Barr, Sandra M.

White, Chris E.

English

University of New Brunswick: Centre for Digital Scholarship Journals

Meguma Terrane Revisited:Stratigraphy, Metamorphism, Paleontology, and ProvenanceGAC–MAC 2012 St. John’s post-meeting field tripChris E. White1 and Sandra M. Barr21 Nova Scotia Department of  NaturalResources, P.O. Box 698, Halifax, NovaScotia B3J 2T9E-mail: whiteCE@gov.ns.ca2 Department of  Earth and EnvironmentalScience, Acadia University, Wolfville, NovaScotia B4P 2R6SUMMARYThis field trip highlights our currentunderstanding of  the unique geologyof  the Meguma terrane of  southernNova Scotia, the most easterly (out-board) component of  the northernAppalachian orogen (Fig. 1, inset).Recent work has changed previousinterpretations of  the terrane and pro-vided new insights into its provenanceand relationship to other peri-Gond-wanan terranes, as well as its history ofaccretion to composite Laurentia in themid- to late Paleozoic.The Meguma terrane is char-acterized by a thick package of  EarlyCambrian to Early Ordovician tur-biditic metasandstone and slate (Gold-enville and Halifax groups), locallyoverlain unconformably by a thinsequence of  slate, quartz ite and vol-canic rocks (Rockville Notch Group)that ranges from Early Silurian to EarlyDevonian (Figs. 1, 2). These rockswere de formed and variably metamor-phosed (greenschist to amphibolitefacies) during the Early to MiddleDevonian Neoacadian orogeny (ca.405–365 Ma), and intruded by numer-ous, late syntectonic  to post-tectonic,mainly Middle to Late Devonian, pera-luminous, granitic plutons (Figs. 1, 2).This orogenic event is not yet wellunderstood but was related, at least inpart, to dextral transpressive accretionof  Meguma terrane against adjacentAvalonia along the Cobequid–Ched-abucto fault system. Subsequent Car-boniferous motion on the fault systemand renewed transpression throughoutthe Meguma terrane was related todocking of  Gondwana (Africa) out-board of  Meguma terrane (Fig. 3). Although long considered amonotonous stratigraphic succession,detailed mapping during the past 15years (e.g. Horne and Pelley 2007;White 2010a, b; White et al. 2009)revealed that the Goldenville and Hali-fax groups can be divided into region-ally extensive and distinctive forma-tions and members (Fig. 2).  An exam-ple is the High Head member in thelower part of  the Goldenville Group(Church Point formation) north ofYarmouth (Fig. 1), which contains apreviously undiscovered assemblage ofdiverse and well preserved Early Cam-brian deep water trace fossils (Gingraset al. 2011). A major breakthrough inunderstanding the stratigraphy was therecognition of  a distinctive markerunit, in many places manganese-richand coticule-bearing, which forms theuppermost unit (100–300 m in thick-ness) of  the Goldenville Groupthroughout the Meguma terrane(White and Barr 2010).  Anotherimportant advance was the recognitionthat the Chebogue Point shear zone(Fig. 1) divides the terrane into north-western and southeastern parts withstratigraphic differences. The forma-tions of  the Rockville Notch Group, aswell as two distinct suites of  mafic sillsand dykes (White and Barr 2004),occur only northwest of  the shearzone (Figs. 1, 2).  Rocks underlying the Gold-enville Group are not exposed andmetamorphic rocks in the Trafalgararea in the northern part of  the terrane(Fig. 1), interpreted previously to rep-resent possible basement units (e.g.Dostal et al. 2006), have been demon-strated to be the result of  contactmetamorphism of  the Goldenville andHalifax groups around Devonian gran-itoid plutons (White et al. 2009; Scal-lion et al. 2011). Gneissic xenoliths inrare mafic dykes in the Sheet Harbourarea (Fig. 1) also have been interpretedto represent Meguma basement (Owenet al. 1988; Greenough et al. 1999).Based on age and isotopic signatures,the gneissic xenoliths were inferred tohave been derived from underlyingAvalonian crust, and have been used asevidence for the argument that Megu-ma has Avalonian basement (Murphyet al. 2004).  