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The Bras d'Or terrane of central Cape Breton Island, Nova Scotia, Canada, contains a well-preserved record of the Ediacaran to early Cambrian evolution of Ganderia, a Gondwana-derived terrane in the northern Appalachian orogen. A complex assemblage of low- to high-grade metasedimentary rocks has varied detrital zircon signatures from laser ablation inductively coupled plasma mass spectrometry U-Pb zircon dating, but combining three or more samples yielded representative age spectra that support correlation of the low- and high-grade metasedimentary rocks throughout the Bras d'Or terrane and the corresponding Ganderian Brookville terrane of southern New Brunswick. In quartzite samples from the McMillan Flowage Formation in the northwestern Bras d'Or terrane, the youngest detrital zircons have ages >900 Ma, in contrast to previously studied psammitic and semipelitic samples from correlative units in the eastern Bras d'Or terrane in which youngest detrital ages are 620-600 Ma. Both quartzite and semipelitic samples from the McMillan Flowage Formation contain Neoproterozoic dates from zircon rims, which reflect metamorphic overgrowths during peak metamorphism at ca. 550 Ma, providing a robust age for peak metamorphism in the Bras d'Or terrane that supports similar, albeit sparse, ages reported previously from monazite and titanite samples. This metamorphism is coeval with the emplacement of voluminous dioritic to granitic plutons that occur throughout the Bras d'Or terrane and form in an Andean-type continental margin subduction zone. New U-Pb zircon ages presented here from plutons in the northern Bras d'Or terrane, combined with previously published ages, are consistent with subduction-related magmatism and associated metamorphism between ca. 575 and 540 Ma. Key words: U-Pb geochronology, Appalachian metamorphism, Bras d'Or terrane, Cape Breton Island, McMillan Flowage Formation, detrital zircon, plutonic ages, Introduction The Bras d'Or terrane of central Cape Breton Island, Nova Scotia (Fig. 1), consists of mainly Ediacaran and Cambrian metamorphic and plutonic rocks overlain unconformably by Carboniferous sedimentary rocks [...]

The Coldbrook Group and related plutons in the Caledonian Highlands of southern New Brunswick contain voluminous late Ediacaran silicic rocks formed in a magmatic event not recognized in other parts of Avalonia in the northern Appalachian orogen. To better constrain the age and origin of these rocks, we used U-Pb zircon dating by laser ablation inductively coupled plasma mass spectrometry to check for older inherited zircon and obtain trace element data, followed by chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-TIMS) to obtain precise dates. Four silicic samples were dated from the Coldbrook Group, one from the Bonnell Brook pluton, and, for comparison, a felsic lithic-crystal tuff sample from the older arc-related Broad River Group. Overlapping CA-TIMS dates of 551.57 [+ or -] 0.23, 551.38 [+ or -] 0.24, and 551.70 [+ or -] 0.20 Ma for samples from the lower, middle, and upper Coldbrook Group, respectively, and 551.71 [+ or -] 0.19 Ma for granite from the Bonnell Brook pluton show that these units crystallized in 760 000 years or less, consistent with a super-eruption event. Rhyolite from the uppermost unit of the Coldbrook Group yielded a younger date of 549.18 [+ or -] 0.09 Ma, but the large extent of that unit is consistent with the possibility of a second younger super-eruption. The felsic lithic-crystal tuff sample from the Broad River Group yielded a date of 615.48 [+ or -] 0.16 Ma, consistent with previously published dates from that group and associated plutons. Differences in zircon chemistry between the Broad River Group sample and the late Ediacaran samples are consistent with the contrasting subduction-related vs within-plate extensional tectonic settings as suggested by previous studies of whole-rock petrological characteristics of the two age groups. Key words: U-Pb zircon dating, super-eruptions, late Ediacaran, Avalonia, zircon chemistry, Introduction The Caledonia terrane of southern New Brunswick, Canada, is a component of Avalonia in the northern Appalachian orogen (Fig. 1, inset). The original relations among the now-geographically separated parts [...]

The MacCodrum Formation is a classical 'lower' Cambrian unit in southeastern Cape Breton Island stratigraphy, described since the 1800s. The age of this formation and its correlation with other Avalonian Cambrian units in eastern Newfoundland and southern New Brunswick have remained uncertain through numerous revisions. Here we present U-Pb CA-TIMS ages from an ash bed in the basal part of the MacCodrum Formation in its type-section on MacCodrum Brook that fix the maximum time of deposition at 531.86 [+ or -] 0.34 Ma. Organic-walled microfossils sampled throughout the MacCodrum Formation type-section yield acritarch taxa identifying the Asteridium-Comasphaerdium Zone, whereas the first acritarchs of the Skiagia-Fimbriaglomerella Zone appear in the overlying Canoe Brook Formation in other sections. The radiometric age and acritarch zonation place the MacCodrum Formation in the upper Fortunian, Cambrian Stage 2. Among trace fossils in the MacCodrum Formation, the meandering trace fossil Didymaulichnus dailyi comb. nov. is of particular note and morphologically identical to the type material from the lower part of the Ratcliffe Brook Formation in New Brunswick. The new radiometric and biostratigraphic data presented here provide the first firm constraints on the age of the MacCodrum Formation and enable more precise correlation with sections in southern New Brunswick and eastern Newfoundland. Key words: acritarch, trace fossils, Cambrian, U-Pb zircon, Avalonia, correlation, Introduction Cambrian rocks in southeastern Cape Breton Island, Nova Scotia (Fig. 1), have been visited and described by geologists since the 1800s (e.g., Fletcher 1878; Matthew 1903; Hutchinson 1952; Landing [...]

