Canadian Journal of Earth Sciences
Depositional timing of Neoarchean turbidites of the Slave craton - recommended nomenclature and type localities
Journal: Canadian Journal of Earth Sciences
Manuscript ID cjes-2016-0098.R1
Manuscript Type: Article
Date Submitted by the Author: 26-Jul-2016
Complete List of Authors: Haugaard, Rasmus; University of Alberta, Earth and Atmospheric Sciences Ootes, Luke; Northwest Territories Geoscience Office, Heaman, Larry; Univ. Alberta, Earth and Atmosphere Hamilton, Michael;Draft University of Toronto, Department of Earth Sciences Shaulis, Barry; University of Alberta, Earth and Atmospheric Sciences Konhauser, Kurt; Dept of Earth and Atmospheric Sciences
Keyword: Slave craton, Neoarchean turbidites, Tuff, U-Pb geochronology
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1 Depositional timing of Neoarchean turbidites of the Slave craton - 2 recommended nomenclature and type localities 3 Rasmus Haugaard 1* , Luke Ootes 2,3,4*, Larry M. Heaman 1, Mike Hamilton 5, Barry J. 4 Shaulis 1, Kurt Konhauser 1 5 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, T6G 2E3, Canada 6 2 Northwest Territories Geological Survey, Box 1320, Yellowknife, NT, X1A 2R3, Canada 7 3Arctic Institute of North America, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 8 1N4, Canada 9 4Current address: British Columbia Geological Survey, Box 9333, Stn Prov Govt, Victoria, BC, V8W 9N3, 10 Canada 11 5Jack Satterly Geochronology Laboratory, Department of Earth Sciences, University of Toronto, Toronto, 12 M5S 3B1, Canada. 13 *Contact: [email protected]; [email protected] 14 15 16 Abstract
17 Two temporally distinct Neoarchean turbidite packages are known to occur in the
18 Slave craton. The older is a greywacke mudstone succession that includes the renowned
19 Burwash Formation (ca. 2661 Ma).Draft In this study, a previously undated tuff bed is
20 demonstrated to have crystallized at ca. 2650.5 ± 1.0 Ma refining the deposition age of
21 these turbidites between ca. 2661 and 2650 Ma. The younger turbidites are locally
22 distinctive as they contain interstratified banded iron formation (BIF). Previous work
23 demonstrated that the younger turbidites were deposited between ca. 2640 to 2615 Ma,
24 based entirely on maximum depositional ages from detrital zircons. A ~3 cm thick felsic
25 to intermediate tuff bed was discovered interbedded with these BIF bearing turbidites.
26 The tuff bed contains a single age population of zircon with a crystallization age of 2620
27 ± 6 Ma defining the depositional timing of these BIF bearing turbidites.
28 New U Pb detrital zircon dates from extensive turbidite sequences in the eastern
29 and central part of the Slave craton are also presented. We use the new and previously
30 published results to recommend nomenclature for these extensive sedimentary rocks in
31 the Slave craton. The ca. 2661 to 2650 Ma turbidites remain part of the previously
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32 ascribed Duncan Lake Group. The younger ca. 2620 Ma turbidites are assigned to the
33 new Slemon Group. Where robust age data exist, we recommend formation names and
34 include type localities for each.
35
36 Key Words: Slave craton; Yellowknife Supergroup; Neoarchean turbidites; Tuff; U-
37 Pb geochronology
38 39
40 Introduction
41 The nature of Archean tectonics is often surmised in part from the preserved 42 igneous record, particularly from theDraft geochemistry of basalts, komatiites, and tonalite 43 trondhjemite granodiorite (TTG) gneisses/plutons (Kröner and Layer 1992; Fan and
44 Kerrich 1997; Arndt et al. 2001; Sharma and Pandit 2003; Condie 2004; Bédard et al.
45 2013), geophysical experiments (e.g., Chen et al. 2009), and mineral inclusions in
46 diamonds from the subcontinental lithosphere (e.g., Shirey and Richardson 2011). The
47 accumulation of Archean clastic sedimentary rocks reflects orogenic uplift, erosion and
48 basin filling; however, due to post depositional metamorphic and structural overprinting,
49 they remain under studied. Further to this, and unlike strata in later Proterozoic and
50 Phanerozoic orogens, Archean sedimentary rocks lack fossils, and thick siliciclastic
51 accumulations generally lack any kind of unique stratigraphic marker horizon (e.g.,
52 Nisbet, 1987). As such, basin models and tectono stratigraphic correlations within and
53 between Archean cratons remain, for the most part, subjective.
54 The use of U Pb zircon geochronology in tuff beds, or detrital zircons in clastic
55 sedimentary rocks, has evolved as the most useful approach to help establish the timing
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56 of deposition of Archean sedimentary rocks and construct more robust regional
57 correlations (e.g., Davis et al. 1990; Fedo et al. 2003; Ferguson et al. 2005; Kositcin et al.
58 2008; Ootes et al. 2009; Rasmussen and Fletcher 2010; Cawood et al. 2012). However,
59 this is wrought with challenges due to a number of reasons, namely: i) the vast majority
60 of Archean sedimentary rocks represent a mixture of polycyclic sedimentary products, ii)
61 synchronous felsic volcanic rocks may not exist (e.g., tuff beds are absent), iii) certain
62 sedimentary processes (e.g. turbidity currents) may have reworked the products of
63 volcanic ash fall events, thus altering their original chronostratigraphic significance.
64 Detrital zircons also provide an imperfect record, as maximum depositional ages may not
65 reflect the youngest single zircon or population of zircons in a sample, which could be
66 millions to hundreds of million yearsDraft older than the actual deposition age. By combining
67 the two approaches, however, some of the challenges with regional correlations and
68 depositional environments can be resolved.
69 Greywacke mudstone sedimentary rocks, deposited by turbidity currents in a
70 below wave base environment are common in Archean supracrustal successions (e.g.,
71 Lowe 1980; Barrett and Fralick 1989; Eriksson et al. 1994; Haugaard et al. 2013). Within
72 the Slave craton, the Yellowknife Supergroup contains some of the largest and best
73 preserved Archean turbidite deposits in the world (Henderson 1970, 1972; Padgham and
74 Fyson 1992; Ferguson et al. 2005). The overall supracrustal stratigraphy consists of
75 approximately 70% of these sedimentary rocks, which is unique amongst Archean
76 cratons (vs. Superior and Yilgarn for example), providing insight into diverse Archean
77 tectonic processes (Padgham and Fyson 1992). The Slave craton turbidites are often
78 monotonous, but Ootes et al. (2009) have divided them into an older and younger
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79 package (I and II). The older includes the well known Burwash Formation, which is
80 spectacularly preserved in the south central part of the craton (e.g. Henderson 1970,
81 1972; Ferguson et al. 2005) and contains a number of interbedded tuff beds that have
82 been dated at ca. 2661 Ma (Bleeker and Villeneuve 1995; Ferguson 2002; Ferguson et al.
83 2005). The younger are locally distinctive as they contain interstratified banded iron
84 formation (BIF); detrital zircon ages indicate these turbidites have maximum deposition
85 ages younger than ca. 2640 Ma, and were deposited more than 20 million years after the
86 Burwash Formation (Perhsson and Villeneuve 1999; Bennett et al. 2005; Ootes et al.
87 2009). The recognition that the younger turbidites are associated with BIF has
88 fundamental importance for: 1) establishing a provenance record for the turbidites; 2)
89 establishing regional correlations Draft across the craton, which are critical in evaluating
90 postulated tectonic evolution models (e.g., Davis et al. 2003; Helmstaedt 2009), and; 3)
91 temporally constraining BIF deposition, allowing insight into the nature of early sea
92 water and by analogy atmospheric and biospheric conditions at that time (e.g., Bekker et
93 al. 2010; Haugaard et al. 2013, 2016).
94 To further evaluate the extent and absolute timing of the turbidite depositional
95 events, we report a new, conventional (isotope dilution) U Pb zircon crystallization age
96 determination for a previously undated tuff bed in the type locality of the Burwash
97 Formation, and the first U Pb zircon eruption age from a tuff bed that is intercalated with
98 the younger BIF bearing turbidites (determined via laser ablation ICP MS). Furthermore,
99 we present new U Pb detrital zircon maximum depositional ages from three turbidite
100 sequences across the Slave craton; these results complement the tuff dates, augment
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101 provenance information from previous Slave craton detrital zircon age studies, and
102 establish new maximum age limits for deposition.
103 Turbidites in the Slave craton have previously been assigned to the Duncan Lake
104 Group, with the Burwash Formation as the type locality (Henderson 1970, 1972). The
105 results of this and previous studies now demonstrate enough evidence to clearly
106 distinguish the younger BIF bearing turbidites from the older Duncan Lake Group. As
107 such, we recommend new nomenclature, referring to these younger turbidites as the
108 Slemon Group and recommend the use of a number of formation names and their type
109 localities across the craton.
110
111 Geological setting Draft
112 The Archean Slave craton is well known for hosting the oldest bedrock exposure
113 in the world, the Acasta gneiss (e.g., Reimink et al. 2014), ca. 2.7 Ga greenstone belts and
114 orogenic gold (e.g., Bleeker and Hall, 2007; Ootes et al. 2011), and kimberlite hosted
115 diamond deposits (e.g., Heaman and Pearson 2010). However, the Slave craton is
116 relatively unique as the supracrustal rock record is dominated by large and extensive
117 Neoarchean turbidite successions deposited over a minimum area of about 32,000 km 2
118 (Henderson 1970, 1972; Ferguson et al. 2005; Bleeker and Hall 2007; Ootes et al. 2009).
119 The turbidite sequences are part of the Duncan Lake Group of the Yellowknife
120 Supergroup (Fig. 1; Henderson 1970) and were deposited on top of or adjacent to older
121 volcanic dominated supracrustal rocks, namely the ca. 2740 2700 Ma Kam Group and
122 the ca. 2660 Ma Banting Group (e.g., Helmstaedt and Padgham 1986; Isachsen and
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123 Bowring 1997). The turbidites include the archetypal, up to 5 km thick, Burwash
124 Formation (Henderson 1970, 1972; Ferguson et al. 2005).
125 Felsic tuff beds are preserved within the Burwash Formation turbidites and have
126 been dated by the isotope dilution thermal ionization mass spectrometry (ID TIMS) U Pb
127 zircon method, providing a robust constraint on the time of turbidite deposition at 2661 ±
128 2 Ma (Bleeker and Villeneuve 1995; Ferguson 2002). While the greywacke mudstone
129 turbidites are commonly monotonous, they are locally distinctive as they contain
130 interstratified oxide silicate BIF and were historically considered correlative to the
131 Burwash Formation (e.g., Bostock 1980, Padgham 1991; Henderson 1998; Jackson
132 2001). The advent of U Pb detrital zircon studies that utilize micro analytical techniques
133 allowed for statistically robust maximumDraft deposition ages to be determined from
134 turbidites in the central and western parts of the craton. That work showed that some of
135 the turbidites, particularly those with interbedded BIF, were deposited 30 million years
136 after the "BIF free" Burwash Formation (Pehrsson and Villeneuve 1999; Bennett et al.
137 2005; Ootes et al. 2009). The three most precise maximum deposition ages from the
138 young turbidites include a concordant 2629 ± 2 Ma date, determined by U Pb zircon (ID
139 TIMS) from a Damoti Lake sample (Pehrsson and Villeneuve 1999), a concordant 2620 ±
140 5 Ma date, determined by U Pb zircon ID TIMS from a Beechey Lake sample
141 (Villeneuve et al. 2001), and a 2625 ± 6 Ma weighted mean age, determined from
142 multiple analyses on single zircons analyzed using the sensitive high resolution ion
143 microprobe (SHRIMP) on a sample from Russell Lake (Ootes et al. 2009). Other
144 maximum deposition ages have been determined from a greywacke in the central part of
145 the craton at Point Lake (2615 ± 13 Ma), and from greywackes in the western part of the
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146 craton near the Emile River (2637 ± 10 Ma; Ootes et al. 2009), and in the vicinity of
147 Kwejinne Lake (2634 ± 8, 2636 ± 3 and 2637 ± 4 Ma; Bennett et al. 2005, 2012). An age
148 of 2616 ± 3 Ma is reported for turbidites in the High Lake area in the northern Slave
149 craton (Henderson et al. 1994) and a 2612 ± 1 Ma date is reported for a lithic tuff bed
150 within turbidites at Wheeler Lake in the southwestern Slave craton (Isachsen and
151 Bowring 1994); the supporting data for these latter two reported ages has not been
152 published. Other previously reported, less statistically robust maximum deposition age
153 data are summarized in Ootes et al. (2009).
