Provenance of the Meguma Terrane, Nova Scotia: Rifted Margin of Early Paleozoic Gondwana

Provenance of the Meguma terrane, Nova Scotia: rifted margin of early Paleozoic Gondwana

John W.F,Waldron, Chris E. White, SandraM. Barr, Antonio Simonetti,and Larry M. Heaman

Abstract: Detrital zircon ages from the lower part of the Late Proterozoic(?)to Middle Cambrian Goldenville Group in the Meguma te(ane of Nova Scotia suggestderivation from local sourcesin the Avalonian and Pan-African orogenson the margins of Early Cambrian Gondwana. Samplesfrom near the top of the group show a brcader distribution, including ages back to Archean. The eNddata show a correspondingtrend, from slightly positive in the lower Coldenville Group to highly negative in the upper Goldenville Group and overlying Upper Cambrian to Lower Ordovician Halifax Group. The trends are consistentwith deposition of the lower part of the Meguma successionin a rift, in which uplifted rift-flanks werc the main source of the early basin fill, whereassubsequent themal subsidenceof rift margins allowed for more widespread sedimentsourcing in younger units. The dft was possibly located between Gondwana and Avalonia, and may have been the locus for separationof Avalonia from Gondwana to form pafi of the Rheic Ocean.

R6sum6: Les 6gesdes zircons d6tritiques du Groupe de Goldenville (Protdrozoiquetardif(?) i Cambrien moyen) dans le terrane de Meguma de la Nouvelle-Ecossesuggdrent une provenancede sourceslocales dans les orogEnesavalonien et pan-atricain sur les bordures du continent de Gondwana au Cambrien pr6coce.Des 6chantillonspr6levds prds du sommet du groupe montrent une distribution plus vaste, incluant des dges arch6ens.Les donn6eseNd montrent une tendancecorre- spondante,de l6garernentpositive dans le Grcupe de Goldenville infdrieur d hautementn6gative dans le Grcupe de Gold- enville sup6deur et dans le Groupe de Halifax susjacent (Cambrien sup6rieure Ordovicien inf6rieur). Les tendances concordent avec la ddposition de la partie inf6rieure de la successionde Meguma dans une fosse d'effondrement; les flancs soulev6sde cette fosse auraient constitu6 la source principale de mat6del de remplissagedu bassin pdmitif alors qu'une subsidencethermique subs6quentedes borduresde la fosse aurait conduit i une source de s6dimentsplus 6tenduepour les unit6s plus jeunes. La fosse d'effondrement 6tait possiblementsitu6e entre le Gondwana et I'Avalonie et elle constitue pos- siblement le lieu de la s6parationde I'Avalonie du Gondwana pour la formation d'une partie de I'oc€an Rh6ique.

[Traduit par la R6daction]