Seismic data show thatthe leading edge of  Meguma has beenthrust over Avalonia (e.g. Keen et al.1991a, b; Loncarevic et al. 1989), pre-sumably during the Neoacadian oroge-ny, but their original relationshipremains unknown.Meguma is generally acceptedto be a peri-Gondwanan terrane,although the specific location along themargin of  Gondwana where it origi-nated remains speculative. Traditionally,the Goldenville and Halifax groupswere interpreted to have been deposit-ed on the continental rise and/or slopeto outer shelf  of  a passive margin thatwas part of, or adjacent to, the NorthAfrican craton during the Cambrian,perhaps in close association withGAC–MAC 2012:FIELD GUIDE SUMMARY8GEOSCIENCE CANADA Volume 39 2012 9Armorica (Schenk, 1971, 1981, 1991,1997), but Amazonian connectionsnow appear more likely (e.g. Keppie1977; Waldron et al. 2009).  Megumaalso has been inferred to be part ofand/or to have travelled with Avalonia(e.g. Landing 2004; Murphy et al. 2004;Nance et al. 2008).  Waldron et al. (2009) conclud-ed that the stratigraphic differencesacross the Chebogue Point shear zone,combined with similarities to Avalon-ian detrital zircon populations, juvenileNd isotopic compositions, and sparsefaunal evidence indicating Avalonianaffinity (Pratt and Waldron 1991), sug-gest that the Meguma terrane formedin a rift  between Gondwana (Amazo-nia) and Avalonia. Based on detritalzircon signatures, Barr et al. (in press)demonstrated similarity in the EarlyCambrian but diverging subsequenthistories after that.  Rifting at ca.520–500 Ma may have moved Avaloniaaway from Gondwana but Megumamoved later (Late Ordovician–EarlySilurian) as evidenced by bimodal vol-canism in the White Rock Formation(MacDonald et al. 2002).  Waldron etal. (2011) emphasized similarities in theCambrian to Tremadocian successionsof  the Meguma terrane to those of  theHarlech Dome of  North Wales, andproposed that both areas were part ofa ‘Megumia domain’ that occupied arift in the margin of  Gondwana. FIELD TRIP ITINERARYDay 1 will focus on the stratigraphyand metamorphism of  the Goldenvilleand Halifax groups along the ‘southshore’ of  Nova Scotia, east of  theChebogue Point shear zone, as well assome of  the granitoid plutons thatintruded those units.  Stops willinclude the pyrite-rich Cunard Forma-tion of  the Halifax Group and under-lying manganiferous Moshers Island,Government Point, and Green Har-bour formations of  the GoldenvilleGroup at both low and high metamor-phic grades, the latter including thespectacular low-pressure/high-temper-ature andalusite–cordierite–staurolitemetapelite in the Shelburne metamor-phic culmination (Fig. 4).  Day 2 will look at rocks northwest ofthe Chebogue Point shear zone, includ-ing the Goldenville and Halifax groupsand metavolcanic and fossiliferousmetasedimentary rocks of  the SilurianWhite Rock Formation of  the lower-most Rockville Notch Group.  We willview the oldest exposed beds of  theGoldenville Group and the trace fossilsof  the High Head member as docu-mented by Gingras et al. (2011), andthe enigmatic contact between the Hal-ifax Group and White Rock Forma-tion, variously described in the past asconformable, unconformable, faulted,and tectonically imbricated.During Day 3 we will focuson stratigraphy in the upper part ofthe Goldenville Group and the overly-ing Halifax Group in the Bear Riverand Wolfville areas, looking at typicallocalities for new formations defined inthe Halifax Group in that area, ages ofwhich are well constrained by acritarchfossils (White et al. 2011).For those interested, anoptional Day 4, not included in theformal part of  the field trip, will con-sist of  stops in the Trafalgar area toview the manganiferous garnet devel-oped in granitoid rocks of  the Trafal-gar plutonic suite as a result of  interac-Figure 1. Simplified geological map of  the Meguma terrane, southern Nova Scotia (after White 2010a). Inset map shows distri-bution of  major tectonic elements of  the northern Appalachian orogen after Hibbard et al. (2006).  