154 Both the older and younger turbidites have been locally to extensively intruded by 155 granitic plutons. The Defeat Suite plutonsDraft have been dated between ca. 2635 to 2620 Ma 156 and they cross cut isoclinal folds (F 1) in the Burwash Formation (Davis and Bleeker
157 1999). The Defeat Suite crystallization ages approximate the maximum deposition ages
158 recorded in the younger BIF bearing turbidites (e.g., Davis et al. 2003; Bleeker and Hall
159 2007; Ootes et al. 2009). This is a key constraint, indicating that the younger turbidites
160 post date the F1 event recorded in the older turbidites. Younger plutonic suites, such as
161 Concession Suite (ca. 2610 2600 Ma) and later granite bloom (ca. 2600 to 2580 Ma),
162 intrude both the older and younger turbidite packages (e.g., van Breemen et al. 1992;
163 Davis et al. 1994; Davis and Bleeker 1999; Bennett et al. 2005; Ootes et al. 2005). The
164 granite bloom coincided with regional greenschist to granulite facies metamorphism
165 (e.g., Davis and Bleeker 1999; Bethune et al. 1999; Pehrsson et al. 2000; Bennett et al.
166 2005; Ootes et al. 2005). The depositional setting of the Burwash Formation is thought to
167 be a rifted arc basin (Ferguson et al. 2005) whereas the depositional setting for the
168 younger BIF bearing turbidites is unclear. Previously proposed depositional models
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169 include a passive margin to foreland basin (Pehrsson 2002), an accretionary wedge
170 setting (Bennett et al. 2005), and a continental back arc basin adjacent to an active Defeat
171 suite magmatic arc (Ootes et al. 2009).
172
173 Methods
174 Approximately 1 1.2 kg of rock material was selected for each of the fine grained
175 turbidite samples. Each sample was cut down to small chips with a rock saw and divided
176 into three batches that subsequently were crushed in a tungsten carbide puck mill. Each
177 batch was crushed and sieved with a 70 mesh (210 micron) disposable nylon. The <210
178 micron sieved rock material was processed on a Wilfley Table to obtain a heavy mineral
179 concentrate and then, multiple passesDraft (up to 0.4 Amperes) on a Frantz magnetic barrier
180 separator to remove moderately to strongly magnetic grains. The non magnetic Frantz
181 fraction was then added to a Methylene Iodide heavy liquid with specific gravity of 3.3
3 182 g/cm for further density separation.
183 The recovered zircon grains were handpicked, secured in an epoxy mount, and
184 subsequently polished. Due to minimum material recovered from the tuff bed at Slemon
185 Lake, the crushed fraction was wash panned over multiple steps ending in a head fraction,
186 a second head fraction, and a tail fraction before hand picking. The majority of the
187 zircons were found in the first head fraction with only minor in the second head fraction.
188 No zircon grains were recovered in the tail fraction. Cathodoluminescence (CL) imaging
189 of zircon grains was obtained using a scanning electron microscope (Zeiss EVO LS15
190 EP SEM) equipped with cathodoluminescent and backscattered detectors.
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191 U Pb isotopic data for zircon from the turbidite samples and from the Slemon
192 Lake tuff were obtained at the University of Alberta and were acquired using a Nu
193 Plasma I multi collector inductively coupled plasma mass spectrometer (ICP MS)
194 coupled to a New Wave laser ablation (LA) system with an operating wavelength of 213
195 nm and energy density of 2 3 J/cm 2. Spot diameter was set to 20 µm. Both the full
196 machine parameters and measurement protocols are outlined in Simonetti et al. (2005,
197 2006). Two zircon standards were analyzed throughout each analytical session; the 1830
198 Ma LH94 15 zircon (Ashton et al. 1999) was used to correct U/Pb fractionation and an
199 in house zircon (OG1) with U Pb ID TIMS age of 3465.4 ± 0.6 Ma (Stern et al. 2009)
200 was analyzed as a blind standard. The weighted mean 207 Pb/ 206 Pb ages of the analyzed
201 OG1 standard are presented in theDraft supplementary data files (Appendix F). Almost all
202 analytical sessions for OG1 overlap within analytical uncertainty of the accepted ID
203 TIMS age. However, an exception occurred for the session involving the Courageous
204 Lake greywacke, and is dealt with below.
205 U Pb dating of the Dettah tuff sample was carried out at the Jack Satterly
206 Geochronology Laboratory (JSGL) at the University of Toronto. From a larger sample
207 sawn out of the outcrop, the ca. 1.5 cm tuff horizon was carefully excised from the
208 enclosing sediments using a thin trim saw (see sample description below). The resulting,
209 clean, isolated slabs, weighing in total approximately 300 g, were reduced using a jaw
210 crusher, followed by grinding briefly in a ring mill. Initial separation of heavy minerals
211 was carried out by multiple passes on a Wilfley table to concentrate zircon. Subsequent
212 work included density separation using methylene iodide, followed by paramagnetic
213 separations with a Frantz isodynamic separator. Approximately 20 zircon grains were
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214 recovered in the least magnetic fractions; best optical quality grains were subsequently
215 hand picked under ethanol using a binocular microscope, choosing the freshest, least
216 cracked grains of zircon. Most grains from the Dettah tuff, however, show a relatively
217 high degree of alteration.
218 Chemical abrasion methods (CA; Mattinson 2005) were used to pretreat the
219 selected Dettah tuff zircons before analysis by ID TIMS. Zircons were annealed in a
220 quartz crucible at 1000 oC for a period of 48 hours. These crystals were then leached
221 briefly in concentrated HF at 200 oC in Teflon bombs (Krogh 1973).
222 Weights of Dettah tuff zircon grains were estimated from photomicrographs.
223 Estimated weights should be accurate to about ±30%. This affects only U and Pb
224 concentrations, not age information,Draft which depends only on isotope ratio measurements.
225 Annealed and leached zircons were rinsed prior to loading into dissolution capsules, into
226 which a 205 Pb 235 U spike was added during sample loading. Zircon was dissolved using
227 concentrated hydrofluoric acid (HF) in Teflon bombs at 200 oC (Krogh 1973) and
228 subsequently redissolved in 3N HCl to promote equilibration with the spike. U and Pb
229 were separated from the solutions using 50 microliter anion exchange columns (Krogh
230 1973). Mixed purified U and Pb solutions were loaded directly onto Re filaments using
231 silica gel and analyzed with a VG354 mass spectrometer in single (Daly) collector, pulse
232 counting mode. Dead time of the measuring system during this time was 20 nsec. The
233 mass discrimination correction for the Daly detector was constant at 0.07%/AMU. Daly
234 characteristics were monitored using the SRM982 Pb standard. Thermal mass
235 discrimination corrections were 0.10+/ 0.03% /AMU. Laboratory blanks at the JSGL are
236 typically less than 1 pg for Pb and 0.1 pg for U.
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237
238 Sample description and results
239 All U Pb zircon data tables are presented in Appendix A E, and the results of the LA
240 ICP MS standards are presented in Appendix F (supplementary files).
241
242 Tuff bed – Slemon Lake turbidites
243 A ca. 3 cm thick, fine to very fine grained, felsic to intermediate tuff bed occurs
244 within the greywacke mudstone turbidites at Slemon Lake in the southwest Slave craton
245 (Figs. 1, 2A C; Table 1). In this area, the turbidites show evidence of three generations of 246 ductile deformation, preserved asDraft folds and foliations and were metamorphosed to 247 greenschist facies (Fyson and Jackson 1991; Jackson 2001). The turbidites are BIF
248 bearing and a well exposed ~0.8 to 1.2 m thick BIF is preserved approximately 1 m
249 below the tuff bed (Fig. 2D). The greywacke hosting the tuff bed is finely laminated and
250 contains a high fraction of biotite and fine grained quartz. The tuff bed is traceable for
251 about 15 m along strike on relatively flat glacially polished outcrop, and is readily
252 distinguished by having a bleached yellow weathered colour relative to the darker
253 greywacke (Figs. 2A and 2B). The bed has a relatively sharp depositional base and a
254 more disturbed upper contact with the greywacke (Fig. 2B). The upper contact represents
255 well developed load structures (flames) as a result of soft sediment deformation (white
256 arrows Fig. 2B). The tuff is composed of randomly distributed fine grained broken quartz
257 fragments set in a very fine grained quartz, biotite, chlorite, and K feldspar matrix (Fig.
258 2C). A weak foliation is defined by biotite and chlorite. The texture and mineralogy is
259 clearly different than the hosting greywacke and together with the similar zircon
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260 population (see below), it shows that only minor reworking (e.g., erosion, soft sediment
261 deformation) of the bed took place. This could be ascribed to the fact that the tuff bed
262 was found within a fine grained mud rich greywacke, which indicate that the tuff bed
263 represents a submarine ash settling event during a period of only weak turbidite
264 deposition.
265 A sample of the tuff bed was collected and separated from surrounding greywacke
266 and mudstone prior to crushing. Zircons are relatively scarce in the tuff bed, compared to
267 the zircon abundance in greywacke samples. The individual zircons are ~50 to 80 µm in
268 size and are mostly subhedral with a stubby to weakly prismatic habit (Fig. 2E). The
269 colour ranges from colourless to pale pink to brown. They are relatively free of inclusions
270 and have only minor growth zonations,Draft as indicated by electron backscatter imaging (Fig.
271 2E). The zircons were analyzed by LA MC ICP MS and all of the zircon grains analyzed
272 (n=17) are modestly discordant and a regression line through the data yields an upper
273 intercept age of 2617.2 ± 4.7 Ma (MSWD=1.08) and a lower intercept of 6 ± 28 Ma (Fig.
274 3A). A weighted mean 207Pb/ 206 Pb age calculation yields an indistinguishable date of
275 2616.6 ± 3.5 Ma (Fig. 3B). When considering only the six most concordant grains in the
276 data set (<7.3% discordant), a best fit discordia line yields an upper intercept age of
277 2620.4 ± 5.7 Ma (lower intercept at 0 Ma); identical to the weighted mean 207 Pb/ 206 Pb
278 date of 2620.4 ± 5.5 Ma (MSWD=1.03) for these same grains (Figs. 3C and 3D). We
279 interpret that the tuff bed was deposited at 2620 ± 6 Ma, which is also the timing of
280 deposition of the interleaved turbidites.
281
282 Tuff bed – Burwash Formation turbidites (Dettah)
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283 On the northeast side of Yellowknife Bay, between Yellowknife Bay and Hay
284 Lake, outcrops of the Burwash Formation turbidites are exposed along the road between
285 the Ingraham Trail and the town of Dettah (Fig. 1). In this area, the turbidites also
286 preserve evidence of three generations of ductile deformation, preserved as folds and
287 foliations and were metamorphosed to greenschist facies (Henderson 1970, 1972). One of
288 these outcrops contains distinctive yellow tan weathered tuff beds interstratified with the
289 turbidites (Fig. 4; Table 1; also see Stop 33 in Bleeker et al. 2007). At this location, the
290 turbidite beds are west striking, steeply dipping, upright (younging to the north), and they
291 progressively change from 1 m thick sand dominated beds to 5 cm thick mud dominated
292 beds over 30 m across strike. Within the thinner, mud dominated beds at the north end of
293 the outcrop occur four tuff beds thatDraft are traceable for ~7 m along strike (Fig. 4). The
294 main tuff bed is 1.5 2 cm thick, and the other three are <5 mm thick (Figs. 4A and 4B).
