper A-1, 24p. Ashton, K.E., Card, C.D. and van Breemen, O. (2007b): Recognition of Paleoproterozoic supracrustal rocks along the Snowbird Tectonic Zone and more evidence for Mesoarchean crust in the southern Rae Province: new TDM data from northwestern Saskatchewan; Saskatchewan Geological Survey, Saskatchewan Industry and Resources, Open File 2007-22, 12p. Ashton, K.E., Hartlaub, R.P., Bethune, K.M., Heaman, L.M., Rayner, N. and Niebergall, G.R. (2013): New depositional age constraints for the Murmac Bay group of the southern Rae craton, Canada; Research, v.232, p.70-88.

Saskatchewan Geological Survey 10 Summary of Investigations 2016, Volume 2 Ashton, K.E. and Hunter, R.C. (2004): Geology of the Camsell Portage area, southern Zemlak Domain, Rae Province (Uranium City Project); in Summary of Investigations 2004, Volume 2, Saskatchewan Geological Survey, Saskatchewan Industry and Resources, Miscellaneous Report 2004-4.2, Paper A-8, 12p. Ashton, K.E., Rayner, N.M. and Bethune, K.M. (2009): Meso- and Neoarchean granitic magmatism, Paleoproterozoic (2.37 Ga and 1.93 Ga) and 2.17 Ga provenance ages in a Murmac Bay Group pelite: U-Pb SHRIMP ages from the Uranium City area; in Summary of Investigations 2009, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of Energy and Resources, Miscellaneous Report 2009-4.2, Paper A-5, 9p. Ashton, K.E., Rayner, N.M., Heaman, L.M. and Creaser, R.A. (2014): New Sm-Nd and U-Pb ages from the Zemlak and south- central Beaverlodge domains: a case for amalgamated Taltson basement complex and proto-Rae cratonic blocks within the Rae Province of northwestern Saskatchewan; in Summary of Investigations 2014, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2014-4.2, Paper A-6, 28p. Berman, R.G., Pehrsson, S., Davis, W.J., Ryan, J.J., Qui, H., and Ashton, K.E. (2013): The Arrowsmith orogeny: geochronological and thermobarometric constraints on its extent and tectonic setting in the Rae craton, with implications for pre-Nuna supercontinent reconstruction; Precambrian Research, v.232, p.44-69. Berman, R.G., Sanborn-Barrie, M., Stern, R.A. and Carson, C.J. (2005): Tectonometamorphism at ca. 2.35 and 1.85 Ga in the Rae Domain, western Churchill Province, , Canada: Insights from structural, metamorphic and in situ geochronological analysis of the southwestern Committee Bay Belt; Canadian Mineralogist, v.43, p.409-442. Bethune, K. (2014): New perspectives on tectonic assembly of the western Rae craton: evidence from the Athabasca region of Saskatchewan, Canada (abstract); Geological Society of America, 2014 Annual Meeting, Vancouver, Paper 291-9. Bethune, K.M., Berman, R.G., Rayner, N. and Ashton, K.E. (2013): Structural, petrological and U-Pb SHRIMP geochronological study of the western Beaverlodge domain: Implications for crustal architecture, multi-stage orogenesis and the extent of the Taltson orogen in the SW Rae craton, Canadian Shield; Precambrian Research, v.232, p.89-118. Bostock, H.H. and Loveridge, W.D. (1988): Geochronology of the Taltson Magmatic Zone and its eastern cratonic margin, District of Mackenzie; in Radiogenic Age and Isotopic Studies: Report 2, Geological Survey of Canada, Paper 88-2, p.59-65. Creaser, R.A., Erdmer, P., Stevens, R.A. and Grant, S.L. (1997): Tectonic affinity of Nisutlin and Anvil assemblage strata from the Teslin tectonic zone, northern Canadian Cordillera: constraints from neodymium isotope and geochemical evidence; Tectonics, v.16, p.107-121. Goldstein, S.L., Onions, R.K. and Hamilton, P.J. (1984): A Sm-Nd isotopic study of atmospheric dusts and particulates from major river systems; Earth and Planetary Science Letters, v.70, p.221-236. Hartlaub, R.P (1999): New insights into the geology of the Murmac Bay Group, Rae Province, northwest Saskatchewan; in Summary of Investigations 1999, Volume 2, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report 99-4.2, p.17-26. Hartlaub, R.P (2004): Archean and Proterozoic evolution of the Beaverlodge Belt, Churchill craton, Canada; Ph.D. thesis, University of Alberta, Edmonton, Alberta, 189p. Hartlaub, R.P., Chacko, T., Heaman, L.M., Creaser, R.A., Ashton, K.E. and Simonetti, T. (2005): Ancient (Meso- to Paleoarchean) crust in the Rae Province, Canada: Evidence from Sm-Nd and U-Pb constraints; Precambrian Research, v.141, p.137-153. Hartlaub, R.P., Heaman, L.M., Ashton, K.E. and Chacko, T. (2004): The Archean Murmac Bay Group: evidence for a giant Archean rift in the Rae Province, Canada; Precambrian Research, v.131, p.345-372. Hartlaub, R.P., Heaman, L.M., Chacko, T. and Ashton, K.E. (2007): Circa 2.3 Ga magmatism of the Arrowsmith Orogeny, Uranium City region, western Churchill Craton, Canada; Journal of Geology, v.115, p.181-195. Heaman, L.M., Erdmer, P. and Owen, J.V. (2002): U-Pb geochronologic constraints on the crustal evolution of the Long Range Inlier, Newfoundland; Canadian Journal of Earth Sciences, v.39, p.845-865. Hunter, R.C., Bethune, K.M., Ashton, K.E. and Yeo, G.M. (2010): Stratigraphy and sedimentology of the Paleoproterozoic Thluicho Lake Group, southwestern Rae Province, Canada: Alluvial basin development in the hinterland of the Taltson Orogen; Journal of Geology, v.118, p.487-508.

