Connecting Cape Breton Island and Newfoundland, Canada Geophysical Modeling of Pre-Carboniferous ‘Basement’ Rocks in the Cabot Strait Area Sandra M

Document generated on 09/24/2021 5:32 p.m.

Geoscience Canada Journal of the Geological Association of Canada Journal de l’Association Géologique du Canada

Connecting Cape Breton Island and Newfoundland, Canada Geophysical Modeling of pre-Carboniferous ‘Basement’ Rocks in the Cabot Strait Area Sandra M. Barr, Sonya A. Dehler and Louis Zsámboki

Volume 41, Number 2, 2014 Article abstract Magnetic and gravity data from northeastern Cape Breton Island, URI: https://id.erudit.org/iderudit/1025341ar southwestern Newfoundland, and the intervening Cabot Strait area were compiled and used to generate a series of maps displaying magnetic (filtered See table of contents total field, first and second derivative) and gravity (Bouguer anomaly onshore, free-air anomaly offshore) information to enhance the anomaly pattern associated with regional geology. With further constraints from previously Publisher(s) published seismic reflection interpretations and detailed maps of onshore geology, five two-dimensional subsurface models were generated. Potential The Geological Association of Canada field anomalies in the offshore can be correlated with onshore faults, rock units, and pre-Carboniferous terranes. In Newfoundland, the Cabot – Long ISSN Range Fault separates Grenvillian basement to the northwest from peri-Gondwanan Port aux Basques subzone basement in the southeast and can 0315-0941 (print) be traced to the Wilkie Brook Fault on Cape Breton Island. The Cape Ray 1911-4850 (digital) Fault/Red Indian Line merges offshore with the Cabot – Long Range Fault so that Notre Dame subzone rocks do not extend across the Cabot Strait area. The Explore this journal Port aux Basques – Exploits subzone boundary crosses the strait but is likely buried by younger rocks onshore in Cape Breton Island. Magnetic halos in the Exploits subzone are probably caused by Silurian – Devonian plutons like those Cite this article in the Burgeo Intrusive Suite. The Exploits – Bras d’Or terrane boundary is located within the Ingonish magnetic anomaly, which was resolved into four Barr, S. M., Dehler, S. A. & Zsámboki, L. (2014). Connecting Cape Breton Island overlapping components representing basement sources intruded into and Newfoundland, Canada: Geophysical Modeling of pre-Carboniferous metasedimentary rocks and dioritic and granodioritic plutons of the Bras d’Or ‘Basement’ Rocks in the Cabot Strait Area. Geoscience Canada, 41(2), 186–206. terrane. The Bras d’Or terrane can be traced to the Cinq-Cerf block and Grey River areas in southern Newfoundland. The interpretations suggest that Bras d’Or terrane ‘basement’ may underlie all of Exploits subzone, and that the Aspy terrane of Cape Breton Island is part of that subzone.

All Rights Reserved © The Geological Association of Canada, 2014 This document is protected by copyright law. Use of the services of Érudit (including reproduction) is subject to its terms and conditions, which can be viewed online. https://apropos.erudit.org/en/users/policy-on-use/

This article is disseminated and preserved by Érudit. Érudit is a non-profit inter-university consortium of the Université de Montréal, Université Laval, and the Université du Québec à Montréal. Its mission is to promote and disseminate research. https://www.erudit.org/en/ 186 Volume 41 2014

HAROLD WILLIAMS SERIES

and used to generate a series of maps pretations suggest that Bras d’Or ter- displaying magnetic (filtered total field, rane ‘basement’ may underlie all of first and second derivative) and gravity Exploits subzone, and that the Aspy (Bouguer anomaly onshore, free-air terrane of Cape Breton Island is part anomaly offshore) information to of that subzone. enhance the anomaly pattern associated with regional geology. With further SOMMAIRE constraints from previously published Les données magnétométriques et seismic reflection interpretations and gravimétriques du nord-est de l’île du detailed maps of onshore geology, five Cap-Breton, dans le sud-ouest de two-dimensional subsurface models Terre-Neuve, et de la région du détroit were generated. Potential field anom- de Cabot contigu, ont été compilées et Connecting Cape Breton alies in the offshore can be correlated utilisées pour produire une série de Island and Newfoundland, with onshore faults, rock units, and cartes affichant les particularités mag- pre-Carboniferous terranes. In New- nétiques (champ total filtré, dérivé pre- Canada: Geophysical foundland, the Cabot – Long Range mière et seconde) et gravimétriques Modeling of pre-Carbonifer- Fault separates Grenvillian basement to (anomalie de Bouguer de la côte, ous ‘Basement’ Rocks in the northwest from peri-Gondwanan anomalie à l’air libre extracôtière) pour Port aux Basques subzone basement in ajouter à la compréhension des motifs the Cabot Strait Area the southeast and can be traced to the d’anomalie de la géologie régionale. Wilkie Brook Fault on Cape Breton En tenant compte des limitations Sandra M. Barr1, Sonya A. Dehler2, Island. The Cape Ray Fault/Red Indi- imposées par les interprétations de and Louis Zsámboki1, 3 an Line merges offshore with the données de levés de sismique réflexion Cabot – Long Range Fault so that déjà publiées et de cartes détaillées de 1Department of Earth and Notre Dame subzone rocks do not géologie continentale, cinq modèles 2D Environmental Science extend across the Cabot Strait area. du sous-sol ont été produits. Des Acadia University The Port aux Basques – Exploits sub- anomalies de champ potentiel en zone Wolfville, NS, Canada, B4P 2R6 zone boundary crosses the strait but is extracôtière peuvent être corrélées avec E-mail: [email protected] likely buried by younger rocks onshore des failles, des unités lithologiques et in Cape Breton Island. Magnetic halos des terranes pré-carbonifères sur la 2Natural Resources Canada in the Exploits subzone are probably côte. Sur l’île de Terre-Neuve, la faille Geological Survey of Canada (Atlantic) caused by Silurian – Devonian plutons de Cabot-Long Range qui sépare le Dartmouth, NS, Canada, B2Y 4A2 like those in the Burgeo Intrusive socle grenvillien au nord-ouest de la Suite. The Exploits – Bras d’Or terrane sous-zone de socle péri-gondwanienne, 3Current address: boundary is located within the Ingo- de Port-aux- Basques au sud-est, peut 63 Barnesdale Ave S nish magnetic anomaly, which was être reliée à la faille de Wilkie Brook Hamilton, ON resolved into four overlapping compo- sur l’île du Cap-Breton. La faille du L8M 2V3 nents representing basement sources Cap Ray et la linéation de Red Indian intruded into metasedimentary rocks se fondent au large avec la faille de SUMMARY and dioritic and granodioritic plutons Cabot – Long Range, ce qui signifie Magnetic and gravity data from north- of the Bras d’Or terrane. The Bras que les roches de la sous-zone de eastern Cape Breton Island, southwest- d’Or terrane can be traced to the Cinq- Notre-Dame ne traversent pas la ern Newfoundland, and the interven- Cerf block and Grey River areas in région du détroit de Cabot. La limite ing Cabot Strait area were compiled southern Newfoundland. The inter- de la sous-zone de Port aux Basques-

Exploits traverse le détroit, mais elle LLaurentia and peri- a Quebec LaurentianL u terranes est vraisemblablement enfouie sous des a r u e Grenville Orogen r n NL e tia Long roches plus jeunes sur l’île du Cap-Bre- n tia a Range n n ton. Les halos magnétiques dans la PEI d Inlier CBI te p NB r e sous-zone Exploits sont probablement ra r Ganderia50°00´N n i- USA e causés par des plutons siluro-dévoniens NS s RIL Line comme c’est le cas de ceux de la Indian séquence intrusive de Burgeo. La lim- Red St. Lawrence Central NDS Gander ite du terrane Exploits-Bras d’Or est Promontory Mobile Zone

Central CF Belt située dans l’anomalie magnétique DHBF Ingonish, laquelle s’est révélée être Mobile HF AAvaloniavalonia Belt BRI ?? Cabot constituée de quatre composantes Notre DameGanderia subzone ?? ?? Strait Blair River superposées représentant des sources A ?? Inlier Bras de socle engoncées dans des roches AAvaloniavalonia Aspy B d’Or métasédimentaires, et dans des plutons M dioritiques et granodioritiques du ter- MMegumaeguma rane de Bras d’Or. On peut suivre le Mira terrane de Bras d’Or jusque dans les 200 km régions du bloc de Cinq-Cerf et de 60°00´W 40 km Grey River dans le sud de Terre- Neuve. Les interprétations permettent Figure 1. Components of the northern Appalachian orogen after Hibbard et al. de penser que le « socle » du terrane de (2006) showing the location of the study area centred on the Cabot Strait between Bras d’Or pourrait constituer l’assise Cape Breton Island and Newfoundland. Abbreviations: DHBF, Dover – Her- rocheuse de la sous-zone Exploits, et mitage Bay Fault; HF, Hermitage Flexure; NDS, Notre Dame subzone; RIL, Red que le terrane Aspy de l’île du Cap- Indian Line. Inset map on upper left shows political areas in northeastern United Breton ferait partie de cette sous-zone. States (USA) and Canada: CBI, Cape Breton Island; NB, New Brunswick; NS, Nova Scotia; NL, Newfoundland; PEI, Prince Edward Island. Lower right inset INTRODUCTION map shows an enlarged view and key to abbreviations for subdivisions in Cape On his pioneering map emphasizing Breton Island. along-orogen correlations of pre-Car- boniferous rocks in the Appalachian orogen in Cape Breton Island com- focused on Carboniferous units and mountain belt, Williams (1978) inferred pared to Newfoundland (Lin et al. faults affecting those units. They that all of Cape Breton Island is part 1994), making it unsurprising that showed pre-Carboniferous basement of the Avalon Zone. In contrast, fewer components have been pre- on their interpretations, but did not Newfoundland, only a few 10s of kilo- served in the relatively small area of speculate on the nature of that base- metres away across the Cabot Strait, Cape Breton Island. In addition, Car- ment. Because the Carboniferous was divided into the Humber, Dun- boniferous cover is relatively more units contribute little to the magnetic nage, Gander, and Avalon zones, inter- extensive in Cape Breton Island com- field signatures, magnetic data have the preted to represent both Laurentian pared to most of Newfoundland, also potential to enable interpretation of and Gondwanan continental margins likely a factor in obscuring older units. the pre-Carboniferous units by com- and the intervening Iapetus Ocean. However, less easily explained is the parison to the onshore areas, where Subsequent decades of geological and presence of rock units in parts of geophysical signatures can be linked to geophysical research resulted in an Cape Breton Island that do not appear particular areas and in some cases to updated and more detailed map of the to have counterparts in southwestern particular units (e.g. Wiseman and Appalachian orogen (Hibbard et al. Newfoundland. Miller 1994; Ethier 2001). In contrast, 2006) on which Cape Breton Island, Linked to the uncertainty in the offshore pre-Carboniferous units like Newfoundland, includes both correlations between units exposed have thicker sediment accumulations Laurentian and Gondwanan compo- onshore in Cape Breton Island and above them than their onshore equiva- nents, and with only the southernmost Newfoundland is the unknown identity lents, and thus Carboniferous units terrane, Mira, considered part of Aval- of the pre-Carboniferous rocks that have greater influence on gravity onia (Fig. 1). However, even though underlie the intervening Cabot Strait. anomalies in the offshore, especially in Laurentian and Gondwanan compo- Carboniferous rocks under the Cabot basins with thicker sequences. nents are now recognized in Cape Bre- Strait are reasonably well known based Loncarevic et al. (1989) used ton Island, the details of how they cor- on their seismic characteristics (e.g. magnetic and gravity maps to infer correlate with their counterparts across Langdon and Hall 1994; Pascucci et al. relations based on map patterns, but the Cabot Strait in Newfoundland are 1999, 2000), but underlying pre-Car- no modeling of the data was attempt- still uncertain (e.g. Barr et al. 1998; bonferous units have not been well ed. In this study we use both recom- Valverde-Vaquero et al. 2006; Lin et al. imaged in seismic studies (e.g. Marillier piled magnetic and gravity maps and 2007). Part of the uncertainty can be et al. 1989). Both Langdon and Hall geophysical modeling, supported by attributed to the narrowness of the (1994) and Pascucci et al. (1999, 2000) previously published seismic reflection 188

data, as a basis for interpreting pre- Cape Breton Island Legend o o 59 58 Carboniferous units and structures Carboniferous sedimentary rocks (mainly) BLAIR RIVER INLIER BRAS D'OR TERRANE RIL Devonian St. George’s Late Cambrian under the Cabot Strait and their corre- Lowland Cove Formation Bay Granitic plutons Mesoproterozoic Meelpaeg Subzone lations with onshore units in both Anorthosite, syenite Cambrian - Ordovician Gneissic rocks Bourinot belt Cape Breton Island and southwestern Neoproterozoic 48º ASPY TERRANE Intermediate-felsic plutonic rocks F Devonian Newfoundland. We then use these Mafic-intermediate plutonic rocks Fisset Brook Formation CF - LRLRF Silurian - Devonian George River Metamorphic Suite RB data to discuss geological similarities F Granitic plutons Bras d’Or Gneiss CRCRF BDFZ Dioritic plutons BIS and differences between northeastern BMSZ LP FZ Ordovician - Devonian CC Cw Orthogneiss (mainly) Cape Breton Island and southwestern IMFZ GBFZ OP Low-grade metamorphic rocks Pt Cinq-Cerf block Notre Dame Newfoundland, and possible reasons High-grade metamorphic rocks Subzone Exploits subzone Port aux Grey River Neoproterozoic Basques for them. Mafic-felsic plutonic rocks Subzone Hermitage Flexure Metasedimentary & metavolcanic rocks Laurentian marginCabot Strait GEOLOGICAL BACKGROUND High-grade metasedimentary rocks

