5 The Meguma terrane is the easternmost accreted terrane of the Appalachian orogen and is dominated by metasedimentary rocks of the Goldenville and Halifax groups (Fig. 1). The Goldenville Group is the most extensive unit in the Meguma terrane and is primarily composed of thick layers of metasandstone separated by thinner layers of meta-siltstone (White 2010). The group has been subdivided into several formations; in the Trafalgar area they include the Taylors Head and Beaverbank formations (Fig. 2). The overlying Halifax Group is composed of slate and metasiltstone with thin beds of metasandstone. It also has been subdivided into formations, including the Cunard and Glen Brook formations in the Trafalgar area (Fig. 2).

6 The Goldenville and Halifax groups were regionally deformed and metamorphosed to greenschist and locally amphibolite facies at ca. 395 Ma during the Neoacadian orogeny (van Staal et al. 2009; White and Barr 2012), an event generally attributed to the collision of the Meguma terrane and a part of Avalonia far east of the part of Avalonia with which the terrane is now juxtaposed along the Cobequid-Chedabucto Fault Zone (Murphy et al. 2011; Waldron et al. 2015; Archibald et al. 2018).

7 Numerous granitic plutons, including the South Mountain Batholith (Fig. 1), intruded the Meguma terrane at about 375–372 Ma. These mainly peraluminous plutons were strongly contaminated by abundant xenoliths and country rock assimilation, although the amount of contamination varies within individual plutons (e.g., MacLean et al. 2003; Clarke 2007; Erdmann et al. 2007, 2009; MacDonald and Clarke 2017). The granitic bodies were emplaced at moderate to shallow depths and were rapidly exhumed, forming narrow contact metamorphic aureoles surrounding the individual plutons (Mahoney 1996; Dostal et al. 2006; Jamieson et al. 2012). After exhumation, both Meguma and Avalonia were overlain by latest Devonian and Carboniferous sedimentary rocks of the Horton and Windsor groups and overlying units (e.g., Murphy et al. 2011; Archibald et al. 2018).

8 The plutons of the Trafalgar suite intruded mainly metasedimentary rocks of the Taylors Head and overlying Beaverbank formations of the Goldenville Group (White and Scallion 2011). The Taylors Head Formation consists mainly of thickly bedded (1 m to several metres) metasandstone interlayered with thin metasiltstone beds generally less than 0.5 m thick. Calc-silicate lenses 1 to 20 cm thick are abundant. Toward the northeastern part of the map area, the Taylors Head Formation becomes progressively more mylonitic. In these areas, micas show preferred crystallographic orientation, go into optical extinction simultaneously, and display S- and C-fabric related to shearing. Post-tectonic staurolite grains in the more pelitic beds are poikiloblastic and include grains of micas which are oriented parallel to the S- and C- fabric, indicating that they overgrew the existing fabric and were the last minerals to form. The staurolite was likely formed during contact metamorphism caused by adjacent plutons, as described below.

9 The thin (100 – 300 m) Beaverbank Formation is in sharp contact with the underlying Taylors Head Formation and with the overlying Cunard Formation (White and Scallion 2011). It is composed of grey laminated metasiltstone, metasandstone, and coticules. The coticules are a distinguishing characteristic of the formation, related to its high Mn content. They form pink, locally ptygmatically folded, Mn-rich beds up to 10 cm thick.

