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Atlantic Geology

Pre-CarbonIferous TectonostratI graphIc Subdivisions of Cape Breton Island, Nova Scotia Sandra M. Barr and Robert P. Raeside

Volume 22, Number 3, December 1986 Article abstract Cape Breton Island can be divided Into four zones on the basis of contrasting URI: https://id.erudit.org/iderudit/ageo22_3art03 stratigraphy, metamorphism, and plutonlsm. A Southeastern zone Is characterized by late Precambrian volcanism and plutonlsm, followed by See table of contents Cambro-Ordovlclan rlft-baslu sedimentation and minor volcanlsm. The Bras d'Qr zone to the northwest Is underlain by gnelsslc basement and overlying platforms! (carbonate and clastic) sedimentary rocks. Intruded by mainly late Publisher(s) Precambrian and Grdovician(?) granitoid rocks. The fflghlands zone has a gnelsslc core flanked by typically lower grade sedimentary and volcanic rocks Atlantic Geoscience Society of probable Precambrian age intruded by diverse and abundant dioritlc to granitic plutons ranging In age from Precambrlfln to Carboniferous. The ISSN Northwestern m^tmA» zone has gnelsslc basement Intruded by varied plutonlc rocks Including anorthosite and syenite, the latter of GrenvUUan age. The 0843-5561 (print) nature and significance of the boundaries between these zones are as yet 1718-7885 (digital) uncertain, but only the Southeastern and Bras d'Qr zones are considered to be part of the Avalon Terrane. Explore this journal

Cite this article Barr, S. M. & Raeside, R. P. (1986). Pre-CarbonIferous TectonostratI graphIc Subdivisions of Cape Breton Island, Nova Scotia. Atlantic Geology, 22(3), 252–263.

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V o l . 22 December, 1986 No. 3

Pre-Carbon Iferous TectonostratI graphic Subdivisions of Cape Breton Island, Nova Scotia

Sandra M. Barr and Robert P. Raeslde Department of Geology, Acadia University Wolfvllle, Nova Scotia BOP 1X0

Cape Breton Island can be divided into four zones on the basis of contrasting stratigraphy, metamorphism, and plutonism. A Southeastern zone is characterized by late Precambrian volcanism and plutonism, followed by Cambro-Ordovician rift-basin sedimentation and minor volcanism. The Bras d'Or zone to the northwest is underlain by gneissic basement and overlying platformal (carbonate and clastic) sedimentary rocks, intruded by mainly late Precambrian and Qrdovician(?) granitoid rocks. The Highlands zone has a gneissic core flanked by typically lower grade sedimentary and volcanic rocks of probable Precambrian age intruded by diverse and abundant dioritic to granitic plutons ranging in age from Precambrian to Carboniferous. The Northwestern Highlands zone has gneissic basement intruded by varied plutonic rocks including anorthosite and syenite, the latter of Grenvillian age. The nature and significance of the boundaries between these zones are as yet uncertain, but only the Southeastern and Bras d'Or zones are considered to be part of the Avalon Terrane.

Des contrastes de stratigraphie. mdtamorphisme et plutonisme permettent de diviser l'ile du Cap-Breton en quatre zones. Dn zone sud-est se distinque par un volcanisme et un plutonisme tardi-prAeambriens auxquels succAdent, au Cambro-Grdovicien, une sAdimentation bassinale de type rift et un faible volcanisme. Au Nord-Ouest, la zone de Bras d ’Or comporte un socle gneissique sur lequel s'est effectuAe une sAdimentation nAritique (terrigAne et A carbonates), le tout injectA de granitoides principalement tardi-prAcambriens et ordoviciens(?). La zone de Highlands englobe un noyau gneissique ceinturA de roches sAdimentaires et volcaniques auxquels s'est typiquement imprimA un mAtamorphisme de faible intensitA et qui sont probablement d'age prAcambrien. Ceux-ci sont totis recoup As par d'abondants plutons dioritiques et granitiques divers dont l'Sge s'Achelonne du PrAcambrien au CaronifAre. La zone de Northwestern Highlands renferme un socle de gneiss recoupA par diverses roches plutoniques dont 1'anorthosite et la syAnite, cette demiAre Atant d'age grenvillien. Le doute subsiste encore en ce qui regarde la nature et la signification des frontiAres entre ces zones; cependant seules la zone sud-est et la zone de Bras d'Or sont considArAes comme appartenant A la laniAre d'Avalon. [Traduit par le journal]