Introduction adiacent to northwest Africa and was transferTed to Lauren- tia during the Acadian orogeny, whereas others have pro- Meguma, the most outboard terrane of the Canadian Ap- posed an origin juxtaposed with westem Amazonia (e.g., palachians (Fig. la), has no clear conelative elsewhere in Keppie 1977) and (or) that Meguma travelled with Avalonia the Appalachian-Caledonideorogen. Although generally re- during the early Paleozoic (Muryhy et al. 2OO4a). garded as a peri-Gondwanan terane, Meguma shows marked contrasts with adjaqent Avalonia, and its origin has We report here the results of U-Pb dating of detrital zircon been controversial. Some authors (e.g., Schenk 1997 and and Sm-Nd isotopic analyses from Cambrian-Ordovician referencestherein) have proposed that Meguma odginated metasedimentaryunits in Meguma that are relevant to this conboversy. The data demonstxatethat sedimentprovenance changedrapidly from a restrictedand juvenile sourceto more Received 6 October 2008. Accepted 27 Jan!aty 2009. Published diverse and isotopically evolved sourceswith abundantPale- on the NRC ResearchPress Web site at cies.nrc.caon 2 March 2009. oproterozoic zircon, consistentwith formation on the Gond- wanan margin in an evolving dft that subsequentlybecame Paper handled by Associate Editor B. Muryhy. inactive and underwentthermal subsidence. J.W.F, Waldronr and L.M. Heaman. Departmentof Eafth and Atmospheric Sciences,University of Alberta, Edmonton, AB Stratigraphic context T6G 2E3. Canada. C.E. White. NS Departmentof Natural Resources,PO Box 698, Meguma is charactedzedby unique stratigraphy, includ- Halifax. NS B3J 2T9. Canada. ing a thick (>10 km) Cambrian (and possibly older) to Early S.M, Barr. Department of Earth and Environmental Science, Ordovician turbiditic clastic succession,historically assigned Acadia Unive$ity, Wolfvi e, NS B4P 2R6, Canada. to the Meguma Group, and divided into a lower, coarser A. Simonetti. Department of Earth and Atmospheric Sciences, grained Goldenville Formation and an upper, dominantly Univenity of Alberta, Edmonton, AB T6G 2E3, Canada;Present fine-grained Halifax Formation. Shatigraphic work (O'Brien address:Department of Civil Engineering & Geological 1988; Waldron 1992) and recent mapping (e.g., White 2007) Sciences,156 Fitzpatrick Hall, University Dame, of Notre Notre resulted in subdivision of thesethick formations and their el- Dame. IN 46556. USA. evation to group status. The entire package now is termed lConesponding author (e-mail: [email protected]). the Meguma Supergroup(White 2008).

Can.J. EarthSci.46: 1-8 (2009) doi:10.1139/E09004 Publishedby NRC Researchkess Can.J. EadhSci. Vol.46,2009

Fig. 1. (a) Meguna Terrane showing units and sample locations. Paleocunent rose diagrams rcprcsentflutes and cunent ipples, corrected for tectonic distortion and rotated to horizontal (Waldron and Jensen 1985; waldron 1988). Inset: Location in Appalachial orogen, afler Hibbard et al. (2006). Fm., Formation; Gp., Group; L.. Lower; U., Upper. (r) Schematic stratigraphiccolumns for Meguma, showing sample bcations. (.) Values of ex6 at 540 Ma, against straligraphicposition, west and easl of ChebogucPoint shear zone (CPSZ). Red line on both plots shows the trend west of the CPSZ. for compffison. Data fiom this study and Clarke and Halliday (1985). Clarke et al. (1988), and Currieet ai. (1998).