Zircon grains from metasiltstone beds in the Precambrian Ashburn Formation were dated to constrain the age of the stromatolite Archaeozoon acadiense. The largest group of analyzed grains consists of mostly well-rounded detrital zircon no younger than 1060 Ma with significant peaks at about 1200-1100, 1500, 1800, 2050, and 2700 Ma, as well as a few Mesoarchean ages. A second population of apparently euhedral grains gives ages in the range 680-400 Ma. The distribution of detrital zircon ages along with field relationships suggest that the Ashburn and Martinon formations are proximal and distal parts of the Green Head Group, respectively, and hence a previously reported maximum depositional age of ca. 602 [+ or -] 8 Ma for the Martinon Formation also applies to stromatolite in the Ashburn Formation. Paleozoic zircon recovered from the Ashburn Formation cannot be detrital because the rocks were intruded and contact metamorphosed by the Golden Grove Plutonic Suite at ca. 550-525 Ma. The Paleozoic zircon grains were found in four independently processed samples and have also been seen in other studies in the region, showing that they are not due to laboratory contamination. Zircon formed during younger magmatic activity may have been transported in hydrothermal fluids and emplaced into these metasedimentary rocks in veins. A single euhedral zircon recovered from an atypically thick vein gave an age of 659 [+ or -] 33 Ma. Hydrothermally transported zircon might provide a window into younger igneous processes for which evidence is not otherwise preserved in this and other areas. Key words: U--Pb geochronology, zircon, hydrothermal transport, detrital ages, Ashburn Formation. Des grains de zircon provenant de lits de metasiltstone dans la Formation precambrienne d'Ashburn ont ete dates afin de circonscrire l'age du stromatolite Archaeozoon acadiense. Le plus grand groupe de grains analyses est principalement constitue de zircons detritiques arrondis d'un age minimum de 1060 Ma avec des pics significatifs a environ 1200-1100, 1500, 1800, 2050 et 2700 Ma, ainsi que quelques ages mesoarcheens. Une deuxieme population de grains en apparence idiomorphes donne des ages dans la fourchette de 680-400 Ma. La distribution des ages de zircons detritiques combinee aux relations de terrain donne a penser que les Formations dAshburn et de Martinon sont les parties proximale et distale du Groupe de Green Head, respectivement, et qu'un age de depot maximum deja publie d'environ 602 [+ or -] 8 Ma pour la Formation de Martinon s'applique egalement aux stromatolites dans la Formation dAshburn. Des zircons paleozo'iques provenant de la Formation dAshburn ne peuvent etre detritiques puisque les roches ont ete recoupees par la serie plutonique de Golden Grove vers 550-525 Ma et en ont subi un meta-morphisme de contact. Les grains de zircon paleozo'iques ont ete trouves dans quatre echantillons traites de maniere independante et ont egalement ete releves dans d'autres etudes dans la region, ce qui demontre qu'ils ne sont pas dus a une contamination en laboratoire. Des zircons formes durant des episodes magmatiques plus recents pourraient avoir ete transported dans des fluides hydrothermaux et mis en place dans des veines dans ces roches metasedimentaires. Un unique grain de zircon idiomorphe provenant d'une veine inhabituellement epaisse a donne un age de 659 [+ or -] 33 Ma. Des zircons transported par des fluides hydrothermaux pourraient ouvrir une fenetre sur des processus ignes plus jeunes dont d'autres preuves ne sont pas preservees dans cette region et ailleurs. [Traduit par la Redaction] Mots-cles: geochronologie U--Pb, zircon, transport hydrothermal, ages de zircons detritiques, Formation d'Ashburn., Introduction The Saint John area of southern New Brunswick, Canada (Fig. 1), has been a centre of geological investigation since the mid part of the 19th century, when the Steinhammer [...]

A large dyke of quartz tholeiitic gabbronorite has been mapped for 59 km in southern New Brunswick, Canada, between Lepreau River in the northeast and Indian Island in the southwest. Scattered outcrops occur along a positive aeromagnetic lineament, providing a dyke strike of N42[degrees]E overall (segments N30[degrees]E to N72[degrees]E), dips of 80[degrees] to 90[degrees]NNW, and widths of 4 to 30 m. A [new.sup.40]Ar/[.sup.39]Ar plagioclase age of 201.67 6 0.35 Ma for the Lepreau River Dyke is similar to dates for the massive North Mountain Basalt in the Fundy Basin to the east. The dyke is associated with the Ministers Island and Christmas Cove dykes, which are indistinguishable in chemistry, petrology, and probable age, and we regard them as segments of the same co-magmatic dyke system. In addition, their petrology is similar to that of the basalts of the adjacent Early Mesozoic Fundy and Grand Manan basins. We propose that the Lepreau River and associated dykes were sources for the regional basin basalts, which in turn are part of the Central Atlantic Magmatic Province (CAMP) that overlaps the Triassic-Jurassic boundary and associated mass extinction event. Key words: Mesozoic dykes, Central Atlantic Magmatic Province (CAMP), flood basalt, Fundy Basin. Un grand dyke de gabbronorite tholeitique quartzifere a ete cartographie sur une distance de 59 km dans le sud du Nouveau-Brunswick (Canada) entre la riviere Lepreau, au nord-est, et l'ile Indian, au sud-ouest. Des affleurements disperses sont presents le long d'un lineament aeromagnetique positif, qui donnent une orientation globale de N[42.sup.o]E pour le dyke (les differents troncons allant de N30[degrees]E a N72[degrees]E), des pendages de 80[degrees] a 90[degrees] vers le NNO et des largeurs de 4 m a 30 m. Un nouvel [age.sup.40]Ar/[.sup.39]Ar sur plagioclase de 201,67 6 0,35 Ma pour le dyke de la riviere Lepreau est semblable a des ages obtenus pour le basalte massif de North Mountain, dans le bassin de Fundy plus a l'est. Le dyke est associe aux dykes de l'ile Minister et de Christmas Cove, dont la chimie, la petrologie et l'age probable sont essentiellement identiques, et nous estimons qu'ils constituent des troncons d'un meme systeme de dykes comagmatiques. Leur petrologie est en outre semblable a celle des basaltes des bassins de Fundy et de Gand Manan attenants, d'age mesozoique precoce. Nous proposons que le dyke de la riviere Lepreau et les dykes associes constituaient des sources pour les basaltes de bassin regionaux qui, eux, font partie de la province magmatique centre atlantique (PMCA) qui chevauche la limite Trias-Jurassique et l'episode d'extinction massive associe. [Traduit par la Redaction] Mots-cles : dykes mesozoiques, province magmatique centre atlantique (PMCA), basalte de plateau, bassin de Fundy., Introduction Flood basalts in large igneous provinces are produced by fissure eruptions, which can be exceptionally large (tens to hundreds of kilometres long), and with huge eruption volumes of tens [...]