INTRODUCTION reconnaissance scale. More recent map­ ping and petrological studies in north­ All of Cape Breton Island has ern Cape Breton Island (Raeside et a l. generally been Included in the Avalon 1986, Barr et a l. 1985a, b, Raeside Zone or Terrane of the Appalachian and Barr this issue, Jamieson and Craw Orogen (e.g. Williams 1978, 1979, 1983) have demonstrated that its O'Brien et a l. 1983, Rast and Skehan geology is distinct from that of 1983, Williams and Hatcher 1983). southeastern, and probably central, However, these interpretations have Cape Breton Island. been based on data from older The purpose of this paper is to geological mapping (e.g. as compiled by propose a subdivision of Cape Breton Keppie 1979), much of which was on a Island into four zones (Fig. 1), which contrast in pre-Carboniferous strati­ MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 22, 252-263 (1986) graphy, metamorphism and plutonism. It

Received May 2. 1986 0711-1150/86/030252-12$2.80/0 Revision Accepted September 5. 1986 253 Barr and Raeside

Fig. 1. Simplified geological map of Cape Breton Island showing the proposed tectonostratigraphic subdivisions. Map is compiled from various sources referenced in the text. SR, Salmon River; GM, Gillis Mountain; DC, Deep Cove; WBF. Wilkie Brook Fault; RRF, Red River Fault. Carboniferous sedimentary rocks include Horton Group and overlying units. MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 254

SOUTHEASTERN BRAS D'OR HIGHLANDS NW HHES1 t RN_ HUil IU1NDS

CARBONIFEROUS CARBONIFEROUS CARBONIFEROUS CARBONIFEROUS Sedimentary rocks Sedimentary rocks Sedimentary rocks II Sedimentary rocks

0EV0N0-CARB0NIFEROUS DEVONO-CARBONIFEROUS DEVONO-CARBONIFEROUS DEVONO-CARBONIFEROUS Sedimentary rocks, Sedimentary & bimodal Sedimentary & bimodal m inor t u f f volcanic rocks volcanic rocks ■ ■ (Fisset Brook Fm) «"5T O /1 Granitoid rocks Granitoid rocks Granitoid rocks ■ s'. Granitoid rocks i l l

ORDOVICIAN? ORDOVIClAN-DEVONIAN? TT) Granitoid rocks Granitoid rocks

Diorite, tonaTite

CAMBRO-ORDOVICIAN CAMBRO-ORDOVICIAN

Sedimentary and Sedimentary and volcanic rocks (mainly volcanic rocks B Kelvin Glen Group) 0 (mainly Bourinot Group)

LATE HADRYNIAN-CAMBRIAN LATE HADRYNIAN-CAMBRIAN LATE HADRYNIAN-CAMBRIAN

»N / I Granitic rocks Diorite to granite Diorite to granite + + (includes Cheticamp pluton) Diorite, tonal1te, 1eucotonalite (in part may be younger)

LATE PRECAMBRIAN LATE PRECAMBRIAN LATE PRECAMBRIAN-EARLY PALEOZOIC? PRECAMBRIAN Volcanic and sedimentary rocks Fourchu Group (and Volcanic rocks (Money Point Group, Crowd!s Mtn Syenite, anorthosite, Giant Lake Complex) (Price Point unit) volcanics, Western Highlands monzodiorite m complex, McMillian Flowage Fm) H George R iv e r Group Paragneiss and orthogneiss Quartzofeldspathic and Gneiss (includes Kellys (Cheticamp Lake, Cape North Group, syenitic gneiss (Polletts Mtn, Barachois River, m undifferentiated gneisses) H Cove Brook Group) Lime H i l l )

