Did Prolonged Two-Stage Fragmentation of the Supercontinent Kenorland Lead to Arrested Orogenesis on the Southern Margin of the Superior Province?
Accepted Manuscript
Did prolonged two-stage fragmentation of the supercontinent Kenorland lead to arrested orogenesis on the southern margin of the Superior province?
Grant M. Young
PII: S1674-9871(14)00062-0 DOI: 10.1016/j.gsf.2014.04.003 Reference: GSF 295
To appear in: Geoscience Frontiers
Received Date: 19 March 2014 Revised Date: 13 April 2014 Accepted Date: 14 April 2014
Please cite this article as: Young, G.M., Did prolonged two-stage fragmentation of the supercontinent Kenorland lead to arrested orogenesis on the southern margin of the Superior province?, Geoscience Frontiers (2014), doi: 10.1016/j.gsf.2014.04.003.
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1 Did prolonged two-stage fragmentation of the supercontinent Kenorland lead to arrested
2 orogenesis on the southern margin of the Superior province?
3 Grant M. Young
4 Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada N6A
5 5B7
6 ABSTRACT
7 Recent geochronological investigations reinforce the early suggestion that the upper part of the
8 Paleoproterozoic Huronian Supergroup of Ontario, Canada is present in the Animikie Basin on
9 the south shore of Lake Superior. These rocks, beginning with the glaciogenic Gowganda
10 Formation, are interpreted as passive margin deposits. The absence of the lower Huronian (rift 11 succession) from the Animikie Basin may be explaineMANUSCRIPTd by attributing the oldest Paleoroterozoic 12 rocks in the Animikie Basin (Chocolay Group) to deposition on the upper plate of a north-
13 dipping detachment fault, which lacks sediments of the rift phase. Following thermal uplift that
14 led to opening of the Huronian Ocean on the south side of what is now the Superior province,
15 renewed uplift (plume activity) caused large-scale gravitational folding of the Huronian
16 Supergroup accompanied by intrusion of the Nipissing diabase suite and Senneterre dikes at
17 about 2.2 Ga. Termination of passive margin sedimentation is normally followed by ocean
18 closure but in the Huronian and Animikie basins there was a long hiatus -- the Great 19 Stratigraphic GapACCEPTED -- which lasted for about 350 Ma. This hiatus is attributed to a second 20 prolonged thermal uplift of part of Kenorland that culminated in complete dismemberment of the
21 supercontinent shortly before 2.0 Ga by opening of the Circum-Superior Ocean. These events
22 caused regional uplift (the Great Stratigraphic Gap) and delayed completion of the Huronian 1
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23 Wilson Cycle until a regional compressional tectonic episode, including the Penokean orogeny,
24 belatedly flooded the southern margin of the Superior province with foreland basin deposits,
25 established the limits of the Superior structural province and played an important role in
26 constructing Laurentia.
27 Keywords: Paleoproterozoic; glaciation; plate tectonics; mantle plumes; supercontinents
28 * Tel.: +1 011 519 473 5692; fax: +1 011 519 661 3198.
29 E-Mail address: [email protected].
30
31 1. Introduction to the Huronian and Animikie basins
32 The evolution of the Great Lakes area during the important transition from Archean to 33 Proterozoic was controlled by evolving plate tecton MANUSCRIPTics. The foundation for early 34 Paleoproterozoic basins was the late Archean supercontinent Kenorland (Williams et al., 1991)
35 which subsequently broke apart on what is now the southern margin of the Superior province.
36 These processes terminated before intrusion of the Nipissing diabase suite at about 2.2 Ga but
37 closure of the Huronian Ocean and deposition in a foreland basin setting did not take place until
38 about 1850 Ma. This exceptionally long time interval, for which there is no stratigraphic record
39 in these basins has been called the Great Stratigraphic Gap (Young, 2013a, fig. 11).
40 The objectivesACCEPTED of this paper are to attempt to explain the complex stratigraphic relationships 41 between early Paleoproterozoic rocks of the Lake Superior and Lake Huron regions and in
42 similar basins in SE Wyoming and in Nunavut, and to place the evolution of these glaciated
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43 basins into the broader context of tectonic events that led to definition of the Superior province.
44 In a broader context an attempt is made to explain the Great Stratigraphic Gap and the unusually
45 long time period – about 650 Ma (from about 2.45 Ga to about 1.80 Ga) -- involved in the
46 Huronian Wilson Cycle. Although the Wilson Cycle was conceived as including events involved
47 in ocean closure followed by re-opening (Wilson, 1966) it is here used in a modified sense to
48 represent events occurring between the initiation of fragmentation of a supercontinent (thermal
49 uplift, extrusion of flood basalts, rifting) and tectonic and sedimentary manifestation of ocean
50 closure and suturing. In other words it refers to the sequence of events from birth to death of an
51 ocean, rather than vice-versa, as in the original usage. Following early suggestions that the
52 Huronian Supergroup of Ontario and western Quebec was equivalent, in a general way to early
53 Proterozoic rocks of northern Michigan, Wisconsin and Minnesota, it was proposed (Pettijohn,
54 1943; Young, 1966; Young and Church, 1966) that some formational correspondence exists 55 between the two basins. Recent geochronological stuMANUSCRIPTdies (Vallini et al., 2006; Craddock et al., 56 2013) have provided support for early suggestions that the upper part of the Huronian
57 Supergroup (Cobalt Group) corresponds to the formations of the Chocolay Group in northern
58 Michigan. There are, however, no satisfactory explanations of how these stratigraphic
59 relationships evolved. The present distribution of these rocks (Fig. 1) must differ considerably
60 from that at the time of deposition for the presence of the much younger Mid-Continent Rift (M.-
61 C.R.) assemblage (~1.1 – 1.0 Ga) means that the southern portion of the Animikie Basin
62 (classical Penokean orogenic belt) was formerly north of its present location. There are several
63 unanswered questionsACCEPTED regarding relationships between the supracrustal Paleoproterozoic rocks of
64 the Huronian Basin and those of the Lake Superior region. These include the reasons for the
65 absence, in the Lake Superior area, of the lower Huronian formations (those older than the
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66 glacial deposits of the Gowganda Formation) and the origin and meaning of the pre-Penokean
67 (~2.2 Ga) deformation of the Huronian Supergroup, first noted almost fifty years ago by Church
68 (1966, 1968). A third unknown is the origin and tectonic significance of the abundant and
69 voluminous mafic intrusions of the Nipissing suite (~2.2 Ga). The Penokean orogeny is now
70 considered to have occurred between about 1890 Ma and 1830 Ma (Schulz and Cannon, 2007). It
71 is proposed that, rather than representing a compressional orogenic episode, primary folding of
72 the Huronian Supergroup, particularly in the area south of the Murray Fault Zone (Fig. 1) may
73 have resulted from large-scale gravitational sliding associated with development of a north-
74 sloping basin, possibly related to ‘back-tilting’ of large fault blocks associated with fault
75 movements and thermal elevation of the area south of the Huronian Basin.
76 Evolution of the Great Lakes area during the early Paleoproterozoic began with emplacement 77 of the Matachewan plume, between 2490 and 2450 MANUSCRIPTMa (Ernst and Bleeker, 2010 and references 78 therein), in the area south of the Huronian Basin. This contributed to stretching and rifting of the
79 late Archean supercontinent Kenorland to produce an ocean on the southern margin of what is
80 now the Superior province. An early manifestation of the break-up process was extrusion of a
81 thin (few hundred m) succession of conglomerates and cross-bedded sandstones (Livingstone
82 Creek Formation) and a thick succession of bimodal volcanic rocks (Thessalon Formation and
83 equivalents) and associated mafic and felsic intrusions (see Bennett, 2006; Melezhik et al., 2013,
84 fig. 7.7). Following this igneous activity a thick (up to about 7 km) succession of sedimentary 85 rocks filled the riftACCEPTED basin that subsequently developed (Young and Nesbitt, 1985; Long, 2004). A 86 different interpretation was favoured by Zolnai et al. (1984) and Bennett et al. (1991) who
87 considered the rift phase to have been very short-lived, involving only the time up to extrusion of
88 the Thessalon Formation, and interpreted the majority of Huronian formations to have formed 4
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89 on a passive margin. This interpretation is, however, called into question because of restriction
90 of all the lower Huronian formations to the area south of the Flack Lake Fault (Fig. 1), and the
91 fluvial character of the thick sandstone formations (Long, 1978). These characteristics stand in
92 marked contrast to those of the widespread marine-influenced Gowganda Formation and
93 succeeding formations of the upper Huronian Cobalt Group (Lyndsey, 1971; Chandler, 1986;
94 Young and Nesbitt, 1985; Miall, 1985). This interpretation of the Huronian Supergroup calls for
95 a two-step process involving an important early rift phase (lower Huronian) followed by
96 development of a passive margin (Gowganda Formation and succeeding formations of the Cobalt
97 Group, or upper Huronian) (Young, 2014, fig.2). Deposition of this thick succession, dominated
98 by siliciclastic sedimentary rocks (Fig. 2) can thus be interpreted as a result of continental rifting
99 and eventual separation initiated by thermal and magmatic activity associated with the
100 Matachewan plume (Ernst and Bleeker, 2010). MANUSCRIPT 101 2. Stratigraphy of the Huronian Basin
102 With the exception of thin, locally developed conglomerates and cross-bedded sandstones of
103 the Livingstone Creek Formation (Fig. 2), the initial history of the Huronian Basin was
104 dominated by extrusion of volcanic rocks at about 2.45 Ga. The subsequent depositional history
105 of the Huronian Basin involved accumulation of a thick succession of sedimentary rocks that
106 includes evidence of three glacial episodes. Much of the Huronian succession has been
107 considered in terms of a thrice-repeated cycle that involves glaciogenic diamictites, followed by 108 mudstones and aACCEPTED thick unit of fluvial sandstones (Fig. 2, right column). Chemical sedimentary 109 rocks are rare but limestones and dolostones are present above the second glacial unit (Bruce