St. Paul Island Pre-Carboniferous Rocks Blair River Inlier Money The Appalachian orogen developed Point Ganderia 47º Aspy 47º during the Paleozoic on the southeast- Aspy Bay Avalonia 0 kilometres 50 ern margin of Laurentia. The Laurent- Pleasant Bay ian margin formed as a result of rifting Neils Harbour Red Head Bras Ingonish Island Newfoundland Legend of Gondwanan continental blocks Middle Head d’Or Laurentian Margin Ganderia Cape Smokey Carboniferous Port aux Basques Subzone Exploits Subzone EHSZ from Laurentia to open the Iapetus Sedimentary rocks Devonian Devonian Mesoproterozoic Granite Granitic rocks Silurian-Devonian Ocean, likely a protracted process dur- Steel Mountain Inlier Silurian-Devonian Rose Blanche Granite Granitic rocks (younger) Mira terrane Notre Dame Subzone Cambrian-Ordovician Granitic rocks (older) ing which larger blocks were removed Kellys Mountain (Avalonia) Silurian Margaree/Kelby Cove Orthogneiss Silurian Plutonic rocks Grand Bay Complex La Poile Group first followed by smaller Laurentian St. Anns Ordovician Port-aux-Basques Complex Ordovician Windsor Point Group Meelpaeg Subzone Harbour le Cou Group fragments with Grenvillian basement, Cambrian-Ordovician Silurian-Devonian Bay du Nord Group & related plutons Sydney Arc/back-arc volcanic rocks Granite Neoproterozoic-Cambrian such as the Dashwoods block in New- “Dashwoods block” Cambrian-Ordovician Cinq-Cerf block o (metasedimentary rocks) MB-GRF 60 Metasedimentary rocks Grey River Enclave foundland (e.g. Waldron and van Staal Boisdale Hills 2001; Cawood et al. 2001; Li et al. 2008; van Staal et al. 2013). Those Figure 2. Simplified geological map of northeastern Cape Breton Island and fragments were later re-attached along southwestern Newfoundland modified after Barr et al. (1992), Valverde-Vaquero et the margin during the Taconic orogeny. al. (2000, 2006), Hibbard et al. (2006), and Lin et al. (2007). Terrane boundaries in Similar detachment of fragments from the Cabot Strait area are after Hibbard et al. (2006). Fault abbreviations (in alpha- the Gondwanan side of the ocean betical order): BDFZ, Bay d’Est Fault Zone; BMSZ; Bay le Moine Shear Zone; resulted in the opening of another CCFZ, Cinq Cerf Fault Zone; CF-LRF, Cabot Fault – Long Range Fault; CRF, ocean, known as Rheic, between those Cape Ray Fault; EHSZ, Eastern Highlands Shear Zone; GBFZ, Grand Bruit Fault fragments and Gondwana (e.g. Nance Zone; IMFZ, Isle-aux-Morts Fault Zone; MB-GRF, McIntosh Brook – Georges and Linnemann 2009), and the trans- River Fault. Unit abbreviations in Newfoundland (in alphabetical order): BIS, Bur- port of the fragments across the clos- geo Intrusive Suite; Cw, Chetwynd Granite; LP, La Poile Granite; OP, Otter Point ing Iapetus Ocean to successively Granite; Pt, Petites Granite; RB, Rose Blanche Pluton. Relevant units in Cape Bre- accrete to the Laurentian margin in a ton Island are identified in Figure 3. series of events known as the Salinic, Acadian, and Neoacadian orogenies. subzone, which includes the Dash- phosed but also Gondwana-derived Ultimately, the arrival of the main mass woods block (Fig. 1). The boundary rocks of Avalonia and associated cover of Gondwana at the margin resulted in between these peri-Laurentian rocks sequences. the Carboniferous – Permian Alleghan- and now-adjacent peri-Gondwanan However, distinction ian orogeny. This long-lasting series of rocks is a deformed zone known as the among Laurentian, Ganderian, and events was accompanied by protracted Red Indian Line. East and southeast Avalonian components is less clear and widespread deformation, meta- of the Red Indian Line is Ganderia, along the southern coast of New- morphism, volcanism, and plutonism which consists of Gondwana-derived foundland, an area known as the Her- along the growing Laurentian margin continental fragments and their cover mitage Flexure (Williams 1978). No throughout much of the Paleozoic (see sequences, traditionally termed the Laurentian basement rocks are exposed summary in van Staal and Barr 2012). Gander Zone (Williams 1978), and in this area, and the Cabot – Long In central Newfoundland, associated complexly deformed, mainly Range Fault juxtaposes Carboniferous the Cabot (or Long Range) Fault sepa- oceanic and volcanic-arc rocks of the cover rocks against Lower Paleozoic rates several Grenvillian inliers and Exploits subzone (e.g. van Staal et al. rocks of the Notre Dame subzone their cover sequences of the Laurent- 2009). Ganderia extends to the east (Fig. 2). The Cape Ray Fault marks the ian margin (traditionally known as the across central Newfoundland as far as eastern margin of the Notre Dame Humber Zone; Williams 1978, 1979) the Dover – Hermitage Bay Fault (Fig. subzone in southwestern Newfound- from the mainly peri-Laurentian ocean- 1) which separates these rocks from land, and is generally interpreted to ic and arc rocks of the Notre Dame mainly less deformed and metamor- connect with the Red Indian Line and GEOSCIENCE CANADA Volume 41 2014 189 hence to separate peri-Laurentian and greenschist-facies conditions (Miller et Strait about 25 km northeast of the peri-Gondwanan components (Fig. 2). al. 1996). The Blair River Inlier has northeastern tip of Cape Breton Island Metasedimentary and metavolcanic age, compositional, and metamorphic (Fig. 2), consists of rocks inferred to rocks east of the Cape Ray Fault are similarities to Grenvillian rocks in the correlate with those of the Money generally assigned to Ganderia (e.g. Humber Zone of Newfoundland, Point area (Lin 1994; Barr et al. 1998). Schofield et al. 1998; Valverde-Vaquero although in the Blair River Inlier the The western part of the Aspy terrane et al. 2000; Hibbard et al. 2006, 2007; Grenvillian rocks were affected by Sil- contains Late Neoproterozoic meta- Lin et al. 2007), and the Isle-aux-Morts urian orogenic activity dated at 425 Ma morphic and plutonic rocks similar to Fault Zone separates the Port aux based on U–Pb ages from titanite and those of the Bras d’Or terrane (Lin et Basques (Gander) subzone from the zircon (Miller et al. 1996; Barr et al. al. 2007; Tucker 2011). Exploits subzone (Fig. 2). South of 1998). Also in contrast to the Humber The Bras d’Or terrane is the Bay d’Est Fault Zone in the Zone, the Blair River Inlier lacks a characterized by low-pressure Exploits subzone (Fig. 2), Silurian vol- widespread Cambrian – Ordovician cordierite – andalusite (or sillimanite) canic and sedimentary rocks of the La passive margin sedimentary sequence, gneiss and low- to high-grade metased- Poile Group lie unconformably on although minor calc-silicate and marble imentary and minor metavolcanic Late Neoproterozoic – Late Cambrian lenses interpreted to be either xenoliths rocks, both intruded by abundant ca. rocks (e.g. Dunning and O’Brien 1989; or fault-bound enclaves in the gneissic 565 – 555 Ma and ca. 500 Ma plutonic Dunning et al. 1990b; O’Brien et al. rocks may be remnants of such a cover rocks (Barr et al. 1990; Dunning et al. 1991; Valverde-Vaquero et al. 2006; Lin (Barr et al. 1998; Miller and Barr 2000). 1990a; Raeside and Barr 1990). The et al. 2007). The Late Neoproterozoic The ca. 580 Ma gabbroic dikes in the older plutons (565 – 555 Ma) are com- rocks include granodiorite and tonalite, Blair River Inlier are similar to other posed of diorite, tonalite, granodiorite together with porphyry intrusions and mafic units found along the northeast- and granite, and are interpreted to have metavolcanic rocks, yielding U–Pb zir- ern Laurentian margin that are likely formed in a continental margin sub- con ages ranging from ca. 686 – 548 associated with opening of the Iapetus duction zone (e.g. Barr and Setter Ma but mostly from ca. 585 – 557 Ma Ocean (Miller and Barr 2004). 1986; Farrow and Barr 1992). The ca. (Valverde-Vaquero et al. 2006). Also Both the Aspy and Bras 500 Ma plutons are of granitic compo- present are Late Cambrian intrusions d’Or terranes to the south of the Blair sition and may have formed by crustal dated at ca. 499 – 495 Ma (Valverde- River Inlier are considered to be part melting during post-orogenic uplift or Vaquero et al. 2006). Hibbard et al. of Ganderia (e.g. Hibbard et al. 2006). during periods of localized extension (2007) termed this area the Cinq-Cerf The Aspy terrane is characterized by within the terrane, perhaps linked to block, a term also adopted here (Fig. Ordovician and Silurian metasedimen- the initial stages of separation from 2). Some workers in Newfoundland tary and metavolcanic rocks affected by Gondwana in the Middle to Late Cam- have interpreted the Cinq-Cerf block Devonian thermal events and wide- brian (White et al. 1994; van Staal and to be part of Avalonia, rather than spread granitic magmatism (Fig. 3). Barr 2012). The variation in level of Ganderia, based on the Neoprotero- The metasedimentary and metavol- exposure in Bras d’Or terrane is con- zoic ages (e.g. O’Brien et al. 1991; canic rocks are assigned to a number sistent with the Bras d’Or terrane hav- Valverde-Vaquero et al. 2006). Most of of different units based on age and ing been thrust over the Aspy terrane; the rest of the Hermitage Flexure con- stratigraphic, structural and metamor- subsequent erosion thus exposes deep- sists of Silurian and Devonian plutonic phic characteristics, and show similari- er levels of the terrane near its bound- rocks, except in the Grey River area ties in ages and rock types to the La ary with the Aspy terrane (Barr et al. (Fig. 2) where Neoproterozoic rocks Poile Group and possibly other units 1995; Lin 2001). form a fault-bounded coastal strip in the Hermitage Flexure area in New- The boundary between the intruded by Devonian granite (Black- foundland (Barr and Jamieson 1991; Bras d’Or terrane and the Avalonian wood 1985; Dickson et al. 1989; Kerr Lin et al. 2007). Major plutonic units in Mira terrane to the southeast is placed and McNicoll 2012). the Aspy terrane include the ca. 375 at the McIntosh Brook – Georges In Cape Breton Island, Ma Black Brook Granitic Suite River Fault (Fig. 2). These Carbonifer- rocks representing the Notre Dame (Yaowanoiyothin and Barr 1991) and ous faults are inferred to mark a major subzone appear to be absent (Barr et ca. 402 Ma Cameron Brook Granodi- change in crustal composition, demon- al. 1998). Laurentian rocks of the orite (Dunning et al. 1990a). The Neils strated by differences in pre-Carbonif- Grenvillian Blair River Inlier, correlat- Harbour Gneiss includes components erous rock types and tectonothermal ed with Grenvillian basement inliers in of the Cameron Brook Granodiorite history across the boundary (e.g. Barr the Humber Zone (Barr and Raeside and Black Brook Granitic Suite, as well et al. 1990, 1995, 1998; Raeside and 1989; Miller et al. 1996; Miller and Barr as biotite-rich paragneiss of uncertain Barr 1990). King (2002) showed sys- 2000), are juxtaposed against peri- protolith and age (Yaowanoiyothin and tematic contrasts in physical properties Gondwanan rocks in the area known Barr 1991). Also potentially important and geophysical characteristics between as the Aspy terrane. The Blair River in the present study is the Ingonish Precambrian rocks in the Bras d’Or Inlier is composed of gneiss, syenite Island rhyolite, a magnetite-rich rhyo- and Mira terranes, and modeled the and anorthosite that have been meta- lite that crops out only on Ingonish terrane boundary as sub-vertical at sur- morphosed partly to granulite facies Island (Barr and Raeside 1998; Fig. 3). face, shallowing to a dip of 50–70° and overprinted at amphibolite- and St. Paul Island, located in the Cabot northwest at depth. Magnetic and 190

Figure 3. Enlarged view of the geo- Carboniferous sedimentary rocks (mainly) St. Georges logical map of northeastern Cape Bre- BLAIR RIVER INLIER BRAS D'OR TERRANE Bay ton Island from Figure 2 with map Devonian Late Cambrian Lowland Cove Formation 48º units relevant to this study identified. Granitic plutons Mesoproterozoic Locations of potential field models 1 Anorthosite, syenite Cambrian - Ordovician through 5 are also shown. Terrane Gneissic rocks Bourinot belt boundaries in the Cabot Strait area are ASPY TERRANE Neoproterozoic after Hibbard et al. (2006). Abbrevia- Devonian Intermediate-felsic plutonic rocks CF - LRF tions: BB, Black Brook Granitic Suite; Fisset Brook Formation Mafic-intermediate plutonic rocks Silurian - Devonian Be, Benacadie Brook Formation; BH, George River Metamorphic Suite Granitic plutons Boisdale Hills pluton; BL, Bell Lakes Bras d’Or Gneiss CRF Plutonic Suite; Bo, Bourinot belt; BP, Dioritic plutons 0 Ordovician - Devonian Laurentian margin Birch Plain Granite; BR, Barachois Notre Dame Orthogneiss (mainly) Magdalen Basin Subzone River Formation; Ca, Cameron Brook Port aux Basques Low-grade metamorphic rocks Granodiorite; Ch, Cheticamp Lake 0 Subzone Gneiss; Cl, Clyburn Brook formation; High-grade metamorphic rocks Line 1 CM, Cross Mountain Pluton; CN, Neoproterozoic Cape North Group; CS, Cape Smokey Mafic-felsic plutonic rocks Cabot Strait Pluton; Fv, Frenchvale Road Metamor- Metasedimentary & metavolcanic rocks Line 2 phic Suite; GB, Glasgow Brook High-grade metasedimentary rocks 0 St. Paul 80 Orthogneiss; GF, Gisborne Flowage Island Quartz Diorite; IB, Indian Brook Gra- nodiorite; IR, Ingonish River Tonalite; KG, Kellys Mountain Gneiss; KM, WBF 0 Money Kellys Mountain Granite; KR, Kathy MPPoint Line 3 47º Aspy Fault 47º Road Diorite; Ma, Margaree Pluton; WS 80 MB-GRF, McIntosh Brook – George Aspy River Fault; MC, Mount Cameron Bay RRF Sydney Basin CN Syenogranite; MF, McMillan Flowage Pleasant MP NH Line 4 Formation; Mo, Middle Aspy River Bay GB CN BB Neils Mo Orthogneiss; MP, Money Point Group; ? Harbour 60 80 NH, Neils Harbour Gneiss; PS, Park Ma MP Red Head Ca Ingonish Island Spur Granite; RRF, Red River Fault; Ch Cl In Middle Head SB, Sarach Brook Metamorphic Suite; IR Cape Smokey Sh, Shunacadie pluton; TL, Timber EHSZ CS PS GF Lake Diorite; WBF, Wilkie Brook WC SB BP Fault; WC, Wreck Cove Dioritic Suite; MF IR Line 5 WS, Wilkie Surgarloaf Granite. CM IB 110 KR 0 Kellys TL Mountain Mira terrane BR PP (Avalonia) St. KM Anns BL KG MC Fv Sydney