10 The overlying Cunard and Glen Brook formations of the Halifax Group are preserved in synclines in the northern, central, and southeastern parts of the map area (Fig. 2). The Cunard Formation is typically black slate with inter-layered metasiltstone and fine-grained metasandstone in sharp conformable contact the underlying manganiferous Beaverbank Formation. Weathered surfaces in the slate are typically rusty due to the weathering of the pyrite, arsenopryite, and other sulphide minerals. In some areas these pelitic rocks have been contact metamorphosed to form andalusite-bearing slate. Chiastolitic andalusite forms randomly oriented, elongate crystals up to 2 cm in length, that overgrew the foliation defined by micas, demonstrating that contact metamorphism post-dated regional metamorphism in the Trafalgar area. The overlying Glen Brook Formation is composed of grey metasiltstone and slate in the lower part and grey metasandstone in the upper part, in which trace fossils such as burrows and grazing trails are abundant. As documented by White et al. (2009b), the regional metamorphic grade in the Trafalgar area is generally in the green-schist facies (chlorite and biotite zones). Contact metamorphism overprinted earlier greenschist facies regional metamorphism in the vicinity of at least some plutons of the Trafalgar Plutonic Suite. The most well investigated contact metamorphic aureole in the map area is that surrounding the western lobe of the Twin Lakes pluton in pelitic rocks of the Cunard Formation as described by White et al. (2009b). Based on the documented mineral assemblages, White et al. (2009b) proposed an approximate maximum pressure and temperature ~2.5 kbar and ~675°C in the contact metamorphic aureole. Overall, the metamorphic mineral assemblages suggest that plutons of the Trafalgar suite were emplaced at ~ 8–8.5 km depth. Based on distribution of map units and structural data, a north-south cross-section of the map area illustrates that folds are inclined to slightly overturned and mainly verge to the south, cut by plutons of the Trafalgar Plutonic Suite (Fig. 2 inset).

11 Faults in the map area are inferred mainly based on off-sets of magnetic anomalies (King 1997a, b, c, 2005). They typically strike northwest and the largest offsets are approximately 1 km (Fig. 2). The West River St. Marys Fault marks the contact between the older units and the Carboniferous Horton Group (Fig. 2). The West River St. Marys Fault has dextral motion, and splays into two separate faults west of the map area (Murphy et al. 2011; Archibald et al. 2018).

12 A zone of mylonite affecting both the metasedimentary rocks and granitoid plutons occurs in the northeastern part of the map area, including the Taylors Head Formation, Hat-tie Lake pluton and to a lesser extent, the Long John Lake pluton (Fig. 2). The mylonite appears to be truncated on the northwest by the West River St. Marys Fault. It extends and widens to the east beyond the map area and includes the mylonitic Kelly Brook pluton of Archibald et al. (2018). The average mylonitic foliation strikes ~270º and dips ~60° with mineral lineations which have a trend and plunge of about 270/10°. Based on feldspar porphyroclasts in oriented thin sections from the Hattie Lake pluton, motion in the mylonite zone was dextral.

21 The Bog Island Lake, Mink Lake, Ten Mile Lake, and Porcupine Lake plutons all consist mostly of fine- to medium- grained quartz diorite grading to tonalite (Figs. 4a, 5). Both quartz diorite and tonalite are dominated by plagioclase (50–75%), with less abundant quartz (10–35%), biotite (<15%), and amphibole (<25%). Accessory minerals include apatite, zircon, ilmenite, and rarely garnet. The proportion of biotite and amphibole varies within each pluton and between plutons; most samples contain both minerals but, in some rocks, only biotite, or more rarely only amphibole, is present. K-feldspar is a minor component (<5%) in some samples. Texture is typically equigranular but plagioclase forms phenocrysts in some places. The plagioclase is commonly zoned, with more calcic cores (An_50–60) and more sodic rims (An_30–50). Some samples also contain sodic plagioclase.

22 A large number of amphibole compositions were obtained by A.K. Chatterjee (unpublished data) from a few samples from the quartz diorite and tonalite plutons. Most are classified as magnesio-hornblende to actinolite but some analyses, especially from the Ten Mile Lake pluton, have higher Na, K, and Ti, and are classified as kaersutite, or have low calcium and are classified as anthophyllite (Puchalski 2012). More systematic study of the amphibole compositions in these plutons is required in order to interpret the significance of the variations.

23 The Bog Island Lake pluton contains up to 5% garnet in some samples, and the grains are subhedral to euhedral and as large as 3 cm. Scallion (2010) and Scallion et al. (2011) suggested that the magma had been enriched in manganese as a result of near-complete assimilation of manganiferous xenoliths derived from the Beaverbank Formation, which led to growth of new orthomagmatic and paraxenocrystic garnet.