295 The tuff beds are all intercalated with the mudstone facies indicating primary settling of
296 ash particles on the ocean floor. All the beds have a relatively sharp base and local
297 evidence for load structures (flames) along the upper contact with the overlying
298 mudstones (Figs. 4A C). These flames have been slightly accentuated by a high angle
299 second generation foliation (Figs. 4A C). The preservation of the tuff and mudstone must
300 represent a period of quiescence and a return to turbidity driven deposition as evident by
301 the capping greywacke bed.
302 The tuff beds are comprised of euhedral quartz grains (~0.2 to 0.3 mm) set in a
303 very fine grained groundmass of quartz, chlorite, and mica (Fig. 4C). Recovered zircons
304 (Fig. 4D and Appendix B) from the thickest bed define a homogeneous looking
305 population, predominantly occurring as variably clear to cloudy colourless to pale grey
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306 brown, elongate slender prisms (up to 5:1 length:breadth). All zircon grains show some
307 degree of alteration, cracks, and the presence of apatite and opaque mineral inclusions.
308 Isotopic results from ID TIMS analysis of single grain zircon fractions from the
309 Dettah tuff are provided in Appendix B. Data from three individual fractions show
310 relatively low to medium concentrations of U (~85 190 ppm), and moderate Th/U ratios
311 (~0.82 0.88), which are typical for magmatic, igneous grains crystallized from felsic
312 magma systems. Total measured common Pb is at the sub picogram level. Analytical
313 results range from being 1.0 1.6% discordant to slightly (0.6%) reverse discordant.
314 Model 207 Pb/ 206 Pb ratios, however, range narrowly between 2650.1 2651.0 Ma. Free
315 regression of the three data points results in an upper intercept age of 2650.4 ± 1.0 Ma
316 with a lower intercept within errorDraft of the origin; we therefore choose to anchor the
317 regression at 0 Ma, equivalently accepting a calculated weighted average 207 Pb/ 206 Pb age
318 for all three analyses at 2650.5 ± 1.0 Ma (2 σ; MSWD=0.3, 73% probability of fit, Fig.
319 4E). We interpret this to represent a robust estimate of the eruption and deposition age of
320 the ash.
321
322 Greywacke beds – Goose Lake and Courageous Lake turbidites
323 Greywacke samples from Goose Lake in the east and Courageous Lake in the
324 east central part of the Slave craton (Fig. 1) share typical textural and mineralogical
325 features. They are fine to medium grained (~0.2 0.5 mm), and contain quartz, biotite,
326 chlorite, K feldspar, and minor plagioclase. The existence of biotite and chlorite, but no
327 garnet in these samples indicates they were metamorphosed within the biotite zone of
328 greenschist facies.
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329 A 0.8 m thick piece of drill core intersection of greywacke (RH18140) from the
330 bottom part of a 100.4 m deep drill hole (#12GSE140) was collected at Goose Lake
331 (Figs. 1A and 5A). The sample underlies the base of the lowest BIF horizon and is part of
332 a ~4 m thick BIF bearing greywacke mudstone unit (Fig. 5A). This is the lowest
333 stratigraphy tested by drilling and therefore likely represents the oldest interval of the
334 drilled part of Goose Lake turbidites. The detrital zircons from the greywacke are
335 euhedral to subhedral with a rounded to subrounded to prismatic habit (Fig. 5B). They
336 range between 30 180 µm in size and vary in colour from clear to pale pink to brown and
337 dark brown, with few having a cloudy appearance. Growth (oscillatory) zoning and
338 mineral inclusions are common (Fig. 5B). Selected zircons were analyzed by LA MC
339 ICP MS. Draft
340 The Goose Lake U Pb detrital zircon results reveal variable zircon populations,
341 representing multiple sources (Fig. 5C). The analyzed zircons fall mostly in the age range
342 of ca. 2760 to 2660 Ma, with probability peaks at ca. 2700 Ma and 2670 Ma (Fig. 5D),
343 consistent with derivation from the underlying volcanic rocks (van Breemen et al. 1992;
344 Isachsen and Bowring 1994, 1997; Villeneuve et al. 2001; Sherlock et al. 2012). Five
345 older grains also occur within the sample (3074 ± 15 Ma, 2849 ± 16, 2820 ± 16 Ma, 2814
346 ± 16 Ma and 2803 ± 15 Ma; Figs. 5B and 5D). The youngest detrital zircon grain at
347 Goose Lake yields a 207 Pb/ 206 Pb age of 2621 ± 18 Ma (1.3% discordance, Figs. 5B and
348 5D), which is interpreted as the maximum deposition age of the sample.
349 A greywacke sample (13AB2206A) was collected from outcrop south of
350 Courageous Lake and east of Matthews Lake (Fig. 6A), where the turbidites were
351 deposited on 2671 +5/ 4 Ma felsic volcanic rocks and are intruded by 2613 +6/ 5 Ma
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352 granitic rocks (Moore 1956; Dillon Leitch 1981; Villeneuve et al. 1993). These turbidites
353 lack interbedded BIF. The sample was collected from the coarsest greywacke near the
354 base of the turbidite succession, just above the contact with the underlying rhyolite and
355 basalt (Fig. 6A). The zircons recovered are morphologically similar by description to
356 those from the Goose Lake sample, and range from 30 to 120 m in their longest
357 dimension, with a fraction of the recovered zircons being highly fragmented (Fig. 6B).
358 Selected zircons were analyzed by LA MC ICP MS.
359 The U Pb detrital zircon results from the Courageous Lake sample reveals
360 variable age populations (although less scattered than for Goose Lake) representing
361 multiple sources (Fig. 7A). All of the analyzed grains are <10% discordant reflecting
362 minimum Pb loss in these sediments.Draft The results indicate that 61 out of 69 grains have
363 ages between ca. 2735 and 2660 Ma (Fig. 7B). There are three probability peaks within
364 this interval at ca. 2720, 2685, and 2665 Ma (Fig. 7B). The youngest grain at Courageous
365 Lake is 2626 ± 14 Ma (9.7% discordance) and the oldest is 2813 ± 13 (5% discordance)
366 (Figs. 6B and 7B). The weighted average of the four youngest grains yields a 207 Pb/ 206 Pb
367 age of 2635 ± 7 Ma (MSWD=1.12; Fig. 7C). This age may be on the young side since the
368 measurements on the OG1 standard during this analytical session yield a weighted
369 average of 3455.5 ± 4.3 Ma, which falls outside the analytical uncertainty of the 3465.4 ±
370 0.6 Ma (TIMS) age of OG1 (see Appendix B supplementary file).
371
372 Ferruginous bed Point Lake turbidites
373 Within the turbidites on the northeast side of Point Lake, 1 to 5 cm thick beds of
374 mafic to intermediate clastic sediments are found intercalated with BIF up to 0.5 m thick
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375 (Figs. 8A and 8B). A more thorough petrographic and geochemical study of these beds
376 can be found in Haugaard et al. (in review). The sedimentary beds differ from the
377 greywackes in that they have about 25 30% modal content of coarse grained ferro
378 hornblende throughout. Still, they contain randomly dispersed biotite flakes and
379 fragmented quartz and, occasionally, feldspar laths. These beds are concordant and folded
380 and deformed together with the BIF units (Fig. 8A). They contain approximately the
381 same concentration of zircon as the more typical greywackes. The zircons range from
382 ~80 to 150 µm in size (Fig. 8C) and from clear and colorless to pale and medium brown
383 in colour. The pale brown zircons often show a cloudy appearance. A major population of
384 zircons shows well developed oscillatory zonation patterns with an elongated prismatic to
385 stubby habits (Fig. 8C). FragmentationDraft and intense corroded edges of some of the zircons
386 can also be viewed in Fig. 8C.
387 The U Pb detrital zircon results are plotted in Figs. 9A and 9B and reveal a zircon
388 population that is generally younger than those in the Goose Lake and Courageous Lake
389 greywacke samples. Most of the zircons have dates that fall into two major age
390 populations that correlate well with the timing of Kam and Banting group volcanism. In
391 addition, there is a younger age peak at ~2610 Ma (Fig. 9B). The five youngest (<10%
392 discordant) grains all overlap within uncertainties (Fig. 9C) and have a weighted mean
393 207 Pb/ 206 Pb age of 2608 ± 6 Ma (MSWD=0.97; Fig. 9D).
394
395 Discussion
396
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397 Recommended nomenclature for Neoarchean turbidites of the Slave
398 craton
399 There is now enough age control to clearly separate the older turbidites from the
400 younger BIF bearing turbidites in the Slave craton. The Burwash Formation was
401 deposited between ca. 2661 Ma and 2650 Ma, as determined from crystallization ages of
402 tuff beds intercalated with the greywacke mudstone turbidites (Figs. 3 and 4; Bleeker and
403 Villeneuve 1995; Ferguson et al. 2005). The F 1 structures identified in the Burwash
404 Formation turbidites are cross cut by Defeat Suite plutons between 2635 and 2620 Ma
405 (Fig. 10; Davis and Bleeker, 1999). The new 2620 ± 6 Ma tuff bed crystallization age in 406 the younger BIF bearing turbidites Draft(Figs. 2 and 3) indicate these sedimentary rocks either 407 post date, or were deposited synchronously with the intrusion of the Defeat Suite plutons;
408 these sedimentary rocks were deposited after uplift and crustal shortening of the older
409 Burwash Formation turbidites. These two chronologically distinct turbidite sequences,
410 therefore, represent separate depositional basins (Ootes et al. 2009).
411 We recommend a new nomenclature for these two distinct turbidite sequences and
412 their type localities. In Phanerozoic, or flat lying Precambrian stratigraphy, the
413 nomenclature of a formation or group generally requires a base, top, and type section.
414 However, such constraints are rarely preserved in Archean stratigraphy; the voluminous
415 nature of the turbidites in the Slave craton and the multiple generations of structural
416 overprinting generally make such criteria impossible to identify. In addition, without a
417 base or top, a measured section is only a minimal assumption of the overall thickness of a
418 unit. Instead, for the turbidites in the Slave craton, we champion that sample locations
419 that have been dated should be considered the type locality for the turbidites in question,
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420 and the formation name assigned should be tied to the dated location and any turbidites
421 traceable from that location. If the location has not been dated it should not be formally
422 considered.
423 We recognize formations that can be correlated with the Burwash Formation and
424 assign these to the Duncan Lake Group (Henderson, 1972; Helmstaedt and Padgham,
425 1986). Utilizing new and previously published tuff crystallization ages and detrital zircon
426 maximum deposition ages we recommend the young BIF bearing turbidites be referred to
427 as the Slemon Group and upgrade type localities with recommended formation names
428 (Figs. 1A and 10; Table 1).
429
430 Duncan Lake Group Draft
431 The Duncan Lake Group terminology first appeared in Henderson (1975) and was
432 used to refer to all of the sedimentary rocks that overlay the Kam Group volcanic rocks at
433 Yellowknife. This included the Burwash Formation and Jackson Lake Formation
434 (Henderson, 1970). Although Henderson considered these sedimentary rocks to be older
435 than the Banting Group volcanic rocks, however, Helmstaedt and Padgham (1986)
436 recognized that these sedimentary rocks are in fact younger than, or laterally equivalent
437 to the Banting Group. Furthermore, they established that the Jackson Lake Formation
438 conglomerates and sandstones are considerably younger and therefore should not be
439 included as part of the Duncan Lake Group. Subsequent U Pb zircon dating has further
440 corroborated this latter interpretation (e.g., Isachsen et al. 1991). Therefore, the Duncan
441 Lake Group and the Burwash Formation specifically refer to the thick accumulation of
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442 turbidites east of Yellowknife Bay of Great Slave Lake (e.g., Henderson 1970, 1975;
443 Ferguson et al. 2005).
444
445 Burwash Formation
446 The archetype of the Duncan Lake Group is the renowned Burwash Formation,
447 which has been investigated in detail on the eastern side of Yellowknife Bay of Great
448 Slave Lake (Henderson 1970, 1972) and in the Hearne Lake area (Ferguson et al. 2005;
449 Fig. 1A). The Burwash Formation, which is estimated to be about 4.5 5 km in thickness
450 (Henderson, 1970), forms a large synclinorium between Yellowknife and the Sleepy
451 Dragon Complex to the east, and continues south and potentially east of this basement
452 culmination (e.g., Stubley, 2005).Draft The type section is south of Burwash Point in
453 Yellowknife Bay where each turbidite cycle (greywacke mudstone) is on average ~0.3
454 0.4 m thick (Henderson 1970).