Big Hill 0 30 Be km o MB-GRF 60 Sh BoisdaleBH HillsBo gravity map patterns indicate that the around the periphery of the Cape Bre- 1989; Gibling et al. 2008). It is over- original terrane boundary has been cut ton Highlands (Fig. 2). Locally, lain by the Viséan Windsor Group, and offset by other faults, consistent Devonian sedimentary and bimodal which also oversteps pre-Carbonifer- with a dynamic post-Devonian tectonic volcanic rocks of the Fisset Brook ous units and includes clastic rocks as history (e.g. Pascucci et al. 2000; King Formation underlie the Carboniferous well as carbonate and evaporite rocks 2002). units, forming the early fill in exten- deposited in a marine environment. sional basins that developed after The Windsor Group is overlain con- Maritimes Basin Devonian orogenesis. The more wide- formably by Viséan to Serpukhovian Onshore, Devonian and Carboniferous spread Tournaisian Horton Group lacustrine rocks of the Mabou Group, sedimentary rocks of the Maritimes occupies fault-bounded basins across which are in turn unconformably over- Basin overlie the older rock units Atlantic Canada (e.g. Hamblin and Rust lain by Pennsylvanian fluvial/lacustrine GEOSCIENCE CANADA Volume 41 2014 191 rocks of the Cumberland Group and the sedimentary fill in the Magdalen direction. The data were converted red mudstone and sandstone of the and Sydney basins. They interpreted St. from NAD 27, UTM Zone 21, to Pictou Group, which extends in places Paul Island to be located on a restrain- WGS84 at the Newfoundland and into the Permian (e.g. Pascucci et al. ing bend along the Cabot Fault. Labrador Department of Natural 2000). In southwestern Newfoundland Resources. This data set was adjusted west of the Cabot Fault in the Bay St. METHODS and leveled so that it could be merged George sub-basin, the Anguille and Most of the digital magnetic and all of smoothly with the magnetic data Codroy groups are equivalent to the the gravity data used in this project obtained from the GSC. Horton and Windsor groups, respec- were obtained from the Geological The merged magnetic data tively, and the Barachois group of Survey of Canada (Natural Resources sets were gridded at a spacing of Newfoundland is probably equivalent Canada). Additional digital aeromag- 0.00625 degrees (~1 km) with an to parts of the Mabou and Cumber- netic data for the St. George’s Bay area adjustable-tension continuous-curva- land groups (e.g. Knight 1983; Lang- were obtained from the Newfoundland ture-surface algorithm using a cylindri- don and Hall 1994). and Labrador Department of Natural cal Mercator projection; the datum Carboniferous sedimentary Resources. The magnetic and gravity remained WGS84 (Wessel and Smith rocks are generally less than 2 km thick data were acquired in point form from 2012). For the total magnetic field onshore in Cape Breton Island but previously gridded compilations to anomaly map, the data were displayed thicken significantly in the offshore, allow them to be re-gridded in the using GMT in UTM projection. Addi- both to the north in the Magdalen desired datum and projection. The tional data filtering was applied to Basin, and to the east in the Sydney datum used for all of the acquired digi- enhance anomalies in the study region, Basin, extending onto southwestern tal data is World Geodetic System 1984 and the first and second vertical deriva- Newfoundland (Fig. 3). Both basins (WGS84), using a geographic coordi- tives were calculated using GMT (Wes- are part of the regional Maritimes nate system. Grids were generated sel and Smith 2012). Basin, which includes most Carbonifer- from the gravity and magnetic digital The digital gravity data ous rocks in Atlantic Canada (e.g. Gib- data using Generic Mapping Tools obtained for this study are a compila- ling et al. 1987). In the Sydney Basin, (GMT 4.5.8), open-source software tion of gravity measurements collected the Horton Group fills extensional that includes about 65 tools for the from marine and ground surveys. The basins within pre-Carboniferous ‘base- manipulation of geographic and Carte- spacing for measurements was 5–10 ment blocks’, bordered by south-dip- sian data sets. The GMT software was km on land, and 2–5 km for ship ping master fault zones (Pascucci et al. developed and is maintained by Paul tracks offshore. All necessary data cor- 2000). The Horton Group is over- Wessel and Walter H.F. Smith rections had been applied to produce stepped by the overlying Windsor and (http://gmtsoest.hawaii.edu/). merged grids, at 2 km resolution, of Mabou groups, which also rest on pre- The digital magnetic data free-air anomalies for onshore and Carboniferous basement rocks (Pascuc- obtained from the Geological Survey Bouguer anomalies for offshore. The ci et al. 2000). The varied styles of of Canada are composed of a compila- gravity anomaly data were re-gridded at superimposed basins have generated a tion of marine survey data and aero- 1.5 km (~0.8 minutes) into the UTM composite depocentre in the Sydney magnetic (1 km) gridded data. The projection for this study. The gravity Basin (Pascucci et al. 2000). marine survey data, of various vintages and magnetic anomaly maps are all dis- The sediment fill in the Mag- and line orientations, had already been played using an artificial illumination dalen Basin is thicker than in the Syd- compiled and adjusted by Verhoef et angle of 315° to enhance southwest – ney Basin but contains equivalent al. (1996) to account for variations in northeast-trending features. stratigraphic units, as well as extensive the magnetic field, to correct cross- The program GM-SYS® volcanic rocks in the central part of over errors, and to filter and remove (PRO) 4.8 was used to generate 5 for- the basin and widespread evaporite acquisition and gridding artefacts. ward models using magnetic and gravi- rocks and associated salt tectonics (e.g. Wavelengths exceeding 400 km were ty data along selected lines across key Langdon and Hall 1994). The Cabot removed from the marine data grid, features in the study area (Fig. 3). The Strait area is located at the boundary and the marine and aeromagnetic sur- models use a present day magnetic between these two basins, and is char- vey blocks were then assembled into a field strength of 43.136552 A/m, incli- acterized by structural complexity new 500 m grid. All data have been nation of 75.686°, and declination of involving both salt tectonics and strike- reduced to the IGRF (International –24.836°. Such models are non-unique, slip faults (Langdon and Hall 1994). Geomagnetic Reference Field). in that a set of specific magnetic and Langdon (1996) and Langdon and Hall The data set for the St. gravity data can be matched by an infi- (1994) used industry reflection seismic George’s Bay area, obtained from the nite number of models. However, data to identify several major strike-slip Newfoundland and Labrador Depart- some constraints are provided by mag- faults in the Cabot Strait and St. ment of Natural Resources, was col- netic susceptibility data available for George’s Bay area. According to Lang- lected by Sander Geophysics Ltd. for rock units in the Bras d’Or and Aspy don and Hall (1994) the Cabot Fault is the Hunt Oil Company in 1993. The terranes and Blair River Inlier in Cape the main fault along which most of the airborne survey was flown with a line Breton Island. These data were strike-slip displacement occurred dur- spacing of 7500 m in the northeast obtained using a hand-held Explorani- ing late Carboniferous deformation of direction, and 3000 m in the southeast um KT-9 Kappameter and are tabulat- 192 ed in King (2002), Cook (2005), and Zsámboki (2012). Data for selected 0 km 50 units are summarized in Appendix A. Some measured density data are available from previous work (King 2002; 48˚ Cook 2005) but in general, density values used in the models were guided by data from similar rock types (e.g. Tenz- er et al. 2011).

MAGNETIC AND GRAVITY MAPS The various geologic zones and sub- St. Paul zones in the study area are character- Island ized by differences in magnetic and gravity anomaly signatures, such as dif- 47˚ ferences in amplitude, wavelength, and nT degree of variability of the anomalies, 500 evident in map view (Figs. 4–7). These 400 IMA 300 signatures are summarized here, focus- 200 100 ing on onshore areas where they can 0 be related at least in part to known -100 -200 geological units. Geological contacts -300 and faults from Figures 2 and 3 are -400 shown as white lines for reference on maps of total magnetic field anomalies (Fig. 4), first and second vertical deriv- 46˚ atives of magnetic field (Figs. 5, 6), and -61˚ -60˚ -59˚ -58˚ -57˚ gravity anomalies (Fig. 7). Carbonifer- Figure 4. Total field magnetic anomaly map of the Cabot Strait area, compiled as ous cover units have generally low sus- described in the text. White lines are the onshore geological map unit boundaries ceptibility (< 2 x 10–3 SI units) and and faults from Figure 2. The large positive anomaly east of Cape Breton Island is hence have little effect on magnetic the Ingonish magnetic anomaly (IMA). signatures. Because they also have relatively low density (< 2600 kg/m3), consistent with their lower measured mediate plutons to the north. variations in sediment thickness have a susceptibilities (average 0.3 – 5 x 10–3 On the first derivative magnet- significant effect on gravity anomalies SI units; Appendix A). A strong linear ic map (Fig. 5), strong linear anomalies (Fig. 7). The gravity anomaly map also magnetic anomaly trends east-west associated with Bras d’Or terrane plu- shows a series of lows in the Cabot through the Middle Head area and tons are more prominent than on the Strait, trending to the southeast, which appears to connect with a very promi- total field anomaly map, particularly in are associated with the deeper water of nent anomaly in the offshore referred the offshore. The Middle Head linear the Laurentian Channel. These anom- to here as the Ingonish magnetic anomaly is accentuated on the first alies are caused by the juxtaposition of anomaly (Fig. 4). Assessing the cause derivative map and extends into the lower density water in the deeper Lau- of this large (up to 500 nT) circular area of the Ingonish magnetic anomaly rentian Channel against the higher den- anomaly is an important aspect of this in the offshore. On this map, the sity sedimentary deposits located on study. The granitic and dioritic rocks Ingonish magnetic anomaly appears either side of the channel. on Middle Head have been correlated less circular, and has been resolved into with the Cape Smokey Granite (aver- two parts, a southern part superim- Bras d’Or Terrane age k = 3.2 x 10–3 SI units) and Wreck posed on a northeast-trending linear Strong positive magnetic anomalies Cove Dioritic Suite (average k = 10.4 x anomaly, and an elongate east-west (200–500 nT) are associated with the 10–3 SI units) on the basis of overall northern part (Fig. 5). plutons that form much of the eastern petrological characteristics (Raeside On the second derivative mag- Bras d’Or terrane (e.g. Indian Brook and Barr 1992). Farther south, magnetic map (Fig. 6), linear trends from Granodiorite and similar plutons, Birch netic anomalies associated with the onshore magnetic (plutonic) units of Plain Granite, Wreck Cove Dioritic Kellys Mountain and especially the the eastern Bras d’Or terrane into the Suite, Ingonish River Tonalite; Fig. 3). Boisdale Hills areas are more subdued, offshore are even more apparent, and These units are also characterized by consistent with the fact that these areas it seems likely that all of the pre-Car- high average measured magnetic sus- are dominated by metamorphic rocks boniferous units of the Bras d’Or ter- ceptibilities in the range of 3–12 x 10–3 and intermediate to felsic plutonic rane extend northeast into the off- SI units (Appendix A; Zsámboki 2012). rocks (e.g. Barr and Setter 1986; Rae- shore. In particular, the Wreck Cove Their host metamorphic units are asso- side and Barr 1990) that are generally Dioritic Suite and Indian Brook Gran- ciated with low magnetic signatures, less magnetic than the mafic to inter- odiorite/Birch Plain Granite appear to GEOSCIENCE CANADA Volume 41 2014 193

