Nd isotope mapping of a Pinwarian-age composite arc belt in the Quebecia terrane of the central Grenville Province, Canada

Precambrian Research 332 (2019) 105409

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Nd isotope mapping of a Pinwarian-age composite arc belt in the Quebecia terrane of the central Grenville Province, Canada Shannon Vautour, Alan Dickin

T

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School of Geography and Earth Sciences, McMaster University, Hamilton, Ontario L8S 4M1, Canada

A B S T R A C T

There continues to be confusion in the geological community concerning the ages of crustal formation and crustal accretion within the central Grenville Province of Quebec. To clarify the geological history of crustal growth in the eastern part of the Quebecia terrane, sixty new Nd isotope analyses are presented from a 60,000 km2 area northwest of Baie Comeau. Most samples yield Pinwarian Nd model ages that suggest them to be derived from juvenile oceanic arc terranes. However, two large slivers with Paleoproterozoic TDM ages attest to the existence of hidden blocks of old crust, which divide the area of juvenile Pinwarian crust into a composite arc belt of smaller accreted terranes. The old crustal blocks probably do not reach the present surface, but represent an igneous crustal protolith of younger I-type magmatism. By comparison with a Mesozoic tectonic analogue, it is proposed that accreted juvenile arc crust with attached slivers of older crust were rifted away from an active margin to the west, and translated eastwards until blocked by the previously accreted Labradoria terrane. Although the Quebecia composite arc belt consists of over 95% of Pinwarian juvenile arc crust, the age of arc accretion was post-Pinwarian. The proposed oblique nature of the accretion process may explain the lack of a major collisional orogen at that time. This paper shows the usefulness of large-scale Nd isotope mapping of Precambrian crustal terranes to clarify complex processes of crustal formation and arc accretion.

1. Introduction The Grenville Province records crustal growth on the southeast margin of Laurentia during much of the Paleo- and Mesoproterozoic, forming what Condie (2013) called the Great Proterozoic Accretionary Orogen (GPAO). Province-wide Nd isotope mapping suggested that crustal growth resulted largely from the accretion of three major juvenile arc terranes (Fig. 1), termed Makkovikia, Labradoria and Quebecia by Dickin (2000). The crustal formation ages of these accreted terranes are approximately 1.9 Ga, 1.7 Ga and 1.5 Ga respectively, and each is associated with an orogenic event, respectively the Makkovikian, Labradorian and Pinwarian orogenies. However, the Pinwarian event is the most enigmatic, because the relationship between crustal formation and orogeny is the least clear. Nd isotope mapping of the Quebecia terrane (Dickin, 2000; Dickin et al., 2010) was based on over 70 samples spread over nearly 100,000 square km. Most samples lay on an excellent Sm-Nd isochron, with a slope age of 1508 ± 47 Ma (2 sigma). Since the average (TDM) Nd model age of these samples was only ca. 50 Ma older than the isochron age, this showed that the Quebecia terrane was built of juvenile arc crust that was extracted from the mantle in a short period of time just prior to 1.51 Ga. However, the presence of a few older TDM ages in the eastern part of the Quebecia terrane raised questions about the extent of older crust within the juvenile arc terrane. Hence, the objective of the present study was to place more detailed geographical constraints on

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crustal formation ages in the eastern part of the Quebecia terrane, and specifically to test for the extent of Paleoproterozoic crustal fragments included within the juvenile Mesoproterozoic terrane. This more detailed picture should help to clarify the relationship between Pinwarian-age crustal formation and orogenic accretion. 2. The Pinwarian event The term Pinwarian was first used by Tucker and Gower (1994) to describe a ‘regionally extensive magmatic event’ based on a strong clustering of 1.47–1.5 Ga U-Pb ages in the vicinity of Pinware in SE Labrador (PW, Fig. 1). These plutons are located within the 1.7 Ga Labradoria terrane of Dickin (2000). Paradoxically, Pinwarian-age plutonism was prominent in this area because it formed highly-differentiated granitic plutons emplaced into older grey gneiss country rocks with Labradorian U-Pb ages around 1.65 Ga (Wasteneys et al., 1997). Consistent with their petrology, the younger Pinwarian plutons were shown by their Nd isotope signatures (Dickin, 2000, 2004) to be largely generated by remelting of older crust, with little new mantle-derived material added to the crust at that time. Gower (1990) noted that between the end of Labradorian activity at 1.60 Ga and the beginning of Pinwarian activity at 1.52 Ga, there was a marked hiatus of magmatism on the Laurentian margin. Gower (1996) attributed this hiatus to the establishment of a passive margin, as evidenced by ‘large tracts of undated metasedimentary gneiss flanking the

Corresponding author.

https://doi.org/10.1016/j.precamres.2019.105409 Received 14 June 2019; Received in revised form 6 August 2019; Accepted 7 August 2019 Available online 08 August 2019 0301-9268/ © 2019 Elsevier B.V. All rights reserved.

Precambrian Research 332 (2019) 105409

S. Vautour and A. Dickin

formation ages to the NE determined by Dickin and Higgins (1992). Hence, the Montauban Group was interpreted as part of the Quebecia terrane. Furthermore, the very homogenous Nd model ages over a large geographic area suggested that this was a large accreted oceanic arc. In contrast, Rivers and Corrigan (2000) suggested that the Quebecia terrane was produced by the same ensialic arc that generated the Pinwarian magmatism further east. A limited degree of support for their model came from the determination of a few older Nd model ages within the Quebecia terrane near Baie Comeau, first identified by Dickin and Higgins (1992). Ensialic arcs are notorious for magma mixing processes, typically giving rise to mixed isotopic signatures. Such a scenario was observed by Martin and Dickin (2005) on the NW side of the Quebecia terrane (asterisk in Fig. 1), where Nd model ages decrease from ca. 2.7 Ga to 1.5 Ga over a distance of ca. 70 km adjacent to the Allochthon Boundary Thrust. Samples with mixed isotopic signatures also had a characteristic petrological signature, with an abundance of quartz monzodiorite gneisses, in contrast to the TTG petrological signature of the Quebecia terrane itself, which is typical of accreted oceanic arc terranes. Notwithstanding the evidence for characteristically different Nd isotope signatures in oceanic and ensialic arcs, there was continued uncertainty in the geological community about the identity and origins of the Quebecia terrane, as evidenced in the review by Rivers et al. (2012). In a ‘crustal-formation age’ map of the Grenville Province based on Nd model ages, the Quebecia terrane was shown as dominantly 1.5–1.6 Ga in age, but in a ‘crustal age map’ of the Grenville Province, the same area was described as dominantly 1.8–1.6 Ga in age, but intruded by 1.45–1.34 Ga plutons. Similarly, on the ‘crustal age map’ of Hynes and Rivers (2010), a very large area of 1.8 – 1.6 Ga Labradorianage crust was shown traversing the whole length of the Grenville Province, with only a narrow strip of younger crust representing the Montauban arc terrane. This model was already refuted by the existing Nd isotope evidence for the Grenville Province (Dickin, 2000). However, the misunderstanding shows that more detailed isotopic work is necessary, in order to clearly demarcate areas of juvenile Pinwarian crust from older reworked Laurentian basement in the central Grenville Province. Subsequent to the publication of the above-mentioned review papers, new U-Pb dating work was carried out by Groulier et al. (2018) in a volcanic/plutonic sequence near Escoumins, in the centre of the Quebecia terrane (Fig. 1). These new data confirm a Pinwarian U-Pb age from the Saguenay area 40 km to the SW (Hébert and van Breemen, 2004; Table 1), and therefore support the large Nd isotope data set of Dickin (2000), by suggesting that the Quebecia terrane consists dominantly of juvenile Pinwarian-age crust. Similar Nd isotope mapping of crustal formation has been carried out in the US Mid-continent, where an ‘Nd line’ about 2000 km long separates Paleoproterozoic crust to the NW from juvenile Mesoproterozoic crust to the SE (van Schmus et al., 1996; Bickford et al. 2015). The crust southeast of the Nd line has an average TDM age of ca. 1.5 Ga, only slightly older than the oldest U-Pb ages of 1.48 Ga in this region (Bickford et al., 2015). Therefore, the crust in this region of the Mid-continent was attributed to accreted juvenile arc terranes that were