Abbreviations in inset map:CBI, Cape Breton Island; NB, New Brunswick; NL, Newfoundland; NS, Nova Scotia; QUE, Québec.10tion with manganiferous rocks of  theBeaverbank formation.REFERENCESBarr, S.M., Hamilton, M.A., Samson, S.D.,Satkoski, A., and White, C.E. in press.Provenance variations in northernAppalachian Avalonia based on detri-tal zircon age patterns in Ediacaranand Cambrian sedimentary rocks, NewBrunswick and Nova Scotia, Canada.Canadian Journal of  Earth Sciences.Dostal, J., Keppie, D.J. Jutras, P., Miller,B.V., and Murphy, B.J. 2006. Evidencefor the granulite-granite connection:penecontemporaneous high-grademetamorphism, granitic magmatismand core complex development in theLiscomb Complex, Nova Scotia,Canada. Lithos, v. 86, p. 77–90.Gingras, M.K., Waldron, J.W.F., White,C.E., and Barr, S.M. 2011. The evolu-tionary significance of  a lower Cam-brian trace fossil assemblage from theMeguma terrane, Nova Scotia. Canadi-an Journal of  Earth Sciences, v. 48, p.71–85.Greenough, J.D., Krogh, T.E., Kamo, S.L.,Owen, J.V., and Ruffman, A. 1999.Precise U–Pb dating of  Meguma base-ment xenoliths: new evidence forAvalonian underthrusting. CanadianJournal of  Earth Sciences, v. 36, p.15–22.Hibbard, J.P., van Staal, C.R., Rankin, D.,and Williams, H. 2006. Lithotectonicmap of  the Appalachian orogen(north), Canada-United States ofAmerica: Geological Survey of  Cana-da Map 2041A, scale 1:1,500,000, 1sheet.Horne, R. J. and Pelley, D. 2007: in MineralResources Branch, Report of  Activi-ties 2006; Nova Scotia Department ofNatural Resources, Report ME 2007-1, p. 71–89.Keen, C.E., Kay, W.A., Keppie, J.D., Maril-lier, F., Pe-Piper, G., and Waldron,J.W.F. 1991a. Deep seismic reflectiondata from the Bay of  Fundy and Gulfof  Maine: tectonic implications for thenorthern Appalachians. CanadianJournal of  Earth Sciences, v. 28, p.1096–1111.Keen, C.E., MacLean, B.C., and Kay, W.A.1991b. A Deep Seismic ReflectionProfile across the Nova Scotia Conti-nental Margin, Offshore EasternCanada. Canadian Journal of  EarthSciences, v. 28, p. 1112–1120.Keppie, J.D. 1977. Plate Tectonic Interpre-tation of  Palaeozoic World Maps(with Emphasis on Circum-AtlanticOrogens and Southern Nova Scotia).Nova Scotia Department of  MinesPaper, 77-3.Landing, E. 2004. Precambrian-Cambrianboundary interval deposition and themarginal platform of  the Avalonmicrocontinent. Journal of  Geody-namics, v. 37, p. 411–435.Loncarevic, B.D., Barr, S.M., Raeside, R.P.,Keen, C.E., and Marillier, F. 1989.Northeastern extension and crustalexpression of  terranes from Cape Bre-ton Island, Nova Scotia, based ongeophysical data. Canadian Journal ofEarth Sciences, v. 26, p. 2255–2267.MacDonald, L.A., Barr, S.M., White, C.E.,and Ketchum, J.W.F. 2002. Petrology,age, and tectonic setting of  the WhiteRock Formation, Meguma terrane,Nova Scotia: evidence for Siluriancontinental rifting. Canadian Journalof  Earth Sciences, v. 39, p. 259–277.Moran, P.C., Barr, S.M., White, C.E., andHamilton, M.A. 2007. Petrology, age,and tectonic setting of  the Seal IslandPluton, offshore southwestern NovaScotia. Canadian Journal of  Earth Sci-ences, v. 44, p. 1467–1478. Murphy, J.B., Fernandez-Suarez, J., Keppie,J.D., and Jeffries, T.E. 2004. Contigu-ous rather than discrete Paleozoic his-tories for the Avalon and MegumaTerranes based on detrital zircon data.Geology, v. 32, p. 585–588.Nance, R.D., Murphy, J.B., Strachan, R.A.,Keppie, J.D., Gutierrez-Alonso, G.,Fernandez-Suarez, J., Quesada, C.,Linnemann, U., D’lemos, R,., and Pis-Figure 2. Schematic summary of  geological events in the Meguma terrane afterWhite (2010a) and references therein.  GEOSCIENCE CANADA Volume 39 2012 11Figure 3. A tectonic model for the Neoacadian orogeny and related pluton emplacement (after Moran et al. 2007). Plutonemplacement in Meguma terrane may have been related to subduction of  the Rheic Ocean lithosphere outboard of  Meguma,likely combined with slab-breakoff  which also caused high-temperature/low-pressure (HT-LP) metamorphism.Figure 4. Regional metamorphic isograd map for the Meguma terrane compiled from data and sources in Raeside andJamieson (1992), White (2003), and unpublished data.12arevsky, S.A. 2008. Neoproterozoic–Early Palaeozoic tectonostratigraphyand palaeogeography of  the peri-Gondwanan terranes: AmazonianWest African connections. In TheBoundaries of  the West African Cra-ton. Edited by N. Ennih and J.-P.Liegeois. Geological Society, London,Special Publications 297, p. 345–383.Owen, J.V., Greenough, J.D., Hy, C., andRuffman, A. 1988. Pelitic xenoliths ina mafic dykes at Popes Harbour, NovaScotia: Implications for the basementof  the Meguma Group. CanadianJournal of  Earth Sciences, v. 25, p.1464–1471.Pratt, B.R., and Waldron, J.W.F. 1991. AMiddle Cambrian trilobite faunulefrom the  Meguma Group of  NovaScotia. Canadian Journal of  Earth Sci-ences, v. 28, p. 1843–1853.  