110 Formation) and rare carbonates and sulphates form part of the Gordon Lake Formation.
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111 The lower age limit of Huronian deposition must be close to that of the Thessalon Volcanic
112 Formation and equivalents, which have yielded dates of 2450 ± 25 (Krogh et al., 1984) and
113 2452.5 ± 6.2 Ma (Ketchum et al., 2013). The time of deposition of the youngest Huronian
114 formation is not precisely known but the Huronian Supergroup is extensively intruded by sills,
115 sheets and dikes of the Nipissing diabase suite, which has been dated at 2217 ± 9 Ma (Corfu and
116 Andrews,1986). The Nipissing event involved more than one intrusive phase but may only have
117 lasted for about 10 Ma (Lightfoot and Naldrett, 1996). An age of ~2.31 Ga was recently reported
118 from a thin tuffaceous unit in the Gordon Lake Formation (Bekker et al., 2010; Rasmussen et al.,
119 2013). These data suggest that Huronian sedimentation spanned the long period from about 2.45
120 Ga to 2.31 Ga (the suggested age of the Gordon Lake Formation) plus the amount of time
121 involved in deposition of the quartz arenites of the overlying Bar River Formation. An upper
122 limit is provided by the ~2.22 Ga age of the Nipissing diabase suite but, with the exception of the 123 two formations mentioned above (Thessalon and Gordo MANUSCRIPTn Lake formations) no individual 124 Huronian formations have yielded precise dates and there may be grounds for questioning the
125 interpretation of the date from the Gordon Lake Formation as indicating its depositional age (see
126 Section 3).
127 Following a long hiatus of about 350 Ma, and the dramatic events surrounding the Sudbury
128 Impact at 1850 Ma (Krogh et sl., 1984), the next sedimentary formations preserved in the
129 Huronian Basin are those of the Whitewater Group. These rocks only occur within the Sudbury
130 structural basin and because they bear little resemblance to any rocks in or near to the Huronian
131 outcrop belt, theirACCEPTED stratigraphic affiliations remained problematic until publication of Dietz’s
132 benchmark paper in 1964 when he made the suggestion that the Sudbury Structure was an impact
133 scar and precise dating of that event by Krogh et al. (1984). It was suggested by several early
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134 workers that the rocks of the Whitewater Group were correlative to the lithologically similar
135 Rove Formation on the north shore of Lake Superior (Young and Church, 1966, p. 79, and
136 references therein) -- a correlation that has only recently been verified by discovery of a
137 widespread breccia layer that is attributed to the Sudbury Impact (Addison et al., 2005; Cannon
138 et al., 2010) and therefore provides a precise time marker that links the widely separated
139 sedimentary successions of the Sudbury structural basin and the Animikie Basin. It was
140 suggested by Cannon et al. (2010) that the Sudbury Impact took place in a basinal environment
141 because of the occurrence of carbonaceous shale fragments in the Onaping Formation (Bunch et
142 al., 1999) but this seems to be unlikely for there is no evidence of deposition of carbon-rich
143 sediments in the Huronian outcrop belt until after the impact had occurred – during deposition of
144 the ‘Black Onaping’ which probably resulted, in part, from reworking of fall-back breccias and
145 includes many carbon-coated clasts. In the Animikie Basin, widespread black carbonaceous 146 shales also overlie the impact layer. MANUSCRIPT 147
148 3. Stratigraphy of the Animikie Basin
149
150 West of the Huronian Basin Paleoproterozoic rocks of the Marquette Range Supergroup are
151 exposed in the area around the western and southern margins of Lake Superior (Fig. 1).
152 Proterozoic supracrustal rocks in northern Michigan, Wisconsin and Minnesota were for many
153 years correlated in a general way to the Huronian succession but because of perceived
154 differences it wasACCEPTED proposed by James (1958) that this practice be discontinued. He suggested
155 that the term “Animikie Series” be used for the Proterozoic successions of the Lake Superior
156 area. As more stratigraphic details of the two areas began to emerge Pettijohn (1943), Young
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157 (1966) and Young and Church (1966) proposed that the upper part of the Huronian succession in
158 Ontario (Cobalt Group) may be correlated to distinctive rock types in the lowest part of the
159 ‘Animikie Series’ -- the Chocolay Group in Michigan. The proposed correlative rock types
160 include glacial diamictites (Gowganda Formation), followed by unusual aluminous
161 orthoquartzites (part of the Lorrain Formation), and carbonate- and sulphate-bearing rocks of the
162 Gordon Lake Formation (Fig. 2). Of particular importance in the proposed correlation were
163 scattered exposures of glaciogenic rocks lying unconformably on Archean basement in the area
164 south of Lake Superior. These are known as the Fern Creek, Enchantment Lake and Reany Creek
165 formations (Pettijohn, 1943; Gair, 1981; Puffett, 1969) and were considered to be correlatives of
166 the regionally extensive Gowganda Formation on the north shore of Lake Huron. The proposed
167 correlation was not accepted by most (e.g. Cannon 1973; Morey, 1973; van Schmus 1976; Sims
168 and Peterman 1983) because available radiometric age determinations were taken to mean that 169 the Lake Superior rocks were entirely younger. Thes MANUSCRIPTe lithostratigraphic correlations (Young, 170 1966; Young and Church, 1966; Ojakangas; 1988; Ojakangas et al. 2001) were eventually
171 supported by geochronological data from detrital zircons and xenotime cements in rocks of the
172 Chocolay Group in northern Michigan (Vallini et al., 2006). It was shown by Vallini et al. (2006)
173 that the rocks of the Chocolay Group, including the glaciogenic diamictites at its base, were
174 older than 2207 Ma, the age of hydrothermal xenotime rims on zircon grains, thus demonstrating
175 temporal equivalence to part of the Huronian Supergroup, as proposed 40 years earlier (Young,
176 1966). As usual, ‘the devil is in the details’. Zircon from the Enchantment Lake Formation
177 yielded a date of ACCEPTED2317 ± 6 Ma and the overlying Sunday Quartzite provided a zircon age of 2306
178 ± 9 Ma, so that these formations are ostensibly older than these ages (or equivalent to them, if the
179 zircons came from contemporary tuffs). Newly published zircon dates (Rasmussen et al., 2013)
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180 from what was considered to be a thin tuffaceous layer in the Huronian Gordon Lake Formation
181 (Fig. 2) were interpreted to indicate a depositional age of about 2308 ± 8 and 10 Ma for that
182 formation. If the lithostratigraphic correlation (with the diagnostic pairing of glaciogenic
183 deposits succeeded by aluminous quartz arenites) is accepted as indicating equivalence to the
184 Huronian Gowganda-Lorrain association, then the interpretation of the age of the Gordon Lake
185 Formation may be suspect for the proposed age would mean the Gordon Lake Formation is older
186 than the Sturgen Quartzite -- presumed equivalent of the Lorrain Formation, which underlies the
187 Gordon Lake Formation (see Fig. 2). An alternative interpretation is that the dated zircons (2308
188 Ma) from the Gordon Lake Formation are detrital and were derived from the same source as
189 those of near-identical age (2306 Ma) in the Sturgeon Quartzite. Thus the Gordon Lake
190 Formation could be younger than the 2.31 date suggested by Rasmussen et al. (2013) and the age
191 from zircons in the glaciogenic Enchantment Lake Formation (2317 Ma) either indicates the 192 depositional age of that formation (as suggested by MANUSCRIPTVallini et al., 2006) or, if these grains are also 193 detrital, could indicate that the formation is younger than that age. Thus the age of the
194 Enchantment Lake Formation (and therefore that of the correlative Gowganda Formation)
195 remains uncertain but is either about 2317 Ma or younger. Acceptance of the 2308 Ma date as
196 the depositional age of the Gordon Lake Formation would mean that there is a very long time
197 interval (almost 100 Ma) between that depositional age and intrusion of the Nipissing diabase at
198 2217±9 Ma , which seems unlikely because there is only a single preserved younger Huronian
199 formation (Bar River Formation), and intrusion of the Nipissing diabase suite is considered to
200 have taken place ACCEPTEDprior to complete lithification of the Huronian sedimentary formations (see
201 Section 7). Although correlation of the Chocolay Group with the upper portion of the Huronian
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202 Supergroup is now generally accepted, the remaining stratigraphic discrepancies between the two
203 adjacent Paleoproterozoic basins (Fig. 2) have not been resolved.
204 Understanding the Paleoproterozoic stratigaphy of the Lake Superior area has been difficult
205 because of a combination of poor exposure and structural complexity but recent studies such as
206 those of Schneider et al. (2002), Schulz and Cannon (2007), and Craddock et al. (2013), together
207 with earlier works such as those of Cannon (1973), Morey (1973), Sims et al. (1983) and
208 Ojakangas et al. (2001), have resulted in development of a plate tectonic scheme that generally
209 resembles that outlined for the Huronian Basin. One major difference is that ‘accreted terranes’
210 are better preserved in the Animikie Basin, whereas to the east they are probably obscured by
211 Paleozoic cover rocks or were involved in younger thermo-tectonic activity associated with the
212 Grenville, and possibly older orogenies. The stratigraphic picture that has emerged in the
213 Animikie Basin may be summarised in terms of three, dominantly sedimentary packages that 214 comprise (from base to top) the Chocolay, Menominee MANUSCRIPT and Baraga groups. The simplified and 215 generalized stratigraphy of these rocks is shown in Fig. 2, together with a comparative section
216 from the Huronian Supergroup. The oldest Proterozoic link between the two areas involves the
217 upper Huronian formations and those of the Chocolay Group, which have near-identical rock
218 types. The thick lower Huronian succession, which is interpreted as a rift-fill, is not known from
219 the Animikie Basin, and rocks equivalent to the iron-rich Menominee Group are not represented
220 in the Huronian Basin. The Chocolay Group is thought to represent erosional remnants of the
221 passive margin succession that is much more fully preserved as the Cobalt Group in the
222 Huronian Basin. ACCEPTEDDeposition of these sediments was followed, in both basins, by a long hiatus of
223 more than 300 Ma.
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224 In the Animikie Basin the first recorded supracrustal rocks following the hiatus or ‘Great
225 Stratigraphic Gap’ of Young (2013a, fig. 11) are those of the Menominee Group which consists
226 of basal sandstones and mudstones and volcanic rocks that are followed by the famous Superior-
227 type iron formations. Volcanic rocks of the Hemlock Formation have provided a date of 1874 ±
228 9 Ma (Schneider et al., 2002). Although there is a large time interval between the Chocolay and
229 Menominee groups some areas show little evidence of structural discordance. These
230 relationships are comparable to those described by Aspler et al. (2001) from a similar succession
231 of similar age (Hurwitz Group) on the west side of Hudson Bay. In the Animikie Basin the
232 overlying Baraga Group is commonly separated from underlying iron formation of the
233 Menominee Group by a widespread unusual breccia that is interpreted as a debris layer related to
234 the 1850 Ma Sudbury Impact (Addison et al., 2005; Cannon et al., 2010). In many areas the
235 impact layer is followed by a black carbonaceous shale which is in turn succeeded by a thick, 236 turbidite-rich succession. The rocks of the Baraga GroupMANUSCRIPT closely resemble those of the 237 Whitewater Group, which is preserved exclusively within the Sudbury structural basin (Fig. 1).