Fig. 1. Crustal formation map of the Grenville Province in eastern Canada, showing major accreted arc terranes of Makkovikia, Labradoria and Quebecia. Localities discussed in the text: Asterisk = ensialic arc NW of Quebecia; M = Manicouagan impact; MO = Montauban; ES = Escoumins; BC = Baie Comeau; PW = Pinware; DH = Disappointment Hill. Box = area of Fig. 2. ABT = Allochthon Boundary Thrust. Modified after Dickin (2004).

north shore of the Gulf of St Lawrence.’ While most of these rocks remain undated, the Pinwarian (1515 Ma) age of an arenite from the Wakeham Group (Fig. 1) was established by bracketing the age of deposition between an overlying lava and the youngest detrital grains in the arenite (van Breemen and Corriveau, 2005). The arenite also contained Archean, Makkovik and Labradorian-age detrital zircons. The Pinwarian event was elevated to the status of an orogeny by Gower (1996), based on the identification of widespread 1.5 Ga thermal activity in the eastern Grenville Province. For example, a 1498 Ma U-Pb age for the Disappointment Hill complex of western Newfoundland (DH, Fig. 1) was argued to date granulite facies metamorphism (Currie et al., 1992). Gower (1996) proposed that Pinwarian orogenesis was caused by the establishment of a new northward-dipping subduction zone on the Laurentian margin, forming an Andean-type continental margin arc. This model was based on U-Pb dating evidence for scattered 1.46–1.52 Ga plutonism over large areas of Labradorian crust in the eastern Grenville Province (Gower and Krogh, 2002). These authors noted that Pinwarian plutonism in the foreland had sub-alkaline chemistry typical of an Andean-type arc, and that calc-alkaline plutons were lacking. However, exactly the latter type of magmatism was found further to the west, where Dickin and Higgins (1992) found a huge area of TTG-type (tonalite-trondhjemite-granodiorite) grey gneisses (subsequently named Quebecia) with generally homogeneous Nd model ages averaging 1.55 Ga. 3. The Quebecia terrane Within the Quebecia terrane of Dickin (2000), most rocks are at upper amphibolite or granulite facies metamorphic grade. However, a small segment of lower metamorphic grade is seen in the Montauban area west of Quebec City (MO, Fig. 1). This area contains a volcanic sequence whose geochemistry was studied by MacLean et al. (1982). Using immobile trace elements, they suggested that the probable environment of formation was an oceanic arc. U-Pb dating of a lapilli tuff within this sequence gave an age of 1.45 Ga (Nadeau and van Breemen, 1994). Hence, Corrigan and van Breemen (1997) interpreted the Montauban succession as an island arc terrane that was accreted to Laurentia shortly before the establishment of a long-lived (Elzevirian) ensialic arc, which formed the nearby 1.4–1.37 Ga La Bostonnais plutonic complex. Dickin (2000) obtained TDM model ages for the Montauban Group that were identical to the large area of Mesoproterozoic crustal

Table 1 Pinwarian U-Pb ages outside the Labradoria terrane. Manicouagan region 1510 ± 7 Ma, Gobeil et al. (1996), mafic pegmatite, Hart Jaune terrane 1497 ± 5 Ma, Augland et al. (2015), Bardoux plutonic suite, Berthe terrane Quebecia terrane 1506 ± 13 Ma, Hebert & van Breemen (2004), Cap de la Mer amphibolite, Saguenay 1502 ± 6 Ma, Groulier et al. (2018), Tadoussac granodiorite, Tadoussac 1492 ± 3 Ma, Groulier et al. (2018), Moulin-a-Baude dacitic tuff, Escoumins Mesoproterozoic terrane, Newfoundland 1498 ± 8 Ma, Currie et al. (1992), Disappointment Hill complex, NFL 1466 ± 10 Ma, Heaman et al. (2002), Western Brook Pond, NFL

2

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S. Vautour and A. Dickin

Ancaster, Ontario, using Li-borate fusion ICP optical emission analysis. The accuracy of their data were ensured by the inclusion of international standards as part of the analytical protocol. The average difference between recommended and measured values for ten major elements from five standards was 0.12 wt%.

remelted ca. 30 Ma later to produce the A-type granite-rhyolite suite seen at the surface. In the granite-rhyolite terranes of the Mid-continent, there is very little evidence for any older Nd model ages southeast of the Nd line (Bickford et al., 2015). In comparison, the discovery of Paleoproterozoic TDM ages in the Quebecia terrane northwest of Baie Comeau (Dickin and Higgins, 1992) can be considered anomalous. Therefore, the objective of the present work was to carry out more detailed Nd isotope mapping in this region to explore the distribution of these older ages, and hence determine their origins.