Legend for Fig. 1. is further suggested that only two of chemical studies of mafic flows, and of these zones can he correlated with the mafic intrusions interpreted to be Avalon Terrane, as defined in eastern cogenetic with the volcanic rocks, Newfoundland and southern New indicate calc-alkalic transitional to Brunswick. The proposal has important tholeiitic affinity (Keppie et a 7. implications for lateral correlations 1979, Macdonald 1983). of terrane s in the northern The Stirling belt to the northwest Appalachians. is apparently more restricted in com­ position and dominated by bimodal flows SOUTHEASTERN ZONE and varied subaqueous pyroclastic and epiclastic rocks containing chert and Southeastern Cape Breton Island is carbonate layers, as well as syngenetic characterized by the Fourchu Group Fe-Zn-Pb-Cu occurrences (Macdonald (Weeks 1954) which consists mainly of 1983). This belt contains much more volcanic rocks, now generally sedimentary material than the coastal metamorphosed to lower greenschist belt and appears less pervasively de­ facies. These rocks occur in five formed and metamorphosed. It was orig­ belts (Fig. 1). The southernmost inally mapped as Cambrian (Weeks 1954) coastal belt serves at present as the but more recent work has indicated a "type area" of the Fourchu Group Precambrian age (Smith 1978, Macdonald because of its excellent coastal ex­ 1983, McMulliri 1984). Smith (1978) posures which have been relatively well referred to part of this belt as the studied (Murphy 1977, Keppie et a l. Giant Lake Complex. 1979, Macdonald 1983). It consists Fourchu Group rocks to the north­ mainly of subaerial pyroclastic rocks west in the East Bay Hills, Sporting and minor mafic to felsic flows. Geo­ Mountain, and Coxheath Hills belts are 255 Barr and Raeside generally less well known, but contain granitoid rocks are generally post- varied pyroclastic rocks and flows tectonic , although locally strongly apparently of calc-alkalic affinity and sheared. Hence it is more probable formed in association with subduetion that the granitoid magmas are younger at a continental margin (Helmstaedt and than the volcanic rocks and represent Telia 1973, Rowan 1985, Sexton 1985). late-orogenic plutonism whereas the Details of stratigraphic relations volcanic rocks were erupted early in within and between these five belts the orogenic cycle. are lacking, making it difficult to These granitoid and metavolcanic compare the rocks directly with those units are overlain unc onf ormably by of the Avalon Terrane of eastern various early Cambrian to Ordovician Newfoundland or elsewhere. Most sedimentary units (Hutchinson 1952, workers have implied correlation with Weeks 1954, Smith 1978, McMullin 1984). much of the Late Hadrynian sequence in Although stratigraphic relations are Newfoundland, from the Love not entirely resolved, Smith (1978) Cove/Harbour Main groups to the Bull assigned most of these units to the Aim/Signal Hill/ Marystown groups (in­ Kelvin Glen Group. The units include ferred to range from about 680 Ma to conglomerate, siltstone, shale, minor less than 600 Ma) and with the Cold- limestone and possibly some volcanic brook Group of southern New Brunswick rocks (Smith 1978). They contain tri- (Rast and Skehan 1983, O'Brien et a l. lobites and brachiopods generally char­ 1983). acteristic of the Atlantic faunal realm The metavolcanic rocks of the (Hutchinson 1952), a fact widely used Fourchu Group are intruded by granitoid in reconstructions of now dispersed plutons which have given Rb-Sr isochron Avalonian terranes (e.g. O'Brien et ages ranging from 544 ± 21 Ma to 577 + al. 1983). 21 Ma (Cormier 1972, 1979; Barr et a l. A group of Devonian granites has 1984a, Sexton 1985). These are gen­ intruded these rocks and the Fourchu erally in agreement with K-Ar ages for Group, forming an arcuate belt from amphiboles from the same units (Sexton Salmon River through Gillis Mountain to 1985, McMullin 1984), except an older Deep Cove (Barr and Macdonald 1985). K-Ar age has been obtained from the The northern boundary of the South­ Coxheath Hills pluton (Stevens et a l. eastern zone is inferred to be a fault 1982). These plutons are nowhere ob­ or series of faults through the south­ served to intrude Cambrian to Ordo­ ern Bras d'Or Lakes and Boisdale vician strata and hence are consid­ Peninsula (Fig. 1). In the Lakes the ered to be late Precambrian rather than presence of the fault is suggested from Cambrian, like apparently similar gran­ the shape of the channels and intense itoid rocks elsewhere in the Avalon shearing and cataclastic deformation in Terrane (e.g. O'Brien et a/. 