Raeside, R.P. and Jamieson, R.A. 1992.Low-pressure metamorphism of  theMeguma terrane, Nova Scotia. Fieldexcursion C-5, GAC-MAC field tripguide, 25 p.Scallion, K., Jamieson, R.J., Barr, S.M.,White, C.E., and Erdmann, S. 2011.Texture and composition of  garnet asa guide to contamination of  granitoidplutons, Governor Lake area, Megumaterrane, Nova Scotia.  The CanadianMineralogist, v. 49, p. 441–458,DOI:10.3749/canmin.49.2.441.Schenk, P.E. 1971. Southern Atlantic Cana-da, northwestern Africa and continen-tal drift. Canadian Journal of  EarthSciences, v. 8, p. 1218–1251.Schenk, P.E. 1981. The Meguma Zone ofNova Scotia – a remnant of  WesternEurope, South America, or Africa? InGeology of  North Atlantic border-lands. Edited by J.M. Kerr, A.J., Fergu-son, and L.C. Machan. Canadian Soci-ety of  Petroleum Geologists Memoir7, p. 119–148.Schenk, P.E. 1991. Events and sea levelchanges on Gondwana’s margin: theMeguma Zone (Cambrian to Devon-ian) of  Nova Scotia, Canada. Geologi-cal Society of  America Bulletin, v. 103,p. 512–521.Schenk, P.E. 1997. Sequence stratigraphyand provenance on Gondwana’s mar-gin: the  Meguma Zone (Cambrian toDevonian) of  Nova Scotia, Canada.Geological Society of   America Bul-letin, v. 109, p. 395–409.   Waldron, J.W.F., White, C.E., Barr, S.M.,Simonetti, A. & Heaman, L.M. 2009.Provenance of  the Meguma terrane,Nova Scotia: rifted margin of  earlyPaleozoic Gondwana. Canadian J. ofEarth Sciences, v. 46, p. 1–9.Waldron J. W. F. Schofield, D.I., White,C.E., and Barr, S.M. 2011. Cambriansuccessions of  the Meguma Terrane,Nova Scotia, Canada, and HarlechDome, North Wales, UK: dispersedfragments of  a peri-Gondwananbasin?  Journal of  the Geological Soci-ety (London), v. 168, p. 83–98.White, C.E. 2003. Preliminary bedrockgeology of  the area betweenChebogue Point, Yarmouth County,and Cape Sable Island, ShelburneCounty, southwestern Nova Scotia. InMinerals and Energy Branch, Reportof  Activities 2002. Edited by D.R. Mac-Donald. Nova Scotia Department ofNatural Resources, Minerals and Ener-gy Branch, Report 2003-1, p. 127–145.White, C.E. 2010a. Stratigraphy of  theLower Paleozoic Goldenville and Hali-fax groups in southwestern Nova Sco-tia. Atlantic Geology, v. 46, p.136–154.White, C.E. 2010b. Pre-Carboniferousbedrock geology of  the AnnapolisValley area (NTS 21A/14, 15, and 16;21H01 and 02), southern Nova Scotia.In Mineral Resources Branch, Reportof  Activities 2009. Edited by D.R.MacDonald and K.A. Mills. Nova Sco-tia Department of  Natural Resources,Report 2010-1, p. 137–155.White, C.E. and Barr, S.M. 2004. Age andpetrochemistry of  mafic sills on thenorthwestern margin of  the Megumaterrane in the Bear River - Yarmoutharea of  southwestern Nova Scotia. InMineral Resources Branch, Report ofActivities 2003. Edited by D.R. Mac-Donald. Nova Scotia Department ofNatural Resources, Report 2004-1, p.97–117.White, C.E., and Barr, S.M. 2010. Litho-chemistry of  the Lower PaleozoicGoldenville and Halifax Groups,southwestern Nova Scotia, Canada:Implications for stratigraphy, prove-nance, and tectonic setting of  Megu-ma, in Tollo, R.P., Bartholomew, M.J.,Hibbard, J.P., and Karabinos, P.M.,eds., From Rodinia to Pangea: TheLithotectonic Record of  theAppalachian Region: Geological Socie-ty of  America Memoir 206, p.347–366.White, C.E., Scallion, K., and MacHattie, T.2009. Geology of  the Governor Lakearea (‘Liscomb Complex’), parts ofNTS sheets 21E/01, 02, 07, and 08,central Nova Scotia. In MineralResources Branch, Report of  Activi-ties 2008. Edited by D.R. MacDonald.Nova Scotia Department of  NaturalResources, Report ME 2009-1, p.151–165.White C.E. T. Palacios, T., Jensen, S., andBarr, S.M. 2011. The Meguma terraneof  southern Nova Scotia: insights onits pre-Carboniferous stratigraphy.Atlantic Geology, v. 47, p. 50.

Meguma Terrane Revisited: Stratigraphy, Metamorphism, Paleontology, and Provenance

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Meguma Terrane Revisited: Stratigraphy, Metamorphism, Paleontology, and Provenance

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