5. Nd isotope results Nd isotope data are presented in Table 2, where they are used to calculate TDM ages using the model of DePaolo (1981). The model age data fall into two main age groups, averaging ca. 1.53 and 1.84 Ga that were previously seen in the study of Dickin and Higgins (1992). These age groups are shown in Fig. 2 by solid squares and open circles respectively, where numbered samples represent new data in Table 2, while published data are un-numbered. The two age suites are attributed to major episodes of crustal formation that correspond to U-Pbdated Pinwarian and Makkovikian (pre-Labradorian) magmatic episodes (Gower and Krogh, 2002). A small group of intermediate Labradorian model ages (1.65–1.79 Ga) was also found (open diamonds). Based on the data presented in Fig. 2, most of the Quebecia terrane in the study area appears to be of Pinwarian crustal formation age, but two elongate crustal fragments have Paleoproterozoic crustal formation ages (referred to here as the Labrieville and Loup Marin blocks). These elongate Paleoproterozoic blocks divide the Quebecia terrene into three large segments, consisting of the main Quebecia terrane to the NW and two smaller segments referred to here as Quebecia East and the Baie Comeau terrane. The latter terrane is more isotopically heterogeneous than the other two terranes (authors’ unpublished data). This area includes additional small fragments of old crust in the immediate vicinity of Baie Comeau, exemplified by two published data points in Fig. 2. Other than three samples that define the edge of the Loup Marin block (# 37–39), the data from this area are not included in the present paper because more detailed work is still in progress. The boundary between the Pinwarian arc terranes and the Paleoproterozoic Berthe terrane to the north is based on the extent of the Plus Value Complex (Moukhsil et al., 2012). This is a paragneiss unit with metagreywacke, metapelite and quartzite lithologies that covers large areas of the Berthe terrane and is thought to be a passive margin supracrustal suite whose depositional age slightly predates the Pinwarian event (Lasalle et al., 2013; Augland et al., 2015). However, small areas of similar lithologies are also found further south within the northern parts of the Quebecia terranes. Therefore, constraints on the Berthe – Quebecia terrane boundary also come from isotopic data. These comprise new Nd data in Table 2, along with published Nd model age data (Dickin and Higgins 1992; Dickin, 2000; Thomson et al., 2011). Additional constraints come from Hf isotope data (Augland et al., 2015), shown by red symbols in Fig. 2. The symbols indicate approximate Hf model ages (Augland et al., 2015; Turlin et al., 2019) based on typical crustal Lu/Hf ratios. Within the Hf data suite, the Okaopeo mangerite and the Bardoux garnet-biotite granite yield Hf model ages of 1.9–2 Ga (red rings), consistent with published Nd model ages for the Berthe terrane (Thomson et al., 2011). On the other hand, the Hulot tonalitic gneiss to the east (red square) yields Hf model ages of 1.5–1.6 Ga, consistent with most of Quebecia. Two samples further south yield intermediate Hf model ages (red diamonds). These may be indicative of small vestiges of Paleoproterozoic crust similar to the Labrieville block within the crustal sources of younger granitoid magmatism. In order to understand the isotopic relationships between our analysed sample suites, they are plotted on the Sm-Nd isochron diagram in Fig. 3. In this diagram, the new data in Table 2 are compared with published Nd data for the Quebecia terrane, subdivided into the main segment and an eastern segment along the line of the Paleoproterozoic Labrieville sliver in Fig. 2. The published data for these two suites are completely colinear, whereas the new Pinwarian data show slightly

4. Sampling and analytical methods Reconnaissance sampling was undertaken over a large region ca. 300 km × 200 km in size to the NW of Baie Comeau (Fig. 1). This region is located within the Hinterland of the Central Grenville Province (Indares and Moukhsil, 2013) to the south of the Allochthon Boundary Thrust (ABT). Since the objective was to determine the formation age of the crust as a whole, sampling was targeted at granitoid orthogneisses of intermediate composition that are believed to form by anatexis of more mafic arc crust. Previous studies (Dickin, 2018) have shown that granitoids of this type, formed above subduction zones, have Nd isotope signatures that are relatively consistent and predictable, allowing reliable estimates to be determined of the formation-age of the crust using the depleted mantle model of DePaolo (1981). As far as possible, samples consisted of homogeneous, medium- to coarse-grained gneisses showing textural evidence of a plutonic protolith, with a minimum degree of migmatization. Both mafic gneisses and gneisses with possible sedimentary provenance were excluded, the former because of the possibility of mixing with a younger mantle-derived component, the latter because of uncertain sedimentary provenance. The sample suite ranges from amphibolite-facies to granulitefacies metamorphic grade (Table 2). However, samples in the granulitefacies show no consistent deviation in Nd model ages from amphibolitefacies rocks, as previously shown by Zelek and Dickin (2013). On average, 1 kg of rock was crushed, after the removal of any weathered, veined or migmatized material, and careful attention was given to obtain a fine powder that was representative of the whole rock. In any given outcrop, the material sampled was, as far as possible, the oldest meta-plutonic material in the outcrop, ignoring post-tectonic intrusions but also ignoring material that was clearly xenolithic. Petrological affinities discussed below attest to our success in sampling only a narrow range of rock-types in a uniform manner across the whole study area. However, in the vicinity of the Labrieville block (see below), samples with a wider range of petrology were collected because of the need to sample at particular locations in order to define the boundary between juvenile Pinwarian-age crust and old Paleoproterozoic crust. Sm-Nd analysis followed our established procedures. After dissolution in Savillex pressure vessels for four days in HF and HNO3, samples were split and one aliquot spiked with a mixed 150Nd-149Sm spike. Analysis by this technique yielded Sm/Nd = 0.2280 ± 2 for BCR-1, in agreement with Thirlwall (1982). Measured Nd blanks were around 0.1 ng, which is negligible relative to the smallest processed sample size of 1 μg Nd. Standard cation and reverse phase column separation methods were used. Nd isotope analyses were performed on a VG isomass 354 mass spectrometer at McMaster University using double filaments and a 4 collector peak switching algorithm, and were normalised to a 146Nd/144Nd ratio of 0.7219. Average within-run precision on the samples was ± 0.000012 (2 sigma), and an average value of 0.51185 ± 2 (2 sigma population) was determined for the La Jolla standard during this work. The reproducibility of 147Sm/144Nd and 143 Nd/144Nd is estimated at 0.1% and 0.002% (1 sigma) respectively, leading to an average uncertainty on each model age of ± 20 Ma (2 sigma), based on empirical experience over several years of analysing duplicate dissolutions. Major element analyses were performed by Activation Laboratories, 3

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Table 2 Nd isotope data for the Quebecia terrane (Metamorphic facies: A = amphibolite; G = granulite). Map#

Sample

Easting Zone 19

Northing NAD 1983

Nd ppm

Sm ppm

Sm147 Nd144

Nd143 Nd144

Tdm Ga

Metam facies

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Quebecia ME 7 PD 8 PD 5 PD 3 BE 8 BE2 BE4 BE6 BE 9 BE15 BE14 FV24 FV20 FV19 FA 7 PI11 PI10 MV10 MV20 PI32 PI 1 PI33

385,940 395,530 393,430 390,610 433,332 437,005 443,006 438,608 436,679 464,240 472,420 449,018 439,660 440,430 363,500 411,169 415,227 405,370 410,660 426,340 437,315 448,510

5,589,950 5,573,390 5,558,750 5,544,250 5,554,421 5,544,474 5,559,923 5,561,333 5,535,508 5,557,950 5,537,980 5,514,007 5,499,750 5,496,410 5,459,000 5,474,428 5,470,693 5,414,520 5,436,910 5,440,750 5,455,428 5,460,560

83.2 117.7 29.8 19.8 41.3 53.4 39.4 42.3 24.3 45.0 10.5 80.1 25.2 48.4 50.8 52.0 40.1 32.70 36.70 40.6 36.1 74.5

11.38 23.70 6.13 3.91 4.90 10.53 8.31 9.81 5.05 9.29 2.07 16.45 5.76 10.57 10.13 11.56 8.25 7.26 6.85 8.83 6.80 14.40

0.0827 0.1217 0.1243 0.1192 0.0717 0.1193 0.1273 0.1402 0.1258 0.1249 0.1192 0.1242 0.1383 0.1319 0.1206 0.1345 0.1243 0.1343 0.1127 0.1315 0.1139 0.1167