Paleomagnetic results and a U--Pb baddeleyite age from the Silurian Mavillette gabbroic sill in southwest Nova Scotia, Canada, provide new evidence about the Paleozoic tectonic evolution of the Meguma terrane. The Mavillette gabbro sill intruded ca. 440-430 Myr old bimodal rift-related metavolcanic and metasedimentary rocks of the White Rock Formation in the Silurian--Devonian Rockville Notch Group. The 426.4 [+ or -] 2.0 Ma Mavillette gabbro age is notably younger than the ca. 440 Ma magmatism, but is part of a geochemically defined suite of within-plate sills and volcanic rocks of the Rockville Notch Group with ages as young as Early Devonian. Paleomagnetic investigation of 13 sites distributed along the Neoacadian (ca. 390 Ma) synclinal limbs of the Mavillette sill reveal magnetization directions that fail a fold test and therefore postdate Silurian emplacement of the gabbro. The post-folding remanence has a mean direction of D = 153.4, I = 17.1[degrees]; [[alpha].sub.95] = 6.5[degrees] (n = 12 sites), with corresponding paleopole 31.9 [degrees]S, 325.2 E; dp = 3.5[degrees], dm = 6.7[degrees] that resembles a pervasive late Carboniferous Kiaman overprint magnetization in North America, but is rotated significantly 22.2[degrees] [+ or -] 8.1[degrees] counter-clockwise (CCW). Mavillette remanence acquisition likely occurred in concert with fluid mobilization related to Alleghanian deformation, recorded locally by ca. 320 Ma muscovite [.sup.40][Ar.sup.-39] Ar ages. Previously published paleomagnetic results from the Meguma terrane also have Carboniferous remanence directions with similar ~24[degrees] CCW discordance. The regional CCW rotation of the southwest Meguma terrane post-dates this ca. 320 Ma tectonothermal remanence acquisition event, likely recording the development of an oroclinal bend of the Meguma terrane during the Alleghanian orogeny. Key words: rift magmatism, terrane accretion, tectonic rotation, Appalachian, overprint magnetization, Meguma orocline, faunal associations.. Les resultats d'analyses paleomagnetiques et un age U-Pb sur baddeleyite du filon-couche gabbroique silurien de Mavillette, dans le sud-ouest de la Nouvelle-Ecosse, Canada, fournissent de nouveaux renseignements sur l'evolution tectonique paleozoique du terrane de Meguma. Le filon-couche gabbro'ique de Mavillette s'est mis en place dans des roches metasedimentaires et metavolcaniques bimodales associees au rifting formees vers 440-430 Ma, de la Formation de White Rock, dans le Groupe siluro-devonien de Rockville Notch. L'age de 426,4 [+ or -] 2,0 Ma du gabbro de Mavillette est sensiblement plus jeune que le magmatisme vers 440 Ma, mais fait partie d'une serie definie par la geochimie de filons-couches et de roches volcaniques intraplaques du Groupe de Rockville Notch, dont les ages vont jusqu'au Devonien precoce. L'etude paleomagnetique de 13 sites repartis le long des flancs du synclinal neoacadien (vers 390 Ma) du filon-couche de Mavillette revele des directions de magnetisation qui echouent une epreuve de plissement et doivent donc etre posterieures a la mise en place du gabbro au Silurien. La remanence post-plissement a une direction moyenne de D = 153,4, I = 17,1[degrees]; [[alpha].sub.95] = 6,5[degrees] (n = 12 sites), avec un paleopole correspondant a 31,9[degrees]S, 325,2E; dp = 3,5[degrees], dm = 6,7[degrees] qui ressemble a une magnetisation penetrante superposee de Kiaman, d'age carbonifere tardif, en Amerique du Nord, mais caracterisee par une rotation antihoraire (AH) significative de 22,2[degrees] 6 8,1[degrees]. L'acquisition de la remanence de Mavillette s'est produite de concert avec la mobilisation de fluides associee a la deformation alleghanienne, dont temoignent localement des ages [.sup.40][Ar.sup.-39]Ar sur muscovite d'environ 320 Ma. Des resultats d'analyses paleomagnetiques publies precedemment pour le terrane de Meguma montrent aussi des directions de remanence carboniferes presentant une discordance semblable de ~24[degrees] AH. La rotation AH regionale du sud-ouest du terrane de Meguma est posterieure a cet episode d'acquisition de remanence tectonothermique, temoignant vraisemblablement du developpement d'une flexion oroclinale du terrane de Meguma durant l'orogenese alleghanienne. [Traduit par la Redaction] Mots-cles : magmatisme de rifting, accretion de terranes, rotation tectonique, Appalaches, magnetisation superposee, oroclinal de Meguma, associations fauniques.., Introduction The Meguma terrane is exposed in the southern half of mainland Nova Scotia (Fig. 1), Canada, and related rocks constituting a larger 'Megumia' (Waldron et al. 2011) also underlie [...]