1983). metavolcanic and granitoid rocks of the The granitoid rocks are composi- Sporting Mountain area (Sexton 1985) tionally expanded (dioritic to and East Bay Hills (McMullin 1984). granitic), calc-alkalic suites with I- Through the Boisdale Peninsula the type features as defined by Chappell boundary follows a previously identi­ and White (1974, 1983). They may be fied major fault that cuts lower Car­ cogenetic with the associated volcanic boniferous units (Giles 1982). This rocks of the Fourchu Group, which are fault is one of many major faults also mainly calc-alkalic (Sexton 1985, crossing southeastern Cape Breton Helmstaedt and Telia 1973, Keppie et Island (Keppie 1979), all of which are a l. 1979). However, this inter­ probably splays from the Minas Geo­ pretation presents some problems as the fracture system (Keppie 1982). Fourchu Group has experienced low-grade The significance of this boundary regional metamorphism and deformation depends on the relation between south­ (Avalonian Orogeny?) whereas the eastern Cape Breton Island and the Bras 256 MARITIME SEDIMENTS AND ATLANTIC GEOLOGY d'Or zone to the north. In Brookville Gneiss and associated Newfoundland, the northern boundary of Greenhead Group (carbonate and clastic the Avalon terrane is the Dover- rocks) in southern New Brunswick (e.g. Hermitage Bay fault, apparently a major Olszewski and Gaudette 1982, O'Brien et crustal suture (Keen et a/. 1986) al. 1983). separating the Avalon and Gander ter- Compositionally expanded I-type ranes. However, it is not likely that granitoid suites of similar age and the Bras d'Or zone of Cape Breton lithology to those of southeastern Cape Island is Gander-equivalent (see Breton Island have intruded the George below). River Group and associated higher grade rocks (Barr and Setter 1984, Justino BRAS D'OR ZONE 1985, Barr et a l. 1982, 1985b). How­ ever, younger granitoid rocks also The Bras d'Or zone is the least occur locally, including large plutons well understood region in Cape Breton of apparent Ordovician or Silurian age Island at the present time. The char­ (Campbell 1980, R.F. Cormier, written acteristic rock unit is the George communication, 1980, Barr et a l. 1982, River Group but its stratigraphy and 1985b), and a small Devonian pluton geographic distribution are not well similar to one of the small Devonian known. Milligan (1970) described plutons in southeastern Cape Breton quartzite, greywacke, slate, marble, Island (Barr et a l. 1984b). and minor mafic volcanic rocks from A significant succession in the widely separated outcrop areas in what Bras d'Or zone is the Middle Cambrian is here termed the Bras d'Or zone, but to Ordovician Bourinot Group and over- was not able to directly correlate lying formations which form a linear among the areas. Most of these rocks belt in the Boisdale Peninsula. These are of low metamorphic grade (except rocks are north of the postulated locally adjacent to intrusions), but boundary with the Southeastern zone, areas of higher grade schist and gneiss but contain an "Atlantic-type faunal also occur in the Bras d'Or zone. The assemblage" (Hutchinson 1952) and are best studied gneiss in the Bras d'Or generally considered "Avalonian", like zone is the Kellys Mountain gneiss sequences of similar age already des­ (Barr et a l. 1982, Jamieson 1984). It cribed in the Southeastern zone. This has yielded Rb-Sr metamorphic ages of implies that the Southeastern and Bras about 700 Ma and is intruded by dio- d'Or zones were probably juxtaposed and rites which have given a Rb-Sr isochron undergoing similar tectonic activity in age of 636 ± 69 Ma (Olszewski et a l. the Cambrian, if not previously. The 1981, Gaudette et a l. 1985). Hetero­ Bourinot Group and overlying formations geneous gneiss (Lime Hill unit) and are in faulted contact with the George intimately associated dioritic rocks River Group but unconformably overlie have also recently been mapped as a late Hadrynian-Cambrian granitoid unit separate from lower grade metased- suites (Barr and Setter 1984, imentary rocks of the George River Helmstaedt and Telia 1973). Although Group in the North Mountain area west in part sedimentary, the Bourinot Group of the Bras d'Or Lakes (Justino 1985), includes bimodal volcanic rocks, and and gneissic units and amphibolites are the succession has been interpreted to also present locally in the Boisdale have formed in a "within-plate" rift Peninsula (Barr and Setter 1984, and environment (Keppie et a l. 1980). unpublished data). The relationship of Following this volcanism and sedimenta­ these higher grade rocks to the George tion, the latter extending into the River Group is as yet unclear. The lower Ordovician, a gap in the strati­ gneisses may represent "basement" to graphic record occurs until the mid- the lower grade rocks, analogous to the Devonian McAdam Lake Formation inferred relationship between the (arkoses, conglomerates and minor vol­ 257 Barr and Raeside canic components) (Helmstaedt and Telia (e.g. Rast and Skehan 1983, O'Brien et 1973, Bell and Goranson 1938). A a l. 1983)? Similarity of late second sedimentary-volcanic succession Hadrynian-Cambrian granitoid suites in also occurs in the Bras d'Or zone, in the Bras d'Or zone and southeastern the western Creignish Hills. This is Cape Breton Island imply similar tec­ considered to be Devono-Carboniferous tonic setting and similar deep crustal and part of the Fisset Brook Formation or upper mantle source rocks at that of the Cape Breton Highlands (Kelley time in these two zones, suggesting and McKasey 1965, Blanchard et a l. that the boundary between them is not 1984). A volcanic succession (Price of the same fundamental nature as the Point unit) in the St. Ann's area, Dover-Hermitage Bay Fault. Are the formerly considered also to be Devono- George River Group and associated Carboniferous (Kelley and McKasey 1965) gneisses correlative with some of the is now known to be intruded by the late