0.511688 0.512179 0.512116 0.512120 0.511758 0.512076 0.512161 0.512263 0.512128 0.512130 0.512160 0.512076 0.512269 0.512170 0.512107 0.512263 0.512118 0.512229 0.512117 0.512209 0.512052 0.512123 av

1.57 1.43 1.58 1.49 1.38 1.56 1.54 1.61 1.58 1.57 1.42 1.64 1.56 1.62 1.53 1.50 1.57 1.56 1.40 1.54 1.51 1.44 1.53

A G G G A G

23 24 25 26 27 28 29 30 31 32 33 34 35 36

QuebeciaE PI25 PI24 FV40 FV41 BE 11 BE 10 BC66 BC62 SV53 SV52 SV50 SV47 SV48 SV43

445,278 446,868 463,281 464,567 470,360 481,570 491,720 500,260 533,610 533,720 532,990 558,410 564,890 555,290

5,436,567 5,430,992 5,453,423 5,452,464 5,523,920 5,514,380 5,502,230 5,495,860 5,524,100 5,518,590 5,513,000 5,526,420 5,527,470 5,514,170

10.8 46.3 47.9 74.3 75.2 8.2 85.7 27.6 50.3 103.4 98.6 30.7 33.7 32.6

1.79 9.09 9.01 13.24 14.03 1.89 15.34 5.92 11.08 19.13 16.90 6.26 6.55 6.50

0.1005 0.1185 0.1138 0.1078 0.1127 0.1389 0.1082 0.1298 0.1332 0.1119 0.1036 0.1232 0.1176 0.1204

0.511903 0.512104 0.511965 0.511919 0.512031 0.512278 0.512027 0.512204 0.512230 0.512025 0.511973 0.512137 0.512103 0.512120 av

1.53 1.50 1.64 1.61 1.53 1.55 1.47 1.52 1.52 1.52 1.48 1.52 1.49 1.51 1.53

A A

37 38 39

BC terrane FV6 MX22 SV38

472,460 552,560 573,400

5,445,900 5,486,628 5,492,640

24.0 24.2 22.0

4.33 5.98 3.29

0.1089 0.1495 0.0902

0.511951 0.512389 0.511728

1.59 1.55 1.62

A A A

40 41 42 43 44 45 46 47 48 49 50 51

Labrieville BE13 BE12 FV23 FV21 FV17 FV16 FV15 FV14 FV13 FV11 FV10 PI28

472,770 467,130 448,038 448,602 441,580 444,970 446,980 449,600 451,030 457,490 461,860 443,689

5,533,370 5,527,060 5,508,638 5,500,027 5,494,580 5,491,210 5,487,460 5,484,110 5,481,450 5,468,000 5,458,480 5,451,490

66.6 26.2 24.4 43.6 37.3 54.5 44.9 47.5 41.0 43.8 35.3 24.3

13.85 5.14 5.61 10.07 6.50 11.60 9.28 10.93 8.05 8.58 7.06 5.45

0.1257 0.1187 0.1387 0.1395 0.1053 0.1288 0.1248 0.1390 0.1187 0.1184 0.1210 0.1352

0.512018 0.511914 0.512058 0.512138 0.511713 0.512049 0.512013 0.512159 0.511888 0.511843 0.511912 0.512121 av

1.78 1.81 1.99 1.86 1.87 1.78 1.76 1.80 1.85 1.92 1.86 1.79 1.84

A A A G A A G G G G G

52 53 54 55 56 57 58 59 60 61 62 63

LoupMarin FV34 BC45 BC43 BC41 BC38 BC37 BC36 BC35 BC34 BC32 MX23 SV39

467,118 502,240 503,090 507,740 512,800 512,940 513,300 515,000 516,280 518,060 554,025 571,680

5,450,520 5,484,700 5,477,350 5,474,930 5,472,500 5,470,020 5,469,120 5,466,270 5,465,350 5,463,110 5,489,780 5,496,260

34.9 49.5 56.2 46.1 51.0 53.1 49.2 73.6 30.5 54.7 28.4 31.0

6.08 9.79 10.81 8.93 9.79 10.37 9.20 15.62 5.87 10.70 6.20 6.52

0.1052 0.1196 0.1163 0.1170 0.1160 0.1181 0.1130 0.1284 0.1163 0.1183 0.1319 0.1273

0.511758 0.511879 0.511811 0.511874 0.511834 0.511897 0.511856 0.512045 0.511909 0.511878 0.512047 0.511977

1.80 1.88 1.93 1.84 1.88 1.82 1.79 1.78 1.77 1.86 1.84 1.88

G G A A

MA67 (pub)

529,700

5,493,700

42.2

8.56

0.1226

0.511925

1.87

Q

P

110 173 111 35 196 179 143 115 110 138 152 243

−51 −3 −151 −272 −38 −18 −40 −75 −65 −31 −39 −76

152 162 161 149 141 162 162 168 157

−37 −13 −15 −15 −65 −46 −25 −54 −46

168

−70

G A A G A G G G G G G A G

A A A A A G A A A A A

G A G

A

(continued on next page) 4

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Table 2 (continued) Map#

Sample

Easting Zone 19

Northing NAD 1983

Nd ppm

Sm ppm

Sm147 Nd144

Nd143 Nd144

Tdm Ga

MA58.1 (pub) MA42.7 (pub)

532,600 536,300

5,486,700 5,475,300

49.2 14.9

9.50 3.11

0.1168 0.1257

0.511791 0.511960 av

1.97 1.87 1.85

Metam facies

Q

P

167 182

−28 −95

Fig. 2. Map of the region between Baie Comeau and Manicouagan, showing the extent of juvenile Pinwarian crust (green) relative to older Paleoproterozoic crustal blocks (yellow, orange) based on new and published Nd isotope data (black symbols) and published Hf isotope data (red symbols). ABT = Allochthon Boundary Thrust. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

6. Lithochemistry

more scatter, possibly because samples were collected with less typical TTG petrology in order to achieve specific geographical coverage. Distinct from these juvenile Pinwarian suites, the Labrieville and Loup Marin blocks have Nd signatures that are colinear with the Paleoproterozoic Berthe terrane to the north, and also with the Paleoproterozoic Barilia terrane of Ontario and western Quebec (Dickin et al., 2008, 2012, 2014). In addition to the published Hf isotope evidence discussed above, Nd isotope data for Pinwarian rocks from Escoumins (Groulier et al., 2018) provide additional constraints on the meaning of the Nd isotope data in Fig. 3. In rocks with Pinwarian U-Pb ages, TDM model ages range from 1.41 in a gabbro-norite to 1.94 Ga in the Escoumins dacitic tuff (plotted in Fig. 3). This suggests that Pinwarian magmatism at Escoumins sampled a range of sources with different crustal residence ages, some juvenile Pinwarian or post-Pinwarian, and others representing an old Paleoproterozoic source similar to the Berthe Terrane. It is likewise suggested that the Paleoproterozoic TDM ages in the Labrieville and Loup Marin blocks represent ancient crustal sources at depth, sampled by Pinwarian or post-Pinwarian magmatism. To obtain additional clues about the nature of these crustal sources, the petrological and geochemical signatures of analysed samples will now be examined.