ble link is suggested between a strong 0 km 50 northeast-trending linear anomaly having a source that appears to coincide with the Money Point Group, and an 48˚ anomaly with a similar trend in Aspy Bay. Strong anomalies that trend east- southeast characterize the northeastern part of the Aspy terrane south of Aspy Bay. Units farther west and south in the Aspy terrane have positive mag- St. Paul netic signatures, including part of the Island Money Point Group and the Margaree Pluton (Figs. 3, 4), consistent with vari- 47˚ able but generally relatively high meas- nT/m ured susceptibilities (Appendix A). 0.09 The Neoproterozoic units in the western part of the terrane have also IMA 0.06 0.03 strong anomalies, consistent with their 0.00 possible link to the Bras d’Or terrane -0.03 (Barr and Raeside 1989). -0.06 The first derivative magnetic -0.09 map (Fig. 5) brings out the prominent east-southeast-trending linear anomalies in the Black Brook Granite Suite 46˚ south of Aspy Bay (Fig. 3). They -61˚ -60˚ -59˚ -58˚ -57˚ extend to the west into the Money Figure 5. First vertical derivative of the total field magnetic anomaly map of the Point Group and Glasgow Brook gran- Cabot Strait study area. White lines are the onshore geological map unit bound- odiorite, although samples from all of aries and faults from Figure 2. Labels for St. Paul Island and Ingonish magnetic those units in that area have low mag- anomaly (IMA) are in the same positions as in Figure 4 for reference. Small arti- netic susceptibilities (Appendix A). facts are apparent at the contacts between data sets of different initial resolutions, The fact that these linear features and can be distinguished by their north-south or east-west orientation (e.g. at intensify on the first derivative map 59.5°W). (Fig. 5) compared to the total field map (Fig. 4) suggests that they are caused continue into the area of the Ingonish Aspy Terrane by shallow features such as mafic magnetic anomaly, which has been The total field magnetic anomaly map dykes; however, no evidence for mafic resolved into smaller elliptical anom- (Fig. 4) shows low and negative mag- dykes or faults was observed during alies superimposed on the linear anom- netic anomalies associated with units in field work in those areas alies. Also prominent are linear trends the eastern part of the Aspy terrane (Yaowanoiyothin and Barr 1991). extending into the offshore from such as the Black Brook Granitic Suite, They terminate in the offshore at weak Kellys Mountain and the Boisdale Hills Neils Harbour Gneiss, Cameron Brook southwest-trending linear anomalies (Fig. 6). These trends are more north- Granodiorite, Clyburn Brook Forma- associated with the edge of the north- easterly than those associated with the tion, Cheticamp Lake Gneiss, and Park ern part of the Ingonish magnetic Mira terrane south of the MacIntosh Spur Granite (Fig. 3). These units all anomaly (Fig. 5). These anomalies are Brook – Georges River Fault (Fig. 3). have low average magnetic susceptibili- also prominent on the second deriva- The Bras d’Or terrane north ty, generally less than 1 x 10–3 SI units, tive magnetic map (Fig. 6). of the Kellys Mountain area is associ- although the Cameron Brook Granodi- The northeastern part of the ated with a strong positive gravity orite is somewhat higher at 3.5 x 10–3 Aspy terrane is characterized by a anomaly (20–40 mGal) that extends SI units (Appendix A). Rhyolite weaker gravity signature (0–10 mGal) into the adjacent offshore (Fig. 7). exposed only on Ingonish Island has compared to the neighbouring Bras This anomaly may be associated with an average susceptibility of 8.4 x 10–3 d’Or terrane (Fig. 7). However, posi- heavy deep crustal rocks that have SI units, but the lack of an associated tive (~20 mGal) gravity anomalies are been brought to shallower depths as anomaly suggests that it is of limited present in the western part of the ter- the Bras d’Or terrane was thrust over extent. The low and negative magnetic rane where Precambrian rocks crop the Aspy terrane, as suggested in the anomalies associated with the Aspy ter- out at surface, and in the south where tectonic models of Barr et al. (1995) rane extend into the offshore, where they may indicate the presence of simi- and Lin (2001). they appear to terminate against the lar rocks at depth. Ingonish magnetic anomaly. A possi- 194

The Notre Dame subzone is 0 km 50 characterized by strong positive and negative anomalies that extend only a short distance into the offshore to the 48˚ southwest, where they appear to terminate abruptly, likely at the extension of the Cape Ray Fault (Fig. 4). The strong positive anomalies (200–500 nT) are linked to ophiolitic and tonalitic arc rocks that characterize the subzone (e.g. van Staal et al. 2009). St. Paul Younger (Silurian) plutonic units dis- Island play both strong and weak signatures, suggesting that they are compositional- 47˚ ly varied. The metasedimentary rocks of the Dashwoods block (Fig. 2) show a strong negative magnetic anomaly, 2 nT/m although a southern lobe assigned to IMA 1e-05 5e-06 that unit by Hibbard et al. (2006) has a 0 strongly positive magnetic signature, -5e-06 more consistent with its designation as -1e-05 Notre Dame arc rocks (Colman-Sadd -1.5e-05 et al. 1990). A strong linear anomaly -2e-05 (400 nT) near the Cape Ray fault and extending offshore appears to be asso- 46˚ ciated with granodioritic rocks of the -61˚ -60˚ -59˚ -58˚ -57˚ Cape Ray Igneous Complex. The Figure 6. Second vertical derivative of the total field magnetic anomaly map of Notre Dame subzone also displays the Cabot Strait study area. White lines are the onshore geological map unit strong positive gravity anomalies (0 to boundaries and faults from Figure 2. Labels for St. Paul Island and Ingonish mag- 40 mGal). netic anomaly (IMA) are in the same positions as in Figure 4 for reference. The adjacent Port aux Basques subzone shows more subdued anom- Blair River Inlier River Inlier is down-faulted in this area alies, which extend to the southwest On the total field anomaly map, the but continues west under Carbonifer- into the offshore. A prominent linear Blair River Inlier is characterized by ous cover. anomaly characterizes the Isle-aux- strong positive anomalies (200–500 Morts Fault, and an adjacent, similar nT) that contrast in orientation and Southwestern Newfoundland anomaly appears to be associated with magnitude with those in the adjacent The Laurentian margin northwest of the Margaree orthogneiss, a metaplu- Aspy terrane (Fig. 4). Susceptibility the Cabot – Long Range Fault in tonic unit of Ordovician age measurements are relatively high in southwestern Newfoundland is charac- (Valverde-Vaquero et al. 2000). The both gneissic and plutonic components terized by subdued magnetic anomalies Exploits subzone southeast of the Isle- of the Blair River Inlier (Appendix A). characteristic of thick Carboniferous aux-Morts Fault is dominated by a pat- Both the first and second derivative cover on Grenvillian basement, as pre- tern of negative anomalies that extends magnetic maps show less linearity in viously investigated by Miller et al. at least to the eastern edge of the map the anomalies of the Blair River Inlier (1990). However, farther north, area. These low and relatively feature- compared to adjacent areas (Figs. 5, 6). Grenvillian basement is exposed in the less magnetic signals are associated A positive anomaly west of the Blair Steel Mountain Inlier, which has a with the Bay du Nord and Harbour le River Inlier implies that similar rocks prominent magnetic signature Cou groups; plutonic components can may continue in the offshore in that (300–500 nT), further accentuated on be discerned as having generally lower area. The abrupt change in signal the first and second derivative magnet- magnetism than associated stratified intensity at the Carboniferous contact ic maps (Figs. 4–6). The anomaly and volcanic units. This pattern differs suggests that an east-west-trending extends to the southwest into the Bay from that of the Meelpaeg subzone fault might be present, with thick Car- St. George Carboniferous basin, an (Fig. 2), consistent with the inclusion boniferous rocks to the north. In con- area known to have shallow Grenville of the latter area in the Gander rather trast to its strong magnetic signal, the basement (e.g. Knight 1982, 1983). than the Exploits subzone (e.g. Hib- gravity anomalies associated with the The magnetic signature of the Steel bard et al. 2006). An elliptical anom- Blair River Inlier are weak (0–10 Mountain Inlier is similar to that of aly with a ‘halo’ effect characteristic of mGal), but indicate some continuation the Blair River Inlier, consistent with plutons (e.g. Cook et al. 2007) is asso- in the offshore (Fig. 7). Dehler and the presence of similar rock types in ciated with the Silurian – Devonian La Potter (2002) proposed that the Blair those two areas. Poile Batholith (Fig. 2) and extends 30 GEOSCIENCE CANADA Volume 41 2014 195

nates against a set of anomalies that 0 km 50 characterize the offshore extension of the Notre Dame subzone. To the northwest, a weaker linear anomaly 48˚ extends from Money Point through and past St. Paul Island, where it fades away. This anomaly supports the correlation between rocks on St. Paul Island and the Money Point peninsula as proposed by Lin (1994), based on his mapping of St. Paul Island. St. Paul To the southeast of St. Paul Island Island, a large elliptical and composite- looking anomaly trends northeast, and 47˚ a smaller circular anomaly occurs farther to the northeast (~ 47.3°N, mGal 59.2°W; Fig. 5). On the first derivative 50 map (Fig. 5), both are characterized by IMA 25 a positive rim and negative core, i.e. 0 they display a halo effect typical of -25 granitic plutons and their adjacent con- -50 tact metamorphic aureoles (e.g. Cook -75 et al. 2007); the elliptical feature may -100 consist of two separate but overlapping anomalies. The linear anomalies 46˚ extending from Aspy Bay in Cape Bre- -61˚ -60˚ -59˚ -58˚ -57˚ ton Island and the Cape Ray and Isle- Figure 7. Bouguer (onshore) and free-air (offshore) gravity anomaly map of the aux-Morts faults in Newfoundland are Cabot Strait study area. White lines are the onshore geological map unit bound- located along the northwestern edge of aries and faults from Figure 2. Labels for St. Paul Island and Ingonish magnetic the elliptical anomaly. anomaly (IMA) are in the same positions as in Figure 4 for reference. On the total field magnetic map (Fig. 4), the Sydney Basin displays km into the offshore (Figs. 5, 6). The may have different basement. several weak linear anomalies trending continuation into the offshore with no toward Newfoundland. These linear loss in magnitude indicates that it is a Cabot Strait trends are much more apparent on the near-surface feature. Similar elliptical The large Ingonish magnetic anomaly first derivative map (Fig. 5), indicating and in this case overlapping halo is a prominent feature on the total field that their sources are relatively shallow anomalies are associated with the Bur- magnetic anomaly map (Fig. 4). The under low-magnetic Carboniferous geo Intrusive Suite (Fig. 2); this pattern central part of the anomaly shows the sedimentary cover. These moderate to is consistent with a composite body highest magnitude (400 – 500 nT) and strong positive elongate anomalies are comprising separate plutons extending as noted above, a narrow anomaly on broken up into smaller sections and into the offshore about 20–30 km the western side of the main anomaly appear to form the background for (Figs. 5, 6). Anomalies associated with appears to connect it to Cape Breton elliptical anomalies associated with the this plutonic suite continue east to the Island in the Middle Head area. On Burgeo Intrusive Suite that characterize Grey River area and make it difficult to the first derivative map, the Ingonish nearshore and onshore Newfoundland. trace the eastward extent of the rela- magnetic anomaly is resolved into a Prominent gravity lows of –20 tively small Cinq-Cerf block (Silurian number of smaller anomalies, some of to –100 mGal characterize the Mag- and older rocks) located west and which are elliptical and some of which dalen Basin in the Cabot Strait area, north of the intrusive suite and south are linear (Fig. 5). The latter appear to coinciding with an area of thick evap- of the Bay d’Est Fault, or to infer how connect with linear trends defined by orite rocks and salt tectonics (Langdon they might link to the Neoproterozoic the onshore Bras d’Or terrane. In con- and Hall 1994; Langdon 1996; Hay- metamorphic rocks of the Grey River trast to its strong magnetic signature, ward et al. 2014). The Sydney Basin area. The gravity anomaly map shows the area of the Ingonish magnetic also shows areas of low gravity anom- few significant anomalies in the Port anomaly displays only weak gravity alies (0 to –80 mGal), one in the Cabot aux Basques and Exploits subzones, in anomalies, up to 10 mGal (Fig. 7). Strait area and one farther south off- contrast to those of the Notre Dame In the Cabot Strait, a long nar- shore from the Mira terrane; these subzone (Fig. 7). The Port aux Basques row anomaly extends offshore from anomalies are superimposed on the subzone has higher positive gravity Aspy Bay and appears to widen and faint trace of the wide, northwest- anomalies (~10 mGal) than the increase in intensity (100 to 500 nT) as trending Laurentian Channel. Exploits subzone, suggesting that it it nears Newfoundland, where it termi- 196

NW (a) LINE 1 SE Figure 8. (on this and the follow- 300 MAGNETICS ing page) Forward models for (a) line 1, (b) line 2, (c) line 3, (d) line 4, and 0 nT (e) line 5. Layers 1, 2, and 3 corre-

model observed spond to the Pictou + Morien, Wind- -300 sor + Mabou, and Horton groups, 0 GRAVITY respectively. Density values assigned 3 -40 to each source are in kg/m . Suscepti- mGal bility values (in italics) are in SI units. observed -80 model Interpretations of rock units and key to abbreviations are summarized in 0 Layer 1 2150 Figure 9.

Layer 2 2650 km PB1 PB1 BD2 GB 3050 ND 3050 PB2 3050 EX1 EX2 0.035 0.035 EX1 0.02 2875 2875 2950 PB2 3050 2900 BD1 0.03 3050 POTENTIAL FIELD MODELS 0.007 0.12 2950 0.001 0.06 2940 0.12 0.001 0.04 10 Two-dimensional models were pre- 0204060km80 pared along 4 northwest – southeast profiles in the Cabot Strait and a single NW (b) LINE 2 SE northeast – southwest profile near MAGNETICS Cape Breton Island (Fig. 3). The goal 200 of the modeling was to correlate geo- nT 0 logic units and boundaries across the -200 observed model offshore realm, and provide linkages to 0 geologic units mapped onshore. The GRAVITY models (Fig. 8a-e) are by nature some- -40

mGal what simplified, as few constraints are

observed model available for thicknesses of sub-sedi- -80 mentary units, and the emphasis is on 0 determining relationships between Layer 1 2150 units, as needed to provide a good

2650 first-order fit to the observed data. As Layer 2 such, the recognition of units with

km 2700 Layer 3 consistent properties on multiple lines, EX1 BD1 GB PB1 PB1 2700 EX1 BD2 3050 2940 and their contrasts with adjacent units, 2875 3050 3050 3050 PB2 PB2 0.001 EX2 0.04 0.007 0.035 0.001 0.035 2950 2950 2900 3050 allowed correlations to be made and 0.12 0.12 0.06 0.02 10 extended across the region. The 0 20 40 60 km 80 process was iterative, as the model pre- dictions were tested against geologic NW (c) LINE 3 SE information and other constraints and MAGNETICS adjusted until a ‘best fit’ product was 200 derived. Figure 9 provides a key to the nT 0 naming of the model units; pre-Car- -200 observed model boniferous units were assigned names

20 GRAVITY based on the terranes inferred to be present at surface, or in some cases -20

mGal arbitrary letter designations.

observed model -60 Line 1 0 Line 1 extends from the Magdalen Layer 1 2150 OUT Basin northwest of the Cabot – Long 2800 Layer 2 0.002 2650 Range Fault to the Sydney Basin in the GB Layer 3 southeast (Fig. 8a). The line crosses BD1

km 2700 2875 2940 two linear magnetic anomalies continu- 0.007 PB1 0.04 BD3 3050 PB2 EX1 ing offshore from the Notre Dame and PB1 EX2b BD2 2940 0.035 3050 2950 3050 2900 3050 0.01 Port aux Basques subzones, and a cir- 0.12 0.035 0.08 0.001 0.02 10 cular halo anomaly to the south (Fig. 020406080km 10), all of which are apparent on the GEOSCIENCE CANADA Volume 41 2014 197