24 The Porcupine Lake pluton contains medium- to coarse-grained dioritic enclaves which in places appear to define a magmatic foliation. The Ten Mile Lake pluton, the most southern component of the Trafalgar suite (Fig. 2) has abundant rounded to lenticular enclaves, ranging in size from a few cm to a few metres that consist of quartz diorite and diorite, as well as metasandstone, andalusite-sillimanite hornfels and coticules derived from the Goldenville and Halifax groups (Scallion 2010). The Ten Mile Lake pluton also includes an area of hornblende gabbronorite sample, but field relations were unclear as to whether this gabbroic rock is a dyke in the pluton, an enclave, or a more mafic component of the pluton itself. Quartz diorite and tonalite samples from the same area of the pluton contain small amounts of relict pyroxene (<1%) which forms cores in amphibole and biotite grains.

25 Based on a combination of texture and estimated modal mineralogy (Fig. 5), the remaining plutons of the Trafalgar Plutonic Suite consist of seven texturally distinct varieties of granodioritic to granitic rocks, including (1) medium- grained equigranular granodiorite which forms the Twin Lakes pluton (Fig. 4b), (2) medium- to coarse-grained porphyritic granodiorite gradational to monzogranite of the West Loon Lake, Pogue Lake, Little Lake and Hattie Lake plutons (Fig. 4c), (3) fine- to coarse-grained, equigranular monzogranite of the Long John Lake, Moose Lake and Seloam Lake plutons (Fig. 4d), (4) equigranular monzogranite with generally coarser grain size (~1 cm in length/diameter) and more abundant quartz (35–48%) of the South Brook pluton (Fig. 4e), (5) fine- to medium-grained monzogranite gradational to syenogranite with phenocrysts of K-feldspar and quartz of the Bottle Brook Lake and Cameron Settlement Road plutons (Fig. 4f), (6) fine-grained monzogranite of the Lower Rocky Lake pluton (Fig. 4g), and (7) fine-grained monzogranite grading to syenogranite which forms the Nelson Lake, East Loon Lake, First Rocky Lake and West River St. Marys plutons (Fig. 4h).

26 Quartz forms 35–45% in all these units and is typically anhedral and interstitial to plagioclase and K-feldspar, except in the Bottle Brook Lake and Cameron Settlement Road plutons where it forms phenocrysts. Undulose extinction and irregular sutured boundaries increase in areas of more deformation. Plagioclase and K-feldspar (microcline) are typically of similar abundance, with plagioclase dominating over microcline in granodioritic rocks. Plagioclase grains tend to be subhedral and myrmekitic texture is common near contacts with K-feldspar. Moderate alteration to saussurite is typical. Hundreds of microprobe analyses of plagioclase in granodioritic and granitic samples (A.K. Chatterjee, unpublished data; Puchalski 2012) show a compositional range from about An₄₀ to An₀, with no consistent differences among rock types except a tendency toward more sodic compositions in the syenogranitic samples. Microcline is typically perthitic and poikilitic, with inclusions of biotite, plagioclase and quartz, and weakly altered to sericite. In non-porphyritic rocks, microcline is anhedral but in the porphyritic West Loon Lake, Pogue Lake, Little Lake and Hattie Lake plutons it is subhedral and up to 3–4 times larger than the other mineral grains in the rock (Fig. 4c).

27 Biotite typically forms less than 4% in most samples. It is pleochroic from pale brown to dark reddish-brown and has been partially to completely replaced by chlorite. It typically contains abundant inclusions of zircon with pleochroic haloes, apatite, and secondary rutile needles. Biotite in the Twin Lakes pluton has higher and more variable Mn and Ti than in the monzogranitic and syenogranitic plutons. Muscovite tends to be more abundant than biotite in the syenogranitic samples but less abundant than biotite in the other rock types. Its composition is close to endmember muscovite, with little substitution of Fe, Mg, or Na (Puchalski 2012).