To categorise their petrological affinity, most samples with Paleoproterozoic Nd model ages were analysed for major elements and selected trace elements (Table 3, Supplementary data). Their petrology and chemistry will be compared with published data for Paleoproterozoic crust from the Berthe terrane south of Manicouagan, along with published data for Juvenile Pinwarian samples (Dickin and Higgins 1992; Dickin, 2000), and with the Bardoux granite and Escoumins felsic tuff discussed above. Samples are characterized in Fig. 4 using the petrochemical Streckeisen grid of Debon and LeFort (1983). This plot aims to describe the petrological affinity of each sample using their Q (quartz) and P (plagioclase vs. K-feldspar) values. Published data for Quebecia and the Berthe terrane (open symbols) are almost entirely confined to the top half of the diagram, equivalent to the tonalite-trondhjemite-granodiorite (TTG) suite, with a small tail from tonalite to diorite. This distribution is characteristic of juvenile oceanic arc terranes with relatively thin crust, in comparison with ensialic arcs that typically tend across the middle of the diagram, with a concentration in the quartzmonzodiorite field (as proposed by Martin and Dickin, 2005). New samples from the Labrieville block (yellow), and the Loup Marin block (orange) are much more concentrated in the monzogranite to granite fields. The composition of the dated Bardoux granite

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Fig. 5. R1 – R2 diagram of Bachelor and Bowden (1985) to discriminate primitive and more mature arc settings of granitoid magmas.

Fig. 3. Sm-Nd isochron diagram showing new data for Pinwarian-age and Paleoproterozoic sample suites relative to references lines based on published data (for references, see text).

crustal sources are carried out in Fig. 5, using the major element discriminant of Bachelor and Bowden (1985). The index R2 [6Ca + 2 Mg + Al] is plotted against R1 [4Si–11(Na + K)–2(Fe + Ti)] in order to discriminate mature arcs (late orogenic) from primitive arcs (pre-collisional). There is significant overlap between the different suites, but rocks with juvenile Pinwarian Nd signatures are more primitive on average than those derived from an old crustal source. This suggests that juvenile magmas were derived from melting of relatively more mafic Pinwarian arc crust, compared with those derived from more felsic (alkali-rich) Paleoproterozoic crustal fragments. In order to test for sedimentary material in the granitoid magma source, new and published samples are plotted in a diagram of metaluminous/peraluminous affinity (Fig. 6), following Augland et al. (2015). On this plot most samples fall within the I-type field of Chappell and White (1974), including all samples from the Labrieville and Loup Marin blocks. This shows that the Paleoproterozoic TDM ages of these samples are not due to addition of sediment to the source, but are attributable to melting of remnants of older igneous continental crust. The Bardoux granite and Escoumins dacitic tuff plot in the same area, again suggesting that sedimentary sources were not a significant contributor to the Paleoproterozoic isotope signatures in these rocks. To further compare the geochemistry of samples with Paleoproterozoic versus juvenile Pinwarian TDM ages, samples are plotted on a bivariate plot of Zr versus Y concentrations in parts per million (Fig. 7). The higher Zr content in samples derived from old crust, relative to juvenile Pinwarian crust (green regression), is consistent with the old crustal sources being more differentiated than the relatively mafic arc crust that typically melts to produce granitoid rocks in oceanic arcs.

Fig. 4. Q-P diagram of Debon and LeFort (1983) which generates an empirical Streckeisen diagram. TN, tonalite; GD, granodiorite; MG, monzogranite; GR, granite; QD, quartz diorite; QMD, quartz monzodiorite; DI, diorite. B = Bardoux granite; E = Escoumins tuff.

7. Discussion: Quebecia composite arc model

(Augland et al., 2015) and the Escoumins dacitic tuff (Groulier et al., 2018) are shown for comparison. Augland et al. suggested that the Bardoux granite was produced by ensialic arc magmatism, which is consistent with an origin by melting of old crustal material. Hence, it is inferred that samples in the Labrieville and Loup Marin block were generated by melting of Paleoproterozoic crustal material, during Pinwarian or post-Pinwarian magmatism. Further exploration of the results of melting juvenile versus old

The model age signatures of the Quebecia and Quebecia East terranes in Figs. 2 and 3 are typical of accreted arc terranes, with a tight clustering of TDM ages within each block or terrane, sharp boundaries between units with different crustal extraction ages, and a lack of any trend of model ages with distance across each terrane. This signature contrasts strongly with the correlated variation of TDM age against distance demonstrated by Martin and Dickin (2005) and Zelek and 6

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terranes separated by the elongate Labrieville and Loup Marin blocks, it is suggested here that Quebecia represents a composite arc belt of the type previously invoked for the Central Metasedimentary Belt (CMB) in Ontario (e.g. Carr et al., 2000). However, the CMB shows several geological features that are not typical of accreted arc terranes. These features include firstly the vast thicknesses of marble in the CMB; secondly the relatively small size of the proposed CMB arc terranes (less than 50 km wide and 100 km long); and thirdly the rift-like chemistry of the CMB mafic rocks (e.g. Holm et al., 1985; Smith and Holm, 1987). Therefore, the geology of the CMB is better attributed to an aulacogen that was subject to later calc-alkaline magmatism (Baer, 1976). This model is supported by Nd isotope mapping (Dickin and McNutt, 2007; Dickin et al., 2016) which shows that the shape of the juvenile crustal zone is explained as a failed back-arc rift with an en echelon series of juvenile crustal segments. In contrast to the aberrant features of the so-called ‘composite arc belt’ in Ontario, the crustal terranes that comprise Quebecia are typical of accreted oceanic arcs. They have the large sizes typical of accreted arc fragments, the mafic rocks have largely calc-alkaline chemistry (MacLean et al., 1982; Groulier et al., 2018), and there is little carbonate material. On the other hand, it remains to explain the origin of the Paleoproterozoic crustal slivers sandwiched between the juvenile arc fragments. To explore this question, Pinwarian tectonic processes in the Grenville Province may be modeled by comparison with Mesozoic tectonic processes in the Sumatra region of Southeast Asia. Like Laurentia, this is a complex assembly of crustal terranes and volcanic arcs with tectonic boundaries between them. West Sumatra is an elongate terrane mostly of Carboniferous age, bounded to the northeast by Permo-Carboniferous units of East Sumatra and to the southwest by the Mesozoic Woyla terrane (Fig. 8). The boundary between West Sumatra and East Sumatra is represented by the Medial Sumatra Tectonic Zone (MSTZ). This 10-km wide shear zone is marked by highly deformed rocks including schists and gneisses, and is believed to be the locus of translation of West Sumatra relative to East Sumatra. It is suggested that West Sumatra moved over 1000 km westwards from an original location at the southeastern extremity of Sundaland (part of Cathaysia) by strike-slip motion along the MSTZ (Barber et al., 2005). The terranes of Quebecia and Quebecia East are comparable in size to East and West Sumatra, while the MSTZ is approximately the same width as the Labrieville sliver. Hence, the Quebecia East terrane, with its attached Labrieville crustal block, is proposed to be a displaced terrane of the Pinwarian continental margin that was torn away from its original location by rifting and transcurrent motion. Although the nearest possible point of origin for the Labrieville block is from the Berthe terrane to the NE, an examination of Figs. 1 and 2 shows that

Fig. 6. Plot of molar % Al2O3/(Na2O + K2O) versus Al2O3/ (CaO + Na2O + K2O) to test for igneous versus sedimentary protolith in crustal granitoids.