b Yarmouth-Digby 12 .#,^,; Easlof CheboouePoinl Halifax-Canso shearione

18 ^^25 CunadFm r'zla 23 -o 2215

JU,C\ t-- )^ o- "church x PoinlFm. B 38

, F$t

tNd at 540t a

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The Goldenville Group is dominated by psammite (meta- Results sandstone), with subordinate pelitic rocks (metasiltstone, slate, argillite). A locality close to tre top of the group U-Pb detrital zircon dating (Figs. la, lb) yielded a Middle Cambrian trilobite faunule Sample 1, from the lowest point in the exposedstuatigraphy (Pratt and Waldron 1991). Nearer the base of the exposed west of the CPSZ (Fig. lb), shows a strongly clustered age Goldenville Group (Fig. 1b), the trace fossil Oklhamia indt- distribution; 7l of 76 grains lie between 750 and 540 Ma. cates an Early Cambrian or possibly late Neoproterozoicage The density distribution has a strong peak at -640 Ma, with (White et al. 2005). The overlying Halifax Group is domi- subsidiary peaks at 560,585, and possibly 700 Ma. The nated by pelite, associatedwith fine- and very fine-grained youngestgrain, at 544 t 18 Ma, representsthe maximum dep- metasandstone.Rare graptolites high in the Halifax Group ositional age of the sampleand henceof the exposedGolden- (Fig. lb) indicate an Early Ordovician age (e.g., Cumming ville Group. Of the remaining grains,two are Neoproterozoic, r985). and three are Paleoproterozoic. -4 Northwest of the Chebogue Point shear zone (CPSZ; Sample 2, from a metasandstonebed km higher in the section, Fig. la), the Halifax Group is overlain unconformably by an Oldhamia-beaing interval of fine-grained meta- sedimentaryrocks Silurian volcanic and sedimentary rocks assigned to the known as the High Head member (White et al- 2005), shows White Rock Formation and equivalent units, deposited in a an even more restricted detrital aee range:all 124 grains give shallow-madne rift environment (MacDonald et al. 2002, ages berween740 and 540 Mi, with distinct peaks at and referencestherein). The overlying Early Devonian Tor- 560,580, and 620 Ma. A grain at 537 t 15 Ma provides brook Formation records shelf conditions (Jensen 1975). In the most reliable ma"ximumdepositio, nal age. addition to the contrast in stratigraphy (Fig. 1b), this part of Meguma is characterizedby abundantmafic sills (White and Sample 5, from the statigraphically highest metasand- Barr 2004; White et al. 2006). Furthermore,our limited pa- stone unit in the Goldenville Group northwest of the CPSZ (Figs. leocurrentdara from rhe area indicatesou(hward paleoflow 1a, 1b), shows a much more diverse age spectrum.A (Fig. 1a), in contrast with northwestward to northeastward large Neoproterozoiccluster (78 of 125 grains) has peats at -550, flow reported elsewhere in the terrane (Schenk 1970; Wal- 590, and possibly 620 Ma. A concordant grain at dron and Jensen1985; Waldron 1988). 529 i 19 Ma representsthe best constraint on depositional age. A second large peak occurs at 2060 Ma. Scattered The basementof Meguma is poorly known. Sm-Nd data grains show Mesoproterozoic and older Paleoproterozoic from mafic and felsic volcanic rocks in the White Rock For- ages. Seven Archean grains range from 2620 to 3036 Ma. mation are mainly positive, suggestingcrustal contamination Sample 13 is from an equivalent stratigraphiclevel east of of mainly mantle-derived magmas (MacDonald et al. 2002) the CPSZ (Fig. lb), adjacentto a fossiliferous Middle Cam- but also consistent with sources in Avalonian basement brian bed (Pratt and Waldron 1991). Of 47 grains (Keppie et al. 1991). Greenoughet a1. (1999) recorded con- with <10% discordance,12 arc late Neoproterozoic,grouped cordant and slightly discordant zircons with Avalonian and at -560, 585, and 62G-640 Ma The remaining 35 grains Pan-African (630-575 Ma) U-Pb ages in xenoliths thoughr range from older Neoproterozoicto Mesoarchean.Abundant to be derived from basement;they also inferred Mesoproter- Paleoproterozoic grains include six grains overlapping ozoic componentsin barementfrom upper inrerceprages within error at - 2135 Ma. Seven Archean grains show projected through discordantzircon fractions. ages scatteredfrom 2540 t 17 to 3110 Ma.

Samplelocations and methods Sm-Nd isotopic analyses The eNddata (calculated at 540 Ma) west of the CPSZ Four metasandstonesamples for detrital zircon dating show a clear change from slighdy positive (+0.78 were collected in the Goldenville Group (Fig. la, lZr). Loca- and +0.86, indicating relatively juvenile sources) in lower tions were chosento cover a wide age span,to include dated samples,to highly negative values ( {.43 to 8.79, consis- fossil localities, and to complement the previous small data tent with more evolved sources) at stratigraphically higher set of Krogh and Keppie (1990). Zircon grains were ex- levels. The ery4values are strongly correlated with detrital tracted, imaged by electron backscatter,and dated by laser zircon ages; the two samples(l and 2) with positive values ablation multicollector-inductively coupled plasma-mass yielded highly restdcted, young detrital zircon populations spectrometry(MC-ICP MS) using the methods of Simonetti (Fig. 2). An upward decreasingtrend continues into the Hal- et al. (2005). Results are shown as probability density plots ifax Group. More data are available east of the CPSZ, where in Fig.2, excluding grains with >107o discordance.These the upward trend toward negatiye €Ndis also clear, reaching samples were also analysedfor their Sm Nd isotopic com- highly negative values (- 16). position, together with additional samples to extend cover- age acrossthe CPSZ, and into the overlying Halifax Group. These data are combined with published Sm Nd data, all Interpretation from east of the CPSZ, but not previously positioned strati- As expected,Meguma detdtal zircon age disftibutions do graphically. Summary results are shown in Figs. lc and 2; not resemble those from the Cambrian of Laurentia. which full tables of results appearin the supplementarydata.2 are characterizedby strong peaks at 1.0-1.3 Ga, and which 'Supplementary datacan be found on the journal web site (http://cjes.nrc.ca)or may be purchasedfrom the Deposiioryof Unpublished Data,Document Delivery, CISTI, NationalResearch Council of Canada,Building M-55, 1200Monteal Road,Ottawa, ON KIA 0R6, Canada(DUD 3903).For moreinformation on obtainingmaterial, refer to http://cisti-icist.nrc-cnrc.gc.ca./unpube.shtml.