28 Accessory minerals include abundant anhedral apatite grains (<0.5 mm), zircon, and disseminated ilmenite. The zircon occurs almost entirely as inclusions in biotite whereas apatite occurs as both inclusions and separate grains. Garnet is a common accessory mineral in the Twin Lakes pluton, occurring in clusters of small grains or as larger poikilitic crystals. The origin of the garnet in that pluton was studied in detail by Scallion (2010) and Scallion et al. (2011). The presence of coticule xenoliths and small clusters of garnet similar to those in coticules suggest that contamination by the manganiferous Beaverbank Formation contributed to the abundance of garnet in this pluton. According to Scallion et al. (2011), garnet-bearing xenoliths were probably assimilated through a combination of processes, including mechanical disaggregation, melting, and chemical diffusion. Some of the garnet grains were interpreted to be direct xenocrysts, whereas others were interpreted to be paraxenocrystic and orthomagmatic, the formation of which was influenced by assimilation of Mn-rich material into the magma. Garnet is rare in most of the granitic plutons, but where present it is euhedral and <0.5 mm in size. The granitic plutons were not included in the study by Scallion (2010) but based on her classification criteria, the garnet is likely to have crystallized from the melt because it has inclusions of igneous minerals such as biotite and forms isolated individual crystals, not associated with other garnet grains.

29 The compiled chemical data include analyses for two hundred and eleven samples representing all plutons of the Trafalgar suite. However, the data are from several different sources going back to the 1980s, and hence vary in quality and in the range of trace elements analyzed. The most complete analyses were done by Puchalski (2012) at ACME Laboratory (now Bureau Veritas) in Vancouver, BC. These analyses represent most of the granitic plutons and rock types, but none is from the Twin Lakes granodiorite and only one is from a quartz dioritic/tonalitic pluton.

30 The quartz dioritic and tonalitic plutons show wide range in SiO₂ from about 50% in gabbroic/dioritic samples to 66% in tonalitic samples with average SiO₂ contents of 54.7, 52.2, 58.4, and 61% in analyzed samples from the Ten Mile Lake, Bog Island Lake, Porcupine Lake, and Mink Lake plutons, respectively (Fig. 6). In contrast to these more mafic plutons, the granodioritic/granitic plutons have average SiO₂ of about 70%, and the granitic plutons average about 72–73% SiO₂ (Fig. 6).

31 Major element oxides are plotted against SiO₂ in Figure 7 to illustrate chemical variation in the plutons. Six samples from the Ten Mile Lake and Bog Island Lake plutons contain between 46 and 50% SiO₂ and are plotted on the vertical axis on Figure 7. Also shown on the figure for comparison are fields for chemical analyses from the Canso plutons of Hill (1991), South Mountain Batholith, and other granitoid plutons in the Meguma terrane based on the compilation of Tate and Merrett (1994) and Tate (1995). Most major element oxides show scattered negative correlation with SiO₂ (Fig. 7). Exceptions are Na₂O and K₂O, which display positive correlation, and P₂O₅ which is approximately constant across the range of SiO₂ (Fig. 7). It is apparent that the dioritic to tonalitic plutons show wide variation which at least in part is the result of the presence of abundant xenoliths of metasedimentary rocks (Scallion 2010; Puchalski 2012). Because of their variability, the fact that they were not sampled during the present study and hence that the abundance of xenoliths in analyzed samples is unknown, and the lack of modern geochemical data from those units, a detailed assessment of their geochemistry is not included here. Similar tonalitic rocks occur in the Canso plutons (Hill 1991), as indicated by the lower SiO₂ parts of the fields defined by those samples from the database of Tate (1995). However, none are as low in SiO₂ as the dioritic plutons associated with the Trafalgar suite (Fig. 7).