metasedimentary units and gneisses of Hadrynian-Cambrian Indian Brook gran- the Cape Breton Highlands? Or is the odiorite (Macdonald and Barr 1985). northern boundary of the Bras d'Or zone The relationship of this isolated a major boundary, perhaps equivalent to calc-alkalic volcanic unit to the the Dover-Hermitage Bay Fault? The George River Group, or to the Fourchu latter explanation is preferred at the Group of southeastern Cape Breton Is­ present time, but more detailed studies land, is not known. of the inferred boundary are needed. The northern boundary of the Bras d'Gr zone is inferred to lie north of HIGHLANDS ZONE the Bras d'Or Lakes and St. Anns Harbour (Fig. 1). The main reasons for Although the nature and location this proposed position of the boundary of the boundary are not yet resolved, are: (i) distinctive late Precambrian- it is clear that the geology of the Cambrian leucogranites occur both north Cape Breton Highlands contrasts marked­ and south of St. Anns Harbour (Barr et ly with that of the Bras d'Or and a/. 1985b, Macdonald and Barr 1985), Southeastern zones just described. The and hence any boundary must lie to the Highlands consist of a core of ortho- north of these leucogranites. (ii) and paragneissic rocks flanked by lower plutonic units can be traced from St. grade metasedimentary and metavolcanic Anns Harbour north along the eastern units (Barr et a7. 1985a, b, Raeside Highlands, east of the inferred bound­ and Barr, this issue). They are in­ ary (Barr et a l. 1985b). (iii) occur­ truded by a variety of granitoid rocks rences of a distinctive gneiss (Bara- which are so similar to those of the chois River gneiss) trend north-north­ Gander Terrane of Newfoundland (e.g. east in the eastern Highlands. The Wilton 1985, Chorlton and Dallmeyer Barachois River gneiss is intruded by 1986) that similar crustal and/or sub- granitoid suites on the east but may crustal source rocks seem implied. have faulted contacts with Highland However, they are also similar to rocks zone units to the west (see next sec­ in the Fleur de Lys belt (Hibbard 1983) tion). (iv) no definite George River and the recently defined Piedmont Group rocks occur north terrane of western Newfoundland of this boundary (Barr et a/. 1985b, (Williams and Hatcher 1983). Raeside and Barr this issue). The oldest units in the Highlands The relationship of the Bras d'Or are inferred to be varied gneissic zone to the Southeastern and Highlands units. Best known are the Cape North zones cannot yet be resolved. Do the Group (Macdonald and Smith 1980) and gneisses and George River Group of the the Cheticarap Lake gneiss (Raeside et Bras d ’Gr zone stratigraphically under­ a l. 1984, Raeside and Barr this lie the Fourchu Group, thus completing issue). The Cape North Group consists the traditional Avalonian stratigraphy of semi-pelitic and pelitic gneiss, 258 MARITIME SEDIMENTS AND ATLANTIC GEOLOGY amphibolite, marble and calc-silicate et a l. 1985a, Macdonald and Smith gneiss. The Cheticamp Lake gneiss 1980). consists mainly of biotite-K-feldspar In the eastern Highlands, strat­ orthogneiss with lenses of migmatized ified rocks are assigned to the mica schists and pelitic gneiss. In McMillan Flowage Formation (Raeside and the western Highlands, gneissic and Barr this issue), consisting of peli­ granitoid rocks form a major unit which tic to psammitic metasedimentary rocks, has not yet been subdivided by detailed quartzite, minor marble and calc- mapping (Barr et a l. 1985a). Zircons silicate rocks, and thin amphibolite from orthogneiss in this unit have layers in a north-south belt over 60 km yielded an U-Pb age of 440 Ma (Jamieson in length. Metamorphic grade increases et aJ. 1986). Gneissic rocks also from lower greenschist facies in the occur in the Gillanders Mountain area south to upper amphibolite facies adja­ (French 1985) and in the Mabou cent to the Cheticamp Lake gneiss with Highlands; in the latter area they which the unit is in faulted contact. occur in an aureole around dioritic On previous maps, many of the rocks now intrusions (Barr and Macdonald 1983). included in the McMillan Flowage Lower grade metamorphic units are Formation were assigned to the George also widespread in the Highlands, River Group (Keppie 1979, Wiebe 1972, although the relations with the Milligan 1970). However, the lack of gneissic units are not yet resolved. significant carbonates in the Formation The Western Highlands volcanic­ makes this correlation tenuous. sedimentary complex (Barr et a/. A distinctive feature of the Cape 1985a) is a major unit in the western Breton Highlands is the variety and Highlands, and includes the Money Point abundance of plutonic rocks. Dioritic Group (Macdonald and Smith 1980), the rocks are widely distributed, forming Jumping Brook Complex (Currie 1982), large, typically foliated bodies; also the Crowdis Mountain volcanics present are separate plutons of leuco- (Jamieson 1981, Jamieson and Doucet tonalite and tonalite. Radiometric ages 1983), and unnamed units in the of these units range from late Gillanders Mountain area (French 1985) Precambrian to Devonian, but it is not and Mabou Highlands (Barr and Macdonald yet clear which are emplacement ages 1983). Although stratigraphy is not and which reflect superimposed younger well known, the