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Fig. 2. Detrital zircon frequency distributions for Meguma, constructed using Isoplot (Ludwig 2003). See supplementary data2 for raw values and details of error propagation. (a) Combined data for Torbrook and White Rock formations, after Murphy et al. (2004a). (r) Sample 13, east of CheboguePoint shearzone (CPSZ), top of Goldenville Group. (c--e)Samples 5, 2, and 1, west of CpSZ, top, middle, and bot- tom, respectively,of Goldenville Group. (, Middle Goldenville Group east of CPSZ after Krogh and Keppie (1990), assumingo.lqo analytical Drecision.

WhiteRock, Torbrook {Murphy et al.

0 Ma 500 1000 1500 3500 tS.picallylack zircons from 2.0 to 2.5 Ga (e.g., Cawood et al. guma, potentially at the unconformity above the Meguma 2007, and referencestherein). Our older samples (1 and 2) Supergroup,and hence do not require a contiguous Avalo- show restricted, dominandy late Neoproterozoic age distri- nlan soulce. butions that resemble some Cambrian units from Avalonia: Sources for 2000-2200 Ma zircon are rare in Laurentia but for example, a sample ftom Great B tain shows peaks at common in pal1s of Gondwana, such as the Eburnian and 550,560,605, and 620 Ma (Murphy et al, 20040).These Birimian orogensof West Africa (Rocci et al. 1991; Lerouge distributions suggest derivation from local sources in the et al. 2006). Similar age sourcesare recordedfrom the Congo - Avalonian Pan-African orogen. Younger samples (5 and craton (e.g., De Waele and Fitzsimons 2007), though associ- 13) show lower ey6 and a broader disribution of detrital zir- ated with a large - 1800 Ma peak. In South America, agesof con ages. These data somewhat resemble results of Krogh 2000 2200 Ma are found in the Amazonian (e.g., Neves et al. and Keppie (1990) (Fig. 2). However, both of our samples 2006) and Sao Francisco (Barbarosaand Sabat6 2002) cta- 5 and 13 contain rar'e Mesoproterozoic grains not recorded tons. Dehital zircons from the La Cebila formation of Arsen- in the Krogh and Keppie (1990) data. Five grains in sample tina(Finney et al.2003.2004)also show a sLrikingpeal in 5, and three more in sample 13, span a range from 1150 to this range, as does the Gondwanan Suwaneeteffane of Flor- 1481 Ma In addition, sample 13 contains three grains with ida (Mueller et al. 1994). Age distributions from European typical "Grenville" ages between 1000 and 1050 Ma. Amorica also show a strong 2,0-2,2 Ga peak (Linnemann et Younger sedimentaryunits in Meguma are similar (Fig. 2): aI.2004). the overlying White Rock and Torbrook formations studied Nance and Murphy (1996) and Linnemann et al. (2004) by Murphy et al. (2004q) have abundant zircon grains be- suggestedthat abundanceof Mesoproterozoiczircon may be tween 540 and 650 Ma, and scattered Mesoproterozoic used to differentiate peri-Gondwanan teffanes originating (1000-1500 Ma) and Paleoproterozoic (1900-2200 Ma) adjacent to Amazonia ftom those originally adjacent to grains. Murphy et al. (2004a) argued that the Mesoprotero- West Africa. The abundance of Eburnian and relative scar- zoic grains in these units require an Avalonian source and city of Grenvillian detrital zircon in our Meguma samples suggested on this basis that Meguma and Avalonia were suggestan origin adjacent to West Africa, but within reach contiguous in the mid-Paleozoic. OuI data show that the of occasional Amazonian grains. An original position adja- mid-Paleozoic units contain distributions closely similar to cent to Morocco (e.g., Schenk 1971) seemsunlikely because those in the underlying Meguma Supergroup; their zircon Moroccan Cambrian successionsare dominated by warm- grains could easily have been derived by erosion within Me- water carbonates.in contrast to clastics and cool-water car-