Fig. 7. Bivariate trace element plot for new Quebecia samples compared with published suites from the study area. Dashed green line = regression for published Quebecia data. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Dickin (2013) in the area NW of Lac St Jean, which was attributed to the establishment of an ensialic arc on the edge of the Laurentian continent. Hence, the isotopic evidence continues to support the genesis of Quebecia as one or more accreted oceanic arc terranes. However, the elongate shapes of the Labrieville and Loup Marin blocks suggest that these represent slivers of an old continental margin that were incorporated between the segments of juvenile accreted arc. This might have occurred if fragments of old crust were rifted away from Laurentia by back-arc spreading, and then incorporated into more juvenile arc terranes. A modern analogue might be the Japanese arc (Hynes, 2010). Based on the division of Pinwarian-age crust in Fig. 2 into major

Fig. 8. Paleogeographic map of SE Asia in the Early Triassic. MSTZ = Medial Sumatra Tectonic Zone. (After Barber et al., 2005). 7

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somewhat more reworked by the 1.3–1.4 Ga Elzevirian ensialic arc. The data in Fig. 9 show that the Muskoka and Nobel domains of Ontario (Dickin et al., 2017) have a very similar Pinwarian model age distribution. Except for a few samples, they have a firm upper TDM age limit of 1.65 Ga, and a tail down to 1.4 Ga attributed to crustal reworking. This suggests that allochthonous crust in Ontario is equivalent to the Quebecia terrane to the east. In contrast, samples from the US Mid-continent southeast of the Nd-line of van Schmus et al. (1996) have a younger TDM age distribution (Bickford et al., 2015). These data have a firm upper bound at 1.55 Ga and a tail down to 1.3 Ga (Fig. 9), around 100 Ma younger than the Quebecia terrane. This suggests that juvenile crust of the US Mid-Continent was accreted from a younger ‘harvesting’ and accretion of oceanic arcs than the Quebecia composite arc belt in Canada. 8. Pinwarian orogenic model Based on similar published U-Pb ages for granitoid magmatism in the Quebecia terrane and in the Pinwarian ensialic arc on the Laurentian foreland, it appears that Pinwarian magmatism was occurring simultaneously above a north-dipping subduction zone under Laurentia and in a 1.5 Ga juvenile offshore arc. However, the Pinwarian orogeny appears to be associated with the continental margin arc (Fig. 10a), rather than with the accretion of the Pinwarian-age juvenile arc terranes. For example, it has been suggested that north-dipping subduction under the Pinwarian ensialic arc led to back-arc rifting at different points along the Laurentian margin, and that the closure of these back-arc basins led to deformation and/or metamorphism that is recognised as the Pinwarian event. This has been invoked within the Wakeham terrane of Eastern Quebec (Rivers and Corrigan, 2000) and the Canyon domain at Manicouagan (Maity and Indares, 2018). In contrast, accretion of juvenile Pinwarian crust at Montauban and Escoumins has been inferred to be a later collisional event, occurring around 1.39 Ga (Sappin et al., 2009; Groulier et al., 2018). The fact that these later arc accretion events did not lead to a major orogeny remains a mystery. However, the lack of a major orogenic event is also evidenced by the preservation of the Plus Value Complex in the Berthe terrane. It has already been established that the Pinwarian event was caused by north-dipping subduction. Therefore, the attempt to subduct a Pinwarian oceanic arc under the Laurentian margin should have caused uplift and erosion of the margin. Since the preservation of the Plus Value Complex suggests that uplift of the margin was limited, we suggest that southward subduction under the Pinwarian oceanic arc led to two subduction zones dipping in opposite directions (Fig. 10b), as seen in the modern Molucca Sea (Simandjuntak and Barber, 1996). The resulting collision (Fig. 10c) could have resulted in relatively little uplift of the Laurentian margin. The lack of major deformation on the suture boundary during (postPinwarian) arc accretion also suggests that the collision was probably oblique, involving substantial transcurrent motion. This can then explain the incorporation of composite arcs that were rifted away from the margin by back arc spreading behind the north-dipping subduction zone. A rifted arc with an attached Paleoproterozoic crustal sliver (Fig. 10d) was probably transported eastwards along the margin until its passage was blocked by the Labradoria terrane that had been accreted to Laurentia nearly 200 Ma earlier. The composite arc was reaccreted there (Fig. 10e), followed by further ensialic arc magmatism. The latter steps were probably repeated more than once, forming a composite arc belt of Pinwarian terranes in the Central Grenville Province (Fig. 2).

Fig. 9. Plot of TDM model ages in Grenville gneisses and rocks from the US Mid-continent as a function of E-W distance. Thick lines represent regressions of age data in each composite terrane. Symbols as in Fig. 3, but also: pale green squares = Quebecia West (Zelek and Dickin, 2013); open squares = Muskoka and Noble domains of Ontario (Dickin et al., 2017); crosses = US juvenile Mesoproterozoic crust (Bickford et al., 2015). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

westward transport of the Labrieville block and Quebecia E from the Berthe terrane is unlikely, due to the presence of the previously accreted Labradoria terrane immediately to the east. There is no evidence that this Labradorian crust was not in approximately its present configuration relative to Laurentia during the Mesoproterozoic. To explore an alterative source for the Labrieville block, crustal formation age data for the Grenville Province are plotted in Fig. 9 as a function of E-W distance. The range of TDM ages for the Labrieville and Loup Marin blocks shows that these cannot be derived from the Labradoria terrane to the east, which has a younger crustal formation age. However, the Barilia terrane to the west has the appropriate TDM age signature to be the source area for these old crustal blocks. Barilia itself probably had an origin very similar to the Berthe terrane, by accretion of a ca. 1.9 Ga oceanic arc to Laurentia during the Penokean orogeny (Dickin and McNutt, 1989). Like the Berthe terrane, the Barilia terrane was reworked by a Labradorian age ensialic arc that was established on the older composite margin, largely obscuring the original 1.85–1.9 Ga crustal formation ages of these terranes (Dickin et al., 2008). Therefore, we propose that Quebecia East was originally accreted at the western end of the Pinwarian continental margin, but was rifted away from this location by back-arc spreading, taking with it a sliver of Paleoproterozoic Laurentian crust that formed the Labrieville block. We attribute the Baie Comeau terrane to a similar process that tore away a fragment of Paleoproterozoic Laurentian crust to form the Loup Marin block. However, our unpublished data for the Baie Comeau terrane suggests that this has significantly more isotopic heterogeneity than the Quebecia or Quebecia East terranes. Therefore, we conjecture that the Baie Comeau terrane may be a fragment of an ensialic arc similar to that observed NW of Lac St Jean. This was probably also transported eastwards along the margin until its motion was blocked by Labradoria. The data in Fig. 9 also provide evidence that defines the westward limit of the Quebecia composite arc belt. It was previously suggested by Zelek and Dickin (2013) that crust to the west of Montauban (Fig. 1) consists of Pinwarian crust similar to the main Quebecia terrane, but