typical sequence thermal events (e.g. Jamieson et a/. appears to be a lower mafic unit 1986, Barr et a l. 1985a). Plutons (metabasalts and mafic tuffs) overlain ranging from granodiorite to granite by interlayered felsic volcanic and are numerous in the western Highlands; pyroclastic rocks interfingered with the Cheticamp granodioritic pluton is clastic sedimentary rocks (pelitic and apparently of early Cambrian age but psammitic). The rocks are complexly others are as young as Devonian. folded, and metamorphic grade ranges Muscovite-biotite granodiorite to into upper amphibolite facies, but tonalite in the central Highlands may greenschist facies rocks are most typi­ be of late Precambrian age. However, cal. In the Cape North area where the diverse Siluro-Devonian to early change from the Money Point to Cape Carboniferous plutons are also present, North Groups has been examined in de­ associated with the central gneissic tail, there is no evidence of either a "core” of the Highlands, and these tectonic or stratigraphic break as in a include muscovite-biotite granodiorite typical basement-cover relationship, and granite, megacrystic granite, and metamorphic grade increases grad­ biotite granite and syenogranite (Barr ually from one group into the other et a l. 1985a). The latter have yielded (Macdonald and Smith 1980). The age of the youngest (early Carboniferous) these rocks is not known, although late ages, and have been interpreted to be Precambrlan is usually suggested (Barr comagmatic with felsic volcanic rocks 259 Barr and Raeside of the Fisset Brook Formation (see of the Polletts Cove Brook Group, an below) (French and Barr 1984, French intimately mixed assemblage of 1985) . This petrologic range in quartzofeldspathic gneiss. amphibolite. Silurian(?) to early Carboniferous granitic gneiss, and minor calcareous Plutonic rocks suggests correlation rocks, intruded by varied diorite, with the Gander Zone of Newfoundland granite, syenite, and anorthosite, and (e.g. Strong 1980), and distinguishes mappable plutons of monzodiorite, an­ the Highlands from the Bras d'Or and orthosite, syenite and granite, as Southeastern zones in Cape Breton described by Raeside et a l. (1986) and Island. Barr et a l. (in press). Discontinous The Fisset Brook Formation occurs occurrences of volcanic and sedimentary locally on the southern and western rocks around the periphery of these periphery of the Highlands. It crystalline rocks have been correlated apparently ranges in age from late with the Devono-Carboniferous Fisset Devonian to early Carboniferous and Brook Formation of the Highlands to the consists of bimodal tholeiitic basalt- south (Kelley and MacKasey 1965, Smith rhyolite with interbedded shales, silt- and Macdonald 1981). stones , and minor pyroclastic rocks (Kelley and MacKasey 1965, Blanchard et DISCUSSION a l. 1984). These rocks appear to have been deposited in small alluvial basins The purpose of this paper has been formed during post-Acadian subsidence to document differences in strat­ and wrench faulting. They grade up igraphy, metamorphism and plutonism into much more widely distributed early within four areas of Cape Breton Carboniferous red beds of the Horton Island. Because of limitations of the Group which were deposited over much of data base, evaluations of the signifi­ Cape Breton Island. cance of the observed differences are preliminary. However, it is clear that NORTHWESTERN HIGHLANDS ZONE the Northwestern Highlands zone is Grenvillian, probably correlative with The northwestern Highlands are the Long Range Inlier-Indian Head Com­ composed of a distinctive assemblage of plex of western Newfoundland, and it basement rocks including felsic and seems probable that at least the South­ mafic gneisses, monzodiorite, anortho­ eastern zone is Avalonian. The Bras site and syenite (Raeside et a l. d'Or zone does not appear to have an 1986) . These rocks, informally termed equivalent in Newfoundland, although the Blair River complex, are separated correlations with the Grey River by major mylonitic fault zones (Red gneisses of southern Newfoundland and River and Wilkie Brook fault systems) with marine clastic rocks and associat­ on the south and east from gneisses and ed limestone-bearing slump breccias on schists of the Cape North and Money the Burin Peninsula in the Avalon Point Groups (Macdonald and Smith 1980) Terrane are a possibility (e.g. which are characteristic of the O'Brien et a l. 1983). By analogy with Highlands zone. Zircons from syenite the generally accepted relationship in the Blair River complex have given a among the Brookville Gneiss, and the U-Pb age of 1045 Ma (Barr et a l. in Greenhead and Coldhrook groups in press), and this combined with the southern New Brunswick (e.g. Rast and lithologies present indicates that the Skehan 1983, O'Brien et a l. 1983), the complex represents Grenvillian base­ Bras d'Or zone may represent a deeper ment , probably correlative with the level of the Southeastern zone, and Long Range Inlier-Indian Head Complex hence both are Avalonian. Similarity and equivalent rocks of western of granitoid units and Cambrian Newfoundland. sequences in the two zones is in sup­ The Blair River complex consists port of this interpretation. 260 MARITIME SEDIMENTS AND ATLANTIC GEOLOGY