Saskatchewan Geological Survey 11 Summary of Investigations 2016, Volume 2 McDonough, M.R., McNicoll, V.J., Schetselaar, E.M. and Grover, T.W. (2000): Geochronological and kinematic constraints on crustal shortening and escape in a two-sided oblique-slip collisional and magmatic orogen, Paleoproterozoic Taltson magmatic zone, northeastern Alberta; Canadian Journal of Earth Sciences, v.37, p.1549-1573. McNicoll, V.J., Thériault, J. and McDonough, M.R. (2000): Taltson basement gneissic rocks: U-Pb and Nd isotopic constraints on the basement to the Paleoproterozoic Taltson magmatic zone, northeastern Alberta; Canadian Journal of Earth Sciences, v.37, p.1575-1596. Panǎ, D.I. (2010): Overview of the geological evolution of the Canadian Shield in the Andrew Lake area based on new field and isotope data, northeastern Alberta (NTS 74M/16); Energy Resources Conservation Board, ERCB/AGS Open File Report 2009-22, 76p. Persons, S.S. (1983): U-Pb geochronology of Precambrian rocks in the Beaverlodge area, northwestern Saskatchewan; M.Sc. thesis, University of Kansas, Lawrence, Kansas, 68p. Ross, G.M. (2002): Evolution of Precambrian continental lithosphere in Western Canada: results from Lithoprobe studies in Alberta and beyond; Canadian Journal of Earth Sciences, v.39, p.413-437. Ross, G.M., Parrish, R.R., Villeneuve, M.E. and Bowring, S.A. (1991): Geophysics and geochronology of the crystalline basement of the Alberta Basin, western Canada; Canadian Journal of Earth Sciences, v.28, p.512-522. Schmidberger, S.S., Heaman, L.M., Simonetti, A., Creaser, R.A. and Whiteford, S. (2007): Lu-Hf, in situ Sr and Pb isotope and trace element systematics for mantle eclogites from the Diavik mine: evidence for Paleoproterozoic subduction beneath the , Canada; Earth and Planetary Science Letters, v.254, p.55-68. Stern, R.A., Card, C.D., Panǎ, D. and Rayner, N. (2003): SHRIMP U-Pb ages of granitoid basement rocks of the southwestern part of the Athabasca Basin, Saskatchewan and Alberta; Radiogenic Age and isotopic Studies: Report 16, Geological Survey of Canada, Current Research 2003-F3, 20p. Unterschutz, J.L.E., Creaser, R.A., Erdmer, P., Thompson, R.I., and Daughtry, K.L. (2002): North American margin origin of the Quesnel terrane strata in the southern Canadian Cordillera: inferences from geochemical and Nd isotope characteristics of Triassic sedimentary rocks; Geological Society of America Bulletin, v.114, p.462-475. van Breemen, O. and Bostock, H.H. (1994): Age of emplacement of Thoa , western margin of Rae Province, Northwest Territories: initiation of rifting prior to Taltson magmatism?; in Radiogenic Age and Isotopic Studies: Report 8, Geological Survey of Canada, Paper 1994-F, p.61-68. Villeneuve, M.E., Ross, G.M., Thériault, R.J., Miles, W., Parrish, R.R. and Broome, J. (1993): Tectonic subdivision and U-Pb geochronology of the crystalline basement of the Alberta Basin, western Canada; Geological Survey of Canada, Bulletin 447, 86p. Van Schmus, W.R., Persons, S.S., Macdonald, R., and Sibbald, T.I.I. (1986): Preliminary results from U-Pb zircon geochronology of the Uranium City region, northwest Saskatchewan; in Summary of Investigations 1986, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report 86-4, p.108-111.

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