455 Although the date of ca. 2650.5 Ma from the Dettah tuff bed in this study (Fig.
456 4E) is younger than the 2661 Ma presented by Bleeker and Villeneuve (1995), it is still
457 comparable. Noteable is that our 2650.5 Ma age is very close to the detrital zircon
458 maximum deposition age obtained from the turbidites at Mosher Lake (Ootes et al. 2009),
459 and collectively these dates show that the turbidites are relatively close temporally to the
460 upper part of Duncan Lake Group (Fig. 10; Table 1).
461
462 Clover Lake Formation
463 A succession of turbiditic sedimentary rocks that occur just north of Clover Lake
464 in the Hope Bay greenstone belt has been described by Sherlock et al. (2012; Fig. 1A).
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465 The sedimentary sequence there contains well bedded greywacke and mudstone facies
466 occasionally with conglomerates containing locally derived clasts. The sedimentary
467 succession has been intruded and is interbedded with the Clover Lake felsic volcanic
468 suite, primarily calc alkaline flow banded rhyolites. These rhyolites show distinct
469 contact textures that suggest emplacement of the volcanics into unlithified wet
470 sediment . A U Pb ID TIMS age for one of the rhyolite flows in this section is 2662.7
471 +3.4/ 2.8 Ma, which is viewed as the minimum age of the turbidites in the Hope Bay
472 greenstone belt (Sherlock et al. 2012). On this basis, we recommend the use of Clover
473 Lake Formation and assign this formation to the Duncan Lake Group (Fig. 1A; Table 1).
474
475 Itchen Lake Formation Draft
476 The Itchen Formation was named by Bostock (1980) to refer to greywacke
477 mudstone turbidites in the central part of the Slave craton that do not contain BIF
478 (Bostock, 1980; Henderson, 1998; Fig. 1A). Bostock (1980) interpreted that the Itchen
479 Formation was younger than the Contwoyto Formation, because the latter is more
480 proximal to the underlying volcanic belts. Ootes et al. (2009) analyzed 58 detrital zircons
481 by the U Pb SHRIMP method and determined a maximum deposition age of 2658 ± 8
482 Ma for the Itchen Formation, indicating that the Itchen Formation is likely older than the
483 BIF bearing Contwoyto Formation. We recommend the Itchen Formation be, from here
484 forward, recognized as the Itchen Lake Formation, and the type locality be the location of
485 the greywacke sampled for detrital zircon analyses (Ootes et al. 2008, 2009). Based on
486 the maximum deposition age, we tentatively retain the Itchen Lake Formation within the
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487 Duncan Lake Group, although it should be recognized that the nature of detrital zircon
488 results allows this formation to potentially be younger.
489
490 Mosher Lake Formation
491 Greywacke mudstone turbidites are well preserved at Mosher Lake in the
492 southwestern Slave craton (Ootes and Pierce 2005; Ootes et al. 2006, 2008, 2009; Fig.
493 1A). A total of 58 detrital zircons from a greywacke sample were dated by the U Pb
494 SHRIMP method and the youngest yielded a maximum deposition age of 2651 ± 6 Ma
495 (Ootes et al. 2006, 2009). These turbidites do not contain interbedded BIF. We
496 recommend referring to these turbidites as the Mosher Lake Formation and the type
497 locality should be considered the Draft location for the detrital zircon sample (Ootes et al.
498 2006, 2008, 2009). Based on the maximum deposition age, we tentatively assign these
499 turbidites to the Duncan Lake Group (Fig. 10; Table 1). Although the nature of detrital
500 zircon results allow that these turbidites could be younger (Ootes et al. 2009), structural
501 data presented in Fyson and Jackson (1991) establish that these turbidites contain a
502 deformation fabric that pre dates fabrics preserved in the Slemon Lake Formation
503 turbidites (see below) that occur to the west at Russell and Slemon lakes.
504
505 The Slemon Group
506 Slemon Lake Formation
507 The Slemon Lake tuff, with its single age zircon population, record coeval
508 volcanic input into the chemical and clastic sediment dominated basin at 2620 ± 6 Ma
509 (Figs. 2 and 3). This date is the best estimate of the age of this tuff bed and constrains the
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510 depositional timing of the turbidites and the interbedded BIF. This is the only tuff bed
511 discovered and dated in the younger BIF bearing turbidites in the craton. We recommend
512 referring to these as the Slemon Lake Formation, and this locality should also be
513 considered as the type locality for the young BIF bearing turbidite sequences in the
514 suggested Slemon Group (Figs. 1A and 10; Table 1). The age is synchronous with or
515 slightly late, relative to the ages of the Defeat Suite plutons (Davis and Bleeker 1999) and
516 likely the precursor sediment was pyroclastic ash derived from Defeat related volcanism
517 in the hinterland of the basin.
518 These BIF bearing turbidites continue eastward to Russell Lake (Jackson 2001;
519 Fig. 1A) where detrital zircon from a greywacke sample has yielded a maximum
520 deposition age of 2625 ± 6 Ma (OotesDraft et al. 2006, 2008, 2009). This further demonstrates
521 that these laterally extensive deposits were all formed after uplift and deformation of the
522 turbidite formations in the Duncan Lake Group.
523
524 Goose Lake Formation (Goose Lake)
525 The youngest detrital zircon age of 2621 ± 18 Ma (1.3% discordance, Figs. 5B
526 and 5D) for the Goose Lake greywacke is the only grain of that age that has been
527 recovered from the sample. This date is, however, consistent with another concordant
528 detrital zircon date of 2620 ± 5 Ma (ID TIMS) reported by Villeneuve et al. (2001) from
529 a greywacke in the Beechey Lake turbidites on the western flank of the Back River
530 volcanic complex (Fig. 1A). Furthermore, euhedral to subhedal zircons from a fine
531 grained felsic sill that intruded the Beechey Lake turbidites yielded an upper intercept at
532 2637 +8/ 6 Ma placing a minimum age on the deposition of these turbidites (Villeneuve
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533 et al. 2001). However, this best fit regression was determined on four zircon fractions,
534 none of which were concordant or had overlapping 95% confidence error ellipses (Fig. 4,
535 Villeneuve et al. 2001).
536 Nevertheless, the U Pb zircon dates from Beechey Lake together with the 2621 ± 18 Ma
537 age from Goose Lake confirm the belonging of these BIF turbidites to the suggested
538 Slemon Group and furthermore correlate the eastern turbidite BIF sequences with the
539 ones from the central and western Slave craton (Fig. 1A).
540 We recommend that the BIF bearing turbidites in the Goose Lake area be referred to as
541 the Goose Lake Formation (Fig. 10; Table 1). While the Mesoarchean Central Slave
542 Cover Group and the Mesoarchean to Hadean Central Slave Basement Complex rocks are
543 not known to be preserved in the easternDraft part of the craton (Bleeker et al. 1999), the five
544 zircon grains from Goose Lake dated between 3074 ± 15 Ma and 2803 ± 15 Ma (Fig. 5D)
545 indicate that older basement was exposed in the source region.
546
547 Salmita Formation (Courageous-MacKay lakes)
548 In the central part of the Slave craton, greywacke mudstone turbidites were
549 deposited stratigraphically on top of the Courageous MacKay lakes greenstone belt (Fig.
550 1A). These turbidites continue well to the east where they may be correlative to the
551 Beechey Lake turbidites that overly the Hackett River greenstone belt (Villeneuve et al.
552 2001; Stubley 2005; Fig. 1A). The detrital zircon age populations for the Courageous
553 Lake sample represent multiple sources with a dominant input of detritus at ca. 2720,
554 2685, and 2665 Ma (Fig. 7B). These ages are consistent with the timing of volcanism in
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555 the underlying volcanic belt and volcanic rocks preserved elsewhere in the craton (van
556 Breemen et al. 1992; Isachsen and Bowring 1997; Sherlock et al. 2012).
557 The youngest zircon grain identified in the sample is 2626 ±14 Ma, although it is
558 modestly discordant (9.7% discordance, Figs. 6B and 7B). The weighted average of the
559 four youngest grains yields a 207 Pb/ 206 Pb age of 2635 ± 7 Ma (Fig. 7C). This age may be
560 on the young side since the measurements on the OG1 standard during this data
561 acquisition yield a weighted average of 3455.5 ± 4.3 Ma, which fall outside the analytical
562 uncertainty of the 3465.4 ± 0.6 Ma (TIMS) age of OG1 (see Appendix F supplementary
563 file). However, we tentatively assign these turbidites as part of the younger Slemon
564 Group. As many of the local geographic names are generally assigned to other
565 stratigraphic units in the area, we recommendDraft the turbidites at this locality be referred to
566 as the Salmita Formation, in recognition of the past producing Salmita gold mine that is
567 located just to the southwest of the sampled location.
568
569 Contwoyto Lake Formation (Point Lake)
570 These BIF bearing turbidites are exposed on the northern and eastern side of Point
571 Lake (Henderson, 1998; Fig. 1A). The use of the name Contwoyto Formation was used
572 by Bostock (1980) who pointed out the occurrence of interbedded BIF, which
573 distinguished these turbidtites from the higher metamorphic grade turbidites that were
574 assigned to the Itchen formation further east (see Henderson 1998). However, Bostock
575 (1980) believed the Contwoyto formation to be older than Itchen formation due to its
576 more proximal nature to volcanic belts. Using detrital zircons, Ootes et al. (2009)
577 suggested the BIF bearing Contwoyto formation is actually younger than the BIF absent
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578 Itchen formation. We recommend the name Contwoyto Lake Formation for BIF bearing
579 turbidites in this area, which is defined by the detrital zircon maximum deposition age of
580 2608 ± 6 Ma (Fig. 9D), and the previously reported youngest identified detrital zircon
581 grain at 2615 ± 13 Ma (Ootes et al. 2009; Fig. 10 and Table 1). As such, we recommend
582 the name Contowyto Lake Formation for these BIF bearing turbidites at Point Lake.
583 The ferruginous clastic sediment sample in this study contains a dominant zircon
584 population (ca. 2720 2660 Ma), likely of Banting or Kam Group affinity (Fig. 9B). There
585 is a probability trough at ca. 2640 2620 Ma, indicating only minimum input from the
586 Defeat Suite (Fig. 9B). The youngest population, at ca. 2610 Ma, indicates a minor
587 proportion of the zircons (n=5) may have been derived from the monzodioritic to
588 granodioritic Concession Suite plutonsDraft (Davis et al., 1994; Figs. 9B, 9C, 9D and 10). The
589 BIF bearing turbidites of the Contwoyto Lake Formation either represent the upper part
590 of Slemon Group turbidites, or may be a separate package of even younger turbidites.
591
592 Damoti Lake Formation
593 At Damoti Lake (Fig. 1A), greywacke mudstone turbidites with interbedded BIF
594 was informally named the Damoti formation by Pehrsson and Villeneuve (1999). They
595 dated 15 detrital zircons by the ID TIMS method and discovered a single concordant
596 grain at 2629 ± 2 Ma, and interpreted this as the maximum deposition age of the sample
597 (Fig. 10; Table 1). This was the first demonstration of turbidites that were clearly younger
598 than the 2661 Ma Burwash Formation of the Duncan Lake Group. We therefore
599 recommend the BIF bearing turbidites in the Damoti Lake area to be referred to as the
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600 Damoti Lake Formation, with the type locality being the sample location of Pehrsson and
601 Villeneuve (1999; Table 1).
602
603 Kwejinne Lake Formation
604 North of Slemon Lake and along the Snare and Emile rivers in the western Slave
605 craton, greywacke mudstone turbidites are extensively preserved (Fig. 1A). At Kwejinne
606 Lake, Bennett et al. (2005) collected a greywacke sample and dated 100 detrital zircons
607 by the LA ICP MS method, the youngest concordant grain of which yielded a maximum
608 deposition age of 2633 ± 9 Ma. The five youngest grains yielded a weighted average
609 207 Pb/ 206 Pb age of 2634 ± 8 Ma. These greywackes do not contain interbedded BIF, but
610 they do continue to the east whereDraft they are preserved at higher metamorphic grades.