The increased understanding of the and Hatcher (1983) which also appear to geology of Cape Breton Island in­ have many geological features in common dicates that terrane boundaries pre­ with the Cape Breton Highlands. viously inferred in the Gulf of St. Although this paper has emphasized Lawrence (e.g. Williams 1978, Williams correlation with Newfoundland, as the and Hatcher 1983) have to be modified, "type area" of northern Appalachian perhaps as suggested in Figure 2. The terranes, the proposed subdivisions Wilkie Brook fault system separating have important implications in northern the Northwestern Highlands from the mainland Nova Scotia which, like Cape Highlands can be interpreted to be an Breton Island, has been generally extension of the surface expression of classified as Avalonian (e.g. O'Brien the eastern boundary of the Humber et a/. 1983, Williams and Hatcher Zone, now marked by the Long Range 1983), and in the rest of the northern Cabot Fault (Fig. 2). This correlation Appalachians. Correlation between Cape implies that the area southeast of the Breton geology and that of northern fault system in Newfoundland, an area mainland Nova Scotia is not readily generally included in the Gander apparent (B. Murphy, personal communi­ Terrane (Williams 1978, Chorlton and cation 1986) and hence a fault may Dallmeyer 1986), is correlative with separate these areas (Fig. 2). Ele­ the Highlands zone, as originally ments of both the Southeastern and proposed by Neale and Kennedy (1975). Bras d'Or zones of Cape Breton Island Alternatively, the Highlands could be are recognizable in southern New correlative with the Fleur de Lys belt Brunswick, but tectonic relations there (Hibbard 1983) or the recently defined appear more complex than in Cape Breton Piedmont Terrane (Fig.2) of Williams Island (e.g. O'Brien et a7. 1983).