Devonian granitoid plulons comprise a major part of the bedrock of northwestern Maine representing the magmatic expression of the Acadian orogeny in this part of the northern Appalachian orogen. They are petrographically diverse with minerals characteristic of both I- and S-type granites, in some cases within the same intrusion, and some are compositionally zoned. New LA-ICP-MS ages presented here elucidate the timing and duration of this magmatism. The earliest phase of granitoid magmatism began around 410-405 Ma with the emplacement of the Flagstaff Lake Igneous Complex, and the presence of contemporaneous mafic rocks suggests that mantle-derived magmas were also produced at this time. Late Devonian ages, ca. 365 Ma, for many intrusions, such as the Chain of Ponds and Songo plutons, reveal that magmatism continued for 45 million years during which compositionally diverse I- and S-type magmas were produced. In addition, there is evidence that intrusive activity was prolonged within some plutons, for example the Rome-Norridgewock pluton and the Mooselookmeguntic Igneous Complex, with 10-15 myr between intrusive units. The new ages suggest a break in magmatism between 400 Ma and 390 Ma apparently separating Acadian magmatism into early and late pulses. The production of lower crustal I-type magmas appears to have been concentrated later, ca. 380-365 Ma, although several S-type granitoids were also emplaced during this period. These Late Devonian plulons display abundant zircon inheritance with ages around 385 Ma, which suggests that the crust was experiencing enhanced thermal perturbations during this extended timeframe. The new data for granitoid plutons in northwestern Maine are consistent with tectonic models for other parts of Ganderia which propose initial flat slab subduction followed by slab breakoff and delamination. Les plutons granitoides du Devonien constituent une tranche importante du substrat rocheux du nord-ouest du Maine representant l'expression magmatique de l'orogenese acadienne dans cette partie de l'orogene appalachien septentrional. Ils constituent une succession petrographiquement diversifiee, composee de mineraux caracteristiques tant des granites de type I que de type S, dans certains cas a l'interieur de la meme intrusion, alors que la composition des aulres plutons regionaux est zonee. Les nouvelles datations par ablation laser et speclrometrie de masse a plasma induclif presentees ici elucidenl le moment ou est survenu ce magmatisme et sa duree. L'episode le plus ancien du magmatisme granitoide a debute vers 410-405 Ma avec la mise en place du complexe de roches eruptives du lac Flagstaff, meme si la presence de roches mafiques contemporaines laisse supposer que des magmas d'origine mantellique ont egalement ete produits a ce moment. Les datations du Devonien tardif faisant remonter a environ 365 Ma de nombreuses intrusions, comme les plutons Chain of Ponds et Songo, revelent que ce magmatisme s'est dans l'ensemble poursuivi durant 45 millions d'annees au cours desquelles des magmas de type I et S de compositions diverses ont ete produits. II existe de plus des preuves que l'activite intrusive s'est prolongee a l'interieur de certains plutons, par exemple le pluton Rome-Norridgewock et le complexe de roches eruptives de Mooselookmeguntic, qui accusent un ecart de 10 a 15 Ma entre les unites intrusives. Les nouvelles datations permettent de supposer une interruption du magmatisme entre 400 et 390 Ma., qui semble separer le magmatisme acadien en impulsions precoce et tardive. La production de magmas de type I crustaux inferieurs semble s'etre concentree a un moment ulterieur, vers 380 a 365 Ma, bien que plusieurs roches granitoides de type S se soient egalement mises en place durant celte periode. Ces plutons du Devonien tardil presentent un heritage abondanl de zircons remontant a peu pres a 385 Ma, ce qui laisse entendre que la croute terrestre a subi des perturbations thermiques de plus en plus prononcees au cours de cet intervalle prolonge. Les nouvelles donnees sur les plutons granitoides du nord-ouest du Maine correspondent aux modeles tectoniques d'autres parties du terrane de Gander, qui supposent une subduction initiale de plaques plates suivie par une rupture des plaques et une delamination. [Traduit par la redaction], INTRODUCTION Granitic magmas produced during collisional tectonic events are important repositories of information regarding (i) the duration of orogenesis, (ii) the role of mantle inputs, both physical and thermal, and [...]

The Margaree pluton extends for >40 km along the axis of the Ganderian Aspy terrane of northern Cape Breton Island, Nova Scotia. The pluton consists mainly of coarse-grained megacrystic syenogranite, intruded by small bodies of medium-grained equigranular syenogranite and microgranite porphyry, all locally displaying rapakivi texture. The three rock types have similar U-Pb (zircon) ages of 363 [+ or -] 1.6, 364.8 [+ or -] 1.6, and 365.5 [+ or -] 3.3 Ma, respectively, consistent with field and penological evidence that they are coeval and comagmatic. The rare earth elements display parallel trends characterized by enrichment in the light rare earth elements, flat heavy rare earth elements, moderate negative Eu anomalies, and, in some cases, positive Ce anomalies. The megacrystic and rapakivi textures are attributed to thermal perturbation in the magma chamber caused by the mixing of mafic and felsic magma, even though direct evidence of the mafic magma is mainly lacking at the current level of exposure. Magma evolution was controlled by fractionation of quartz, K-feldspar, and Na-rich plagioclase in molar proportions of 0.75:0.12:0.13. The chemical and isotopic (Sm-Nd) signature of the Margaree pluton is consistent with the melting of preexisting continental crust that was enriched in heat-producing elements, likely assisted by intrusion of mantle-derived mafic magma during Late Devonian regional extension. The proposed model involving magma mixing at shallow crustal levels in a cryptic silicic-mafic magma chamber during post-Acadian extension is consistent with models for other, better exposed occurrences of rapakivi granite in the northern Appalachian orogen. Key words: rapakivi, megacrysts, U-Pb zircon, Devonian, crystal fractionation, PER diagrams. Le pluton de Margaree s'etale sur plus de 40 km le long de l'axe du terrane ganderien d'Aspy du nord de l'île du Cap-Breton (Nouvelle-Ecosse). Le pluton est principalement constitue de syenogranite megacristique à grains grossiers, recoupe par de petits corps de syenogranite equigranulaire à grains moyens et de porphyre microgranitique, qui presentent tous une texture rapakivi. Les trois types de roche donnent des âges U-Pb sur zircons semblables de 363 [+ or -] 1,6, 364,8 [+ or -]1,6 et 365,5 [+ or -] 3,3 Ma, respectivement, ce qui concorde avec des observations petrologiques et de terrain indiquant qu'ils sont contemporains et comagmatiques. Les terres rares presentent des spectres paralleles caracterises par un enrichissement des terres rares legeres, des tronçons des terres rares lourdes plats, des anomalies negatives moderees d'Eu et, dans certains cas, des anomalies de Ce positives. Les textures megacristique et rapakivi sont attribuees à une perturbation thermique dans la chambre magmatique causee par le melange de magmas mafique et felsique, bien que des preuves directes de la presence d'un magma mafique soient generalement absentes au niveau d'exposition actuel. L'evolution du magma etait controlee par la cristallisation fractionnee du quartz, du feldspath potassique et du plagioclase riche en Na dans des proportions molaires de 0,75:0,12:0,13. Les signatures chimique et isotopique (Sm-Nd) du pluton de Margaree concordent avec la fusion de croûte continentale preexistante qui etait enrichie en elements thermogenes, vraisemblablement aidee par l'intrusion de magma mafique derive du manteau durant l'extension regionale au Devonien tardif. Le modele propose qui comprend le melange de magmas à des niveaux crustaux peu profonds dans une chambre magmatique siliceuse-mafique cryptique durant l'extension post-acadienne concorde avec les modeles proposes pour d'autres cas mieux exposes de granite rapakivi dans le nord de l'orogene des Appalaches. [Traduit par la Redaction] Mots-cles: rapakivi, megacristaux, U-Pb sur zircons, Devonien, cristallisation fractionnee, diagramme de Pearce., Introduction Rapakivi granite sensu stricto is characterized by the presence of plagioclase-mantled K-feldspar, independent of K-feldspar morphology or origin (Ramo and Haapala 1995). The debate over the formation of rapakivi [...]