238 As pointed out by Cannon et al. (2010) there appears to be a profound and rapid change in the
239 sedimentary regime of the Animikie Basin from mostly shallow water oxidative conditions under
240 which the iron formations accumulated, to deposition of fine grained, black, carbonaceous
241 mudstones, formed in a reducing environment. It is possible that this rapid environmental
242 change was due, in part, to near-extirpation of marine photosynthetic micro-organisms due,
243 among other things, to widespread (global?) distribution of fine debris thrown into Earth’s
244 atmosphere duringACCEPTED the Sudbury Impact, so that photosythetic activity would have been inhibited
245 and ocean temperatures would have been lowered (Young, 2013a, fig. 11).
246
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247 4. Previous interpretations of tectonic setting
248
249 There have been various interpretations of the tectonic setting that influenced the distribution
250 and nature of Paleoproterozoic rocks in the Great Lakes area. It was proposed by Dietz and
251 Holden (1966) that the Huronian rocks represent a ‘miocline’, or passive margin. It was
252 suggested (and later retracted) by Hoffman et al. (1974) that the East Arm of Great Slave Lake
253 was the site of a Paleoproterozoic aulacogen. In an attempt to explain westward thinning of the
254 Huronian Supergroup, it was suggested (Young, 1983) that the Huronian Basin could be
255 interpreted in the same way. It was also pointed out in the same paper (Young, 1983, table 1)
256 that there was a distinct change from ‘graben-style tectonics’ to a ‘downwarp stage’ at the time
257 of deposition of the Gowganda Formation. The same change in sedimentary style was noted by 258 Long and Lloyd (1983) who proposed that the HuroniaMANUSCRIPTn Supergroup formed in an intracratonic 259 transpressional oblique-slip basin that evolved into a typical passive margin during deposition of
260 the upper Huronian sediments. Following detailed investigation of the Gowganda Formation in
261 the southern part of the Huronian outcrop belt, Young and Nesbitt (1985) suggested a classical
262 rift-to-drift interpretation of the Huronian Basin In which the entire lower Huronian succession
263 was considered as a restricted, mainly non-marine, rift-fill, in contrast to the widespread (largely
264 marine) upper Huronian succession. Most of the lower Huronian sedimentary rocks were
265 considered by Zolnai et al. (1984), Bennett et al. (1992) and Riller et al, (1997) to have been 266 deposited on a passiveACCEPTED margin, restricting the rift phase to a very short-lived episode of 267 volcanism near the base of the supergroup but, based on stratigraphical and sedimentological
268 arguments, Young and Nesbitt (1985) and Long (2004, pp. 208-209) concluded that all of the
269 lower Huronian formations (see Fig. 2) were deposited in a rift setting. Most compelling are the 12
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270 wide distribution of the upper Huronian rocks, compared to the restricted, fault-bounded nature
271 of the lower Huronian formations, and the presence of marine indicators in the upper Huronian
272 succession and their dearth (or absence) in the lower portion. The absence of the lower Huronian
273 succession in the Animike Basin has not been convincingly explained, although Young (1983)
274 suggested that these stratigraphic relationships are comparable to what is observed in northern
275 parts of the Huronian outcrop belt where Paleoproterozoic deposition began with the Gowganda
276 or Lorrain formations. In a comprehensive survey of the relationship between pre-existing
277 sutures, mantle plume activity, and continental break-up Buitera and Torsvik (2014, fig. 10) it
278 was suggested that in cases where plume activity is involved (active rifting), flood basalt will
279 precede the onset of rifting. In the Huronian basin, flood basalts of the Thessalon Formation
280 were described as erosional remnants (Bennett 2006), and thick (up to 1700 m) fanglomerates of
281 the Aweres Formation (thought to be equivalent to the MIsssissagi Formation) were interpreted 282 as being due to uplift, which was probably rift fau lting.MANUSCRIPT The basal pert of the Aweres Formation 283 contains abundant mafic volcanic fragments which are replaced upwards by basement granite
284 clasts, suggesting removal of the volcanic cover from its Archean basement. This suggests that
285 rifting in the Huronian Basin was taking place (initiated?) after extrusion of the Thessalon
286 Formation and equivalents. Perhaps the basal conglomerates and sandstones of the Livingstone
287 Creek Formation formed in response to doming related to emplacement of the mantle plume.
288 Following extrusion of the Thessalon Formation flood basalts and associated rocks rifting was
289 initiated and siliciclastic rocks were shed from fault scarps and from orthogonal fault-bounded
290 basin margins suchACCEPTED as those associated with the ancestral Kapuskasing Tectonic Zone.
291 Most of the sedimentary rocks in the Animikie Basin are considered to have been deposited in
292 some sort of collisional setting, either partly as back-arc basin deposits (Schneider et al., 2002; 13
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293 Schulz and Cannon, 2007) or as classical foreland basin sediments related to ocean closure
294 (Hoffman, 1987; Young, 2002).
295 5. Post-depositional tectonic history
296 Although there have long been problems in establishing widely accepted stratigraphic
297 correlations between the Animikie and Huronian basins it has commonly been assumed that the
298 rocks of both basins formed at approximately the same time and were later deformed during the
299 Penokean orogeny. During early structural investigations of the Huronian Supergroup it was
300 pointed out by Church (1966, 1969) that major folding of the Huronian rocks in the area south of
301 the Murray Fault Zone (Fig. 1) took place at about 2.2 Ga, close to the time of intrusion of the
302 Nipissing diabase suite. This conclusion is based on field evidence showing that the axes of both
303 major structures, such as the McGregor Bay anticline, and minor folds are transected by diabase 304 intrusions, and on the presence of highly irregular andMANUSCRIPT pod-shaped diabase bodies, suggesting 305 magmatic invasion of incompletely consolidated sediments (Card, 1976a; Young, 1983; Young
306 et al., 2001; Long, 2004; Shaw et al., 1999). Large diabase sheets tend to occur in anticlines
307 such as the McGregor Bay anticline (Young, 1966, fig. 1) and this, together with their general
308 absence from major synclines in the southern part of the Huronian Basin, suggests that the folds
309 were developed prior to intrusion – anticlines acting as traps and synclines as barriers to rising
310 magmas.
311 There is also evidence that the Huronian rocks were folded before development of the main
312 cleavage in argillaceousACCEPTED Huronian units. The same cleavage developed later than the Sudbury
313 breccias, which, together with shatter cones, are commonly attributed to the passage of shock
314 waves through the rocks at the time of the Sudbury impact (1.85 Ga). Thus the cleavage is
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315 potentially attributable to the Penokean orogeny that deformed the rocks of the Animikie Basin
316 much later than the development of the first major folds of the Huronian outcrop belt.
317 There is also abundant evidence of significant flattening in the southern part of the Huronian
318 outcrop belt. Thin vein-like, sand-filled clastic dikes in mudstones (now argillites) have been
319 considerably deformed into ‘ptygmatic’ - style folds, and strain shadows are commonly
320 developed around clasts in diamicttes with a fine grained matrix. Although early deformation in
321 the southern part of the Huronian Basin was attributed by some to the Penokean orogeny,
322 geochronological evidence suggesting that the Penokean orogeny began at about 1.89 Ga means
323 that the first folding of the Huronian Supergroup occurred more than 300 Ma earlier.
324 It was suggested by Riller et al. (1999) that the Huronian rocks were involved in an early
325 orogenic episode termed the Blezardian orogeny. These authors were of the opinion that 326 fragmentation of the Archean ‘supercontinent’, Keno MANUSCRIPTrland, was initiated at a very early date, 327 following extrusion of the basal Huronian volcanic rocks at about 2.45 Ga. Stratigraphic and
328 sedimentological evidence suggests that break-up did not take place until the time of deposition
329 of the Gowganda Formation (Young and Nesbitt, 1985; Long, 2004), making it unlikely that
330 orogeny took place during what was essentially a lengthy tensional episode. The existence of the
331 Blezardian orogeny is predicated to some degree on interpretation of two small granitic
332 intrusions (Creighton and Murray plutons) which occur near the Murray Fault Zone on the south
333 side of the Sudbury basin. These granites have yielded dates of about 2.45 and 2.43 Ga which are 334 close to the time ACCEPTEDwhen Huronian deposition began so that they are probably co-magmatic with 335 rift-related volcanic rocks (Jolly et al., 1992) near the base of the Huronian Supergroup in the
336 Sudbury area. Interpretation of structures in and around the granites is highly controversial
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337 (Dutch, 1979; Card,1979). These small granitic intrusions may be part of the igneous activity
338 associated with the formative (rift) stage of the Huronian Basin. The Blezardian orogeny is
339 believed to have occurred between 2.4 and 2.2 Ga (Riller et al., 1999) but this is precisely the
340 time during which the Huronian Supergroup accumulated. It is difficult to understand how a 200
341 Ma-long mountain building event (Blezardian orogeny) could have taken place in the same area
342 and at the same time as the Huronian sedimentary succession was being deposited in a
343 extensional setting that involved a long rift phase and development of a passive margin. Even if
344 the very early rift-drift transition is accepted so that most of the Huronian Supergroup
345 accumulated on a passive margin, as suggested by Riller et al. (1999), it is difficult to reconcile
346 this with a contemporaneous orogeny. Folding of the thick, mainly sedimentary Huronian
347 Supergroup, by whatever mechanism, must be later than its deposition, which ended before 2.2
348 Ga, when intrusion of the Nipissing diabase took place. Certainly orogeny can accompany 349 sedimentation in a compressional setting such as a forelandMANUSCRIPT basin but if the Huronian Supergroup 350 is correctly interpreted as a rift basin that developed into a passive margin, then the dominant
351 tectonic regime was extensional.
352 The tectonic history of the Animikie Basin is much less controversial. There is now general
353 agreement that Paleoproterozoic sedimentation in the Lake Superior area (at least in the south
354 shore area) began with local glacial deposits, followed by deposition of super-mature sands and a
355 carbonate-rich unit. These formations, and equivalents elsewhere in the Animikie Basin, are 356 correlated to the ACCEPTEDfirst three passive margin formations of the upper Huronian Cobalt Group. 357 The thick succeeding package is much younger (~1.89 – 1.83 Ga) according to reviews by
358 Schneider et al. (2002) and Schulz and Cannon (2007) and is believed to be related to docking of
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359 island arcs and microcontinents during a complex history of ocean closure and accretion of
360 ‘foreign’ terranes. In the Animikie Basin supracrustal rocks formed during the accretion phase
361 comprise two, mainly sedimentary groups – the Menominee and Baraga.