NW (d) LINE 4 SE 600 MAGNETICS 300 nT 0 observed model

GRAVITY 0

mGal -40 observed model

0 Layer 1 OUT 2150 2800 Layer 2 0.002 2650

Layer 3

km 2700 EX1 GB BD3 BD1 MC PB1 3050 H1 H2 BD2 2940 PB2 PB1 IIR MID AV 2875 0.001 2940 0.01 2700 0.007 3050 2950 3050 2800 2950 3000 2950 3050 0.04 0.15 2820 0.035 0.12 0.035 0.06 0.18 0.12 0.16 0.02 0.008 10 0204060km 80 100

Figure 8. (continued). SW (e) LINE 5 NE MAGNETICS 600 300 nT 0 observed model pretation of Langdon and Hall (1994). GRAVITY Faults are not identified in these layers 20 because of the lack of physical property contrasts, but seismic interpretations mGal -20 indicate that they are present (e.g. observed model Langdon and Hall 1994). Pre-Carboniferous rocks (sub- 0 sequently referred to as ‘basement’) lie Layer 1 2150 at depths of approximately 4 to 6 km Layer 2 2650 below the sea floor. The central positive magnetic anomaly is inferred to Layer 3 2700 reflect basement sources PB1 and PB2 km (Figs. 8a, 10); PB2 is interpreted as plu-

BD3 BD1 H2 MID tonic rock that intrudes PB1 in two 2940 2940 3000 locations. These plutons are represent- 2950 0.11 0.055 0.10 0.18 ed by the two most northwestern anomaly peaks in the profile. The 10 0 20 40 km 60 lower magnitude but wider anomaly to the southeast represents the smaller magnetic halo in the Cabot Strait (Fig. magnetic profile. along the profile, increasing into the 10), as shown in the model by base- The model for this profile Magdalen Basin to the north and Syd- ment source EX2, which is inferred to shows two sedimentary layers 1 and 2, ney Basin to the south. Layer 2 is have intruded a less magnetic unit than interpreted to correspond to the Pictou thicker, varying between 1800 m and PB1, identified as EX1. The positive + Morien and Windsor + Mabou 5700 m, and thins to the south. Hor- gravity anomaly in the profile is attrib- groups, respectively, based on pub- ton Group rocks may be present in the uted to a combination of PB1 and lished interpretations of seismic reflec- lower part of Layer 2 but could not be PB2. Lower gravity values are seen tion profiles in the area (Langdon and conclusively identified on the models over unit EX2, which is interpreted as Hall 1994). Thickness of sedimentary or seismic interpretations. They appear an intrusive unit. layer 1 ranges from 300 m to 2650 m only as a thin unit on the seismic inter- Northwest of PB1, less mag- 198

Metavolcanic and Water: 1026, 0 Water PB1 (PAB): 3050, 0.035 MID (intrusion): 3000, 0.12 Granitoid pluton (IMA) metasedimentary rocks

Layer 1 (sed): 2150, 0 PB2 (PAB): 2950, 0.12 Margaree orthogneiss BD1 (Bras d’Or): 2940, 0.04 Granitoid pluton Pictou+Morien groups & equivalent

Layer 2 (sed): 2650, 0 Windsor+Mabou groups OUT (outcrop): 2800, 0.002 Metavolcanic and BD2 (Bras d’Or): 3050, 0.02 Granitoid pluton metasedimentary rocks Meta-igneous and Layer 3 (sed): 2700, 0 Horton Group ND (Notre Dame): 2875, 0.03 BD3 (Bras d’Or): 2940, 0.01 Granitoid pluton metasedimentary rocks

McAdams Lake Fm, EX2b (Exploits): 2900, 0.08 Granitoid pluton IIR (rhyolite): 2800, 0.08 Ingonish Island rhyolite MC (sed): 2700, 0.015 minor syenite Meta-igneous and Granitoid pluton H1 (intrusion): 2950, 0.18 Granitoid pluton (IMA) AV (Avalon): 2820, 0.008 EX2 (Exploits): 2900, 0.06 metasedimentary rocks

Metavolcanic and Gneiss, anorthosite, EX1 (Exploits): 3050, 0.001 H2 (intrusion): 2950, 0.16 Granitoid pluton (IMA) GB (Grenville): 2875, 0.007 metasedimentary rocks syenite

Figure 9. Summary of density and magnetic susceptibility values for units depicted in the forward-modeling profiles, and an interpretation of their geological significance. Density units are kg/m3 and magnetic susceptibilities are in SI units. Magnetic highs H1, H2, and MID are inferred sources of the Ingonish magnetic anomaly (IMA). netic sources are interpreted to represent Notre Dame subzone basement 0 km 50 (ND), and Grenville basement (GB). ND basement has density similar to GB but slightly higher susceptibility. 48˚ The contact between GB and ND is suggested in the model to be a steep, Li ne 1 south-dipping fault, which coincides Line 2 Grenville Basement with the Cabot Fault as interpreted by Langdon and Hall (1994) on Seismic ND PB1 PB2 Ex2 EX1 Line 81-1103. The nearly vertical Line 3 boundary between basements ND and PB1 is inferred to be the offshore Ex2 BD2 PB1 BD1 extension of the Cape Ray Fault (Fig. Ex2 10). BD2 47˚ BD1 Bras d’Or terrane The near-vertical boundary PB2 PB1 Ex2b BD2 Ex1 between basement sources PB2 and IIR Ex1 H1 BD2 BD3 nT/m EX1 is inferred to be the offshore MID Mira terrane extension of the Isle-aux-Morts Fault H2 (Avalonia) 0.09 BD1 Zone, which onshore also separates BD2 0.06 MC 0.03 more magnetic rocks of the Port-aux- BD3 0.00 Basques subzone from less magnetic Line 5 Line 4 -0.03 rocks of the Exploits subzone (Fig. 4). -0.06 At the southeastern end of the line, -0.09 rising gravity and magnetic signatures are inferred to be associated with base- 46˚ ment sources designated BD1 and -61˚ -60˚ -59˚ -58˚ -57˚ BD2. As discussed below, BD1 and Figure 10. First vertical derivative of the total field magnetic anomaly map of the BD2 are interpreted to represent com- Cabot Strait study area (as in Figure 5), overlain by the inferred offshore extent of ponents of the Bras d’Or terrane. faults, terrane boundaries, and rock units. White lines onshore are the geological map unit boundaries from Figure 2. Red dashed lines indicate locations for model Line 2 profiles, also shown in Figure 3. Line 2 crosses from the Magdalen Basin at the northwestern end to the central part of the Cabot Strait (Figs. graben (Fig. 8b), similar to the inter- Sydney Basin at the southeastern end; 3, 4, 8b, 10). As on the model for line pretation of Langdon and Hall (1984) like line 1, it includes both linear mag- 1, sedimentary layers 1 and 2 vary in for nearby seismic lines. netic anomalies in the central part of thickness – layer 1 from 600 m to 3 The basement in the central the Cabot Strait, but also crosses the km and layer 2 from 2 km to 4 km. part of the model is composed of PB1 northeastern part of the large, north- Layer 3 (Horton Group?) appears in and PB2, with PB2 again interpreted to east-trending elliptical anomaly in the this model but only in two small have intruded into basement PB1, as GEOSCIENCE CANADA Volume 41 2014 199 seen on the model for line 1. Base- about 1.3 to over 3 km. and in the southeastern part of the ment source PB2 is related to the two To explain St. Paul Island, a model. All three layers thicken to the magnetic peaks in the central part of basement source termed OUT is northwest toward the Magdalen Basin. the profile; these peaks coincide with brought to the surface in a schematic In the northwestern part of the linear magnetic anomalies extend- representation of a positive flower line 4, the basement is interpreted to ing from southwestern Newfoundland structure (Fig. 8c), consistent with seis- be Grenville, as on lines 1, 2, and 3. toward Cape Breton Island. The large mic interpretations offshore (Langdon The basement source termed OUT, positive magnetic anomaly in the cen- and Hall 1994). Source OUT has been introduced in line 3 at St. Paul Island, tral part of the profile is caused by assigned density and susceptibility val- is brought again to the surface in a source EX2, interpreted to be plutonic ues to represent the rocks on St. Paul schematic representation of a positive as on line 1 because of the halo effect Island but the values are only loosely flower structure (Fig. 8d). Source OUT seen on the map and profile. Howev- constrained. Few gravity and magnetic represents the rocks on the Money er, the EX2 body in line 2 is separate anomaly measurements have been Point peninsula but the match between from the EX2 source in line 1 because made over the island, and the model predicted and observed anomalies is their magnetic anomalies are separate does not provide a good match to this poor and the area remains a challenge in map view (e.g. Fig. 10). The north- feature. Geological mapping has to model. The northern margin of western part of line 2 does not include shown that the rocks on St. Paul Island OUT is the Wilkie Brook Fault and the the ND basement source seen on the correlate with those of the Money southern margin is the Aspy Fault (Fig. line 1 model, and instead shows PB1 Point and Cape North groups of the 3); the two faults appear to merge at basement juxtaposed against Grenville Aspy terrane (Lin 1994). depth in the model. basement (GB) at a steeply north-dip- As on lines 1 and 2, the linear The basement sources under ping fault inferred to be the Cabot magnetic anomaly southeast of St. Paul Aspy Bay to the south of the merged Fault as seen in map view (Fig. 10). Island is associated with basement fault are interpreted to be PB1 and The positive gravity anomaly source PB2, but unlike the other lines, PB2, as also seen on models 1, 2, and in the profile is attributed to basement only one anomaly and hence one PB2 3. Basement source EX1 and a lower sources PB1 and PB2, with additional source is present. The elliptical, halo- density source IIR (Ingonish Island contributions from thinner sedimenta- type magnetic anomaly to the south- rhyolite) are also present on line 4, the ry layers, whereas the relative gravity east is associated with a basement latter contributing to the flank of the low in the southeastern part of the source identified as EX2b because it large Ingonish magnetic anomaly. profile is related to source EX2, as also has the same density as source EX2 However, the bulk of the large positive seen on line 1. As on line 1, increasing but slightly higher magnetic suscepti- magnetic anomaly is associated with magnetic and gravity trends are attrib- bility. Like EX2 on lines 1 and 2, basement sources H1, MID, and H2, uted to basement sources BD1 and source EX2b is responsible for the which, like the Ingonish Island rhyolite, BD2. negative gravity anomaly in this part of are not seen on profiles 1, 2, or 3. the profile. These basement sources Lower susceptibility but higher density Line 3 are at a similar depth as on profiles 1 unit MID separates the higher suscep- Line 3 (Fig. 8c) crosses St. Paul Island, and 2. tibility and lower density H1 and H2 the linear magnetic anomaly southeast Line 3 crosses inferred base- sources. These basement sources are of the island, the southwestern part of ment sources BD1 and BD2 seen on located at depths of about 5.5 to 7 km the large elliptical halo anomaly in lines 1 and 2, but also passes over a below sea level and together extend Cabot Strait, and a linear anomaly east somewhat different source, identified about 25 km along line 4. of the Ingonish magnetic anomaly as BD3, which is associated with a Basement sources BD1, BD2 (Figs. 3, 10). In contrast to lines 1 and gravity anomaly similar to BD1 and and BD3 to the southeast are associat- 2, three sedimentary layers are identi- BD2, but a negative magnetic anomaly, ed with low to negative magnetic fied on the model for line 3, consistent an effect explained in the model by anomalies and slightly negative gravity with seismic interpretations in the decreasing sediment thickness and anomalies. At about 95 km along the region (e.g. Pascucci et al. 2000). The lower magnetic susceptibility in BD3. profile, basement source AV is inter- maximum sediment thickness on the preted as the Mira terrane (Avalonia), model is ~5.7 km in the central part of Line 4 characterized in this area by lower den- the profile, and the total thickness of Line 4 (Fig. 8d) extends from north- sity than the adjacent Bras d’Or terrane sedimentary layers decreases toward west of Money Point to the southeast units. A small inlier (MC) overlying the south. Sediment thickness is less across the Ingonish magnetic anomaly the boundary is interpreted to to the northwest of St. Paul Island and the inferred position of the schematically represent the McAdam compared to the southeast, but increas- boundary between the Bras d’Or and Lake Formation, known to overlie the es rapidly into the Magdalen Basin, Mira terranes (Fig. 10). On this model terrane boundary onshore (King 2002). especially the thickness of layer 2, the thickness of layer 1 varies from 1 Predicted magnetic anomalies are, on which contains halite west of the km to almost 3 km. Layer 2 also varies average, 100 nT higher than observed Cabot Fault. In the same area, depth from 480 m to 3.4 km, the thickest values at this end of the line; an to the top of the underlying Grenville part lying over the central part of the improved fit would require either basement source (GB) varies from profile. Layer 3 is thickest in Aspy Bay thicker sedimentary layers or increased 200 susceptibility in the basement units, km. Zone, which separates the Silurian La neither of which seems a suitable Also clear from the magnetic Poile Group from the mainly Neopro- interpretation based on seismic and maps, as well as a comparison of mod- terozoic rocks of the Cinq-Cerf block other constraints. els 1 and 2, is the fact that the Notre (Fig. 2), although in places the Silurian Dame subzone does not extend far rocks sit unconformably on the older Line 5 into the Cabot Strait. It is likely that rocks (e.g. Lin et al. 2007). Hence the Profile 5 (Fig. 8e) extends northeast the Cape Ray Fault merges with the boundary might connect instead with from the Kellys Mountain area to cross Cabot – Long Range Fault to cut off the Bay d’Est Fault Zone, which sepa- profile 4 at right angles (Figs. 3, 10). the Notre Dame subzone north of the rates the La Poile Group on the south- Total thickness of layers 1, 2, and 3 is location of line 2 (Fig. 10), and hence east from the Bay du Nord Group, a about 5 km and varies only slightly not as far south as shown in the inter- unit characteristic of the Exploits sub- along the model, to a maximum of pretation of Hibbard et al. (2006). zone in the area. A third alternative, about 5.5 km in the central part. The Isle-aux-Morts Fault sepa- based on the observation that the Thicknesses of individual layers 1, 2, rates the Port aux Basques subzone muted magnetic signature of EX1 in and 3 do not vary significantly in this from the Exploits subzone onshore in the offshore is similar to that of the model, although layer 2 is slightly southwestern Newfoundland. The Harbour le Cou Group, is a connection thicker than the others. The basement Port aux Basques subzone is an area of with the Bay le Moine Shear Zone (Fig. source responsible for the Ingonish varied and complex geology dominated 2), implying that the Exploits subzone magnetic anomaly on this profile is H2, by metamorphic rocks (e.g. Schofield et rocks exposed onshore in southwest- which is again flanked by MID. The al. 1993, 1998; Valverde-Vaquero et al. ern Newfoundland overlie BD sources latter source produces much of the 2000) and is generally considered to be and that those ‘cover rocks’ are not locally high gravity anomaly. A contact part of the Gander Zone based on its present in the offshore. that appears to dip to the south or metasedimentary components (Hib- On model lines 1, 2, and 3, southwest is interpreted between H2 bard et al. 2006). Although Silurian – the EX1 – BD2 boundary can be and adjacent unit BD1. A small Devonian metamorphic history shows traced to the southwest as far as the amount of BD2 may be present similarities to that of the Aspy terrane Ingonish magnetic anomaly, where it is between the two units, but this could (Burgess et al. 1995; Barr et al. 1998), obscured by the source(s) of that fea- not be clearly determined. Much of the rock types such as the ca. 475 Ma Mar- ture and cannot be identified. On Fig- line is underlain by basement source garee orthogneiss are not present in ure 10 it is inferred to follow the BD1, which generates a strong positive the Aspy terrane, and the two areas boundary between H1 and MID into magnetic anomaly relative to source have not been directly correlated in the Middle Head area to connect with BD3 at the southwestern end of the previous studies (Barr et al. 1998). the southern margin of the Cameron model (Fig. 8e). Basement sources Instead, Aspy terrane rocks have been Brook Granodiorite and Clyburn MID and H2 are inferred to have correlated with those in the La Poile Brook Formation (Fig. 3). The magnet- intruded Bras d’Or terrane sources Group and Cinq-Cerf block (Barr and ic and gravity maps indicate that the (BD1 and 3), as also shown on line 4. Jamieson 1991; Barr et al. 1998; Lin et boundary between Aspy and Bras d’Or al. 2007). Based on models 1 through terranes is located just north of Middle DISCUSSION 3, the boundary between the Port-aux- Head, placing both the Clyburn Brook Basques and Exploits subzones can be Formation and the Cameron Brook Correlation of Major Faults and traced southwest to within 30 km of Granodiorite in Aspy terrane (Fig. 2). Terrane Boundaries Across the the Aspy terrane (Fig. 10). The bound- This position is consistent with inter- Cabot Strait ary position on line 4 is suggested to pretations based on geological maps of Both the Blair River Inlier and Lau- swing more east-west but cannot be the area, but those studies also suggest rentian margin are underlain by traced onshore because it is obscured that the original position of the Grenvillian rocks, the southeastern by the Black Brook Granitic Suite. boundary was through the Black Brook margins of which are marked by the The boundary seen on lines 1, Granite Suite (Yaowanoiyothin and Wilkie Brook and Cabot – Long Range 2, and 3 between EX1 and BD2 is Barr 1991), or along the northern mar- faults, respectively (Fig. 2). Models 1, inferred to represent the boundary gin of the Cameron Brook Granodior- 2, 3, and 4 enable the edge of Grenvil- between the Exploits subzone and ite following the Eastern Highlands lian basement, and hence the coinci- older rocks represented onshore by the Shear Zone (Figs. 2, 3; Lin 1995). The dent Cabot – Long Range Fault, to be Bras d’Or terrane in Cape Breton Ingonish Island rhyolite crops out only traced from southwestern Newfound- Island and the Cinq-Cerf block in on Ingonish Island, but we postulate land to the Wilkie Brook Fault, more southwestern Newfoundland. The that a similar highly magnetic but low- or less as interpreted by Langdon and continuation of this boundary into density body may occur farther off- Hall (1994) based on seismic data. southwestern Newfoundland is not shore, composing basement source IIR One significant implication from the clear because the elliptical anomaly (Ingonish Island rhyolite) on model 4 models not apparent from the work of extending offshore from the La Poile and contributing to the low gravity Loncarevic et al. (1989) is that Grenvil- Granite occurs in the critical area. anomaly associated with the northern lian basement in the Blair River Inlier One possible connection, as shown on edge of the Ingonish magnetic anom- may extend to a depth of at least 10 Figure 10, is with the Cinq-Cerf Fault aly (Fig. 8d). GEOSCIENCE CANADA Volume 41 2014 201