New U-Pb zircon ages from volcanic, plutonic, and sedimentary units in the Avalonian Caledonia terrane of southern New Brunswick provide better timing constraints in this geologically complex area. Previous ca. 620 Ma ages from the Broad River Group are now corroborated by additional dates from felsic tuff in the Gordon Falls Formation and rhyolite in the former Fairfield (now East Branch Black River) Formation of 620 [+ or -] 5 Ma and 622 [+ or -] 1.9 Ma, respectively. Combined with ages ranging from ca. 625 Ma to 615 Ma from cross-cutting plutons, the data suggest that the minimum age of the Broad River Group is about 615 Ma. A quartz-feldspar porphyry dyke in mafic volcanic rocks of the previously undated Long Beach Formation yielded an igneous crystallization age of 685 [+ or -] 10 Ma, the oldest unit yet dated in the Caledonia terrane but similar in age to porphyry in the Stirling belt in the Avalonian Mira terrane of Nova Scotia. The age of the Coldbrook Group was constrained previously by U-Pb (zircon) ages of volcanic rocks between 560 and 550 Ma as well as by similar ages from comagmatic plutons. Five additional samples from both volcanic and plutonic units lie in the same range of 560-550 Ma, including errors, demonstrating that the Coldbrook Group and related plutons formed in less than 10 million years. Such a large volume of mainly felsic magma erupted and emplaced in a short time span suggests a 'supereruption/supervolcano' environment such as the late Cenozoic southwestern USA but not yet recognized at ca. 560-550 Ma elsewhere in Avalonia. Two units yielded Paleozoic ages: felsite of the Bloomsbury Mountain Formation with a zircon population at 427 [+ or -] 9 Ma, indicating a Silurian maximum emplacement age, and dacite of the Grassy Lake Formation with several zircon grains at 382.8 [+ or -] 8.3 Ma, indicating a maximum age of middle Devonian, the first rocks of this age to be identified in the Caledonia terrane. De nouveaux ages U - Pb sur zircon provenant d'unites volcaniques, plutoniques et sedimentaires dans le terrane avalonien Caledonie du sud du Nouveau-Brunswick fournissent de meilleures contraintes temporelles dans cette region geologiquement complexe. Les ages d'environ 620 Ma precedemment obtenus du Groupe de Broad River sont maintenant appuyes par des dates supplementaires provenant du tuf felsique dans la Formation de Gordon Falls et de la rhyolite dans l'ancienne Formation de Fairfield (maintenant East Branch Black River) de 620 [+ or -] 5 Ma et 622 [+ or -] 1,9 Ma, respectivement. Combine avec des ages allant de 625 Ma a 615 Ma a partir de plutons encaisses, les donnees suggerent que l'age minimum du Broad River Group est d'environ 615 Ma. Un dyke de porphyre de quartz-feldspath dans des roches volcaniques mafiques de la Formation de Long Beach non datee a donne un age de cristallisation ignee de 685 [+ or -] 10 Ma, la plus ancienne unite encore datee dans le terrane de Caledonie mais similaire en age au porphyre dans la ceinture de Stirling dans le terrane avalonien Mira de la Nouvelle-Ecosse. L'age du Groupe de Coldbrook etait auparavant limite par les ages U - Pb (zircon) des roches volcaniques entre 560 et 550 Ma, ainsi que par les ages similaires des plutons co-magmatiques. Cinq echantillons supplementaires provenant des unites volcaniques et plutoniques se situent dans la meme periode de 560 a 550 Ma, y compris les erreurs, demontrant que le Groupe de Coldbrook et les plutons associes se sont formes en moins de 10 millions d'annees. Un volume aussi important de magma principalement felsique ayant entre en eruption et mis en place dans un court laps de temps suggere un environnement de 'super-eruption / supervolcan' tel que le sud-ouest du Cenozoique superieur aux etats-Unis, mais pas encore reconnu entre 560-550 Ma ailleurs dans la zone d'Avalonia. Deux unites ont donne des ages paleozoiques: la felsite de la Formation de Bloomsbury Mountain avec une population de zircon a 427 [+ or -] 9 Ma, indiquant un age de mise en place maximal du Silurien, et la dacite de la Formation de Grassy Lake avec plusieurs grains de zircon a 382,8 [+ or -] 8,3 Ma, indiquant un age maximal du Devonien moyen, premieres roches de cet age identifiees dans le terrane de Caledonie. [Traduit par la redaction], INTRODUCTION The Caledonia terrane is a large area of mainly Neoproterozoic rocks that forms the Avalonian part of southern New Brunswick, extending from the Saint John area to the northeast [...]