362 The Menominee Group lies unconformably on rocks of the Chocolay Group but some areas
363 show little or no structural discordance. The sequence consists of basal sandstones and
364 mudstones and includes volcanic rocks (Schneider et al., 2002). The Superior-type iron
365 formations are mostly in the upper part of the Menominee Group. These rocks were considered
366 by Schneider et al. (2002) to have formed in foreland extrusion basins associated with tectonic
367 emplacement of the Pembine-Wassau arc terrane, whereas they were interpreted as back-arc
368 basin deposits by Fralick et al. (2002) and Schulz and Cannon (2007).
369 Discovery of a thin but extensive layer of breccia interpreted as a product of the Sudbury 370 impact (Addison et al., 2005; Cannon et al., 2010 a ndMANUSCRIPT references therein) provides a precise date 371 of 1850 Ma for the end of deposition of the Menominee Group which is followed by a
372 widespread black and grey shale unit and a thick succession of turbidites comprising the Baraga
373 Group. Ash beds near the base of the Baraga Group have yielded dates of 1832 Ma and 1836 Ma
374 (Addison et al., 2005) and a date of 1878 Ma was obtained from an ash bed within the underlying
375 Gunflint Formation (Fralick et al., 2002). The succession of the Baraga Group finds a close
376 analogue in the Whitewater Group of the Sudbury basin (Figs. 1, 2) where carbon-rich rocks of
377 the upper (‘black’) portion of the Onaping Formation (Fig. 2) and overlying carbonaceous shales 378 of the Onwatin FormationACCEPTED were attributed by Young (2013a) to an extinction event following the 379 huge Sudbury impact.
380 6. Genesis of the Animikie and Huronian Basins
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381 The salient aspects of stratigraphic relations between the two Paleoproterozoic basins in the
382 Great Lakes area are shown in Fig. 2). Both basins have some common formations, which are
383 critical in establishing their contemporaneity. Those that are present in only one basin also shed
384 important light on the tectonic evolution of the two areas. Correlation of the upper Huronian
385 formations with those of the Chocolay Group is an old idea that has only recently received
386 confirmation from geochronological investigations (Vallini et al., 2006; Craddock et al., 2013).
387 Likewise, recognition of widespread debris from the Sudbury impact event has provided critical
388 support for correlation of the Onwatin and Chelmsford formations with the Baraga Group.
389 Most telling among formations that are known from only one basin are those that comprise
390 the thick lower part of the Huronian succession (Fig. 2). As discussed above, these rocks are
391 considered to represent the rift phase of the Huronian Basin.
392 The key to understanding these stratigraphic relat MANUSCRIPTionship may lie in the elegant model for 393 continental separation by detachment faults developed by Lister et al. (1986). A simplified
394 version of the proposed mechanism is shown in Fig. 3. There are marked contrasts in thickness
395 and character of stratigraphic successions developed on ‘upper’ and ‘lower’ plates of a continent
396 that separated by displacement on a detachment fault system. The lower plate (the portion
397 beneath the detachment fault) should include tilted crustal blocks, containing rift deposits and
398 draped by a much more extensive passive margin succession. These relationships match
399 perfectly those observed in the Huronian Basin. The area south of the Flack Lake Fault and its 400 projection to the ACCEPTEDeast is taken to represent the rift basin although the M.F.Z. probably played a 401 major role as a down-to-basin fault, for it is the locus of significant thickness changes in many
402 formations. The Gowganda Formation was the first to overstep the Flack Lake Fault to lie
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403 directly on Archean basement rocks in a large area to the north of the the Huronian rift basin,
404 signalling the subsidence that typically results from thermal relaxation during formation of a
405 continental margin.
406 The Animikie Basin may be interpreted in terms of the same model, except that the
407 detachment fault dipped in the opposite direction (to the north) so that it represents the upper
408 plate, which provides an explanation for the absence of sediments formed during the rift-phase
409 (Fig. 3). In this interpretation the lower plate, carrying the missing lower Huronian succession
410 would have been transported elsewhere as the ocean widened. It was suggested by Roscoe and
411 Card (1993) that the identical stratigraphic succession of Paleoproterozoic rocks preserved in SE
412 Wyoming (Young, 1975; 1970) might be the displaced and rotated ‘other side’ of the Huronian
413 Basin (see also Heaman, 1997, fig. 3, Bleeker, 2004 and Ernst and Bleeker, 2010) but, if the 414 Wyoming rocks originated in the vicinity of the GreMANUSCRIPTat Lakes, they are more likely to be the 415 displaced southern portion of the Animikie Basin, for the Snowy Pass Supergroup of Wyoming
416 includes the rift package (missing from the Animikie Basin) that is the hallmark of a lower plate
417 assemblage.
418 Switching of the dip direction of detachment faults was described by Lister et al. (1986, fig, 3)
419 (Fig. 3) as commonly occurring across transfer faults. A possible candidate for such a fault is the
420 southern part of the Kapuskasing Tectonic Zone (Fig. 4), which includes crustal scale faults that
421 transect the Superior province. Palinspastic reconstruction involving removal of the Mid- 422 Continent Rift zoneACCEPTED (~1.1 Ga) results in a 70 to 100 km northerly displacement of the southern 423 portion of the Animilie Basin (Riller, 1996, fig. 7; Craddock et al., 2013, fig. 3) (Fig. 4).
424 Generalised paleocurrent directions in the Huronian Basin, mainly from fluvial sandstones, are
19
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425 shown in Fig. 4 (arrows). Paleocurrents from fluvial formations suggest derivation of much of
426 the clastic fill from the sides of the Huronian Basin, possibly as a result of subsidence of the
427 basin related to movements in the ancestral Kapuskasing Structural Zone and, more
428 speculatively, a possible uplifted block near the region now occupied by the much younger
429 Timiskaming graben (Fig. 4).
430 On the west side of the Kapuskasing Structural Zone, here referred to as the Kapuskasing
431 Fault Zone or K.F.Z. (Fig. 4) the Matachewan dike swarm (2.49 - 2.45 Ga) takes on a
432 northwesterly trend, whereas it has a NNW trend to the east of the K.F.Z. The westward swing
433 in direction was attributed by Halls and Davis (2004) and others to rotation of continental blocks
434 but a more recent analysis by Evans and Halls (2010) concluded that re-orientation of the dike
435 swarm was due to dextral displacement along the K.F.Z. and thrusting within the Kapuskasing 436 Structural Zone at about 1900 Ma. These tectonic acMANUSCRIPTtivities may have been the result of 437 northward or north-northeasterly displacement of th e southern portion of the Animikie Basin on
438 the west side of the K.F.Z. during closure of the ocean to the south. Lateral displacement on
439 transfer faults such as the K.F.Z., and possibly another similar fault near what is now the western
440 branch of the Mid-Continent Rift system, would have resulted in a more indented southern
441 margin to the Penokean orogen than is apparent on modern geological maps (Fig. 1).
442 The Menominee Group is not present in the Huronian Basin. These rocks possibly resulted
443 from early local (northward-directed?) subduction in the Animikie Basin at about 1875 Ga 444 (Schulz and Cannon,ACCEPTED 2007). In the Huronian Basin the oldest-preserved post-Huronian 445 sedimentary rocks are those of the Whitewater Group which appear to have followed closely on
446 the Sudbury Impact at 1.85 Ga.
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447 7. The role of plume activity
448 In the Huronian Basin the sedimentary record began with local deposition of conglomerates
449 and sandstones of the Livingstone Creek Formation, followed by extrusive and intrusive igneous
450 activity at about 2.45 Ga. The igneous activity is widely interpreted as a manifestation of rifting
451 in the vicinity of the southern margin of the Superior province (Jolly et al., 1992; Long, 2004;
452 Bennett, 2006). This early igneous phase is possibly an expression of the Matachewan plume
453 (Halls et al., 1994; Bleeker, 2004; Ernst and Bleeker, 2010) which also left a huge fan-shaped
454 array of mafic dikes in the Archean basement north of the Huronian Basin (Fig. 4). The
455 Matachewan plume was active between about 2490 and 2450 Ma (Ernst and Bleeker, 2010, fig.
456 7, and references therein), so that the basal Huronian volcanic episode may represent its dying
457 phase (Fig. 5, part A). To the west, across the K.F.Z. the Animikie Basin was also initiated but 458 with opposite polarity so that the detachment fault dippedMANUSCRIPT north. Thus when continental 459 separation took place and the upper Huronian (passi ve margin) succession blanketed the rift
460 assemblage in the Huronian Basin, the Paleoproterozoic record in the Animike Basin began with
461 deposition of the passive margin assemblage of the Chocolay Group directly on Archean
462 basement (Fig, 5, part B).
463 Deposition of the Huronian Supergroup is known to have taken place between about 2.45 Ga,
464 the age of the basal lavas and 2.2 Ga, the date of the Nipissing diabase. This long time interval
465 (~250 Ma) may be considerably shortened if the recently reported date of 2.31 Ga from the 466 Gordon Lake FormationACCEPTED (Rasmussen et al., 2013) is from a contemporary tuff horizon but, as 467 discussed above (section 3) the dated sircons may be detrital, in which case the depositional age
468 is probably younger. Quartz arenites of the Bar River Formation were deposited above the
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469 Gordon Lake Formation (and possibly additional sediments that were subsequently eroded), then
470 the entire succession was folded (most notably in the south) and intruded by the Nipissing
471 diabase suite, at about 2.2 Ga. Both major folding and intrusive activity may have occurred
472 before complete consolidation of the host rocks, for many large- and small-scale folds have an
473 unusual, irregular appearance on detailed maps (Card 1976b; Young, 1983. figs. 4, 5) and there
474 is abundant evidence of penetration of sediments from one formation into those adjacent. These
475 unusual folds and the abundance of sedimentary intrusions may be the result of large scale
476 gravitational sliding and crumpling of semi-consolidated sediments. The presence of
477 hydrothermal xenotime coatings of about the same age on zircons in the Chocolay Group
478 (Vallini et al. (2006) may also indicate that these rocks were also incompletely consolidated
479 (permeable) at about 2.2 Ga. According to Lister et al. (1986) the trailing edge of the lower plate
480 should become elevated due to unloading as the upper plate moves away. The sediments in the 481 lower portion of the Huronian Supergroup may well MANUSCRIPT have developed a northerly dip following 482 sedimentation because of ‘back-tilting’ due to contemporary displacement on down-to-basin
483 faults such as the Murray and Flack Lake faults. An alternative (or additional) explanation for
484 gravitational displacement of the Huronian sediments may be thermal uplift in the area
485 immediately south of the Huronian outcrop belt. This is approximately the same area as that
486 occupied by the Matachewan plume about 200 Ma earlier (Fig. 4). The similar location may be
487 coincidental or possibly there was was a structural or compositional inheritance from the earlier
488 plume that influenced emplacement of the younger one. It was suggested by Halls et al. (2008)
489 that the MarathonACCEPTED plume, which was inactive for almost a billion years, reappeared in the form of
490 the ca. 1.1 Ga Mid-Continent Rift system but the reasons for the occurrence of plume activity in
491 the same locality remain obscure. This mechanism (Fig. 5, parts C, D) and similar thermal uplift
22
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492 in many areas throughout what would later become the Superior Province, could explain the
493 hiatus between the termination of Huronian sedimentation and deposition of the Whitewater
494 Group, and provide a magmatic source for the Nipissing diabase intrusions, the timing of which
495 has always been enigmatic. It was suggested by Roscoe and Card (1993) that the Nipissing
496 diabase suite represents the rift-drift transition, or was emplaced in a wide rift basin (Bleeker,
497 2004) but these interpretations seem unlikely in view of the fact that no Huronian sedimentary
498 rocks are known to be younger than the magmatic episode which, if it signalled formation of a
499 passive margin, should have initiated subsidence and deposition of a thick succession of shallow
500 marine sediments. Stratigraphic evidence supports earlier formation of a passive margin at the
501 time of deposition of the Gowganda Formation. In order to explain the unusual timing of the
502 Nipissing event, it was suggested by Buchan et al. (1998) and Palmer et al. (2008) that the
503 intrusions could have been derived from an area that was far removed from the Huronian Basin 504 and its tectonic evolution – from the Ungava plume, MANUSCRIPT about 1,000 km to the NE. It was proposed 505 that the thick mafic sheets and sills in the Huronian Basin were delivered from the NE by the