On the Newfoundland side of River Inlier, and with measured suscep- (Fig. 10). the Cabot Strait, it is difficult to trace tibility (Appendix A). Southeast of the Basement source EX1 has rel- the Bras d’Or terrane onshore because fault, PB1, having a density of 3050 atively high density of 3050 kg/m3 but of abundant plutons that extend into kg/m3 and susceptibility of 35 x 10–3 SI very low susceptibility of 1 x 10–3 SI the offshore from the Burgeo Intrusive units, is the dominant basement units. The low susceptibility is consis- Suite. As noted above, the boundary source. The relatively high density tent with the low-level anomalies asso- with the Exploits subzone is inferred (and susceptibility) suggests an abun- ciated with EX1 in the offshore, and in to connect onshore with the Cinq-Cerf dance of mafic metavolcanic rocks (e.g. its inferred continuation onshore in the Fault Zone, because the Cinq-Cerf Tenzer et al. 2011). This basement Harbour le Cou and Bay du Nord block contains rocks of Precambrian – source broadly represents the meta- groups. Miller et al. (1990) reported a Early Paleozoic age similar to those of morphic rocks (both metasedimentary comparable average susceptibility of the Bras d’Or terrane (O’Brien et al. and meta-igneous) of the Port aux 2.7 x 10–3 SI units for 7 samples from 1991; Barr et al. 1998). Farther to the Basques subzone in southwestern the Bay du Nord Group. As noted in east in the area south of the Grey Newfoundland. It is not clear from the previous section, it is not clear that River Enclave, the elliptical shapes of the geophysical maps that any of these any units of EX1 are exposed in Cape plutons in the offshore extension of rocks continue into Cape Breton Island Breton Island, although they may very the Burgeo Intrusive Suite change to and, as yet, none have been specifically well continue under younger units in more linear shapes typical of Bras d’Or recognized (Barr and Jamieson 1991; the eastern part of the Aspy terrane. terrane units, suggesting that the Bras Barr et al. 1998; Lin et al. 2007) The Clyburn Brook Formation and d’Or terrane extends into that area On line 3, unit OUT with other units assigned to the Money (Fig. 10). density 2800 kg/m3 and susceptibility 2 Point Group appear to be too young The contact between the Bras x 10–3 SI units represents the rocks (Silurian) to be correlative with the d’Or and Mira terranes is crossed only exposed on St. Paul Island. Details of Ordovician Harbour le Cou and Bay on line 4, where it appears as an almost the complex geology, including a posi- du Nord groups, although age con- vertical boundary between higher den- tive flower structure based on the seis- straints are limited. Units such as the sity basement source BD3 and lower mic interpretation of Langdon and undated, more magnetic body of density basement source AV (Fig. 8d). Hall (1994), cannot be resolved at the Money Point Group west and north- In map view, this location is marked by scale of the modeling. The match west of the Black Brook Granitic Suite subtle changes in magnetic signature between observed and calculated (Fig. 3) could be part of EX1, and that are most apparent on the second anomalies in this part of profile 3 is ghostly and unexplained east-southeast derivative map (Figs. 6, 10). This result poor, and better constraints are need- magnetic trends in the pluton could is not consistent with that of King ed, including more gravity data and represent relict EX1 in the subsurface. (2002) who modeled the boundary in rock property measurements for The Black Brook Granitic Suite has a the Boisdale Hills onshore as steeply Money Point and St. Paul Island and magnetic signature in map view similar north dipping, with near-surface Mira the nearby surrounding areas, so that to that of the Rose Blanche Granite in units having higher density (2820–2840 gravity errors in the models can be bet- Newfoundland (Fig. 2), but their differ- kg/m3) than Bras d’Or terrane units ter constrained and reduced. OUT ent ages (ca. 420 – 414 vs. 373 Ma) (2710–2720 kg/m3) and lower magnetic (part of the Cape North and Money preclude their correlation. susceptibility based on measured val- Point groups) could be a component in Basement sources EX2 and ues. Based on the models of King PB1, or an unrelated rock assemblage. EX2b, with density of 2900 kg/m3 and (2002), deeper parts of the Mira ter- Unit PB2, having a density of susceptibility of 60–80 x 10–3 SI units, rane (down to 5 km) also have higher 2950 kg/m3 and susceptibility of 120 x are considered to represent Silurian – density and lower susceptibility than 10–3 SI units, is interpreted to consist Devonian plutons equivalent to com- equivalent basement in the Bras d’Or of plutonic rocks in PB1 basement. ponents of the Burgeo Intrusive Suite terrane. The northern band of PB1 is cut off and/or the La Poile Granite, both of by the Cape Ray Fault before it reaches which exhibit halo anomalies of similar Pre-Carboniferous Basement Units southwestern Newfoundland, but the size and shape onshore and offshore in on Profile Models southern belt appears to continue the Hermitage Flexure area (Fig. 10). Models derived for magnetic and gravi- onshore from line 1 into the Margaree These units extend as far as line 3 but ty anomalies on profiles 1, 2, 3, and 4 orthogneiss (Fig. 10). The latter is a do not appear to continue to line 4 or all show Grenville basement (GB) composite unit consisting of amphibo- to Cape Breton Island (Fig. 10). This northwest of the inferred location of lite, dioritic orthogneiss, tonalitic termination is consistent with the lack the Cabot – Long Range – Wilkie orthogneiss with mafic enclaves, of plutons having ages of 429 – 414 Brook faults (Fig. 8a-d). In the mod- granitic orthogneiss, and minor ultra- Ma in the Aspy terrane (Lin et al. els, GB is assigned a density of 2875 mafic rocks (Valverde-Vaquero et al. 2007). In contrast, the Aspy terrane is kg/m3 and magnetic susceptibility of 7 2000), and is associated with a strong characterized by abundant ca. 400 – x 10–3 SI units (Fig. 9), consistent with positive magnetic signature onshore 365 Ma plutons (e.g. Cameron Brook, the rock types likely to be present (Fig. 4). To the southeast, the PB2 Black Brook, Park Spur, Salmon Pool, based on exposed Grenvillian units in anomaly is truncated at the inferred Margaree) which appear to be lacking western Newfoundland and the Blair Port aux Basques – Exploits boundary in southwestern Newfoundland. These 202