611 There they are preserved as migmatites and contain abundant BIF enclaves. Detrital
612 zircon cores were dated by Bennett et al. (2012) and the youngest of 68 analyses yielded
613 a maximum deposition age of 2636 ± 3 Ma. Northwest of Kwejinne Lake, along the
614 Emile River at Mattberry Lake, Archean greywacke mudstone turbidites underlie
615 Proterozoic quartzite and quartz pebble conglomerate and both were deformed together in
616 the Proterozoic (Fyson and Jackson 2008; Jackson 2008; Bennett et al. 2012). Detrital
617 zircons from the Archean greywacke were dated by the LA ICP MS method by Bennett
618 et al. (2012) and the youngest grains of 79 analyses indicate a maximum deposition age
619 of 2637 ± 4 Ma.
620 All three of the above samples share similar maximum deposition ages and are
621 proximal to Kwejinne Lake, and we therefore recommend they be referred to as the
622 Kwejinne Lake Formation (Fig. 10; Table 1). The type locality should be considered the
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623 location at Kwejinne Lake dated by Bennett et al. (2005). While the maximum deposition
624 ages are younger than the ca. 2661 Ma Burwash Formation of the Duncan Lake Group,
625 the maximum deposition ages are comparable to the oldest Defeat Suite plutons (Davis
626 and Bleeker 1999). These turbidites locally contain interbedded BIF and occur along
627 strike of the Slemon Lake Formation, and because they are younger than the youngest
628 detrital zircons dated, we assign these to the Slemon Group.
629
630 Emile River Formation
631 In the western Slave craton, north of the Damoti Lake Formation, turbidites with
632 interbedded BIF occur within the core of a Central Slave Basement Complex bounded
633 synclinorium (Ootes et al. 2008; Fig.Draft 1A). Ootes et al. (2009) dated 66 detrital zircons
634 from a greywacke sample by the SHRIMP method, and determined a maximum
635 deposition age of 2637 ± 10 Ma (Fig. 10). We recommend these turbidites be referred to
636 as the Emile River Formation (Table 1) with the type locality being the detrital zircon
637 sample location in Ootes et al. (2008, 2009). As these turbidites contain interbedded BIF
638 and have a maximum deposition age distinctly younger than the 2661 Ma deposition age
639 of Burwash Formation of the Duncan Lake Group, we tentatively recommend these be
640 assigned to the Slemon Group (Table 1).
641
642 Wheeler Lake Formation
643 Isachsen and Bowring (1994) report an age from a tuff, interbedded with BIF bearing
644 turbidites east of Wheeler Lake, of 2612 ± 1 Ma (Fig. 1A). Ootes et al. (2009) dismissed
645 this and interpreted that it was likely an intrusive sill that was dated in that study as the
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646 sample location could not be confirmed in the field and many porphyry sills occur in the
647 area (Ootes and Pierce 2005). However, since that time it has been confirmed that it was
648 in fact a tuff bed that was sampled near Wheeler Lake and dated in that study (W. Fyson,
649 personal communication, 2010). Due to the new results from the Contowyto Lake
650 Formation (above), the ca. 2612 Ma deposition age for the BIF bearing Wheeler Lake
651 turbidites is considered as permissible. We recommend referring to the turbidites in the
652 Wheeler Lake area (Brophy 1995; Ootes and Pierce 2005) as the Wheeler Lake
653 Formation (Table 1). The type locality for these should be considered as the location
654 dated by Isachsen and Bowring (1994), on the southeast side of Wheeler Lake (Figs. 1A
655 and 10).
656 Draft
657 James River Formation (High Lake)
658 In the northern Slave craton, in the vicinity of High Lake, slates, siltstones and
659 greywackes overly older volcanic belts (Jackson 1985; Henderson et al. 1995, 2000; Fig.
660 1A). The mudstones and siltstones have long been considered to be younger than the
661 greywackes and Henderson et al. (2000) indicate a deposition age (their unit Asl) of ca.
662 2616 to 2612 Ma. However, numerous plutons of similar age occur throughout the area
663 and it is not clear from that work what was dated, felsic dykes or concordant sills, or
664 interbedded felsic volcanic layers (Henderson et al. 2000). In addition, no interbedded
665 BIF have been reported from these sedimentary rocks. Therefore, we cautiously assign
666 these sedimentary rocks to the Slemon Group. Regardless of their age, we recommend
667 they be referred to as the James River Formation (Table 1). The type locality should be
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668 considered the location with reported date from a concordant dacitic porphyry body at
669 2616 ± 3 Ma (Henderson et al. 1995).
670
671 Composite stratigraphy
672 Depositional ages and field relations among the turbidites in the Slave craton
673 show that these can be separated into at least two separate packages; an older (>2640 Ma)
674 Duncan Lake Group and a younger (<2640 Ma) Slemon Group (Fig. 10; Table 1). Since
675 the older turbidites are uplifted, folded and later cut by the ca. 2628 Ma Defeat pluton, we
676 arbitrary put the border between the two groups at 2640 Ma, as illustrated in Fig. 10. This 677 age may be slightly older or younger.Draft The backbone of this new stratigraphy is the 678 depositional ages of the tuff beds interbedded with the greywacke mudstone turbidites.
679 The Burwash Formation of the Duncan Lake Group was deposited between ca. 2661 Ma
680 and 2650 Ma whereas the newly discovered 2620 ± 6 Ma tuff bed defines the age of a
681 younger BIF bearing turbidite package at Slemon Lake, referred to as the Slemon Group
682 here. This age indicates that these turbidites either post date, or were deposited
683 synchronously with the intrusion of the ca. 2635 2620 Ma Defeat Suite plutons (Fig. 10).
684 These younger turbidites of the Slemon Group were deposited after uplift and crustal
685 shortening of the older Burwash Formation turbidites. The is furthermore supported in
686 the detrital zircon record of the Slemon Group (Figs. 5D, 7B and 9B and Figs. 5 and 8 in
687 Ootes et al. 2009) that shows only a minor input of synchronous zircons derived from
688 juvenile (~2620 Ma) sources. Rather, the greywackes of the Slemon Group contain
689 detrital zircons that are similar in age to zircons in the older volcanic belts, indicating
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690 further uplift and erosion of those belts, or recycling of the Duncan Lake Group sediment
691 into the Slemon Group turbidite BIF basin.
692
693
694 Future considerations
695
696 It is evident from the above that the Point Lake date, along with the Wheeler Lake and
697 High Lake dates (Isachsen and Bowring, 1994; Henderson et al., 1995), may represent an
698 even younger event of turbidite BIF depoition and therefore we cannot exclude the 699 potential existence of a third packageDraft of turbidites within the craton. Collectively, these 700 dates may reflect minor contribution from the younger (2610 2600 Ma) Concession
701 Suite. Unfortunately, however, the data from High Lake and Wheeler Lake is reported
702 without supporting analytical data. Consequently, the young dates from these locations
703 need further confirmation as these could also represent the upper components of the
704 Slemon Group depositional basin; therefore, without further evidence, they are currently
705 included within the Slemon Group.
706 Locating tuff beds within greywacke mudstone turbidites is challenging as these
707 beds are volumetrically minor and often only are a few cm thick. However, their
708 importance in constraining the Neoarchean stratigraphy of the Slave craton, and other
709 Archean cratons, is crucial for resolving regional stratigraphic relationships. Finding
710 additional tuff beds and younger clastic sedimentary units in these sections will help to
711 better constrain the deposition ages and duration of sedimentation in many turbidite
712 sequences in the craton. For example, the 2620 ± 6 Ma crystallization age of the tuff bed
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713 at Slemon Lake presented in this study provides a critical date and horizon in further
714 establishing previously unknown younger stratigraphic relationships in these turbidite
715 basins and evaluating tectonic processes across the Slave craton.
716 The results of this study imply that an unconformity should exist somewhere
717 between the Duncan Lake Group and the Slemon Group. Although these extensive
718 turbidite deposits often are monotonous and indistinct, future fieldwork and bedrock
719 mapping should emphasize the importance of finding this internal Slave craton boundary
720 that likely exists as an angular unconformity.
721 The Burwash Formation of the Duncan Lake Group has been well studied
722 (Henderson 1970, 1972; Yamashita and Creaser 1999; Ferguson et al., 2005), but the
723 petrology of the Slemon Group hasDraft not been investigated to the same extent. Thorough
724 sedimentologically focussed petrological work comparing the Duncan Lake and Slemon
725 groups is recommended. In addition to the now identified BIF association with the
726 younger Slemon Group, such study should further reveal any petrological differences
727 between these temporally distinct turbidite sequences. This would not only have profound
728 importance on the crustal composition and tectonic development of the craton but would
729 also help to characterize the depositional basins that accumulated these extensive
730 turbidite deposits during the Neoarchean.
731
732 Conclusions
733 The U Pb zircon results for tuff and greywacke samples investigated in this study
734 refine the depositional ages for Neoarchean turbidite packages in the Slave craton. A tuff
735 bed occurs within the BIF bearing turbidites at Slemon Lake, and yields a U Pb zircon
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736 depositional age of 2620 ± 6 Ma. For the first time, this date constrains the depositional
737 age for the younger BIF bearing turbidites in the southwest of the Slave craton. A
738 previously undated tuff bed in the Burwash Formation turbidites yields a U Pb zircon age
739 of 2650.5 ± 1.0 Ma. This new age is ca. 10 million years younger than previously
740 reported tuff ages from the Burwash Formation, indicating a longer depositional time
741 frame than previously considered.
742 At Goose Lake in the eastern Slave craton, the youngest zircon grain yields an age
743 of 2621 ± 18 Ma (1.3% discordant). These are BIF bearing turbidites and for the first
744 time the depositional timing of turbidites can be linked from west to east across the
745 craton. At Courageous Lake, turbidites yield a maximum deposition age of 2635 ± 7 Ma.
746 At Point Lake, coarse grained mafic to intermediateDraft sediment beds are intercalated with
747 the BIF unit. The detrital zircons obtained from these beds define a maximum
748 depositional age of 2608 ± 6 Ma, supporting that these either are distinctly younger than
749 the ca. 2620 Ma BIF bearing turbidites, or they are higher in the stratigraphic sequence.
750 The two new tuff ages, in concert with previously published data, allow the
751 breakout of the younger BIF bearing turbidite sequence from the Duncan Lake Group.
752 The ca. 2661 to 2650 Ma Burwash Formation remains the archetype of the Duncan Lake
753 Group and we propose the Itchen Lake Formation, Mosher Lake Formation, and Clover
754 Lake Formation should also be included within this group. The type localities for the
755 formations are the dated sample locations. We propose that the demonstrably younger,
756 BIF bearing turbidites, be referred to as the Slemon Group. The archetypal locality for
757 the Slemon Group is the tuff sample site in the proposed Slemon Lake Formation. Using
758 maximum deposition ages that are comparable and younger than the crystallization age of
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759 the tuff, we recommend a number of other formation names, their type localities being
760 the sections with dated sample locations. Further petrological work on these two groups
761 is recommended to help resolve depositional environments, and to further help the
762 understanding of Archean tectonic processes.