506 Senneterre dikes which are approximately the same age as the Nipissing intrusions. (Fig. 6).
507 Although the Senneterre dikes and Nipissing intrusions may well be co-magmatic, it is possible
508 that the source was located beneath the Huronian Basin. The sills and sheets are thick and
509 abundant throughout the Huronian outcrop belt, whereas the Senneterre dike suite is quite sparse,
510 so that the Nipissing intrusions may have formed closer to the magma reservoir. The Senneterre
511 dikes may have been derived from the Nipissing magma pool, rather than the other way round.
512 The sub-concordantACCEPTED nature of many Nipissing intrusions probably resulted from equalization of
513 magmatic and lithostatic pressures as the magma rose through the thick sedimentary pile in the
514 manner described by Anderson (1951) and Caldwell and Young (2012, p. 241). The Senneterre
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515 dikes could therefore be part of a swarm that is only exposed beyond the confines of the thick
516 Huronian cover. The passive margin succession in the Animikie Basin (upper plate) was uplifted
517 to some degree but escaped the early folding and massive intrusive event that affected the
518 Huronian Supergroup (Fig. 5D), although it was affected by hydrothermal xenotime coatings on
519 zircon grains at about the same time (Valloni et al. (2—6).
520 8. Plate tectonic activity during ocean closure
521 Following early folding and intusion of the Nipissing diabase there was a long hiatus (~350
522 Ma) represented, in the Huronian Basin by the unconformity between folded rocks of the
523 Huronian Supergroup and breccias (Onaping Formation) related to the Sudbury Impact. These
524 coarse deposits are succeeded by black carbon-rich, stratified breccias (the so-called ‘Black
525 Onaping’), which is overlain by black shales of the Onwatin Formation and a thick succession of 526 proximal turbidites -- the Chelmsford Formation (Fi MANUSCRIPTg. 2). Deposition of the Whitewater Group 527 followed the Sudbury Impact which is widely believed to have been responsible for formation of
528 the Sudbury Igneous Complex (e.g. Dietz, 1964; Grieve et al., 1991; Spray et al., 1995) at 1850
529 Ma (Krogh et al., 1984).
530 The post-break-up history of the Animikie Basin has been summarized by Schneider et al.
531 (2002) and Schulz end Cannon (2007). As schematically depicted in Fig. 7, part A, ocean
532 closure is considered to have begun at about 1890 Ma when the Huronian Basin was being
533 subjected to subaerial erosion. Deposition of the Menominee Group, which probably took place
534 in a back-arc basinACCEPTED setting, occurred some time after initiation of subduction at about 1890 Ma.
535 so that the stratigraphic hiatus in the Animikie Basin is slightly shorter than that involved in the
536 Huronian Basin (Fig. 7, part B). Following the Sudbury impact the stratigraphy of the two areas
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537 is similar but the post-impact succession, in the eastern basin, is only preserved within the
538 Sudbury structural basin whereas to the west, the impact layer is succeeded by a widely
539 distributed succession of black shales and turbidites (Ojakangas et al., 2001; Fralick et al., 2002;
540 Hemming et al., 1995; Cannon et al., 2010). These deposits comprise a coarsening- and
541 shallowing-upward sequence on a grand scale, representing encroachment of an orogen from the
542 south and development of a classical foredeep and foreland basin. This phase probably took
543 place between about 1850 Ma, the time of the Sudbury Impact and inferred time of docking of
544 the Marshfield terrane (Shultz and Cannon, 2007) (Fig. 7C), and some time after 1835 Ma when
545 deposition of the Rove Formation began on the north shore of Lake Superior (Addison et al.,
546 2005). The unconformity in the most northerly part of the Animikie Basin (Maric and Fralick,
547 2005) between deposition of the iron-rich Gunflint Formation and arrival of the first sediments of
548 the Baraga Group may be due to northward advance of the Penokean orogen and may have 549 involved migration of a peripheral bulge. A date o fMANUSCRIPT 1878 Ma was reported by Fralick et al. 550 (2002) from near the top of the Gunflint Formation, whereas an age of 1835 Ma from a tuff near
551 the base of the Rove Formation (Maric and Fralick, 2005) indicates a significant hiatus (Fig. 2).
552 A much younger detrital zircon date of 1780 Ma (Heaman and Easton, 2005) from a sandstone
553 about 400m stratigraphically higher in the Rove Formation indicates that deposition of
554 carbonaceous mudstones near the base was extremely slow, producing a highly condensed
555 section. 556 Interpretation ACCEPTEDof this time period is more speculative in the Huronian Basin because the 557 southernmost exposures of the Huronian Supergroup are hidden by the waters of Lake Huron and
558 early Paleozoic rocks on the NE perimeter of the Michigan Basin. To the southeast the Huronian
559 Supergroup disappears into the exhumed roots of the Grenville orogen (Quirke and Collins, 25
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560 1930). It was tentatively suggested by Dickin and McNutt (1989), on the basis of Nd model ages,
561 that the area of the Grenville province lying immediately SE of the Huronian Basin (Fig. 4) had
562 an Archean protolith. These rocks may represent part of Kenorland that was uplifted during the
563 Penokean orogeny, and later incorporated into the Grenville province or they could be remnants
564 of a foreign Archean microcontinent like the Marshfield terrane in the Lake Superior area (Fig.
565 7C). A collisional suture was placed by Dickin and McNutt (1989) between these rocks and a
566 possible island arc of Penokean age to the southeast. The presence of Archean rocks in the area
567 SE of Sudbury may explain the Archean provenance of foreland basin deposits of the
568 Chelmsford Formation in the Sudbury basin (Hemming et al., 1996), if there was Penokean uplift
569 in the area that later became the locus of the Grenville Front.
570 9. Implications of the proposed model
571 The Paleoproterozoic sedimentary history of the MANUSCRIPTAnimikie and Huronian basins terminated 572 with deposition of the foreland basin successions of the Baraga and Whitewater groups. The
573 supracrustal rocks of both basins were strongly affected by tectonic events associated with
574 closure of the Huronian Ocean to the south – the Penokean orogeny, beginning at about 1890 Ma
575 with consumption of oceanic crust to produce island arcs of the Pembine-Wassau terrane and
576 possibly northward subduction giving rise to back-arc development in the Animikie Basin (Fig.
577 7A). Docking of th P.-W.T. against the southern margin of the Animikie Basin at aboui 1870 Ma
578 and a change from northerly to southerly subduction would have led to termination of back-arc 579 basin formation andACCEPTED initiated crustal thickening and loading that led to the diachronous 580 development of a foredeep and a peripheral bulge. At the same time island arc terranes may have
581 been accreted in the vicinity of the southern and southeastern margins of the Huronian Basin
26
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582 (Dickin and McNutt, 1989). Termination of the Penokean orogeny is indicated by emplacement
583 of ‘stitching plutons’ in the Animikie Basin at about 1830 Ma (Schulz and Cannon, 2007).
584 Crustal separation associated with development of the Mid-Continent Rift between about 1.1
585 Ga and 1.0 Ga caused significant southerly displacement of part of the Animikie Basin relative to
586 the Huronian Basin (Fig. 1). The marked change in direction of the Matachewan dikes on the
587 west side of the Kapuskasing Fault Zone (Halls et al., 1994; Evans and Halls, 2010) could be the
588 result of northward compressional displacement on the west side of the fault zone, associated
589 with collisions during the Penokean orogeny. The suggested plume, south of the Huronian Basin,
590 (near the site of the older Matachewan plume) may have caused thermal uplift leading to
591 gravitational folding, and provided a magmatic source for the Nipissing diabase suite at about 2.2
592 Ga.
593 9.1. The Hurwitz Basin MANUSCRIPT 594 It was suggested by Bleeker (2004) and Ernst and Bleeker (2010, fig. 8) that the
595 Paleoproterozoic Hurwitz Group (including glacial deposits) in the Hearne province on the west
596 side of Hudson Bay (Bell, 1974; Young, 1973; Aspler and Chiarenzelli, 1997) originated in the
597 Great Lakes region but the wide distribution (>250,000 square km) of the Hurwitz Group and
598 correlatives in the Hearne province (Bell, 1974, fig. 1; Aspler et al., 2001, figs 1, 2) may provide
599 evidence against juxtaposition of these large areas (together with others such as the Wyoming
600 Basin and Fennoscandian shield) against the much smaller Huronian Basin. Early paleomagnetic
601 studies by ChristieACCEPTED et al. (1975) suggested that the Hurwitz Group has not undergone significant
602 displacement relative to the Superior province but this question will only be resolved with further
603 geochronological and paleomagnetic investigations.