PIEDMONT TERRANE

0 100 200 300 L---- 1____ i____ i KM

Fig. 2. Possible terranes and terrane boundaries in the northern Appalachians (modified from Williams and Hatcher 1983). Slash pattern indicates Avalon Terrane. Stippled area is late Precambrian — early Paleozoic miogeocline (Humber Zone of Williams 1979). 261 Barr and Raeside

The model of Figure 2 implies correla­ BARR. S.M. and MACDONALD. A.S. 1985. Diverse tion between the Cape Breton Highlands environments of polymetallic mineralization and the Gander-equivalent Miramichi associated with Devonian granitoid plutons, southeastern Cape Breton Island, Nova Scotia. zone of New Brunswick. Similarities in In Taylor, R.P. and Strong, D.F. (eds.) the plutonic rocks of the Miramichi Extended Abstracts of Papers Presented at the zone (e.g. Fyffe et a/. 1981) and the CIM Conference on Granite-Related Mineral Deposits, September 15-17, Halifax, Canada, pp. Cape Breton Highlands are apparent, but 21-24. stratigraphic correlations are not as BARR. S.M. and MACDONALD. A.S. 1983. Geology of obvious. the Mabou Highlands. western Cape Breton In conclusion, although Cape Breton Island, Nova Scotia. Abstract in Program with Abstracts, 8. Geological Association of Canada- Island is a relatively small area of Mineralogical Association of Canada, Joint the northern Appalachians, it occupies Annual Meeting, 48 p. a strategic position in attempts to BARR. S.M., SANGSTER, D.F. and CORMIER, R.F. correlate geological subdivisions be­ 1984a. Petrology of early Cambrian and Devono- Carboniferous intrusions in the Loch Lomond tween Newfoundland and the mainland. complex, southeastern Cape Breton Island, Nova The increasingly apparent complexity of Scotia. In Current Research, Part A, Geo­ the geology in Cape Breton Island em­ logical Survey of Canada, Paper 84-1A, pp. 203- phasizes the problems inherent in pro­ 211. posing regional tectonostratigraphic BARR, S.M., YIP CH0Y, R. and COLWELL, J.A. and OLDALE, H.S. 1984b. Granitoid rocks and correlations. associated copper skara mineralization, Whycocomagh Mountain, Cape Breton Island. ACKNOWLEDGEMENTS Maritime Sediments and Atlantic Geology, 20, pp. 43-55. BARR, S.M. and SETTER. J.R.D. 1984. Petrology We thank the colleagues and of granitoid rocks of the Boisdale Hills, students who have worked with us in central Cape Breton Island, Nova Scotia. Cape Breton Island to obtain the data Nova Scotia Department of Mines and Energy, Paper 84-1, in press. on which this paper is largely based, BARR, S.M., O'REILLY, G.A. and 0 ’BEIRNE, A.M. especially A.S. Macdonald, R.A. 1982. Geology and geochemistry of selected Jamieson, V.A. French, D.W. McMullin, granitoid plutons of Cape Breton Island. M. Justino, R.F. Cormier, P.K. Smith, Nova Scotia Department of Mines and Energy, J.R.D. Setter, and A.J. Sexton. We Paper 82-1, 176 p. BELL, and GORANSON, 1938. Bras d'Or sheet. also thank F. Chandler for his support Department of Mines and Resources, Map 359A. of Cape Breton projects. Our work has BLANCHARD, M-C.. JAMIESON. R.A., and MORE, E.B. been funded by operating grants to the 1984. Late Devonian-Early Carboniferous vol- authors from the Natural Sciences and canism in western Cape Breton Island, Nova Scotia. Canadian Journal of Earth Sciences, Engineering Research Council of 21, pp. 762-774. Canada and Research contracts with CAMPBELL, R.M. 1980. Creignish Hills Pluton, the Geological Survey of Canada to the Nova Scotia. Nova Scotia Department of Mines authors. and Energy, Mineral Resources Division, Report 80-1, pp. 111-115.____ CHAPPELL, W. and WHITE, A.J.R. 1974. Two con­ trasting granite types. Pacific Geology, 8, pp. 173-174. ____ CH0RLT0N, L.B. and DALIHEYER, R.D. 1986. Geo­ BARR, S.M., RAESIDE, R.P. and VAN BREEMEN, 0. chronology of Early to Middle Paleozoic tec­ Grenvillian basement In the northern Cape tonic development in the southwest Breton Highlands, Nova Scotia, Canadian Journal Newfoundland Gander Zone. Journal of Geology, of Earth Sciences, In press. 94, pp. 67-89. BARR, S.M., JAMIESON, R.A. and RAESIDE, R.P. CORMIER, R.F. 1979. Rubidium/strontium ages of 1985a. Igneous and metamorphic geology of Nova Scotian granitoid plutons. Nova Scotia the Cape Breton Highlands. Geological Asso­ Department of Mines and Energy Report 79- ciation of Canada-Mineralogical Association of 1. pp. 143-147. Canada, Joint Annual Meeting, Excursion Guide CORMIER, R.F. 1972. Radiometric ages of grani­ .10, 48 p. tic rocks, Cape Breton Island, Nova Scotia. BARR, S.M. RAESIDE, R.P. and MACDONALD, A.S. Canadian Journal of Earth Sciences, 9, pp. 1985b. Geological mapping of the southeast­ 1074-1086. ern Cape Breton Highlands, Nova Scotia. In CDRRIE, K.L. 1982. Paleozoic supracrustal rocks Current Research, Part B, Geological Survey of near Cheticamp, Nova Scotia. Maritime Sed­ Canada, Paper 85-IB. pp. 103-109. iments and Atlantic Geology, 18. pp. 94-103. MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 262

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