Middle and Late Devonian plutons are ment source BD3. The latter is postu- boniferous and pre-Carboniferous associated with co-magmatic bimodal lated to represent plutonic units of the boundary would provide better con- volcanic rocks (Fisset Brook Forma- Boisdale Hills pluton (r = 2820 kg/m3; straints on the basement. Another lim- tion; Fig. 3), and appear to be related k = 8.21 x 10–3 SI units) based on pro- iting factor in the study is the potential to widespread extension; this extension jections of geophysical trends in these field database. Although magnetic data culminated in the formation of the rocks into the offshore (Fig. 10). are quite detailed, gravity data are rela- Magdalen Basin (e.g. Dunning et al. Source BD3 is in contact across the tively sparse, and a more detailed data- 2002), but apparently had much less postulated continuation of the McIn- base would allow better resolution in effect in southwestern Newfoundland. tosh Brook – Georges River Fault with the models. In much of the study Basement sources BD1, BD2, basement source AV, considered to area, both onshore and offshore, gravi- and BD3 represent a composite base- represent the Avalonian Mira terrane in ty data were collected at too large a ment that is dominated by plutonic that area. line spacing and hence were gridded rocks but likely also includes metasedi- too coarsely for high-resolution inter- mentary rocks such as the McMillan CONCLUSIONS AND CAVEATS pretations. The models are by necessity Flowage Formation (r = 2810 kg/m3; k The geophysical models presented here simplified to make best possible use of = 2.10 x 10–3 SI units) and Kellys support correlation of major faults and available geophysical constraints and Mountain Gneiss (r = 2810 kg/m3; k = orogen components between New- geologic information; it should be rec- 3.47 x 10–3 SI units). In the models, foundland and Cape Breton Island ognized that depth and thickness varia- these sources have been assigned den- across the Cabot Strait. The Cabot – tions may trade-off against other sities of 2940, 3050, and 2940 kg/m3, Long Range Fault can be traced to the parameters such as density and suscep- respectively, and susceptibilities of 40, Wilkie Brook Fault in Cape Breton tibility, so the models are not unique. 20, and 10 x 10–3 SI units, similar to Island and separates Grenvillian base- Finally, the modeling proce- measured values in onshore plutonic ment to the northwest from peri- dure relies on the availability of mag- units such as Kellys Mountain Diorite Gondwanan basement to the south- netic susceptibility and density data for and Indian Brook Granodiorite. Unit east. The Cape Ray Fault/Red Indian rock units in the study area. Such data BD1 is associated with a strong quasi- Line merges offshore with the Cabot – are very scarce for units in southwest- linear anomaly that extends across the Long Range Fault and hence Notre ern Newfoundland. The database for strait and may be linked to the strong Dame subzone rocks do not extend magnetic susceptibility in Cape Breton anomaly at the intersection of profiles across the Cabot Strait. The Port aux Island is relatively good, but density 4 and 5 (Fig. 10). It cannot be traced Basques – Exploits boundary crosses data are limited. Furthermore, at the into a specific map unit onshore, but the strait but appears to be buried by scale of the modeling, only large units could match plutonic belts in the Bois- younger rocks onshore in Cape Breton could be included, most of which are dale Hills (Fig. 10). Island. Magnetic halos in the Exploits composite, and the averages obtained On models generated for lines subzone are likely caused by Silurian – from the susceptibility measurements 4 and 5, basement sources H1, MID Devonian plutons like those in the may not be representative of the whole and H2 are linked to the large Ingonish Burgeo Intrusive Suite. The Bras d’Or unit. Problems such as those encoun- magnetic anomaly seen on the total terrane can be traced to the Cinq-Cerf tered in trying to model the St. Paul field map (Fig. 4). H1 is interpreted to block and Grey River areas in southern Island area demonstrate the scale prob- be north of the Bras d’Or – Exploits Newfoundland, and hence Bras d’Or lem. boundary but has density and suscepti- terrane ‘basement’ may underlie all of Nonetheless, in spite of these bility consistent with various plutonic Exploits subzone. many limitations, at a regional scale the units of the Bras d’Or terrane, and However, these geological models demonstrate the variations could have been emplaced after terrane interpretations are limited by a lack of between the disparate geologic units juxtaposition. Basement source H2 constraints from high-quality deep seis- and contribute to ongoing efforts to could be a pluton like the Kellys mic reflection data in the Cabot Strait delineate major units and boundaries in Mountain Diorite. MID is associated area. Such data would help to resolve the offshore. They also provide expla- with a lower magnetic anomaly and pre-Carboniferous units, the nature and nations for some of the apparent geo- higher density; its modeled susceptibili- orientation of their contacts, and their logical differences between northeast- ty (12 x 10–3 SI) is comparable to values depth extent, as has been done in ern Cape Breton Island and southwest- measured in the plutonic units of the Newfoundland as a result of the Litho- ern Newfoundland, and enhance pre- eastern Bras d’Or terrane such as the probe East project (e.g. van der Velden vious attempts at map-view correla- Indian brook Granodiorite (14.99 x et al. 2004). Currently available seismic tions by providing at least an approxi- 10–3 SI) and Birch Plain Granite (12.07 data enable mapping of Carboniferous mation of the distribution of map x 10–3 SI). units to a depth of only 3.5 to 4.0 s units and position of crustal bound- Basement source BD2, con- (e.g. Pascucci et al. 2000). Deeper Car- aries at depth. sidered to be a composite unit repre- boniferous units are more difficult to senting plutonic and metamorphic interpret, limiting the ability to con- ACKNOWLEDGEMENTS units of the Bras d’Or terrane, is in strain the shape of the underlying This paper is based in part on the MSc contact near the southeastern end of basement bodies. Seismic data with thesis project of Louis Zsámboki at profile 4 with slightly different base- higher resolution images at the Car- Acadia University. Support for his GEOSCIENCE CANADA Volume 41 2014 203 project was provided by an Acadia Cape Breton Island and Newfound- land Appalachians: U/Pb ages and University Graduate Award, a Services land, northern Appalachian orogen: tectonic significance: Geology, v. 17, p. Contract with Natural Resources Cana- Canadian Journal of Earth Sciences, v. 548–551, http://dx.doi.org/ da, and a NSERC Discovery Grant to 35, p. 1252–1270, 10.1130/0091-7613(1989)017 S. Barr. We thank Lori Cook from the http://dx.doi.org/10.1139/e98-016. <0548:LPEPCI>2.3.CO;2. Blackwood, R.F., 1985, Geology of the Dunning, G.R., Barr, S.M., Raeside, R.P., Newfoundland and Labrador Depart- Grey River area, south coast of New- and Jamieson, R.A., 1990a, U–Pb zir- ment of Natural Resources for provid- foundland: Current Research, New- con, titanite, and monazite ages in the ing a more recent magnetic data set for foundland Department of Mines and Bras d‘Or and Aspy terranes of Cape the St. George’s Bay area. Energy, Mineral Development Divi- Breton Island, Nova Scotia: Implica- sion, Report 84-1, p. 153–164. tions for igneous and metamorphic REFERENCES Burgess, J.L., Brown, M., Dallmeyer, R.D., history: Geological Society of Ameri- Barr, S.M., and Jamieson, R.A., 1991, Tec- and van Staal, C.R.V., 1995, ca Bulletin, v. 102, p. 322–330, tonic setting and regional correlation Microstructure, metamorphism, ther- http://dx.doi.org/10.1130/0016- of Ordovician– Silurian rocks of the mochronology and P-T-t deformation 7606(1990)102<0322:UPZ- Aspy terrane, Cape Breton Island, history of the Port aux Basques TAM>2.3.CO;2. Nova Scotia: Canadian Journal of gneisses, southwest Newfoundland, Dunning, G.R., O’Brien, S.J., Colman-Sadd, Earth Sciences, v. 28, p. 1769–1779, Canada: Journal of Metamorphic S.P., Blackwood, R.F., Dickson, W.L., http://dx.doi.org/10.1139/e91-158. Geology, v. 13, p. 751–776, O’Neill, P.P., and Krogh, T.E., 1990b, Barr, S.M., and Raeside, R.P., 1989, http://dx.doi.org/10.1111/j.1525- Silurian Orogeny in the Newfound- Tectono-stratigraphic terranes in Cape 1314.1995.tb00257.x. land Appalachians: The Journal of Breton Island, Nova Scotia: Implica- Cawood, P.A., McCausland, P.J.A., Dun- Geology, v. 98, p. 895–913, tions for the configuration of the ning, G.R., 2001, Opening Iapetus: http://dx.doi.org/10.1086/629460. northern Appalachian orogen: Geolo- Constraints from the Laurentian mar- Dunning, G.R., Barr, S.M., Giles, P.S., gy, v. 17, p. 822–825, gin in Newfoundland: Geological McGregor, D.C., Pe-Piper, G., and http://dx.doi.org/10.1130/0091- Society of America Bulletin, v. 113, p. Piper, D.J.W., 2002, Chronology of 7613(1989)017<0822:TSTICB>2.3.C 443–453, http://dx.doi.org/ Devonian to early Carboniferous rift- O;2. 10.1130/0016-7606(2001)113 ing and igneous activity in southern Barr, S.M., and Raeside, R.P., 1998, Petrol- <0443:OICFTL>2.0.CO;2. Magdalen Basin based on U–Pb (zir- ogy and tectonic implications of Colman-Sadd, S.P., Hayes, J.P., and Knight, con) dating: Canadian Journal of metavolcanic rocks in the Clyburn I., 1990, Geology of the Island of Earth Sciences, v. 39, p. 1219–1237, Brook area and on Ingonish Island, Newfoundland: Newfoundland http://dx.doi.org/10.1139/e02-037. northeastern Cape Breton Island, Department of Mines and Energy, Ethier, M., 2001, Re-interpretation of the Nova Scotia: Atlantic Geology, v. 34, Geological Branch, Map 90-01. geology of the Cape Breton High- p. 27–37. Cook, L.A., 2005, Evaluating the sources lands using combined remote sensing Barr, S.M., and Setter, J.R.D., 1986, Petrolo- of the East Point Magnetic Anomaly, and geological databases: Unpublished gy of granitoid rocks of the Boisdale southern Gulf of St. Lawrence based MSc thesis, Acadia University, Hills, central Cape Breton Island, on magnetic, gravity, and seismic data: Wolfville, NS, 126 p. Nova Scotia: Nova Scotia Department Unpublished MSc thesis, Acadia Uni- Farrow, C.E.G., and Barr, S.M., 1992, of Mines and Energy, Paper 84-1, 75 versity, Wolfville, NS, 113 p. Petrology of high-alumina hornblende p. Cook, L.A., Dehler, S.A., and Barr, S.M., and magmatic epidote-bearing plutons, Barr, S.M., Dunning, G.R., Raeside, R.P., 2007, Geophysical modeling of southeastern Cape Breton Highlands, and Jamieson, R.A., 1990, Contrasting Devonian plutons in the southern Nova Scotia: Canadian Mineralogist, v. U–Pb ages from plutons in the Bras Gulf of St. Lawrence: implications for 30, p. 377–392. d‘Or and Mira terranes of Cape Bre- Appalachian terrane boundaries in Gibling, M.R., Boehner, R.C., and Rust, ton Island, Nova Scotia: Canadian Maritime Canada: Canadian Journal of B.R., 1987, The Sydney Basin of Journal of Earth Sciences, v. 27, p. Earth Sciences, v. 44, p. 1551–1565, Atlantic Canada: an upper Paleozoic 1200–1208, http://dx.doi.org/10.1139/E07-038. extensional basin in a strike-slip set- http://dx.doi.org/10.1139/e90-127. Dehler, S.A., and Potter, D.P., 2002, Deter- ting, in Beaumont, C., and Tankard, Barr, S.M., Jamieson, R.A., and Raeside, mination of nearshore geologic struc- A.J., eds., Sedimentary Basins and R.P., 1992, Geology, Northern Cape ture off western Cape Breton Island, Basin-Forming Mechanisms: Atlantic Breton Island, Nova Scotia: Geologi- Nova Scotia, using high-resolution Geoscience Society, Special Publica- cal Survey of Canada Map 1752A, marine magnetics: Canadian Journal of tion 5, p. 269–285. scale 1:100 000. Earth Sciences, v. 39, p. 1299–1312, Gibling, M.R., Culshaw, N., Rygel, M.C., Barr, S.M., Raeside, R.P., Miller, B.V., and http://dx.doi.org/10.1139/e02-057. and Pascucci, V., 2008, The Maritimes White, C.E., 1995, Terrane evolution Dickson, W.L., O’Brien, S.J., and Hayes, Basin of Atlantic Canada: Basin cre- and accretion in Cape Breton Island, J.P., 1989, Aspects of the Mid-Paleo- ation and destruction in the collisional Nova Scotia, in Hibbard, J., Cawood, zoic magmatic history of the south- zone of Pangea: Sedimentary Basins P., Colman-Sadd, S., and van Staal, C., central Hermitage flexure area, New- of the World, v. 5, p. 211–244, eds., New perspectives in the foundland: Newfoundland Depart- http://dx.doi.org/10.1016/S1874- Appalachian orogen: Geological Asso- ment of Mines, Geological Survey of 5997(08)00006-3. ciation of Canada, Special Paper 41, p. Newfoundland, Report 89-1, p. 81–95. Hamblin, A.P., and Rust, B.R., 1989, 391–407. Dunning, G.R., and O’Brien, S.J., 1989, Tectono-sedimentary analysis of alter- Barr, S.M., Raeside, R.P., and White, C.E., Late Proterozoic–early Paleozoic crust nate-polarity half- graben basin-fill 1998, Geological correlations between in the Hermitage flexure, Newfound- successions: Late Devonian–Early 204