763
764
765
766
767 Acknowledgements
768 We gratefully acknowledge the help from Birger Rasmussen and Bryan Krapež for
769 providing field assistance at SlemonDraft Lake, Mark Labbe, Joshua Davies and Jesse
770 Reimink for support during sample preparation, Josh Davies and Jesse Reimink for
771 discussions on zirconology, Andy DuFrane for great help on the ICP MS. Pilot Samantha
772 Merritt provided excellent field support. Lastly, Rachel Abbott, Francois Berniolles, and
773 Dave Smith of Sabina Gold and Silver Corporation provided great help at Goose Lake
774 drill camp. This work was funded by Polar Continental Shelf Program (PCSP project
775 number 65412) to RH and LO, the Natural Sciences and Engineering Research Council
776 of Canada (NSERC) to KK and LH, the Northwest Territories Geological Survey, Sabina
777 Gold and Silver Cooperation, the Circumpolar/Boreal Alberta Research Grants (C/BAR)
778 program of the CCI Canadian Circumpolar Institute (Grant #CG428). This is NWT
779 Geological Survey Contribution #0098.
780
781
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782 References 783 784 Arndt, N.T., Bruzak, G., and Reischmann, T. 2001. The oldest continental and oceanic 785 plateaus: Geochemistry of basalts and komatiites of the Pilbara Craton, Australia. 786 Geological Society of America Special Papers, 352: 359–387. 787 788 Barrett, T.J., and Fralick, P.W. 1989. Turbidites and iron formations, Beardmore 789 Geraldton, Ontario: application of a combined ramp/fan model to Archaean clastic and 790 chemical sedimentation. Sedimentology, 36: 221–234. 791 792 Bédard, J.J., Harris, L.B., and Thurston, P.C. 2013. The hunting of the snArc. 793 Precambrian Research, 229: 20–48. 794 795 Bekker, A., Slack, J.F., Planavsky,Draft N., Krapež, B., Hofmann, A., Konhauser, K.O., and 796 Rouxel O.J. 2010. Iron formation: The sedimentary product of a complex interplay 797 among mantle, tectonic, oceanic, and biospheric processes. Economical Geology, 105: 798 467–508. 799 800 Bennett, V., Jackson, V.A., and Rivers, T. 2005. Geology and U Pb geochronology of the 801 Neoarchean Snare River terrane: tracking evolving tectonic regimes and crustal growth 802 mechanisms. Canadian Journal of Earth Sciences, 934: 895–934. 803 804 Bennett, V., Rivers, T., Jackson, V.A. 2012. A compilation of U Pb zircon primary 805 crystallization ages from Paleoproterozoic southern Wopmay Orogen, Northwest 806 Territories. Northwest Territories Geoscience Office, NWT Open Report 2012 003, 157 807 p. 808 809 Bethune, K.M., Villeneuve, M.E., and Bleeker, W. 1999. Laser 40 Ar/ 39 Ar 810 thermochronology of Archean rocks in Yellowknife Domain, southwestern Slave 811 Province: insights into the cooling history of an Archean granite greenstone terrane. 812 Canadian Journal of Earth Sciences, 36: 1189–1206
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904 Helmstaedt, H., and Padgham, W.A. 1986. A new look at the stratigraphy of the 905 Yellowknife Supergroup at Yellowknife, NWT: implications for the age of gold bearing 906 shear zones and Archean basin evolution. Canadian Journal of Earth Sciences, 23: 454– 907 475. 908 909 Helmstaedt, H., 2009. Crust–mantle coupling revisited: The Archean Slave craton, NWT, 910 Canada. In Proceedings of the 9th International Kimberlite Conference. Edited by 911 Stephen Foley, Sonja Aulbach, Gerhard Brey, Herman Grütter, Heidi Höfer, Dorrit 912 Jacob, Volker Lorenz, Thomas Stachel and Alan Woodland. Lithos 112, 1055 1068. 913 914 Henderson, J. B. 1998. Geology of the Keskarrah Bay area, District of Mackenzie, 915 Northwest Territories. Geological Survey of Canada Bulletin 527, 122 p. 916 917 Henderson, J. B. 1975. SedimentologyDraft of the Archean Yellowknife Supergroup at 918 Yellowknife, District of Mackenzie. Geological Survey of Canada, Bulletin 246, 62 p. 919 920 Henderson, J. B. 1972. Sedimentology of Archean turbidites at Yellowknife, Northwest 921 Territories. Canadian Journal of Earth Sciences, 9: 882 902. 922 923 Henderson, J.B. 1970. Stratigraphy of the Yellowknife Supergroup, Yellowknife Bay– 924 Prosperous Lake Area, District of Mackenzie. Geological Survey Canadian Paper, 70 26. 925 926 Henderson, J. R.; Henderson, M. N.; Kerswill, J. A.; and Dehls, J. F. 2000. Geology, 927 High Lake greenstone belt, Nunavut. Geol. Surv. Can. Map 1945A, scale 1 ∶100; 000. 928 929 Henderson, J.R., Kerswill, J.A., Henderson, M. N., Villeneuve, M., Petch, C. A., Dehls, 930 J.F., and Okeefe, M.D. 1995. Geology, geochronology, and metallogeny of High Lake 931 greenstone belt, Archean Slave Province, Northwest Territories. Geological Survey of 932 Canada Current Research 1995 C, 97–106. 933
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934 Isachsen, C. E., and Bowring, S. A. 1994. Evolution of the Slave craton. Geology, 22: 935 917–920. 936 937 Isachsen, C., and Bowring, S. 1997. The Bell Lake group and Anton Complex: a 938 basement cover sequence beneath the Archean Yellowknife greenstone belt revealed and 939 implicated in greenstone belt formation. Canadian Journal of Earth Science, 189: 169– 940 189. 941 942 Jackson, V. A. 1985. Geology of the Keskarrah Bay area, parts of NTS areas 86 H/6 and 943 86 H/7. Northwest Territories Geoscience Office EGS 1985 8:1 map, scale 1:50,000. 944 945 Jackson, V. A. 2001. Report on the geology of the northern Russell Lake area (85O=4). 946 Northwest Territories Geoscience Office, EGS 2001–03, 90 p. 947 Draft 948 Jackson, V.A. 2008. Preliminary geological map of part of the South Wopmay orogen 949 (parts of NTS 86B and 86C; 2007 updates); descriptive notes to accompany 1:100 000 950 scale map. Northwest Territories Geological Survey, NWT Open Report 2008 007, 53 p. 951 and 1 map, scale 1:100,000. 952 953 Jaffey, A.H., Flynn, K.F., Glendenin, L.E., Bentley, W.C. and Essling, A.M. 1971. 954 Precision measurement of half lives and specific activities of 235U and 238U. Physical 955 Review, 4: 1889 1906. 956 957 Kositcin, N., Brown, S.J.A., Barley, M.E., Krapež, B, Cassidy, K.F., and Champion, D.C. 958 2008. SHRIMP U–Pb zircon age constraints on the Late Archean tectonostratigraphic 959 architecture of the Eastern Goldfields Superterrane, Yilgarn Craton. Western Australia. 960 Precambrian Research, 161: 5–33. 961 962 Krogh, T.E. 1973. A low contamination method for hydrothermal decomposition of 963 zircon and extraction of U and Pb for isotopic age determinations. Geochimica et 964 Cosmochimica Acta, 37: 485 494.
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995 Ootes, L., Buse, S., Davis, W.J., and Cousens, B.C. 2005. U Pb ages from the northern 996 Wecho River area, southwestern Slave Province, Northwest Territories: constraints on 997 late Archean plutonism and metamorphism. Geological Survey of Canada Current 998 Research, 2005 F2, 13 p. 999 1000 Ootes, L., Davis, W.J., and Jackson, V.A. 2006. Two turbidite sequences in the Russell 1001 Lake–Mosher Lake area: SHRIMP U Pb detrital zircon evidence and cor relations in the 1002 southwestern Slave craton, North west Territories. Geological Survey Canada Current 1003 Research, 2006 A7, 15 p 1004 1005 Ootes, L., Davis, W.J., Bleeker, W., and Jackson, V.A. 2008. Geologic overview of 1006 greywacke samples col lected from the western Slave craton. Northwest Territories 1007 Geoscience Office, NWT Open Report 2008 012, p. 14. 1008 Draft 1009 Ootes, L., Davis, W.J., Bleeker, W., and Jackson, V.A. 2009. Two Distinct Ages of 1010 Neoarchean Turbidites in the Western Slave Craton: Further Evidence and Implications 1011 for a Possible Back Arc Model. The Journal of Geology 117 (1): 15–36. 1012 1013 Ootes, L., Morelli, R., Lentz, D.R., Falck, H., Creaser, R.A., and Davis, W.J., 2011. The 1014 timing of Yellowknife gold mineralization: a temporal relationship with crustal anatexis? 1015 Economic Geology, v. 106, p. 713 720. 1016 1017 Padgham, W.A., and Fyson, W.K. 1992. The Slave Province: a distinct Archean craton. 1018 Canadian Journal of Earth Sciences, 29: 2072 2086. 1019 1020 Pehrsson, S., and Villeneuve, M. 1999. Deposition and imbrication of a 2670–2629 Ma 1021 supracrustal sequence in the Indin Lake area, southwestern Slave Province, Canada. 1022 Canadian Journal of Earth Sciences, 36: 1–21. 1023
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1024 Pehrsson, S.J., Chacko, T., Pilkington, M., Villeneuve, M.E., and Bethune, K. 2000. 1025 Anton terrane revisited: late Archean exhumation of a moderate pressure granulite 1026 terrane in the western Slave Province. Geology, 28: 1075–1078. 1027 1028 Rasmussen, B., and Fletcher, I. R. 2010. Dating sedimentary rocks using in situ U Pb 1029 geochronology of syneruptive zircon in ash fall tuffs <1 mm thick. Geology, 38 (4): 299– 1030 302. 1031 1032 Sharma, R., and Pandit, M. 2003. Evolution of early continental crust. Current Science, 1033 84 (8): 1–7. 1034 Shirey, S.B., and Richardson, S.H. 2011. Sart of the Wilson cycle at 3 Ga shown by 1035 diamonds from subcontinental mantle. Science, 333:434 436. 1036 1037 Sherlock R. L., Shannon A., HebelDraft M., Lindsay D., Madsen J., Sandeman H., Hrabi B., 1038 Mortensen J. K., Tosdal R. M. and Friedman R. 2012. Volcanic stratigraphy, 1039 geochronology, and gold deposits of the archean hope bay greenstone belt, nunavut, 1040 Canada. Econ. Geol. 107, 991–1042. 1041 1042 Simonetti, A., Heaman, L. M., Hartlaub, R. P., Creaser, R. A., MacHattie, T. G., and 1043 Böhm, C. 2005. U–Pb zircon dating by laser ablation–MC–ICP–MS using a new multiple 1044 ion counting Faraday collector array. Journal of Analytical Atomic Spectrometry, 20: 1045 677–686. 1046 1047 Simonetti, A., Heaman, L. M., Chacko, T., and Banerjee, N. R. 2006. In situ petrographic 1048 thin section U–Pb dating of zircon, monazite, and titanite using laser ablation–MC–ICP 1049 MS. International Journal of Mass Spectrometry, 253: 87–97. 1050 1051 Stern, R.A., Bodorkos, S., Kamo, S.L., Hickman, A.H., Corfu, F. 2009. Measurement of 1052 SIMS Instrumental Mass Fractionation of Pb Isotopes During Zircon Dating. 1053 Geostandards and Geoanalytical Research, 33 (2): 145–168. 1054
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1055 Stubley, M.P. 2005. Slave Craton: interpretive bedrock compilation. Northwest 1056 Territories Geoscience Office, NWT NU Open File 2005 01:Digital files and 2 maps. 1057 1058 Van Breemen, O., Davis, W.J., King, J.E., 1992. Temporal distribution of granitoid 1059 plutonic rocks in the Archean Slave Province, northwest Canadian Shield. Canadian 1060 Journal of Earth Sciences, 29: 2186–2199. 1061 1062 Villeneuve, M.E. 1993. Preliminary geochronological results from the Winter Lake Lac 1063 de Gras Slave Province NATMAP project, Northwest Territories. In: Radiogenic Age 1064 and Isotopic Studies: Report 7, Geological Survey of Canada, Paper 93 2, pp. 29–38. 1065 1066 Villeneuve, M., Lambert, L., van Breemen, O., and Mortensen, J. 2001. Geochronology 1067 of the Back River volcanic complex, Nunavut Northwest Territories. Geological Survey 1068 of Canada Current Research 2001 F2,Draft 8 p. 1069 1070 Yamashita, K.; Creaser, R. A.; and Villeneuve, M. E. 2000. Integrated Nd isotopic 1071 evidence and U Pb detrital zircon systematics of clastic sedimentary rocks from the Slave 1072 Province, Canada: evidence for extensive crustal reworking in the early to mid Archean. 1073 Earth Planet. Sci. Lett. 174:283–299. 1074 1075 1076 1077 Captions
1078
1079 Figure 1A . Geological map of the Slave craton showing the distribution of greywacke
1080 mudstone turbidites and older volcanic belts. Coloured location names refer to the
1081 recommend nomenclature in this study. Note the extent of exposed basement, which is
1082 from bedrock mapping and Nd isotopes in ca. 2.63 2.58 Ga granitic rocks. The U Pb age
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1083 dating of each location is shown in Table 1. Map modified from Bleeker et al. (1999);
1084 Davis and Hegner (1992); Bennett (2006); Buse (2006); Yamashita et al. (1999).
1085
1086 Figure 1B. The Neoarchean stratigraphy of the Slave craton. CSCG = Central Slave
1087 Cover Group; BIF = banded iron formation. Map and stratigraphy modified after Bleeker
1088 (2002) and Ootes et al. (2009).