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Fig. 3. Possible Cambrian paleocontinentalreconstruction showing potential location of Meguma. Reconstructionfor 500 Ma based on Murphy et al. (2004c) and Linnemann et al. (2004). Positionsof peri Gondwanantenianes are poorly constrainedby available paleomag- netic data and are based mainly on statigraphic and provenancelinkages. Position of Gande a (van Staal et al. 1996) is also speculative. Distribution of crustal agesis basedon Cawood er al. (2007) and Li et al. (2008).

I Mesoproterozoicofogens (ca. 1.0-1.6 ca) lYounger Paleoproterozoicorogens(1.6-2.0Ga) m OlderPaleoproterczoic orogens (2.0-2.2 ca) mE Proterozoicorogens of * uncertainage

:a *-c *s

Possibleperi- Gondwananriftsystem

Peri-Gondwanan terraneswith abundant Mesoproterozoicdekitus .l::;:i.i::,t,,.,.,1:t|/,.l.tz Peri-Gondwananterranes withabundant Paleopro- terozoic(2.0-2.2 Ga) detritus bonatesin Avalonia and Meguma (e.g.,Landing 1996;Linne- guma Supergroup. Mafic intrusions west of the CPSZ mann et al. 2004). An origin on the north African margin is (White and Bar 2004), and stratigraphic contrasts across conceivable, as 1 Ga zircon is abundant in Cambrian- the zone, also are consistentwith a rifi. Although no coarse Ordovician sandstonefrom Israel and Jordan (Kolodner et al. or subaerial clastic sedimentary rocks have been described 2006), but the Meguma distuibutionsdo not resemble those from the Meguma succession,its base and margins are un- reported liom central European terranes believed to have ori- exposed; we would predict less mature sediments at depth ginated along this part of the Gondwananmargin (Fig. 3). below the curent deepestlevel of exposure,consistent with The upward trend in our data, from relatively juvenile the kends in ep6 data (Fig. lc). At least one margin of the Pan-African and Avalonian sources to more diverse, older proposed rift must have provided a cratonic source for the populations is mirrored in the ep6data, indicating that it is a older zircons observed; however, the postulated rift may general f-eature of the Meguma Supergroup. The trend is have developed within a continental margin setting and most easily explained by deposition in a rift or other exten- might have formed in a ftanstensionalenvironment as envis- sional envfuonmentthat subsequentlybecame inactive; up- aged for Canbrian Avalonia (e.g., Nance and Murphy lifted flanks were the main early source, whereas 1996). subsequent thermal subsidence allowed more widespread Similarities to Avalonian detdtal ztcon populations,juve- sourcing. A dft envircnment helps to explain the thickness nile isotopic compositions, and the consistency of sparse (>10 km) and rapid accumulation (>250 mm/ka) of the Me- faunal evidence with Avalonian affinitv Pratt and Waldron