Carboniferous Horton Group, Cape Langdon, G.S., and Hall, J., 1994, Devon- http://dx.doi.org/10.1139/e89-192. Breton Island, Nova Scotia: Basin ian–Carboniferous tectonics and basin Marillier, F., Keen, C.E., Stockmal, G.S., Research, v. 2, p. 239–255, deformation in the Cabot Strait area, Quinlan, G., Williams, H., Colman- http://dx.doi.org/10.1111/j.1365- eastern Canada: American Association Sadd, S.P., and O’Brien, S.J., 1989, 2117.1989.tb00038.x. of Petroleum Geologists Bulletin, v. Crustal structure and surface zonation Hayward, N., Dehler, S.A., Grant, A.C., 78, p. 1748–1774. of the Canadian Appalachians: impli- and Durling, P., 2014, Magnetic anom- Li, Z.X., Bogdanova, S.V., Collins, A.S., cations of deep seismic reflection alies associated with salt tectonism, Davidson, A., De Waele, B., Ernst, data: Canadian Journal of Earth Sci- deep structure and regional tectonics R.E., Fitzsimons, I.C.W., Fuck, R.A., ences, v. 26, p. 305–321, in the Maritimes Basin, Atlantic Cana- Gladkochub, D.P., Jacobs, J., Karl- http://dx.doi.org/10.1139/e89-025. da: Basin Research, v. 26, p. 320–337, strom, K.E., Lu, S., Natapov, L.M., Miller, B.V., and Barr, S.M., 2000, Petrology http://dx.doi.org/10.1111/bre.12029. Pease, V., Pisarevsky, S.A., Thrane, K., and isotopic composition of a Hibbard, J.P., van Staal, C.R., Rankin, D., and Vernikovsky, V., 2008, Assembly, Grenville basement fragment in the and Williams, H., 2006, Lithotectonic configuration, and break-up history of northern Appalachian orogen: Blair map of the Appalachian orogen Rodinia: A synthesis: Precambrian River Inlier, Nova Scotia, Canada: (north), Canada-United States of Research, v. 160, p. 179–210, Journal of Petrology, v. 41, p. America: Geological Survey of Cana- http://dx.doi.org/10.1016/j.precam- 1777–1804, http://dx.doi.org/ da Map 2041A, scale 1:1 500 000, 1 res.2007.04.021. 10.1093/petrology/41.12.1777. sheet. Lin, S., 1994, Geology of St. Paul Island Miller, B.V., and Barr, S.M., 2004, Meta- Hibbard, J.P., van Staal, C.R., and Miller, and the Cape North-Money Point area morphosed gabbroic dikes related to B.V., 2007, Links among Carolinia, (NTS 11N/01), Nova Scotia, and evi- opening of Iapetus Ocean at the St Avalonia, and Ganderia in the dence for west-over-east thrusting Lawrence Promontory: Blair River Appalachian peri-Gondwanan realm, (abstract): Nova Scotia Department Inlier, Nova Scotia, Canada: The Jour- in Sears, J.W., Harms, T.A., and of Natural Resources, Mines and nal of Geology, v. 112, p. 277–288, Evenchick, C.A., eds., Whence the Energy Branch, Report 94-2, p. 31. http://dx.doi.org/10.1086/382759. Mountains? Inquiries into the Evolu- Lin, Shoufa, 1995, Structural evolution and Miller, B.V., Dunning, G.R., Barr, S.M., tion of Orogenic Systems: A Volume tectonic significance of the Eastern Raeside, R.P., Jamieson, R.A., and in Honor of Raymond A. Price: Geo- Highlands shear zone in Cape Breton Reynolds, P.H., 1996, Magmatism and logical Society of America Special Island, the Canadian Appalachians: metamorphism in a Grenvillian frag- Papers, v. 433, p. 291–311, Canadian Journal of Earth Sciences, v. ment: U–Pb and 40Ar/39Ar ages from http://dx.doi.org/10.1130/2007.2433( 32, p. 545–554, the Blair River Complex, northern 14). http://dx.doi.org/10.1139/e95-046. Cape Breton Island, Nova Scotia, Kerr, A., and McNicoll, V., 2012, New Lin, Shoufa, 2001, 40Ar/39Ar age pattern Canada: Geological Society of Ameri- U–Pb geochronological constraints associated with differential uplift along ca Bulletin, v. 108, p. 127–140, from mineralized granites in southern the Eastern Highlands shear zone, http://dx.doi.org/10.1130/0016- Newfoundland: in Current Research, Cape Breton Island, Canadian 7606(1996)108<0127:MAMI- Newfoundland and Labrador Depart- Appalachians: Journal of Structural AG>2.3.CO;2. ment of Natural Resources, Geologi- Geology, v. 23, p.1031–1042, Miller, H.G., Kilfoil, G.J., and Peavy, S.T., cal Survey, Report 12-1, p. 21–38. http://dx.doi.org/10.1016/S0191- 1990, An integrated geophysical inter- King, M.S., 2002, A geophysical interpreta- 8141(00)00174-7. pretation of the Carboniferous Bay St. tion of the Mira-Bras d‘Or terrane Lin, Shoufa, van Staal, C.R., and Dubé, B., George Subbasin, Western Newfound- boundary, southeastern Cape Breton 1994, Promontory-promontory colli- land: Bulletin of Canadian Petroleum Island, Nova Scotia: Unpublished MSc sion in the Canadian Appalachians: Geology, v. 38, p. 320–331. thesis, Acadia University, Wolfville, Geology, v. 22, p. 897–900, Nance, R.D., and Linnemann, U., 2009, NS, 195 p. http://dx.doi.org/10.1130/0091- The Rheic Ocean: Origin, evolution, Knight, I., 1982, Geology of the Carbonif- 7613(1994)022<0897:PPCITC>2.3.C and significance: GSA Today, v. 18, p. erous Bay St. George subbasin: New- O;2. 4–12, http://dx.doi.org/ foundland Department of Mines and Lin, Shoufa, Davis, D.W., Barr, S.M., van 10.1130/GSATG24A.1. Energy, Mineral Development Divi- Staal, C.R., Chen, Yadong, and Con- O’Brien, B.H., O’Brien, S.J., and Dunning, sion, Map 82–1, scale 1:125 000. stantin, M., 2007, U–Pb geochrono- G.R., 1991, Silurian cover, Late Pre- Knight, I., 1983, Geology of the Carbonif- logical constraints on the evolution of cambrian–Early Ordovician basement, erous Bay St. George Subbasin, west- the Aspy terrane, Cape Breton Island: and the chronology of Silurian oroge- ern Newfoundland: Government of Implications for relationships between nesis in the Hermitage Flexure (New- Newfoundland and Labrador, Depart- Aspy and Bras d’Or terranes and Gan- foundland Appalachians): American ment of Mines and Energy, Mineral deria in the Canadian Appalachians: Journal of Science, v. 291, p. 760–799, Development Division, Memoir 1, 358 American Journal of Science, v. 307, http://dx.doi.org/10.2475/ajs.291.8.7 p. p. 371–398, http://dx.doi.org/ 60. Langdon, G.S., 1996, Tectonics and basin 10.2475/02.2007.03. Pascucci, V., Gibling, M.R., and deformation in the Cabot Strait area Loncarevic, B.D., Barr, S.M., Raeside, R.P., Williamson, M.A., 1999, Seismic strati- and implications for the Late Paleo- Keen, C.E., and Marillier, F., 1989, graphic analysis of Carboniferous zoic development of the Appalachians Northeastern extension and crustal strata on the Burin Platform, offshore in the St. Lawrence Promontory: expression of terranes from Cape Bre- Eastern Canada: Bulletin of Canadian Unpublished Ph.D. thesis, Memorial ton Island, Nova Scotia, based on Petroleum Geology, v. 47, p. 298–316. University of Newfoundland, St. geophysical data: Canadian Journal of Pascucci, V., Gibling, M.R., and John’s, NL, 331 p. Earth Sciences, v. 26, p. 2255–2267, Williamson, M.A., 2000, Late Paleo- GEOSCIENCE CANADA Volume 41 2014 205

zoic to Cenozoic history of the off- Geological Society America Bulletin, v. Canada: Canadian Journal of Earth shore Sydney Basin, Atlantic Canada: 116, p.1485–1498, Sciences, v. 16, p. 792–807, Canadian Journal of Earth Sciences, v. http://dx.doi.org/10.1130/B25518.1. http://dx.doi.org/10.1139/e79-070. 37, p. 1143–1165, van Staal, C.R., and Barr, S.M., 2012, Wiseman, R., and Miller, H.G., 1994, Inter- http://dx.doi.org/10.1139/e00-028. Lithospheric architecture and tectonic pretation of gravity and magnetic data Raeside, R.P., and Barr, S.M., 1990, Geolo- evolution of the Canadian Appalachi- from southwestern Newfoundland gy and tectonic development of the ans, in Percival, J.A., Cook, F.A., and and their correlation with Lithoprobe Bras d’Or suspect terrane, Cape Bre- Clowes, R.M., eds., Tectonic Styles in East seismic lines 89-11 and 89-12: ton Island, Nova Scotia: Canadian Canada Revisited: the LITHOPROBE Canadian Journal of Earth Sciences, v. Journal of Earth Sciences, v. 27, p. perspective: Geological Association of 31, p. 881–890, 1371–1381, Canada, Special Paper 49, p. 41–95. http://dx.doi.org/10.1139/e94-080. http://dx.doi.org/10.1139/e90-147. van Staal, C.R., Whalen, J.B., Valverde- Yaowanoiyothin, W., and Barr, S.M., 1991, Raeside, R.P., and Barr, S.M., 1992, Prelimi- Vaquero, P., Zagorevski, A., and Petrology of the Black Brook Granitic nary report on the geology of the Rogers, N., 2009, Pre- Carboniferous, Suite, Cape Breton Island, Nova Sco- northern and eastern Cape Breton episodic accretion-related, orogenesis tia: Canadian Mineralogist, v. 29, p. Highlands, Nova Scotia: Geological along the Laurentian margin of the 499–515. Survey of Canada, Paper 89-14, 39 p. northern Appalachians, in Murphy, Zsámboki, L., 2012, Geophysical modeling Schofield, D.I., Winchester, J.A., and van J.B., Keppie, J.D., and Hynes, A.J., eds., in the Cabot Strait - St. Georges Bay Staal, C.R., 1993, The Isle aux Morts Ancient Orogens and Modern Ana- area between Cape Breton Island and metabasalt, southwest Newfoundland: logues: Geological Society, London, western Newfoundland, Canada: in Current Research, Part D, Geologi- Special Publications, v. 327, p. Unpublished MSc thesis, Acadia Uni- cal Survey of Canada, Paper 93-lD, p. 271–316, versity, Wolfville, NS, 201 p. 39–46. http://dx.doi.org/10.1144/SP327.13. Schofield, D.I., van Staal, C.R., and Win- van Staal, C.R., Whalen, J.B., Valverde- Received August 2013 chester, J.A., 1998, Tectonic setting Vaquero, P., Zagorevski, A., and Accepted as revised March 2014 and regional significance of the ‘Port Rogers, N., 2013, Evidence for hyper- First published on the web aux Basques Gneiss’, SW Newfound- extension during Late Ediacaran–Early March 2014 land: Journal of the Geological Socie- Cambrian opening of the Iapetus ty, v. 155, p. 323–334, Ocean in the northern Appalachians http://dx.doi.org/10.1144/gsjgs.155.2. and British Caledonides (abstract): 0323. GAC-MAC Winnipeg 2013, Program Tenzer, R., Sirguey, P., Rattenbury, M., and with Abstracts, p. 193. Nicolson, J., 2011, A digital rock den- Verhoef, J., Roest, W.R, Macnab, R., sity map of New Zealand: Computers Arkani-Hamed, J., and members of & Geosciences, v. 37, p. 1181–1191, the project team, 1996, Magnetic http://dx.doi.org/10.1016/j.cageo.201 anomalies of the Arctic and North 0.07.010. Atlantic oceans and adjacent land Tucker, M.A., 2011, Geology and mineral areas: Geological Survey of Canada occurrences in the Faribault Brook Open File 3125, 255 p. +300 figures. area, Cape Breton Island, Nova Scotia: Waldron, J.W.F., and van Staal, C.R., 2001, Unpublished MSc thesis, Acadia Uni- Taconian orogeny and the accretion of versity, Wolfville, NS, 259 p. the Dashwoods block: A peri-Laurent- Valverde-Vaquero, P., Dunning, G.R., and ian microcontinent in the Iapetus van Staal, C.R., 2000, The Margaree Ocean: Geology, v. 29, p. 811–814, orthogneiss: an Ordovician, peri- http://dx.doi.org/10.1130/0091- Gondwanan, mafic-felsic igneous 7613(2001)029<0811:TOATAO>2.0. complex in southwestern Newfound- CO;2. land: Canadian Journal of Earth Sci- Wessel, P., and Smith, W.H.F., 2012, The ences, v. 37, p. 1691–1710, Generic Mapping Tools (GMT) ver- http://dx.doi.org/10.1139/e00-053. sion 4.5.8: GMT Manual Pages, Valverde-Vaquero, P., Dunning, G.R., and SOEST/NOAA. Available from: O’Brien, S.J., 2006, Polycyclic evolu- http://gmt.soest.hawaii.edu/gmt4/gm tion of the Late Neoproterozoic base- t/html/GMT_Docs.html. ment in the Hermitage Flexure region White, C.E., Barr, S.M., Bevier, M.L., and (southwest Newfoundland Appalachi- Kamo, S., 1994, A revised interpreta- ans): New evidence from the Cinq- tion of Cambrian and Ordovician Cerf gneiss: Precambrian Research, v. rocks in the Bourinot belt of central 148, p. 1–18, http://dx.doi.org/ Cape Breton Island, Nova Scotia: 10.1016/j.precamres.2006.03.001. Atlantic Geology, v. 30, p. 123–142. van der Velden, A.J., van Staal, C.R., and Williams, H., (compiler), 1978, Tectonic Cook, F.A., 2004, Crustal structure, lithofacies map of the Appalachian fossil subduction, and the tectonic Orogen: Memorial University of New- evolution of the Newfoundland foundland, St. John’s, NL, Map 1, Appalachians: Evidence from a scale 1:1 000 000. reprocessed seismic reflection survey: Williams, H., 1979, Appalachian Orogen in 206

$33(1',;$6XPPDU\RIGHQVLW\DQGPDJQHWLFVXVFHSWLELOLW\GDWDIRUVHOHFWHGURFNXQLWV LQ&DSH%UHWRQ,VODQG Density1 Magnetic Susceptibility2 (g/cm3)(x10-3 SI units) Range Avg Range Avg n Carboniferous sedimentary units +RUWRQ*URXS 0DERX*URXS 0RULHQ*URXS 3LFWRX*URXS :LQGVRU*URXS Bras d'Or terrane metamorphic units %DUDFKRLV5LYHU)RUPDWLRQ %HQDFDGLH3RQG)RUPDWLRQ %RXULQRW%HOW )UHQFKYDOH5RDG0HWDPRUSKLF6XLWH .HOO\V0RXQWDLQ*QHLVV 0F0LOODQ)ORZDJH)RUPDWLRQ Bras d'Or terrane plutonic units %LUFK3ODLQ*UDQLWH %RLVGDOH+LOOV3OXWRQ &DSH6PRNH\*UDQLWH &URVV0RXQWDLQ*UDQLWH *LVERUQH)ORZDJH4XDUW]'LRULWH ,QGLDQ%URRN*UDQRGLRULWH .DWK\5RDG'LRULWLF6XLWH .HOO\V0RXQWDLQ*UDQLWH .HOO\V0RXQWDLQ'LRULWH 0RXQW&DPHURQ6\HQRJUDQLWH 6KXQDFDGLH3OXWRQ 7LPEHU/DNH'LRULWLF6XLWH :UHFN&RYH'LRULWH Aspy terrane metamorphic units &DSH1RUWK*URXS &KHWLFDPS/DNH*QHLVV &O\EXUQ%URRN)RUPDWLRQ ,QJRQLVK,VODQG5K\ROLWH 0RQH\3RLQW*URXS 6DUDFK%URRN0HWDPRUSKLF6XLWH Aspy terrane plutonic units %ODFN%URRN*UDQLWLF6XLWH &DPHURQ%URRN*UDQRGLRULWH *ODVJRZ%URRN*UDQRGLRULWH 0DUJDUHH3OXWRQ *UDQLWH 1HLOV+DUERXU*QHLVV :LONLH6XJDU/RDI*UDQLWH Blair River Inlier $QRUWKRVLWH6\HQLWH *QHLVVLF5RFNV

8QLWVDUHLQDOSKDEHWLFDORUGHUE\WHUUDQHDQGURFNW\SH 'HQVLW\HVWLPDWHVDUHEDVHGRQVLPLODUURFNW\SHVIURP7HQ]HUHWDO LQWKHDEVHQFHRIVXFKGDWD IURPWKHVWXG\DUHD,QWKHPRGHOVGHQVLW\YDOXHVZHUHVHOHFWHGZLWKLQWKHSODXVLEOHUDQJHIRUWKHOLNHO\URFNW\SHVSUHVHQ 0HDVXUHGVXVFHSWLELOLW\GDWDDUHIURP=ViPERNL $VQRWHGLQWKHWH[WPRVWXQLWVFRQWDLQDZLGHYDULHW\RIURFNW\SHVDQGKHQFHWKHPHDVXUHPHQWVYDU\DFFRUGLQJO\ $WWKHVFDOHRIWKHPRGHOVWKHDYHUDJHYDOXHVDUHSUREDEO\UHDVRQDEO\UHSUHVHQWDWLYHRIWKHXQLWV