9. Implications for Precambrian terrane mapping This paper is an example of the successful integration of large-scale Nd isotope mapping with (published) detailed-scale U-Pb geochronology. As summarized in the introduction, U-Pb dating of specific 8

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involved in successive arc accretion events that formed the Precambrian Shield of North America. Acknowledgements We appreciate constructive criticism from Journal Editor Victoria Pease and from Pat Bickford and an anonymous reviewer that helped to improve this paper. We acknowledge McMaster University for scholarship support and we thank Lisa Slaman and Stephanie Kimmerle for assistance in the field. References Augland, L.E., Moukhsil, A., Solgadi, F., Indares, A., 2015. Pinwarian to Grenvillian magmatic evolution in the central Grenville Province: new constraints from ID–TIMS U-Pb ages and coupled Lu–Hf S–MC–ICP–MS data. Can. J. Earth Sci. 52, 701–721. Baer, A.J., 1976. The Grenville Province in Helikian times: a possible model of evolution. Philos. Trans. R. Soc. Lond. 280, 499–515. Bachelor, R.A., Bowden, P., 1985. Petrogenetic interpretation of granitoid rock series using multi-cationic parameters. Chem. Geol. 48, 43–55. Barber, A.J., Crow, M.J., Milsom, J.S., 2005. Sumatra: Geology, Resources and Tectonic Evolution. Geological Society Memoir no 31. Bickford, M.E., Van Schmus, W.R., Karlstrom, K.E., Mueller, P.A., Kamenov, G.D., 2015. Mesoproterozoic-trans-Laurentian magmatism: A synthesis of continent-wide age distributions, new SIMS U-Pb ages, zircon saturation temperatures, and Hf and Nd isotopic compositions. Precambr. Res. 265, 286–312. Carr, S.D., Easton, R.M., Jamieson, R.A., Culshaw, N.G., 2000. Geologic transect across the Grenville orogeny of Ontario and New York. Can. J. Earth Sci. 37, 193–216. Chappell, B.W., White, A.J.R., 1974. Two Contrast. Granite Types Pacific Geol. 8, 173–174. Condie, K.C., 2013. Preservation and recycling of crust during accretionary and collisional phases of Proterozoic orogens: A bumpy road from Nuna to Rodinia. Geosciences 3, 240–261. Corrigan, D., van Breemen, O., 1997. U-Pb age constraints for the lithotectonic evolution of the Grenville Province along the Mauricie transect, Quebec. Can. J. Earth Sci. 34, 299–316. Currie, K.L., Van Breemen, O., Hunt, P.A. and Van Berkel, J.T., 1992. Age of high-grade gneisses south of Grand Lake, Newfoundland. Debon, F., LeFort, P., 1983. A chemical-mineralogical classification of common plutonic rocks and associations. Trans. R. Soc. Edinb. Earth Sci. 73, 135–149. DePaolo, D.J., 1981. Neodymium isotopes in the Colorado Front Range and crust –mantle evolution in the Proterozoic. Nature 291, 193–197. Dickin, A.P., 2000. Crustal formation in the Grenville Province: Nd isotope evidence. Can. J. Earth Sci. 37, 165–181. Dickin, A.P., 2018. Radiogenic Isotope Geology, third ed. Cambridge University Press. Dickin, A.P., 2004. Mesoproterozoic and Paleoproterozoic crustal growth in the eastern Grenville Province: Nd isotope evidence from the Long Range inlier of the Appalachian orogen. In: Tollo, R.P., Corriveau, L., McLelland, J.M., Bartholomew, M.J. (Eds.), Proterozoic tectonic evolution of the Grenville orogen in North America. Geological Society of America Memoir 197, pp. 495–503. Dickin, A.P., Cooper, D., Guo, A., Hutton, C., Martin, C., Sharma, K.N.M., Zelek, M., 2012. Nd isotope mapping of the Lac Dumoine thrust sheet: implications for large scale crustal structure in the SW Grenville Province. Terra Nova 24, 363–372. Dickin, A.P., Herrell, M., Moore, E., Cooper, D., Pearson, S., 2014. Nd isotope mapping of allochthonous Grenvillian klippen: evidence for widespread ‘ramp-flat’ thrust geometry in the SW Grenville Province. Precambr. Res. 246, 268–280. Dickin, A.P., Higgins, M., 1992. Sm/Nd evidence for a major 1.5 Ga crust-forming event in the central Grenville province. Geology 20, 137–140. Dickin, A., Hynes, E., Strong, J., Wisborg, M., 2016. Testing a back-arc ‘aulacogen’model for the Central Metasedimentary Belt of the Grenville Province. Geol. Mag. 153, 681–695. Dickin, A.P., McNutt, R.H., 1989. Nd model age mapping of the southeast margin of the Archean Foreland in the Grenville Province of Ontario. Geology 17, 299–302. Dickin, A.P., McNutt, R.H., 2007. The Central Metasedimentary Belt (Grenville Province) as a failed back-arc rift zone: Nd isotope evidence. Earth Planet. Sci. Lett. 259, 97–106. Dickin, A.P., McNutt, R.H., Martin, C., Guo, A., 2010. The extent of juvenile crust in the Grenville Province: Nd isotope evidence. GSA Bull. 122, 870–883. Dickin, A.P., Moretton, K., North, R., 2008. Isotopic mapping of the Allochthon Boundary Thrust in the Grenville Province of Ontario, Canada. Precambr. Res. 167, 260–266. Dickin, A., Strong, J., Arcuri, G., Van Kessel, A., Krivankova-Smal, L., 2017. A revised model for the crustal structure of the SW Grenville Province, Ontario, Canada. Geol. Mag. 154, 903–913. Gobeil, A., Clark, T., David, J., 1996. Nouvelles données géochronologiques U-Pb dans le Complexe métamorphique de Manicouagan. Projet Abitibi-Grenville Lithoprobe. Atelier 96, 29–30. Gower, C.F., 1990. Mid-Proterozoic evolution of the eastern Grenville province, Canada. 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Fig. 10. Tectonic model for Pinwarian and post-Pinwarian events leading to the formation of the Quebecia composite arc belt.

meta-igneous units with well-defined field contexts has provided chronological ‘snap-shots’ of a few small geographical areas. However, for deeply exhumed Precambrian orogens such as the Grenville belt it is difficult to use conventional geological mapping techniques to interpolate crustal accretion processes between areas of detailed study. Nd isotope mapping provides a cost-effective method of interpolating crustal formation ages between areas of detailed study, using U-Pb dated samples to control the interpretation of Nd isotope data. The result is similar to the operation of the human eye. Small high-resolution ‘snap-shots’ are obtained from the fovea when the eye rapidly tracks between objects of interest. On the other hand, a lower-resolution but wider spatial context is provided by peripheral vision. The successful integration of these two systems by the brain provides an overall awareness that is both panoramic and detailed. In the case of the Quebecia terrane, Nd isotope mapping has delineated blocks of older crust within a younger composite arc belt that might otherwise have been overlooked or misunderstood. The delineation of these older blocks provides vital geographic constraints, allowing us to reconstruct the large-scale tectonic processes that were 9