The Trafalgar Plutonic Suite intruded metasedimentary rocks of the Goldenville and Halifax groups in the northeastern part of the Meguma terrane of southern Nova Scotia at about 374 Ma, based on previously published U-Pb and (40) Ar/(39) Ar mineral ages. Using field and petrographic observations, the suite is divided into 20 different plutons on the combined basis of variations in grain size (fine, medium, or coarse), texture (equigranular or porphyritic) and modal mineralogy (quartz diorite/tonalite, granodiorite, monzogranite, and syenogranite). The granodiorite, monzogranite, and syenogranite plutons are relatively uniform in composition with little variation in mineralogy or chemistry within each pluton or between plutons of the same lithology. In contrast the quartz diorite/tonalite plutons show mineralogical and chemical variation, both within and between plutons. The granodiorite, monzogranite, and syenogranite plutons closely resemble other peraluminous granitoid plutons characteristic of the Meguma terrane. The quartz diorite/tonalite plutons are varied but chemically resemble minor Devonian mafic intrusions elsewhere in the Meguma terrane. Like other plutons of the Meguma terrane, the Trafalgar Plutonic Suite has chemical characteristics of volcanic-arc to syn-collisional granitoid rocks and likely has experienced extensive contamination by metasedimentary material as documented by previous studies of plutons in the Meguma terrane. The minor quartz diorite/tonalite plutons are additional examples of the mafic rocks that have been proposed in tectonic models of the Meguma terrane to have facilitated melting of the lower crust to generate granodioritic parent magmas, followed by crystal fractionation and extensive contamination by metasedimentary material. La suite plutonique de Trafalgar s'est mise en place dans les roches metasedimentaires des groupes de Goldenville et Halifax dans la partie nord-est de la zone de Meguma au sud de la Nouvelle-Ecosse a environ 374 Ma, d'apres des ages U-Pb et (40)Ar/(39)Ar deja publies. a partir d'observations sur le terrain et petrographiques, la suite se divise en 20 plutons, base sur un ensemble de caracteristiques telles que la variation granulometrique (fin, moyen ou grossier), la texture des roches (equidimensionnel ou porphyritique) et la proportion mineralogique (diorite quartzifere/tonalite, granodiorite, monzogranite et syenogranite). La composition des plutons constitues de granodiorite, de monzogranite et de syenogranite est relativement uniforme avec peu de variation mineralogique ou chimique au sein de chacun des plutons ou d'un pluton a un autre de lithologic semblable. En revanche, les plutons formes de diorite quartzifere/tonalite presentent des variations mineralogiques et chimiques a l'interieur du meme pluton et a travers la suite plutonique. Les plutons constitues de granodiorite, de monzogranite et de syenogranite ressemblent etroitement aux autres granitoides peralumineux de la zone de Meguma. Les plutons de diorite quartzifere/tonalite sont variables mais chimiquement comparables aux intrusions mafiques devoniens retrouves ailleurs dans la zone de Meguma. Comme plusieurs autres plutons de la zone de Meguma, la suite plutonique de Trafalgar possede des caracteristiques chimiques semblables aux granitoides de type arc volcanique a syncollisionnel et ayant sans doute subi une contamination significative des roches metasedimentaires, tels que documente dans des etudes precedentes sur les plutons de la zone de Meguma. Les moins vastes plutons formes de diorite quartzifere/tonalite constituent des exemples supplementaires de roches mafiques qui furent presentees dans des modeles tectoniques de la zone de Meguma comme ayant contribuees a la fusion de la croute inferieure et ainsi generer un magma parent granodioritique, suivi d'une cristallisation fractionnee combinee a une contamination importante provenant des roches metasedimentaires. [Traduit par la redaction], INTRODUCTION The Trafalgar Plutonic Suite (White et al. 2009a, b; White and Scallion 2011) is an assemblage of granitoid plutons in the Trafalgar area near the northern margin of the [...]

Southern New Brunswick consists of a collage of fault-bounded belts of Late Neoproterozoic igneous and metamorphic rocks, early Paleozoic sedimentary, metamorphic and igneous units, and overlying Carboniferous and locally Triassic sedimentary rocks. The area also contains the boundary between Avalonia and Ganderia as interpreted in the northern Appalachian orogen. New detrital zircon ages reported here provide improved understanding of depositional ages and provenance of diverse Neoproterozoic to Carboniferous rocks in this complex area. Detrital zircon data from samples with Neoproterozoic maximum depositional ages indicate a dominantly Gondwanan provenance with strong influence from the Amazonian craton. However, quartzite from The Thoroughfare Formation on Grand Manan Island contains dominanly 2 Ga zircon grains, consistent with derivation from the West African craton. The age spectrum is similar to that of the Hutchins Island Quartzite in the Isleboro block in Penobscot Bay, Maine, strengthening the possibility of correlation between the two areas. Cambrian samples also show prominent peri-Gondwanan provenance with strong influence from F.diacaran to early Cambrian arc magmatism. The maximum depositional ages of these samples are consistent with previous interpretations of Cambrian ages based on fossil correlations and field data. A Carboniferous sample from Avalonia shows a significant contribution from Devonian magmatism as the youngest detrital component, although its depositional age based on field relationships is Carboniferous. The results exemplify the need to integrate multiple datasets in making interpretations from detrital zircon data. Le sud du Nouveau-Brunswick est constitue d'un collage de ceintures delimitees par des failles de roches ignees et metamorphiques du Neoproterozoique tardif, d'unites sedimentaires, metamorphiques et ignees du Paleozoique precoce, ainsi que de roches sedimentaires sus-jacentes du Carbonifere et, par endroits, du Trias. Le secteur comprend egalement la frontiere etablie entre Avalonia et Ganderia selon son interpretation a l'interieur de la partie septentrionale de l'orogene des Appalaches. De nouvelles datations de zircon detritique rapportees ici permettent une meilleure comprehension des ages sedimentaires et de la provenance des diverses roches neoproterozoiques a carboniferes dans ce secteur complexe. Les donnees relatives au zircon detritique obtenues des echantillons faisant etat d'ages sedimentaires remontant au maximum au Neoproterozoique signalent une provenance en predominance gondwanienne avec une forte influence du craton amazonien. Le quartzite de la Formation The Thoroughfare sur l'ile Grand Manan renferme toutefois predominament des grains de zircon de 2 Ga, ce qui correspond a une derivation du craton de l'Afrique occidentale. Le spectre de l'age est similaire a celui du quartzite de l'ile Hutchins a l'interieur du bloc Isleboro dans la baie Penobscot, au Maine, ce qui renforce la possibilite d'une correlation entre les deux secteurs. Les echantillons du Cambrien font eux aussi etat d'une provenance perigondwanienne prononcee, marquee d'une forte influence d'un magmatisme d'arc de l'Ediacarien au Cambrien precoce. Les ages sedimentaires maximaux de ces echantillons correspondent aux interpretations anterieures des datations du Cambrien basees sur des correlations de fossiles et des donnees d'echantillonnage sur le terrain. Un echantillon du Carbonifere provenant d'Avalonia revele une contribution prononcee du magmatisme devonien a titre d'element detritique le plus recent, mais son age sedimentaire le situe au Carbonifere d'apres les relations etablies sur le terrain. Les resultats illustrent la necessite d'une integration de plusieurs ensembles de donnees pour effectuer des interpretations a partir de donnees provenant de zircon detritique. [Traduit par la redaction], INTRODUCTION AND GEOLOGICAL SETTING Southern New Brunswick consists of a complex assemblage of three fault-bounded belts of mainly Neoproterozoic rocks with minor Paleozoic rocks termed (from southeast to northwest) Caledonia, [...]