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604 9.2. The Wyoming Basin
605 Based on earlier-noted strong stratigraphic similarities (Blackwelder, 1926; Young, 1975;
606 Houston et al., 1992; Karlstrom et al., 1984), it was proposed by Roscoe and Card (1993) that
607 the Snowy Pass Supergroup in SE Wyoming might have been juxtaposed against the Huronian
608 Basin before being moved to its present situation, some 2,000 km to the SW. If the large
609 displacement and rotation of the Wyoming province are accepted, then it is much more likely
610 that these Paleoproterozoic rocks represent the lower plate succession of the Animikie Basin,
611 rather than the ‘other side’ (upper plate portion) of the Huronian Basin which would likely have
612 lacked the lower (rift-related) portion of the Huronian stratigaphy. Because of similarities
613 between the Wyoming succession and that of South Dakota (Kurtz, 1981) about 500 km to the
614 NE, it is possible that the Snowy Pass Supergroup is a ‘Huronian-type’ lower plate succession 615 developed ‘in situ’ on a southwesterly extension of MANUSCRIPTthe same continental margin (Young, 2013b, 616 fig. 3). On the other hand the near-identical stratigraphic successions in the Wyoming and Great
617 Lakes basins make the case for juxtaposition more compelling than those of others such as the
618 Hurwitz and Fennoscandian basins.
619 10. The Great Stratigraphic Gap
620 One of the most puzzling aspects of the evolution of the Huronian and Animikie basins is the
621 presence of a large hiatus (325-350 Ma) (Fig. 8). This significant break – the ‘Great Stratigraphic
622 Gap’ of Young (2013a, fig. 11) -- separates a passive margin sequence (upper Huronian and
623 Chocolay Group)ACCEPTED from rocks formed in back-arc and foreland basin settings (Menominee/Baraga
624 groups and Whitewater Group). A similar ‘cryptic’ hiatus (without atructural discordance),
625 between 2.11 Ga and 1.91 Ga, was documented by Aspler et al. (2001) in the Hurwitz Basin. The
28
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626 hiatus has not been demonstrated in SE Wyoming where a thick succession of Paleoproterozoic
627 rocks (Snowy Pass Supergroup) accumulated on what is now the southern margin of the Archean
628 Wyoming craton (Karlstrom et al., 1984; Houston and Karlstrom, 1992; Houston et al., 1992).
629 Although these rocks have a near-identical stratigraphy to the entire Huronian Supergroup, the
630 topmost formations, Towner Greenstone and French Slate have no equivalents in the Huronian
631 Supergroup. The French Slate is, however similar in character to carbonaceous mudstones at the
632 base of the Baraga Group in the Animikie Basin and to the Onwatin Formation in the Sudbury
633 basin. The nature of the contact between carbonate rocks of the Nash Formation near the top of
634 the Snowy Pass Supergroup (S.P.S.) and the Towner Greenstone is unknown (not exposed). It
635 was suggested by Houston and Karlstrom (1992) that the two youngest formations could
636 represent deposition in a foreland basin setting related to docking of an island arc complex to the
637 south. Unfortunately there are no geochronological data to resolve the question of age 638 relationships between these formationx (Towner Gree MANUSCRIPTnstone and French Slate) and underlying 639 units of the Snowy Pass Supergroup but it is speculated that a large hiatus (the Great
640 Stratigraphic Gap) may be present between the Nash Formation and Towner Greenstone. The
641 Snowy Pass Supergroup (at least as high as the Nash Formation) was intruded by diabase and
642 gabbroic bodies some of which were emplaced at about 2000 Ma (Karlstrom et al., 1984). Open
643 folds in the lower part of the S.P.S. are cut by sill-like igneous bodies but they tend to take the
644 form of dikes in the higher formations and age relations between the two sets of intrusions are
645 not known. These igneous bodies (and some of the folding that affected at least the lower part of
646 the S.P.S.) certainlyACCEPTED preceded the major 1700 – 1800 Ma orogenesis (Karlstrom et al., 1984)
647 preserved in the Cheyenne Belt to the south. Thus the Great Stratigraphic Gap, if it exists in the
648 Wyoming Basin, could have occurred between about 2 Ga and 1.8 Ga, so that it may have started
29
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649 later and been of shorter duration than that documented in the Huronian Basin (see Young, 2013
650 a, fig. 11). Likewise in the Hurwitz Basin the hiatus discovered by Asplet et al. (2001) did not
651 involve an angular discordance and appears to span the period between about 2.11 and 1.91 Ga.
652 There is no obvious explanation for such a long hiatus in sediment accumulation (or at least
653 preservation) following break-up of a large region of continental crust (Kenorland) and
654 deposition of a passive margin succession. The most likely explanation is perhaps a relative fall
655 in sea level so that the area in question was subaerially exposed. There is no obvious reason to
656 invoke a significant sea level drop for the last sediments before the G.S.G. are mostly interpreted
657 as passive margin deposits formed in the aftermath of the extensive Huronian glaciation
658 (Gowganda Formation) under a transgressive regime. It is also unlikely that a eustatic lowering
659 of sea level would have persisted for such a long period of time. The alternative is that a large 660 region of continental crust was uplifted -- one possibleMANUSCRIPT cause is orogenic thickening, as for 661 example in the long-lived Appalachian fold belt, bu t there is no evidence of orogenic
662 compression in the Great Lakes area until the Penokean orogeny, which is later than the G.S.G.
663 The remaining mechanism is long-lived or repeated thermal uplift, as a result of large scale
664 upwelling from the mantle, of the large interior part of Kenorland, that later became the Superior
665 province. Emplacement of the Nipissing diabase suite and Senneterre dike swarm at about 2.2
666 Ga may signal renewed thermal activity in the vicinity of the older Matachewan plume.
667 Associated uplift may have triggered large scale displacement of the Huronian sediments, 668 leading to widespreadACCEPTED development of an enigmatic early, ‘soft sediment’ fold episode. There is 669 abundant evidence of plume activity in this area between about 2218 Ma (Senneterre dikes) and
670 2065 Ma (Fort Francis dikes), making it plausible that the Nipissing diabase suite was a
671 manifestation of the same process. The effects of the proposed thermal buoyancy were greatest 30
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672 near the Great Lakes area and diminished in strength and duration to the west and northwest
673 (Fig. 9A) until, as in the Hurwitz Basin, the hiatus began later (at about 2.11 Ga) and only lasted
674 about 200 Ma (as opposed to about 350 Ma in the Huronian Basin). The period of the Great
675 Stratigraphic Gap, between about 2.2 Ga and 1.87 Ga is precisely the time when widespread
676 thermal uplift took place throughout most of the area now included in the Superior province.
677 Thermal upwelling culminated in continental break-up around the margins of the Superior
678 province, followed by sedimentation, volcanism and intrusive activity. These events began at
679 about 2.03 Ga in the Richmond Gulf area on the east side of Hudson Bay (Chandler and Parrish,
680 1989), at 2.04 Ga in the Cape Smith Belt and at 2.17 Ga in the Labrador Trough (Maurice et al.,
681 2009, fig. 3)
682 According to Condie et al. (2009) the ~2.45 Ga igneous activity that accompanied initiation of 683 the Huronian Basin was followed by a long magmaticMANUSCRIPT lull which lasted until about 2.2 Ga when 684 the Nipissing diabase sills and dike swarms of appr oximately the same and somewhat younger
685 age were intruded in the Great Lakes area and throughout much of the Superior province (Ernst
686 and Bleeeker, 2010). It was suggested (Young, 2013a) that glaciations in the Huronian Basin,
687 and in a large area that is now the western part of the Superior provine (Fig. 9A) may have been
688 initiated as a result of drawdown of CO 2 due to weathering related to uplift of the supercontinent
689 Kenorland. Low atmospheric CO 2 levels and glaciations may also have been influenced by a
690 dearth of igneous activity between 2.45 and 2.2 Ga (Condie et al., 2009). Mantle plume activity 691 around the peripheryACCEPTED of the region that became the Superior province would have caused 692 renewed uplift, including that in the vicinity of the Huronian Basin, where the Huronian Ocean
693 already existed. At the same time, between about 2.17 and 2.03 Ga, new sedimentary basins were
694 appearing elsewhere. Thus formation of sedimentary basins around the margins of the Superior 31
ACCEPTED MANUSCRIPT
695 province appears to have been controlled by the sporadic nature of mantle plume activity
696 (Condie et al., 2009) and its different effects on different areas. These younger basins do not
697 contain glacial deposits so that, in spite of renewed uplift the ‘Huronian Glacial Event’ had
698 terminated, perhaps in response to renewed magmatic activity, which would have raised CO 2
699 levels in the atmosphere (Condie et al., 2009).
700 Between about 2.45 Ga and 2.2 Ga the Huronian, Animikie and Wyoming basins developed
701 in response to thermal uplift and crustal fragmentation that appears to have been restricted to
702 what is now the southern margin of the Superior province. Following establishment of a passive
703 margin and oceanic crust to the south there was an extended period of thermal uplift, beginning
704 at about 2.2 Ga that marked the beginning of the G.S.G. These events probably ushered in a new
705 episode of sea floor spreading in the area to the south of the Great Lakes while, to the NE the 706 same thermal upwelling initiated basin formation inMANUSCRIPT a huge area around the Ungava peninsula 707 (Maurice et al., 2009. fig. 3). Closure of the Huronian Basin may therefore have been aborted, or
708 ‘put on hold’ by a second wave of thermal plume activity that served to define the future outline
709 of the Superior province. The Penokean orogeny does not mark completion of the Huronian
710 Wilson Cycle but rather forms part of a much later ‘Circum-Superior’ orogen. The Great
711 Stratigraphic Gap bears witness to a second period of thermal uplift that was harbinger to the
712 large-scale fragmentation of Kenorland and the reassembly that defined the Superior province
713 and was an integral part of the building of Laurentia.
714 11. Tectonic summaryACCEPTED
715 Hot spot activity around the southern and western margins of what is now the Superior
716 province caused uplift, intrusion of radial dike swarms such as the Matachewan at ca 2.45 Ga,
32
ACCEPTED MANUSCRIPT
717 rifting and separation to form new continental margins in the south, and cause crustal thinning in
718 the Hurwitz Basin (Fig. 9A), which was interpreted by Aspler and Chiarenzelli (1997) as an
719 intracratonic basin.
720 The Huronian Supergroup and correlatives, including widespread glacial sediments (Fig. 9A),
721 were deposited in these basins between 2.45 Ga and 2.2 Ga, a period characterized by a global
722 dearth of igneous activity (Condie et al., 2009). Uplift of the western part of the Superior
723 province may have contributed to the onset of glaciations. Intrusion of the Nipissing diabase
724 suite and folding (gravitational displacement?) of the Huronian Supergroup took place at about
725 2.2 Ga when renewed mantle plume activity began, this time on a larger scale, eventually
726 defining the borders of the Superior province.
727 Between about 2.2 Ga and deposition of the Whitewater Group, following the Sudbury Impact 728 at 1.85 Ga, there was a stratigraphic hiatus of about MANUSCRIPT350 Ma and although slightly shorter in areas 729 to the west (Hurwitz, and possibly the Wyoming Basins) (Fig. 9A) this break is present in early
730 Paleoproterozoic basins throughout the western part of the Superior province. During the time of
731 the Great Stratigraphic Gap the entire Superior province (and surrounding areas of Kenorland)
732 may have been located above a large area of mantle upwelling (superswell).