1089
1090 Figure 2. Slemon Lake tuff bed. (A, B) Field photos of the tuff bed interbedded in a
1091 greywacke. The contact between tuff and greywacke is characterized by a sharp base and
1092 a more uneven upper contact with load structures developed as a result of soft sediment
1093 deformation (white arrows in B). (C)Draft Crossed polarized micro photo of the tuff showing
1094 randomly dispersed fragmented quartz crystals set in a more fine grained biotite (Bi) +
1095 chlorite (Chl) + quartz (Qtz) groundmass. Inset shows a well crystallized prismatic zircon
1096 (Zrn). (D) Field photo of the BIF at Slemon Lake immediately 1 m underneath the tuff
1097 bed. (E) Backscatter image of relatively unzoned zircons from the tuff bed at Slemon
1098 Lake.
1099
1100 Figure 3. LA MC ICP MS U Pb zircon results for the Slemon Lake tuff bed. (A) U Pb
1101 concordia diagram showing a straight line through all the zircons (n=17) plotted. (B)
1102 weighted mean 207 Pb/ 206 Pb age of 2616.6 ± 3.5 Ma of the zircons plotted in (A). (C) U Pb
1103 concordia diagram of the six most concordant grains from the sample. (D) A weighted
1104 mean 207 Pb/ 206 Pb age of 2620.4 ± 5.5 Ma of the six concordant grains. This date defines
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1105 the crystallisation age of the tuff bed and constrains the depositional timing of the
1106 turbidites and the interbedded BIF. See text for further explanations.
1107
1108 Figure 4. The Dettah tuff bed in the Burwash Formation, northeast of Yellowknife Bay
1109 (see also Bleeker et al. 2007, p. 163), exposed along the road between the Ingraham Trail
1110 and the town of Dettah. (A) Field photo of the tuff bed. (B) Close up image of the tuff
1111 bed in (A). Note the ultra fine lamina of ash within the mudstone facies. The zircons
1112 extracted for this study are from the thickest tuff bed shown. (C) Photomicrograph
1113 (crossed polarized light) of the tuff bed showing bimodal distribution of quartz (qtz)
1114 grains in a fine grained chlorite (chl), biotite (bi), and muscovite (mu) groundmass. (D)
1115 Photomicrograph of selected zirconDraft grains from the tuff bed. (E) A U Pb concordia plot
1116 showing ID TIMS data for three single grain zircon fractions (ZA, ZB, ZC) from the
1117 Dettah tuff. Error ellipses and age calculation are shown at the 2 σ level of uncertainty.
1118 The weighted average 207 Pb/ 206 Pb age (and anchored upper intercept age) for these three
1119 fractions from the tuff is 2650.5 ± 1.0 Ma.
1120
1121 Figure 5. Goose Lake greywacke. (A) Illustration of the Goose Lake core sample
1122 showing greywacke mudstone turbidites associated with BIF. The sample in this study
1123 was obtained from the lower part of the lower greywacke. (B) Cathodoluminescence
1124 (CL) images of the selected zircon grains. (C) LA MC ICP MS U Pb detrital zircon
1125 results showing U Pb concordia diagram of all the zircons analyzed. (D) Histogram with
1126 probability curve for the detrital zircons (<10% discordance). Note the youngest grain at
1127 2621 ± 18 Ma (1.3% discordance) and the >2800 Ma grains which suggest the existence
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1128 of older basement lithologies. A large part of the zircons correlate in age with Kam and
1129 Banting Group detritus.
1130
1131 Figure 6. Courageous Lake greywacke. (A) Field photos of the greywacke sample
1132 collected from the Courageous Lake turbidites. (B) Cathodoluminescence (CL) images of
1133 the selected zircon grains.
1134
1135 Figure 7. Courageous Lake greywacke showing the LA MC ICP MS U Pb detrital
1136 zircon results. (A) U Pb concordia diagram showing all the zircons analyzed. (B)
1137 Histogram with probability curve for the detrital zircons (<10% discordance). Note the
1138 high frequencies of Banting Group Draftdetritus. (C) The weighted mean 207 Pb/ 206 Pb age of the
1139 four youngest grains is 2635 ± 6.7 Ma, which we define as the maximum deposition age
1140 and likely these zircons are source from the Defeat magmatic arc.
1141
1142 Figure 8 . Point Lake ferruginous sediment. (A, B) Field photo of the Point Lake coarse
1143 grained ferruginous sediment beds within the turbidite BIF sequence. (C) Backscatter
1144 image of representative zircons from the ferruginous sediment beds. The grains are well
1145 zoned but occasionally intensive fragmented and corroded.
1146
1147 Figure 9. LA MC ICP MS U Pb detrital zircon results from the Point Lake ferruginous
1148 sediment. (A) U Pb concordia diagram showing all the zircons analyzed. (B) Histogram
1149 with probability curve for the detrital zircons (<10% discordance). In addition to the high
1150 input of Banting Group detritus, note the probability peak at 2608 Ma, which indicate
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1151 detrital input from the differentiated Concession Suite magmatic rocks. (C) U Pb
1152 concordia diagram of the youngest five grains. (D) The weighted mean 207 Pb/ 206 Pb age
1153 for the five grains are 2607.5 ± 6.4 Ma, which could suggest the existence of an even
1154 younger turbidite BIF sequence in the craton.
1155
1156 Figure 10 . Composite U Pb ages for turbidites in the Slave craton with the recommend
1157 revised nomenclature for the Duncan Lake Group (Henderson 1970, 1972; Helmstaedt
1158 and Padgham 1986; Fergusson 2002; Fergusson et al. 2005) and the proposed Slemon
1159 Group (this study). See text for further explanations.
1160 Draft
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A"A B B
BIF
Draft
BIF
Courageous Lake BIF (S-?)
? - Assignment S - Salmita uncertain
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Draft
210x238mm (150 x 150 DPI)
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data-point error ellipses are 2σ 0.65 data-point error symbols are 2σ A 2700 B n = 17 0.55 2680 2600 2660 0.45 U 2200
238 2640
Pb/ 0.35 1800 age(Ma) Pb 2620 206 206
1400 2600 0.25 Pb/
n = 17 207 1000 2580 0.15 Intercepts at 6±28 & 2617.2±4.7 [±8.2] Ma 2560 MSWD = 1.08 Mean = 2616.6±3.5 [0.13%] 95% conf. Wtd by data-pt errs only, 0 of 17 rej. 0.05 Draft2540 1 3 5 7 9 11 13 15 MSWD = 1.03, probability = 0.42 207Pb/235U
data-point error symbols are 2σ data-point error ellipses are 2σ 2650 0.56 C D n = 6 0.54 2640 2700 0.52 2630 2620 2660 0.50 U 2580 2540 238 Pb age(Ma) Pb 2620 0.48 2500 206
Pb/ 2460 206
2420 Pb/ 0.46 2610 n = 6 207 0.44 Intercepts at 2600 0.42 0 & 2620.4 +5.7/-5.7 Ma MSWD = 0.84 Mean = 2620.4±5.5 [0.21%] 95% conf. 0.40 2590 Wtd by data-pt errs only, 0 of 6 rej. MSWD = 0.84, probability = 0.5 9.5 10.5 11.5 12.5 13.5 207Pb/235U https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 52 of 65
Draft
259x211mm (150 x 150 DPI)
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2676±18 2849±16 A B 2715±16
2698±15 2750±16
2699±15
2763±15 2711±16 2621±18 2676±18
Draft2711±18 2664±16 2814±16 3074±15 100 μm 2704±16 data-point error ellipses are 2σ 0.65
C 16 3000 D 2705
Kam and Ban ng Group probabilityRelative 2800 14 0.55 12 2670 n = 61 2600 Youngest grain = 2621±18 Ma U 10 238 2400 0.45 8 Defeat magma c arc Pb/ Number
206 2200 6 2000 n = 76 4 0.35 1800 Intercepts at 2 1561±200 & 2797±34 [±36] Ma MSWD = 4.9 0 0.25 2550 2650 2750 2850 2950 3050 3150 4 8 12 16 20 207Pb/206Pb age (Ma) 207Pb/235U https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 54 of 65
A
Draft B 2694±13 2728±18
2626±14 2709±13 2767±13 2669±14 2668±14 2712±14 C 2813±13 100 μm 2686±14 2677±14
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data-point error ellipses are 2σ
0.60 A 3000
0.56 12 2800 2665 Kam and Banting 0.52 B Group n = 69 10 2685 probabilityRelative 2600 Youngest grain= 2626±14 Ma U
238 0.48 8
Pb/ 2400
206 0.44 2720 6 Defeatmagmatic arc
2200 Number 0.40 n = 69 4
2000 Intercepts at 0.36 915±410 & 2718±22Draft [±24] Ma 2 2635 MSWD = 1.7 1800 0.32 0 4 8 12 16 20 2600 2640 2680 2720 2760 2800 2840 2880 207Pb/235U 207Pb/206Pb age (Ma)
data-point error symbols are 2σ 2655 C
2645
2635 Pb age(Ma) Pb 206 2625 Pb/
207 Youngest 4 grains 2615 Mean = 2635.4±6.7 [0.25%] 95% conf. Wtd by data-pt errs only, 0 of 4 rej. MSWD = 1.12, probability = 0.34 2605 (error bars are 2σ)
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A B Greywacke
BIF BIF BIF BIF
BIF BIF Greywacke Greywacke BIF Draft Ferruginous sediment 2602±15 2610±14 C 2616±15 RHNWT-29
2695±15 2735±14
2769±14 2681±14
2665±15 2598±15 2654±14 50 μm 2613±14
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data-point error ellipses are 2σ 0.56 A 2700 9 2687 Kam and 0.52 Banting Group 8 B n = 43 probabilityRelative Youngest grain = 2500 0.48 7 2598 ± 15 Ma U 6
238 2300 0.44 2660 5 ConcessionSuite Pb/ Defeatmagmatic arc
206 0.40 2100 4 Number
3 2608 0.36 n = 51 2 Intercepts at 0.32 531±290 & 2704±19 [±20] Ma 1 MSWD = 5.5 0 0.28 2560 2600 2640 2680 2720 2760 2800 2840 6 8 10 12 Draft14 207Pb/206Pb age (Ma) 207Pb/235U
data-point error ellipses are 2σ data-point error symbols are 2σ
C 2635 D 0.52 2700
2600 2625
0.48 2500 2615 U Pb age(Ma) Pb
238 2400 2605 0.44 206 Pb/ Pb/ 206 2595 207 Youngest 5 grains 0.40 Intercepts at 2585 0 +0/-0 Ma & 2606.5 +9.1/-9.3 Ma Youngest 5 grains MSWD = 0.43 2575 Mean = 2607.5±6.4 [0.25%] 95% conf. 0.36 Wtd by data-pt errs only, 0 of 5 rej. MSWD = 0.97, probability = 0.42 9 10 11 12 13 14 (error bars are 2σ) 207Pb/235U https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 58 of 65