Zircon grains from a granitic pegmatite clast from conglomerate at the base of the Ross Island Formation on Grand Manan Island indicate an igneous crystallization age of 664.1 [+ or -] 4.6 Ma. The clast also contains abundant older inherited grains back to the Archean. Muscovite in the same clast and an additional similar clast yielded cooling ages of 607.0 [+ or -] 3.7 Ma and 619.6 [+ or -] 4.1 Ma, respectively, providing a maximum depositional age for the host conglomerate of the Ross Island Formation. The Seven Hundred Acre Island Formation in the Islesboro block in Penobscot Bay, Maine, contains a granitic pegmatite dyke of similar age, suggesting that it was close to the site of deposition of the Ross Island Formation of Grand Manan Island in the late Ediacaran. This suggestion is supported further by similarity in rock types and detrital zircon spectra between the Seven Hundred Acre Island Formation and The Thoroughfare and Kent Island formations on Grand Manan Island. Des grains de zircon provenant d'un ciaste de pegmatite granitique du conglomerat a la base de la Formation de Ross Island sur l'ile Grand Manan signalent une cristallisation ignee survenue il y a 664,1 [+ or -] 4,6 Ma. Le ciaste renferme egalement une abondance de grains herites plus ages remontant a l'Archeen. La muscovite dans le meme ciaste et un ciaste similaire supplementaire a accuse des ages de refroidissement de 607,0 [+ or -] 3,7 Ma et de 619,6 [+ or -]4,1 Ma, respectivement, ce qui definit l'age maximal de la sedimentation du conglomerat hote de la Formation de Ross Island. La Formation de Seven Hundred Acre Island dans le bloc d'Islesboro a l'interieur de la baie de Penobscot, dans le Maine, abrite un dyke de pegmatite granitique d'age similaire, ce qui laisse supposer qu'il se trouvait pres de l'emplacement de la sedimentation de la Formation de Ross Island sur l'ile Grand Manan au cours de l'Ediacarien tardif. La similarite des types rocheux et des spectres de zircons detritiques entre la Formation de Seven Hundred Acre Island et les formations de Thoroughfare et de Kent Island sur l'ile Grand Manan appuient une telle supposition. [Traduit par la redaction], INTRODUCTION Pre-Mesozoic rocks are exposed on the southeastern third of Grand Manan Island and adjacent offshore islands in the Bay of Fundy (Figs. 1, 2). Published U-Pb (zircon) ages have [...]

The White Rock Formation is the lowermost formation of the Rockville Notch Group, an assemblage of Silurian--Devonian rocks preserved in five areas along the northwestern margin of the Meguma terrane of Nova Scotia. The formation consists mainly of mafic and felsic metavolcanic rocks, interlayered with and overlain by marine metasedimentary rocks. Felsic metatuff has now been dated from four locations near both the bottom and top of the volcanic pile and yielded a narrow age range (with errors) of about 446-434 Ma. These dates confirm a 30 Ma hiatus after deposition of the Early Ordovician Hellgate Formation in the underlying Halifax Group. This hiatus is coeval with the 'Sardian gap' in the Lower Palaeozoic of peri-Gondwanan Europe. The metavolcanic--metasedimentary assemblage is overlain by mainly metasiltstone with abundant quartzite and metaconglomerate lenses; some of the latter were previously interpreted to be Ordovician tillite, an interpretation no longer viable. New detrital zircon data from metasedimentary samples indicate that the major sediment sources for the White Rock Formation have ages of ca. 670-550 and ca. 2050 Ma, similar to ages from the underlying Goldenville and Halifax groups. A smaller population of Mesoproterozoic zircon grains indicates that the Meguma terrane interacted with a terrane composed mainly of Mesoproterozoic crust during the Silurian and Devonian. The occurrence of the 'Sardian gap' and the detrital zircon record constrain the palaeoposition of the Meguma terrane to have been close to Cadomia and West Africa in the Early Cambrian to Early Silurian. Key words: U-Pb dating, Appalachian orogen, detrital zircon, Cadomia. La Formation de White Rock est la formation basale du Groupe de Rockville Notch, un assemblage de roches siluro--dévoniennes préservé dans cinq secteurs le long de la bordure nord-ouest du terrane de Meguma en Nouvelle-Écosse. La formation est principalement composée de roches métavolcaniques mafiques et felsiques, des roches métasédimentaires marines leur étant interstratifiées et superposées. Les âges de métatufs felsiques de quatre emplacements différents près de la base et du sommet de l'empilement volcanique ont maintenant été établis et ils définissent une petite fourchette (dans la marge des erreurs) allant d'environ 446 à 434 Ma. Ces âges confirment l'existence d'un hiatus de 30 Ma après le dépôt de la Formation de Hellgate à l'Ordovicien précoce, dans le Groupe d'Halifax sous-jacent. Ce hiatus est du même âge que le << hiatus sardien >> dans le Paléozoïque inférieur de l'Europe péri-gondwanien. L'assemblage métavolcanique--métasédimentaire est surmonté principalement par des métasiltstones avec d'abondantes lentilles de quartzite et de métaconglomérat, ce dernier ayant été, dans certains cas, interprété comme étant de la tillite ordovicienne, une interprétation maintenant réfutée. De nouvelles données sur des zircons détritiques d'échantillons métasédimentaires indiquent que les principales sources de sédiments pour la Formation de White Rock ont des âges d'environ 670-550 et environ 2050 Ma, semblables aux âges des Groupes de Goldenville et d'Halifax sous-jacents. Une petite population de grains de zircon mésoprotérozoïques indique que le terrane de Meguma a interagi avec un terrane composé principalement de croûte mésoprotérozoïque durant le Silurien et le Dévonien. La présence du << hiatus sardien >> et les âges des zircons détritiques permettent de fixer le paléo-emplacement du terrane de Meguma à proximité de la Cadomie et de l'Afrique de l'Ouest du Cambrien précoce au Silurien précoce. [Traduit par la Rédaction] Mots-clés: datation U-Pb, orogène appalachien, zircon détritique, Cadomie., Introduction The Meguma terrane is the most outboard of the collage of continental fragments that was assembled during the mid-Paleozoic to form the northern Appalachian orogen (Fig. 1, inset). It [...]