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1991) favour a location generally between Gondwana and Cawood, P.A., Nemchin, A.A., Strachan,R., Prave, T., and Krab Avalonia. Although our data suggest that the Meguma dft bendam, M. 2007. Sedimentary basin and detrital zircon record became inactive during the Middle Cambrian, they do not along East Laurentia and Baltica du ng assembly and breakup indicate whether this changerepresents a transition to a pas- of Rodinia. Journal of the ceological Society, 164: 257-275. sive margin environment or whether it indicates that the doi: 10. I 14,1/0016-76492006I 15. later Meguma sedimentswere deposited in an intracratonic Clarke, D.B., and Halliday, A.N. 1985. Sm/Nd isoropic investiga- "failed rift." Subsidence analyses from Avalonia suggest tion of the age and origin of the Meguma Zone metasedimentary that its separationand the opening of the Rheic Ocean did rocks. CanadianJoumal of Earth Sciences,22: 102-107. not begin until the Early Ordovician (e.g., Prigmore et al. Clarke, D.B., Halliday, A.N., and Hamilton, P.J. I988. Neodymiurn 1997), supporting the idea that the Early Cambrian rift was and strontium isotopic constraintson the origin of the peralumi- a failed one. However, other workers (Landing 1996, 2005) nous granitoids of the South Mountain Batholith, Nova Scotia, Canada. Chemical argue that Avalonia was separatedfrom Gondwana by the Ceology. Isotope Geoscience Section, 73: l5 24. doi:10.1016i01689622(88)90018-8. Early Cambrian, in which case our data may record the Cumming, L.M. 1985. Halifax Slate graptolite localiry, Nova opening of part of the Rheic Ocean. Numerous published re- Sco- tia. /n Cur.ent research,part A. Ceological Survey of Canada constructionsof peri-Condwanan terranesin the Early Pale- Paper,85-lA, pp-215)21. ozoic differ in detail, but agree that Avalonia and related Currie, K.L., Whalen, J.8., Davis, W.J., Longstaffe, F.J., and Cou- Appalachian tefianes were located along a previously active sens,B.L. 1998. Geochemicalevolution of peraluminousplutons margin of Gondwana (e.g., Nance and Murphy 1996; Linne- in southem Nova Scotia, Canada:a pegmatite-poorsuite. Lithos, mann et al. 2004; Murphy et al.2O04c,2006). In Fig. 3, we 44. ll'7 140. doi:10.1016/500244937(98)00051-6. therefore speculatethat Meguma was originally located be- De Waele, B., and Fitzsimons, l.C.W. 2007. The nature and timing tween Avalonia and West Africa, in the rifi system along of Palaeoproterozoicsedimentation at the southeasternmargin of which the Rheic Ocean opened. Present data are insufficient the Congo Craton; zircon U/Pb geochronology of plutonic, vol- to determine whether Meguma accompaniedAvalonia after canic and clastic units in northem Zambia. Precambrian Re- the opening of the Rheic Ocean or stayed behind nearer search,159: 95-l 16. doi:10.1016/j.precanres.2007.06.004. Gondwana- Finney, S.C., Gleason, J.D., Gehrels, G.E., Peralta, S., and Aceno- laza, G.2OO3. Early Gondwanan connection for the Argentine Conclusions Precordillera terrane. Earth and Planetary Science Letters,205: 349-359.doi: 10. I 016/50012-821X(02)01063-4. The lowest exposed units of the Meguma Supergroup of Finney, S.C., Gleason, J.D., cehrels, G.E., Peralta, S., and Aceno- southernNova Scotia display detrital zircon populations ard lMa, G.2OO4. Corrigendum to "Early Gondwanan connection Srn-Nd isotopic characteristics consistent with derivation for the Argentine Precordillera terrane". Eafih and Planetary from the Avalonian Pan-African orogen. Upsection, far- ScienceLetters, 219: 413. doi:10.1016/50012-821X(04)00009-3. travelled ancient detritus ftom West Africa and (or) Amazo- Greenough,J.D., Krogh, T.E., Kamo, S.L., Owen, J.V., and Ruff- nia becomes