Youngest detrital zircon Key magma c Age (Ma) Tuff bed West Central East events B Beechy Lake greywacke (Villeneuve et al. 2001) C Courageous Lake greywacke (this study) Granite cuts turbidite Clover Lake greywacke (Sherlock et al. 2012) 2600 Cl Concession D Damo Lake greywacke (Pehrsson and Villeneuve 1999) magma c suite E Emile River greywacke (Ootes et al. 2009) P G Goose Lake greywacke (this study) 2610 H High Lake dacite (Henderson et al. 1995, 2000) W Slemon I Itchen Lake greywacke (Ootes et al. 2009) P+ H Group K Kwejinne Lake greywacke (Benne et al. 2005) Younger than M Mosher Lake greywacke (Ootes et al. 2006, 2009) 2620 B G ~2640 Ma P Point Lake ferruginous clas c sediment (this study) P+ Point Lake greywacke (Ootes et al. 2009) R Defeat R Russell Lake greywacke (Ootes et al. 2009) Draftmagma c D suite 2628 ± 3 Ma** W Wheeler Lake greywacke (Isachsen and Bowring, 1994) 2630 Defeat pluton cuts folded Burwash Fm. Tuff bed Burwash Forma on (2661 ± 2.4 Ma, Bleeker and Villeneuve 1995) K C E Tuff bed Burwash Forma on (2650.5 ± 1 Ma, this study)
Tuff bed Slemon Lake (2620 ± 6 Ma, this study) 2640 * Age of youngest rhyolites of Ban ng Group volcanic rocks (Mortensen et al. 1992)
**Age of Defeat pluton cross-cu ng F1 folds of Burwash Forma on (Davis and Bleeker 1999) Duncan 2650 M Lake Group Older than ~2640 Ma
I
2660 Cl 2661±3.3, 2661±1, 2658±1 Ma*
Bimodal volcanism Ban ng Group
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Table 1. Summary of age constraints on the depositional timing of turbidites in the Slave craton. Name and Latitude, Deposition location Longitude Lithology Age (Ma) Methods Reference Watta Lake - N62°16'53'' Tuff 2661 ± 2 TIMS Bleeker and southwest Slave W113°6'38'' Villeneuve craton (1995)
Dettah - N62°29'25" Tuff 2650.5 ± 1 ID-TIMS This study southwest Slave W114°17'13" craton
Itchen Lake - N65°25’8” Greywacke 2658 ± 8 SHRIMP Ootes et al. east of Point Lake, W112°15’7” (turbidite) (DZ, max. (n=60) (2009) central Slave deposition age) craton Mosher Lake - N63°5’55” Greywacke 2651 ± 6 SHRIMP Ootes et al. southwest Slave W115°25’43” (turbidite) Draft(DZ, max. (n=58) (2009) craton depositon age) Clover Lake - N67°40'07'' Rhyolite 2662.7 +3.4/−2.8 TIMS (n=5) Sherlock et al. Hope Bay belt, W106°27'33'' (min. deposition (2012) northeast Slave age) craton
Slemon Lake - N63°23'95'' Tuff 2620 ± 6 LA-ICP-MS This study southwestern W116° 04' 55'' (n=17) Slave craton
Goose Lake - N65° 33' 59'' Greywacke 2621 ± 18 (DZ, LA-ICP-MS This study east Slave craton W112° 32' 48'' (turbidite) max. depositon (n=61) age)
Beechey Lake - N65°05'27" Greywacke 2620 ± 5 (DZ, TIMS (n=6) Villeneuve et east Slave craton W108°14'25" (turbidite) max. deposition al. (2001) age)
Courageous Lake - N64°05'45" Greywacke 2635 ± 7 Ma LA-ICP-MS This study central Slave W111°14'30" (turbidite) (DZ, max. (n=69) craton depositon age)
Point Lake - N65°15'49'' Ferruginous clastic 2608 ± 6 (DZ, LA-ICP-MS This study central Slave W112°58'4'' sediment max. depositon (n=43) craton (turbidite) age)
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Damoti lake - west- N64°9'60'' Greywacke 2629 ± 2 (DZ, TIMS (n=15) Pehrsson and southwest Slave W115°5'59'' (turbidite) max. depositon Villeneuve craton age) (1999)
Kwejinne Lake ~N63°46'00'' Greywackes 2634 ± 8 LA-ICP-MS Bennett et al. area - southeast W115°47'55'' (turbidites) 2636 ± 3 (n=100, 79, (2005, 2012) Slave craton 2638 ± 4 68) (DZ, max. depositon ages)
Emile River - west N65°4’45” Greywacke 2637 ± 10 SHRIMP Ootes et al. Slave craton W115°5’43” (turbidite) (DZ, max. (n=66) (2009) (Acasta area) depositon age) Wheeler Lake - N63°18’29” Presumably tuff 2612 ± 2 TIMS (n=?) Isachsen and southwest Slave W114°47’53” (analytical data not Bowring (1994) craton published)
High Lake - north N67°2’00” Porphyritic dacite 2616 ± 3 Ma TIMS (n=4) Henderson et Slave craton W110°54’20” body between al. (1995) greywacke and mudstone facies *Tentatively assigned to the Slemon Group. See textDraft for further explanations.
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Summary of age constraints on the depositional timing of turbidites in the Slave craton. Suggested Suggested Interpretation Formation name Group name Crystallization age Burwash Formation of tuff (type locality) Duncan lake Group
Crystallization age Burwash Formation of tuff (type locality) Duncan lake Group
Weigted mean Itchen lake age of youngest Formation Duncan lake grain Group
Weigted mean Mosher Lake Duncan lake age of youngest Formation GroupDraft grain Crystallization age Clover Lake of rhyolite body Formation intruding wet Duncan lake turbidite sediment Group
Crystallization age Slemon Lake of tuff, weighted Formation (type mean of 6 locality) Slemon Group concordant grains Youngest zircon Goose Lake Formation Slemon Group
Youngest zircon Goose Lake Formation Slemon Group
Weighted mean Salmita Formation age of youngest 4 Slemon Group* grains
Weighted mean Contwoyto Lake age of youngest 5 Formation grains Slemon Group
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Youngest Damoti Lake concordant grain Formation Slemon Group
Age defined by Kwejinne Lake regression of Formation selected Slemon Group discordant grains
Weighted mean Emile River age of youngest Formation Slemon Group grains Age reported Wheeler Lake without Formation supporting Slemon Group analytical data Age reported James River without Formation Slemon Group supporting analytical data Draft
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Appendix F. Zircon U-Pb data on the OG1 standard with known (TIMS) age of 3465.4 ± 0.6 Ma (Stern et al., 2009). The boxes underneath the Table are the weighted mean
Ratios Grain # 206 Pb (cps) 204 Pb (cps) 207 Pb/ 206 Pb 2 σ 207 Pb/ 235 U Point Lake ferruginous clastic sediment OG1-1 304115 155 0.29630 0.00257 29.51760 Goose Lake greywacke OG1-2 244822 213 0.29792 0.00262 29.29302 Courageous Lake greywacke OG1-3 331914 163 0.29865 0.00257 29.66143 Slemon Lake tuff OG1-4 342977 146 0.29875 0.00258 29.13758 OG1-5 386672 145 0.30001 0.00260 29.81720 OG1-1 867873 176 0.29658 0.00285 29.21116 OG1-2 922056 190 0.29592 0.00275 29.88370 OG1-3 891604 184 0.29578 0.00277 29.78059 OG1-4 1081667 295 0.29602 0.00280 29.14195 OG1-5 1118434 310 0.29731 0.00287 29.06448 OG1-6 1022593 274 0.29662 0.00276 29.67735 OG1-7 661052 336 0.29762 0.00278 29.34022 OG1-8 474805Draft 81 0.30016 0.00288 28.96945 OG1-9 339229 12 0.30094 0.00279 29.43172 OG1-10 591339 169 0.30074 0.00279 30.03626 OG1-1 523645 2 0.29824 0.00242 27.06341 OG1-2 528247 5 0.29791 0.00244 28.91981 OG1-3 393879 0 0.29690 0.00242 29.83608 OG1-4 475893 3 0.29641 0.00240 28.70065 OG1-5 279000 9 0.29613 0.00242 29.04111 OG1-6 380704 26 0.29619 0.00239 28.22968 OG1-7 347427 84 0.29787 0.00240 29.16792 OG1-8 569657 102 0.29765 0.00244 28.58146 OG1-1 456495 122 0.29893 0.00245 28.66064 OG1-2 308694 10 0.29906 0.00240 27.65838
Mean 207 Pb/ 206 Pb = 3465.0±8.7 Mean 207 Pb/ 206 Pb = 3455.5 [0.25%] 95% conf. [0.13%] 95% conf. Wtd by data-pt errs only, 0 of 2 rej. Wtd by data-pt errs only, 0 of 8 rej. MSWD = 0.0058, probability = 0.94 MSWD = 0.51, probability = 0.83
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Zircon U-Pb data on the OG1 standard with known (TIMS) age of 3465.4 ± 0.6 Ma (Stern et al., 2009). The boxes underneath the Table are the weighted mean
Ages (Ma) 2 σ 206 Pb/ 238 U 2 σ 207 Pb/ 206 Pb 2 σ 207 Pb/ 235 U 2 σ 206 Pb/ 238 U 2 σ
1.64821 0.72253 0.03985 3451 13 3471 53 3506 147 1.70442 0.71311 0.04101 3459 14 3463 56 3470 153 1.67617 0.72032 0.04023 3463 13 3476 54 3497 149 1.27529 0.70737 0.03035 3464 13 3458 42 3449 114 1.38504 0.72083 0.03289 3470 13 3481 45 3499 122 1.23987 0.71434 0.02953 3452 15 3461 41 3475 110 1.05854 0.73241 0.02503 3449 14 3483 34 3542 92 1.14417 0.73024 0.02721 3448 14 3480 37 3534 101 1.15081 0.71400 0.02737 3450 15 3458 38 3474 102 1.22305 0.70900 0.02904 3456 15 3456 40 3455 109 1.23773 0.72564 0.02950 3453 14 3476 40 3517 109 1.24496 0.71499 0.02959 3458 14 3465 41 3477 110 1.21925 0.69999 0.02869 3471Draft 15 3452 40 3421 108 1.29977 0.70931 0.03063 3475 14 3468 42 3456 114 1.38782 0.72436 0.03279 3474 14 3488 44 3512 121 1.04696 0.65814 0.02489 3461 13 3386 37 3260 96 1.50753 0.70405 0.03624 3459 13 3451 50 3436 136 1.31150 0.72884 0.03148 3454 13 3481 42 3529 116 1.38638 0.70225 0.03344 3452 13 3443 46 3429 125 1.15105 0.71127 0.02759 3450 13 3455 38 3463 103 1.13494 0.69125 0.02722 3450 12 3427 39 3387 103 1.09751 0.71019 0.02610 3459 12 3459 36 3459 98 1.12810 0.69642 0.02689 3458 13 3439 38 3407 101 1.17415 0.69537 0.02791 3465 13 3442 39 3403 105 1.35117 0.67076 0.03232 3465 12 3407 47 3309 124
Pb = 3455.5 ±4.3 Mean 207 Pb/ 206 Pb = 3458.7±7.7 [0.22%] Mean 207 Pb/ 206 Pb = 3461.6±5.9 [0.17%] 95% conf. 95% conf. pt errs only, 0 of 8 rej. Wtd by data-pt errs only, 0 of 10 rej. Wtd by data-pt errs only, 0 of 5 rej. MSWD = 0.51, probability = 0.83 MSWD = 2.2, probability = 0.020 MSWD = 1.12, probability = 0.35
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Zircon U-Pb data on the OG1 standard with known (TIMS) age of 3465.4 ± 0.6 Ma (Stern et al., 2009). The boxes underneath the Table are the weighted mean 207 Pb/ 206 Pb age.
% discord.
-2.0 -0.4 -1.3 0.6 -1.1 -0.8 -3.5 -3.2 -0.9 0.1 -2.4 -0.7 1.9 Draft 0.7 -1.4 7.4 0.9 -2.8 0.8 -0.5 2.3 0.0 1.9 2.3 5.8
5.9 [0.17%] pt errs only, 0 of 5 rej. MSWD = 1.12, probability = 0.35
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