733 Starting at about 2.0 Ga ocean formation took place all around the margins of the Superior
734 province (Fig. 9B), followed by docking and collision of island arcs and continental fragments to
735 produce the Trans-Hudson, New Quebec and Penokean orogens and the Cheyenne belt that,
736 together completelyACCEPTED surrounded the Superior province (Fig. 9C). It was at this time that the Great
737 Stratigraphic Gap ended in the Great Lakes area with spilling of a great apron of turbiditic
738 sediments onto the southern margin of the Superior province or with the (slightly earlier)
33
ACCEPTED MANUSCRIPT
739 deposition of BIF in back-arc settings (Menominee Group of the Animikie Basin). Ocean
740 closure and collisional orogeny occurred from about 1.86 Ga to 1.73 Ga and was an important
741 element in the amalgamation of Laurentia.
742 12. Conclusions
743 Stratigraphic relationships between the Animikie and Huronian basins may be explained by
744 the detachment fault model of Lister et al. (1986). The absence of the lower Huronian
745 succession in the neighbouring Animikie Basin may be due to the Chocolay Group being an
746 upper plate assemblage.
747 Early folding of the Huronian Supergroup, formerly attributed to an early phase of the
748 Penokean orogeny or to the enigmatic Blezardian orogeny, is thought to be the result of large-
749 scale north-directed gravitational displacement of the semi-consolidated Huronian succession as 750 a result of thermal uplift of the area south of the Huronian MANUSCRIPT Basin. These early mass movements 751 were accompanied by intrusion of the Nipissing diabase suite at ca. 2.2 Ga, both of which are
752 attributed to mantle plume activity.
753 The Sudbury impact event at 1850 Ma provides a unique time marker in the Great Lakes
754 region permitting correlation of the Baraga and Whitewater groups – both foreland basin
755 assemblages of the Penokean orogen.
756 Similar Paleoproterozoic successions in the Wyoming and Hurwitz basins record a similar
757 tectonic history butACCEPTED the Hurwitz area may have formed on stretched lithosphere, rather than
758 representing break-up and ocean formation.
34
ACCEPTED MANUSCRIPT
759 The Huronian Wilson Cycle was initiated by thermal uplift of the Neoarchean supercontinent,
760 Kenorland, culminating in its break-up coincident with deposition of the glaciogenic Gowganda
761 Fornation, the lowest formation of the upper part (Cobalt Group) of the Huronian Supergroup.
762 In a ‘normal’ Wilson Cycle deposition of these passive margin sediments would be followed by
763 ocean closure but in the case of the glaciated basins around the western perimeter of the Superior
764 province there was an exceptionally long hiatus that is attributed to a second episode of mantle
765 upwelling. These events delayed termination of the Huronian Wilson Cycle until closure of a
766 second much more extensive series of ocean basins that existed from about 2.1 Ga to 1.8 Ga
767 around the periphery of what later became the Superior province. Thus the exceptionally long
768 time (>600 Ma) involved in the Huronian Wilson Cycle may be attributed to its being interrupted
769 by and incorporated into a second Wilson Cycle that resulted in definition of the borders of the
770 Superior structural province and contributed to the amalgamation of Laurentia. MANUSCRIPT 771 Acknowledgements
772 I am grateful for financial assistance in past years from the Natural Science and Engineering
773 Research Council of Canada (NSERC). I am equally grateful for shared experience and expertise
774 of scientific friends and colleagues including W. R. Church, M. J. Frarey, S. M. Roscoe, K. D.
775 Card, J. A. Robertson, G. Bennett, H. W. Nesbitt and C. M. Fedo. I cannot overemphasize the
776 contribution of graduate students such as Darrel Long, Esko Parviainen, Fred Chandler, Randy
777 Junnila, Lawrence Bernstein and Ali Panahi whose energy and enthusiasm were an inspiration. 778 Let us hope that ACCEPTEDthe next generation will find the solutions to remaining problems and that we at 779 least pointed in the right direction. I am grateful to the journal for prompt review and efficient
780 editorial processing..
35
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781
782
783
784
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1007 Wilson, J.T., 1966. Did the Atlantic close and then re-open? Nature 211, 676-681.
1008 Young, G.M., 1966. Huronian stratigraphy of the McGregor Bay area, Ontario: relevance to the
1009 paleogeography of the Lake Superior area. Canadian Journal of Earth Sciences 3, 203-210.
1010 Young, G.M., 1970.ACCEPTED An extensive early Proterozoic glaciation in North America?
1011 Palaeogeography, Palaeoclimatology, Palaeoecology 7, 85-101.
47
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1012 Young, G.M., 1975, Geochronology of Archean and Proterozoic rocks in the southern district of
1013 Keewatin: discussion, Canadian Journal of Earth Sciences 12, 1250-1254.
1014 Young, G.M., 1983. Tectono-sedimentary history of Early Proterozoic rocks of the Great Lakes
1015 region. In: Medaris Jr., L.G. (Ed.), Early Proterozoic Geology of the Great Lakes region.
1016 Geological Society of America Memoir 160, 15–32.
1017 Young, G.M., 2002. Stratigraphic and tectonic settings of Proterozoic glaciogenic rocks and
1018 banded iron-formations: relevance to the snowball Earth debate. Journal of African Earth
1019 Sciences 35, 451-466.
1020 Young, G.M., 2013a. Precambrian supercontinents, glaciations, atmospheric oxygenation,
1021 metazoan evolution and an impact that may have changed the second half of Earth history.
1022 Geoscience Frontiers 4, 247-261. MANUSCRIPT 1023 Young, G.M., 2013b. Climatic catastrophes in Earth history: two great Proterozoic glacial
1024 episodes. The Geological Journal 48, 1-21.
1025 Young, G.M., 2014. Contradictory correlations of Paleoproterozoic glacial deposits: Local,
1026 regional or global controls? Precambrian Research 247, 33-44..
1027 Young, G.M., Church, W.R., 1966. The Huronian System in the Sudbury District and adjoining
1028 areas of Ontario: a review. Proceedings of the Geological Association of Canada 17, 65-82.
1029 Young, G.M., Long,ACCEPTED D.G.F., Fedo, C.M., Nesbitt, H.W., 2001. The Paleoproterozoic Huronian 1030 Basin: product of a Wilson cycle accompanied by glaciation and meteorite impact.
1031 Sedimentary Geology 141-142, 233–254.
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1032 Young, G.M., Nesbitt, H.W., 1985. The lower Gowganda Formation in the southern part of the
1033 Huronian outcrop belt, Ontario, Canada: Stratigraphy, depositional environments and
1034 tectonic setting. Precambrian Research 29, 265-301.
1035 Zolnai, A.I., Price, R.A., Helmstaedt, H., 1984. Regional cross section of the Southern Province
1036 adjacent to Lake Huron, Ontario: implications for the tectonic significance of the Murray
1037 Fault Zone. Canadian Journal of Earth Sciences 21, 447–456.
1038
1039 Figure Descriptions
1040 Figure 1. Geological sketch map (after Riller et al., 1997, fig. 1 and Schulz and Cannon, 2007,
1041 fig. 2) to show the present relationship between Paleoproterozoic rocks of the Lake Superior and 1042 Lake Huron areas. Note that the volcanic and sedimeMANUSCRIPTntary rocks of the Mid-Continent Rift (1.1 - 1043 1.0 Ga) must have caused displacement of the Paleop roterozoic rocks in the Lake Superior area.
1044 Opening of the Mid-Continent Rift (M.-C.R.) may have been accommodated by movement on a
1045 proposed southerly extension of the Kapuskasing Fault Zone (K.F.Z.) into the narrow
1046 southeastern portion of the M.-C.R. in Michigan and a possible similar fault zone extending to
1047 the SW from the west end of Lake Superior. The continental margin in the Lake Superior area
1048 must have lain in a northward indentation relative to the Huronian margin on the east side of the
1049 K.F.Z. (see Fig. 3). Arrows in the M.-C.R. show displacement of the Paleoproterozoic Animikie 1050 Basin during openingACCEPTED of the M.-C.R. Straight and curved lines in the Superior Province represent 1051 dike swarms. Additional abbreviations: A.B. – Animikie Basin; F.L.F. – Flack Lake Fault; H.B.
1052 – Huronian Basin; M.F.Z. – Murray Fault Zone; P.-W. & M.- Pembine-Wassau and Marshfield
49
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1053 Terranes; S.B. Sudbury Basin; W.G. – Whitewater Group; W.R.B. – Wolf River Batholith (1.47
1054 -1.48 Ga).
1055 Figure 2. Generalised stratigraphy of Paleoproterozoic rocks of the Animikie Basin (Lake
1056 Superior) and Huronian Basin (Lake Huron area). Note that the lower Huronian succession is not
1057 present in the Animikie Basin and the iron-rich Menominee Group is absent from the Huronian
1058 Basin. These stratigraphic gaps are shown by the pattern of vertical lines. All other formations
1059 appear to be present in both basins. The two basins may be separated by a southerly extension of
1060 the Kapuskasing Fault Zone (K.F.Z.), which is thought to have acted as a transfer fault
1061 separating the Animikie and Huronian basins. See text for discussion, interpretation and sources
1062 of geochronological data. Most ages from the Animikie Basin are from the north shore of Lake
1063 Superior. For additional dates see Cannon et al. (2010). The date from the Hemlock Formation is 1064 from Schneider et al. (2002) and is from the MarqueMANUSCRIPTtte Range area on the south shore of Lake 1065 Superior.
1066 Figure 3. Block diagram, simplified from Lister et al. (1986, fig. 3A) to show possible
1067 relationships between the Paleoproterozoic stratigraphy of the Animikie and Huronian basins.
1068 Note that the Huronian Basin corresponds to a lower plate configuration, where the rift-stage is
1069 preserved. In contrast, the Animikie Basin is interpreted as an upper plate above a north-dipping
1070 detachment fault -- sediments formed during the ritt phase are absent and the preserved
1071 succession begins with sedimentary rocks formed on a passive margin (Chocolay Group = upper 1072 Huronian formations).ACCEPTED Note that in the Animikie Basin the lower plate, with its rift-filling 1073 succession was removed during separation during ocean formation. This model provides an
1074 explanation for the absence of the lower Huronian rift succession in the Animikie Basin.