abundant. Paleoproterozoicgrains everywhere man, A- 1999. PreciseU-Pb dating of Meguma basementxeno- outnumber Mesoproterozoic "Grenvillian" grains. These liths: new evidence for Avalonian undefihrusting. Canadian charactedsticsindicate that during latest Neoproterozoicand Journalof EarthSciences,36: 15 22. doi:10.1139/cjes-36-l15. Early Cambrian time Meguma was probably located in a rift Hibbard, J., van Staal, C.D.R., and Williams, H.2006. Geology, between West Africa and Avalonia, perhaps the one along Lithotectonic Map of the AppalachianOrogen (South), Canada which Avalonia separatedin the Early Cambdan or Early United States of America. Geological Survey of Canada, Map 02096A, scale I : I Ordovician. Age distributions previously reported from Si- 500000. Jensen,L.R. 1975. The Torbrook Formation. ludan to Devonian units in Meguma are consistentwith der- 1'l Ancient sediments of Nova Scotia. Edited by I.M. Harris. Society of Economic Pa- ivation from younger pa s of the Goldenville Group; leontologists and Mineralogists, Eastern Section Guidebook, Meguma, therefore, did not necessarilytravel with Avalonia pp.63-74. dudng the mid-Paleozoic. Keppie, J.D. 19'1'/.Plate tectonic interprctation of palaeozoicworld Acknowledgements maps (with emphasison Circum-Atlantic Orogens and Southem Nova Scotia). Departmentof Mines, Nova Scotia, Papet 7'7-3. Financial support was provided by Natural Sciencesand Keppie, D.J., Dostal, J., Murphy, B., and Cousens,B.L. 1997. Pa- Engineering ResearchCouncil of Canada grants to JWFW, laeozoic within-plate volcanic rocks in Nova Scotia (Canada)re- SMB, and LMH and the Nova Scotia Depafimenr of Natural interpreted: isotopic constraints on magmatic source and Resources(NSDNR) operating budget for CEW. We appre- palaeocontinental rcconstructions. Geological Magazine, 134: ciate the assistanceof Judy Schultz in preparing samples. 425447. dol:10.1017/5001675689700719X. Damian Nance, journal referees Meg Thompson and Cees Kolodner, K., Avigad, D., Mcwilliams, M., Wooden, J.L., Weiss van Staal, and Associate Editor Brendan Murphy made sug- brod. T.. and Feinstein. S. 2006. Provenanceof north Condwana gestionsthat improved the manuscdpt. Cambrian Ordovician sandstone:U-Pb SHRIMP dating of detri, tal zircons frcm Israel and Jordan. Ceological Magazine, 143: References 367-391.doi: 10.1017/5001 6756805001640. Krcgh, T.E., and Keppie, J.D. 1990. Age of detrital zircon and tita Barbarosa,J.S.F., and Sabat6,P. 2002. Ceological features and the nite in the Meguma Group, southem Nova Scotia, Canada: Paleoproterozoiccollision of four Archean ctustal segmentsof Clues to the origin of the Meguma Terane. Tectonophysics, the Sao Francisco Craton, Bahia, Brazil. A synthesis.Anais da 177: 30'7-323. doi: 10.l0l6/0040-195 1(90)90287-L Academia Brasileira de Ciencias [Annals of rhe Brazilian Acad- Landing, E. 1996. Avalon; insular continent by the latest Precam- emy of Sciences.l,74:343 359. brian. 1rr Avalonian and related peri-Gondwanan terranes of the

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- Bear River Yarmouth arca of southwestemNova Scotia. Iz Forrnation(Meguma Group), southwestemNova Scotia.Atlantic Mineml R€sourcesBranch, Report of activities 2c/].3.Edited by Geology,41: 83. D.R. MacDonald. Nova Scotia Department of Natural Re- White, C.E., Ban, S.M., and Toole,R.M. 2006.New insighrson sources,Report 20M-1, W,97-117. the origin of the Meguma Group in soudrwestemNova Scotia, White, C.E.,cirgras, M.K., andWaldroq J.W.F.2005. New fossil Canada.Nova Scotia Depaftnent of Natural Resowces,Mineral evidencefor an Early Cambdan age for the lower Goldenville ResourceBranch, Open File lllustration, ME 2006-2.

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