32 The granodioritic and granitic plutons show more chemical similarity, and the majority of samples cluster quite closely; generally, the textural differences among the plutons are not reflected in chemical differences. Their chemical compositions and trends are similar to those of the South Mountain Batholith and other granitic plutons of the Meguma terrane, including the Canso plutons. Also similar are high Rb (Fig. 8a), correlative with potassium, and the decrease in Ba and Sr with increasing SiO₂ (Figs. 8b, c). Such variations, like those in the major element oxides, are indicative of strong control by feldspars and micas during magma evolution, as demonstrated by Puchalski (2012) using Pearce Element Ratio analysis (e.g., Pearce 1968; Stanley 2017). The more immobile elements Nb, Y, and Zr also show similar patterns in the Trafalgar suite as in other Meguma terrane plutons, and typically decrease with increasing SiO₂ (Figs. 8c, d, e) likely related to fractionation of accessory phases such as zircon, monazite, and apatite as inclusions in biotite.

33 Most samples are only weakly to moderately peraluminous, with A/CNK ratios more than 1 but less than 1.2 (Fig. 9). This is consistent with the ubiquitous presence of the moderately peraluminous minerals biotite and muscovite and rarely garnet, but absence of highly peraluminous magmatic minerals such as cordierite and andalusite, in contrast to the common presence of those minerals in the highly peraluminous granite in South Mountain Batholith (Clarke 2019).

34 Although REE patterns in the granodiorite and granite plutons are broadly similar, the total REE abundance shows a slight decrease in the younger units and the Eu anomaly (Eu/Eu*) becomes progressively larger (Fig. 10). Similar trends of decreasing REE with magma evolution were explained in units of the South Mountain Batholith by fractionation of plagioclase and biotite (Muecke and Clarke 1981). Part of the effect may be due to removal of zircon, monazite, and other REE-bearing accessory phases during biotite fractionation, and those minerals typically occur as inclusions in biotite.

35 The trends in major element data in the granodioritic and granitic plutons of the Trafalgar Plutonic Suite (Fig. 7) are consistent with evolution from the same or similar parent magma by fractionation of minor biotite, sodic plagioclase (An₂₀), muscovite and K-feldspar and enrichment in quartz, as demonstrated by Puchalski (2012) using Pearce Element Ratio modelling (data not shown here). Puchalski (2012) also suggested that the tonalite/quartz diorite plutons are more varied in composition than the more felsic plutons and show less coherent inter-element correlations, and hence may not be co-magmatic with the felsic plutons. Ferromagnesian minerals such as biotite and hornblende and more calcic plagioclase were more involved in the evolution of the tonalite/quartz diorite magmas (Puchalski 2012).

36 Although no new isotopic data were obtained by Puchalski (2012), samples from the Trafalgar area had been analysed previously for Sm, Nd, Rb, and Sr isotopes by Clarke et al. (1993). Based on the locations of those samples with respect to the map units of this study (Fig. 2), most of the analyses (eleven) are from samples of the dioritic-tonalitic plutons (Fig. 11). They define a trend from positive (+3.8) to negative (-5) εNd with increasing ⁸⁷Sr/⁸⁶Sr ratios from 0.703 to 0.709 (Fig. 11). Four granodioritic and monzogranite samples from the Twin Lakes, West Loon Lake, and Moose Lake plutons all have negative εNd values (-1.67 to -5.96) and ⁸⁷Sr/⁸⁶Sr ratios of 0.707 to 0.709. Samples from three metasedimentary xenoliths in the plutons and from the Halifax and Goldenville groups all have more negative εNd values and higher ⁸⁷Sr/⁸⁶Sr ratios. The well-defined trend on this diagram is consistent with contamination of magmas that formed the Trafalgar suite by metasedimentary material from the Goldenville and Halifax groups. This conclusion is supported by the observation that monzogranite sample LG-004 from the collection of Giles and Chatterjee (1986) from the Moose Lake pluton has the most negative εNd value and highest ⁸⁷Sr/⁸⁶Sr ratio of the plutonic rocks and contains obvious xenolithic metasedimentary material consistent with that interpretation. It is also consistent with other studies (e.g., MacDonald and Clarke 2017) which have demonstrated that such contamination is widespread in Meguma terrane plutons.