50
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1075 Figure 4. Geological sketch map of the northern Great Lakes area with the southern part of the
1076 Animikie Basin displaced northwards to simulate its approximate location prior to opening of the
1077 Mid-Continent Rift. Note that the Huronian and Animikie basins (see Fig. 1) are separated by
1078 the Kapuskasing Fault Zone. The Huronian Basin is thought to represent a lower plate succession
1079 (see Fig. 5) and the Animikie Basin an upper plate. The Matachewan dike swarm northwest of
1080 the Huronian basin shows a change in direction across the K.F.Z. that may be due to dextral
1081 movement along the fault during northward compression of the Animikie Basin during
1082 emplacement of ‘foreign terranes’ during the Penokean orogeny, Regional paleocurrent patterns
1083 in the Huronian Basin are shown in simplified form by black arrows. Evidence of lateral
1084 transport of sediment near the west and east borders of the Huronian Basin may reflect uplift on
1085 bounding transform faults. Three heavy circles represent the approximate locations of mantle
1086 plumes (after Bleeker, 2004 and Ernst and Bleeker, 2010). These are thought to have been 1087 responsible for thermal elevation of a large area in theMANUSCRIPT SW part of the Superior Province. Most 1088 map symbols and abbreviations are explained in the caption to Fig. 1. Additional abbreviations:
1089 F.F.P. – Fort Francis Plume; G.P. – Grenville Province; Lo. Pl. – Lower Plate; N.F.Z. – Niagara
1090 Fault Zone; Up. Pl. – Upper Plate; Ma.P – Matachewan Plume; Mt.P. – Marathon Plume. Note
1091 that later olume activity in the same general location as the Matachewan Okume is thought to be
1092 responsible for intrusion of the Nipissing diabase suite (~2.2 Ga) in the Huronian Basin and
1093 possibly the Sennerre dyke swarm (see Fig. 6). 1094 Figure 5. CartoonACCEPTED (after Lister et al., 1986) to represent some aspects of the tectonic history of 1095 the Huronian and Animikie basins from the initiation of Huronian deposition (at approximately
1096 2.45 Ga) to intrusion of the Nipissing diabase suite at about 2.2 Ga. A. As detachment begins in
1097 both basins, related to the Matachewan plume, a rift basin succession accumulates on the lower 51
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1098 plate in the Huronian Basin and there is no sediment accumulation on what will become the
1099 Animikie Basin (upper plate). B. Following break-up a passive margin succession (upper
1100 Huronian) blankets the rift assemblage in the Huronian Basin. The same formations (Chocolay
1101 Group) are deposited on the upper plate of the Animilie Basin. C. Sedimentation ceases,
1102 possibly due to moderate uplift related to reactivation of a mantle plume near the locus of the
1103 older Matachewan plume. D. Continued thermal uplift in the Huronian Basin leads to
1104 gravitational displacement of the southern portion of the incompletely consolidated Huronian
1105 Supergroup and intrusion of the Nipissing diabase suite. The Animikie Basin is less affected by
1106 these events because it is farther removed from the thermal uplift.
1107 Figure 6. Sketch map of the eastern part of the Superior province (after Palmer et al., 2007, fig.
1108 1) to show the spatial relationships among the Nipissing diabase intrusions (shown in white) in 1109 the Huronian Basin, the Matachewan and Ungava plumeMANUSCRIPTs and associated dike swarms. On the 1110 basis of flow directions obtained from magnetic ani sotropy studies it was suggested by Palmer et
1111 al. (2007) that the Senneterre dikes and Nipissing intrusive rocks could have been derived from
1112 the Ungava plume near the NE extremity of the Superior province. An alternative interpretation
1113 of these data is that the magmatic source lay beneath and near to the Huronian Supergroup,
1114 which captured most of the magma in the form of sub-concordant intrusions and that the
1115 Senneterre dikes are a distal expression of the same magmatic pulse in the form of NE-trending
1116 dykes in the basement rocks. It is proposed that the origin of this magmatism (and the uplift held 1117 responsible for earlyACCEPTED gravitational folding of the Huronian sediments) was renewed activity at 1118 around 2.2 Ga in the same vicinity as the older Matachewan plume. Radiating dyke swarms in
1119 the area north of Lake Superior suggested slightly younger plume activity (Marathon and Fort
1120 Francis plumes of Ernst and Bleeker, 2010) in the same general region (see Fig. 8, inset). 52
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1121 Figure 7. Interpretation of the tectonic history of the Animikie Basin (modified from Schulz and
1122 Cannon, 2007) during the Penokean orogeny between about 1890 Ma and 1830 Ma, compared to
1123 events in the Huronian Basin during the same time interval. North (N) and south (S) directions
1124 are shown in part A but also apply to parts B and C. A. As ocean closure by subduction began
1125 beneath the Pembine-Wassau island arc terrane (P.-W.T.) rift deposits of the lower Huronian
1126 (L.H.) and the upper Huronian (U.H.) passive margin remained somewhat elevated under the
1127 weakening influence of a thermal plume centred in the Lake Huron area (see Fig. 6). Note
1128 northward subduction under the Animikie Basin, which may have initiated formation of back arc
1129 basins (B.A.B.) in which the Menominee Group began to accumulate before 1874 Ga, the age of
1130 volcanic rocks in the Menominee Group (Schneider et al., 2002). A similar age was obtained
1131 from the Gunflint Formation on the north side of Lake Superior (Fralick et al., 2002). B.
1132 Docking of the P.-W.T. against the passive margin in the Animikie Basin led to continuing 1133 deposition of the Menominee Group (M.G.) above theMANUSCRIPT Chocolay Group (C.G.). These rocks are 1134 not represented in the Huronian Basin, where ocean closure was probably due to southerly
1135 subduction so that back arc basins did not develop there. The Huronian Basin was subjected to a
1136 large asteroid impact at 1850 Ma. The Sudbury Impact and its widely scattered debris (Cannon et
1137 al., 2010) provide a precise time marker throughout the Great Lakes area. C. Following docking
1138 of the Marshfield terrane (M.T. of part A), foreland basin deposits of the Baraga Group (B.G.)
1139 were deposited in the Animikie Basin. A similar collision south and southeast of the Huronian
1140 outcrop belt produced a foreland basin (F.B.) whose deposits are uniquely preserved as the
1141 Whitewater GroupACCEPTED in the down-folded remnant of the impact scar known as the Sudbury
1142 structural basin. Small arrows indicate the dominant sediment transport directions. The
1143 postulated Archean terrane SE of the Huronian Basin is based on work by Dickin and McNutt
53
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1144 (1989) which suggests the presence of Archean rocks in the area southeast of the Grenville Front,
1145 and on evidence of an Archean provenance for sandstones of the Chelmsford Formation
1146 (Hemming et al., 1996). This collisional and compressive episode represents the main expression
1147 of the Penokean orogeny in the Huronian Basin and produced extensive flattening, imposed a
1148 strong cleavage, tightened pre-existing folds and produced some new ones. Note that many of the
1149 events depicted in the diagram were probably diachronous.
1150 Figure 8. The Great Stratigraphic Gap (G.S.G.) in time and space. Note that the G.S.G. occupies
1151 between about 200 and 350 Ma in the basins represented in the diagram and occurs between
1152 development of a passive margin and foredeep. One possible exception is the iron formation-
1153 bearing Menominee Group in the Animikie Basin, which may have developed in back-arc
1154 settings. The G.S.G is longest in the Huronian Basin and decreases with increasing distance from 1155 that region. The most extensive glacial deposits are MANUSCRIPTthose of the Gowganda Formation which are 1156 assumed to be approximately synchronous thoughout all the basins, Likewise the Sudbury
1157 Impact and its ejecta layer provide a time line at 1.85 Ga in the Great Lakes area. The reason for
1158 the G.S.G. is not known but its association with large scale gravitational displacement of the
1159 Huronisn Supergroup and with intrusions of the Nipissing diabase suite may indicate that uplift
1160 was associated with mantke upwelling in the Great Lakes area. B.I.F. – banded iron formation.
1161 See text for fuller discussion.
1162 Figure 9. A. Sketch map of North America at about 2.3 Ga to show the distribution of 1163 PaleoproterozoicACCEPTED basins containing glaciogenic deposits. Note that most are at or near to the 1164 margins of the western part of the Superior Province. Abbreviations for glaciated basins are as
1165 follows: AB – Animikie Basin; Ch – Chibougamau area; HB – Huronian Basin; HtB Hurwitz
54
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1166 Basin. According to Aspler et al. (2001) the Hurwitz basin was intracratonic but the others were
1167 located in areas of continental separation that resulted in opening of the Huronian Ocean in the
1168 area that became the southern margin of the Superior province. The rift-drift transition is thought
1169 to have occurred at the time of deposition of the widespread Gowganda Formation, The
1170 postulated extent of the Gowganda ice sheet is shown by the heavy dashed line and white arrows
1171 indicate the generalized direction of ice movement. Note that these glaciated basins are restricted
1172 to the western portion of the Superior province. B. The same area at about 2.0 Ga. Ocean
1173 opening has occurred round the remainder of the Superior province, producing the Trans-Hudson
1174 Ocean and the Labrador Trough. To accommodate the complex shape of the emerging Superior
1175 province the opening was probably much more complex, with fragmentation of cratonic blocks
1176 on the outside of the oceans. This great break-up event represents the second, and by far the
1177 greatest release of thermal energy in this region after the formation of Kenorland at the end of 1178 the Archean. Formation of the Huronian Ocean was MANUSCRIPT an early, more localised manifestation of the 1179 same phenomenon but closure of the Huronian Ocean did not occur until about 1850 Ma when
1180 the Penokean collisions took place and foreland basin formation occurred, bringing the Great
1181 Stratigraphic Gap to an end. Arrows show inferred movement directions of crustal blocks. C.
1182 Ocean closure and development of orogenies around the perimeter of the central ‘nucleus’ at
1183 about 1.8 Ga defined the final form of the Superior province and belatedly brought the Huronian
1184 Wilson Cycle to a close. In a sense the glaciated basins represent an abortive attempt at break-up
1185 of Kenorland that was ‘put on hold’ until it was incorporated into the more successful circum-
1186 Superior cycle inACCEPTED the events ascribed to the Penokean orogeny. Amalgamation of the cratonic
1187 blocks around the Superior province played an important role in the assembly of Laurentia.
1188 Additional abbreviations: CSB – Cape Smith Belt; NQO – New Guebec orogen; PO – Penokean
55
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1189 orogen; RG – Richmond Gulf area. Arrows show inferred direction of movement of crustal
1190 blocks.
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Research Highlights
• The detachment fault model can explain stratigraphical relations between the Huronian and Animikie Basins.
• The lengthy Huronian Wilson Cycle (600 Ma) is due to two-phase break-up of Kenorland.
• The Penokean orogeny is part of a regional event that defined the Superior province and amalgamated Laurentia.
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