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Rivers, T., Culshaw, N., Hynes, A., Indares, A., Jamieson, R., Martignole, J., 2012. The Grenville Orogen–a post-lithoprobe perspective. Special Paper 49 In: Tectonic Styles in Canada: The lithoprobe perspective. Geological Association of Canada, pp. 97–236. Rivers, T., Corrigan, D., 2000. Convergent margin on southeastern Laurentia during the Mesoproterozoic: tectonic implications: Canadian. J. Earth Sci. 37, 359–383. Sappin, A.A., Constantin, M., Clark, T., van Breemen, O., 2009. Geochemistry, geochronology, and geodynamic setting of Ni–Cu ± PGE mineral prospects hosted by mafic and ultramafic intrusions in the Portneuf-Mauricie Domain, Grenville Province, Quebec. Can. J. Earth Sci. 46, 331–353. Simandjuntak, T.O., Barber, A.J., 1996. Contrasting tectonic styles in the Neogene orogenic belts of Indonesia. Geol. Soc. Lond., Spec. Publ. 106, 185–201. Smith, T.E., Holm, P.E., 1987. The trace element geochemistry of metavolcanics and dykes from the Central Metasedimentary Belt of the Grenville Province, southeastern Ontario, Canada. Geol. Soc. Lond. Spec. Publ. 33, 453–470. Thirlwall, M.F., 1982. Systematic variation in chemistry and Nd-Sr isotopes across a Caledonian calc-alkaline volcanic arc: implications for source materials. Earth Planet. Sci. Lett. 58, 27–50. Thomson, S.D., Dickin, A.P., Spray, J.G., 2011. Nd isotope mapping of Grenvillian crustal terranes in the vicinity of the Manicouagan Impact Structure. Precambr. Res. 191, 184–193. Tucker, R.D., Gower, C.F., 1994. A U-Pb geochronological framework for the Pinware terrane, Grenville Province, southeast Labrador. J. Geol. 102, 67–78. Turlin, F., Vanderhaeghe, O., Gervais, F., André-Mayer, A.S., Moukhsil, A., Zeh, A., Solgadi, F., 2019. Petrogenesis of LREE-rich pegmatitic granite dykes in the central Grenville Province by partial melting of Paleoproterozoic-Archean metasedimentary rocks: Evidence from zircon U-Pb-Hf-O isotope and trace element analyses. Precambr. Res. 327, 327–360. Van Breemen, O.V., Corriveau, L., 2005. U-Pb age constraints on arenaceous and volcanic rocks of the Wakeham Group, eastern Grenville Province. Can. J. Earth Sci. 42, 1677–1697. Van Schmus, W.R., Bickford, M.E., Turek, A., Van der Pluijm, B.A., Catacosinos, P.A., 1996. Proterozoic geology of the east-central Midcontinent basement. Geol. Soc. Am. Spec. Pap. 308, 7–31. Wasteneys, H.A., Kamo, S.L., Moser, D., Krogh, T.E., Gower, C.F., Owen, J.V., 1997. U-Pb geochronological constraints on the geological evolution of the Pinware terrane and adjacent areas, Grenville Province, southeast Labrador, Canada. Precambr. Res. 81, 101–128. Zelek, M., Dickin, A., 2013. Nd isotope mapping of crustal terranes in the Parent-Clova area, Quebec: Implications for the evolution of the Laurentian margin in the Central Grenville Province. Geosciences 3, 448–465.

Groulier, P.A., Indares, A., Dunning, G., Moukhsil, A., Wälle, M., 2018. Peri-Laurentian, Pinwarian-age oceanic arc crust preserved in the Grenville Province: Insights from the Escoumins supracrustal belt. Precambr. Res. 311, 37–64. Heaman, L.M., Erdmer, P., Owen, J.V., 2002. U-Pb geochronologic constraints on the crustal evolution of the Long Range Inlier, Newfoundland. Can. J. Earth Sci. 39, 845–865. Holm, P.E., Smith, T.E., Grant, B.D., Huang, C.H., 1985. The geochemistry of the Turriff metavolcanics, Grenville Province, southeastern Ontario. Can. J. Earth Sci. 22, 435–441. Hébert, C., van Breemen, O., 2004. Mesoproterozoic basement of the Lac St. Jean Anorthosite Suite and younger Grenvillian intrusions in the Saguenay region, Québec: Structural relationships and U-Pb geochronology. In: Tollo, R.P., Corriveau, L., McLelland, J.M., Bartholomew, M.J. (Eds.), Proterozoic tectonic evolution of the Grenville orogen in North America. Geological Society of America Memoir 197, pp. 65–80. Hynes, A., Rivers, T., 2010. Protracted continental collision—Evidence from the Grenville orogen. Can. J. Earth Sci. 47, 591–620. Hynes, E.E., 2010. Nd isotope delineation of crustal terranes in the Bancroft area of Ontario and the Saguenay and Baie Comeau regions of central Quebec: Ensialic rifting and arc formation. Unpublished MSc thesis. McMaster University. Indares, A., Moukhsil, A., 2013. Geon 12 crustal extension in the central Grenville Province, implications for the orogenic architecture, and potential influence on the emplacement of anorthosites. Can. J. Earth Sci. 50, 955–966. Lasalle, S., Fisher, C.M., Indares, A., Dunning, G., 2013. Contrasting types of Grenvillian granulite facies aluminous gneisses: Insights on protoliths and metamorphic events from zircon morphologies and ages. Precambr. Res. 228, 117–130. MacLean, W.H., St. Seymour, K., Prabhu, M.K., 1982. Sr, Y, Zr, Nb, Ti, and REE in Grenville amphibolites at Montauban-les-Mines, Québec. Can. J. Earth Sci. 19, 633–644. Maity, B., Indares, A., 2018. The Geon 14 arc-related mafic rocks from the central Grenville Province. Can. J. Earth Sci. 55, 545–570. Martin, C., Dickin, A.P., 2005. Styles of crustal formation on the southeast margin of Laurentia: evidence from the central Grenville province, Lac St Jean, Quebec. Can. J. Earth Sci. 42, 1643–1652. Moukhsil, A., Solgadi, F., Lacoste, P., Gagnon, M., David, J., 2012. Géologie de la région du lac du Milieu (SNRC 22O03, 22O04, 22O06, 22J13 et 22J14). Ministère des Ressources naturelles et de la Faune, RG 1, 31. Nadeau, L., van Breemen, O., 1994. Do the 1.45-1.39 Ga Montauban Group and the La Bostonnais Complex Constitute a Grenvillian Accreted Terrane? Geological Association of CanadaMineralogical Association of Canada, Programs with Abstracts, pp. A81.

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