Granitoid plutons are a major component of pre-Carboniferous rocks in Cape Breton Island and knowledge of the time and tectonic setting of their emplacement is crucial for understanding the geological history of the island, guiding exploration for granite-related economic mineralization, and making along-orogen correlations. The distribution of these plutons and their petrological characteristics have been used in the past for recognizing both Laurentian and peri-Gondwanan components in Cape Breton Island, and for subdividing the peri-Gondwanan components into Ganderian and Avalonian terranes. However, ages of many plutons were assumed on the basis of field relations and petrological features compared to those of the relatively few reliably dated plutons. Seventeen new U--Pb (zircon) ages from igneous units reported here provide enhanced understanding of the distribution of pluton ages. Arc-related plutons in the Aspy terrane with ages of ca. 490 to 475 Ma likely record the Penobscottian tectonomagmatic event recognized in the Exploits subzone of central Newfoundland and New Brunswick but not previously recognized in Cape Breton Island. Arc-related Devonian plutonic activity in the same terrane is more widespread, continuous, and protracted (445 Ma to 395 Ma) than previously known. Late Devonian magmatism in the Ganderian Aspy terrane is similar in age to that in the Avalonian Mira terrane (380 to 360 Ma) but the tectonic settings are different. In contrast, magmatic activity in the Bras d'Or terrane is almost exclusively arc-related in the Late Ediacaran (580 to 540 Ma) and rift-related in the Late Cambrian (520 to 490 Ma). The new data support the terrane distinctions previously documented. Les plutons granitoïdes sont des composants importants des roches précarbonifères de l'île du Cap Breton, et il est crucial de connaître le moment et le cadre tectonique de leur mise en place pour comprendre l'évolution géologique de l'île, orienter l'exploration de la minéralisation économique liée au granite et établir des corrélations le long de l'orogène. La distribution des plutons et leurs caractéristiques pétrologiques ont été utilisées dans le passé pour reconnaître les composants laurentiens et périgondwaniens dans l'île du Cap Breton et pour subdiviser les composants périgondwaniens entre les terranes gandériens et les terranes avaloniens. Cependant, l'âge de bon nombre de plutons a été présumé en fonction des observations sur le terrain et de leurs caractéristiques pétrologiques comparativement à celles des plutons datés de manière fiable, relativement peu nombreux. Dix sept nouveaux âges U-Pb sur zircon fondés sur des unités ignées et déclarés dans le présent document permettent de mieux comprendre la répartition selon l'âge des plutons. Dans le terrane d'Aspy, des plutons liés à l'arc dont les âges se situent environ entre 490 et 475 Ma illustrent vraisemblablement l'événement tectonomagmatique penobscottien reconnu dans la sous-zone de la rivière Exploits dans le centre de Terre Neuve, mais qui n'a pas été reconnu auparavant à l'île du Cap-Breton. L'activité plutonique Dévonien liée à l'arc dans le même terrane est plus répandue, continue et prolongée (445 Ma à 395 Ma) qu'on ne le croyait antérieurement. Le magmatisme du Dévonien tardif dans le terrane gandérien d'Aspy est d'un âge semblable à celui du terrane de Mira de l'Avalonien (380 Ma à 360 Ma); toutefois, les milieux tectoniques sont différents. En revanche, l'activité magmatique dans le terrane de Bras d'Or est quasi exclusivement liée à l'arc dans l'Édiacarien tardif (580 Ma à 540 Ma) et liée au rift dans le Cambrien tardif (520 Ma à 490 Ma). Les nouvelles données appuient les distinctions documentées antérieurement au sujet des terranes. [Traduit par la redaction], INTRODUCTION Cape Breton Island, Nova Scotia, is a granite-lover's paradise. Granitoid plutons constitute more than half of pre-Carboniferous rocks on the island and more than 120 different plutons, many of [...]

The Park Spur pluton (PSP) is located in the central Cape Breton Highlands, near the eastern margin of the Aspy terrane and its tectonic contact with the adjacent Bras d'Or [...]

Small plutons of mafic to intermediate composition are locally associated with the abundant Devonian granitic plutons that intruded the Goldenville and Halifax groups in the eastern Meguma terrane of mainland [...]

The Coldbrook Group is a unique suite of Late Ediacaran volcanic and epiclastic rocks that together with related plutons was emplaced in the Avalonian Caledonia terrane of southern New Brunswick. [...]

The Creignish Hills and North Mountain areas of southwestern Cape Breton Island consist mostly of Neoproterozoic rocks typical of the Ganderian Bras d'Or terrane. U-Pb ages presented here for detrital zircon in the Blues Brook Formation of the Creignish Hills confirm a depositional age no greater than about 600 Ma. Although it is possible that some components of the formation are much older, similarities in rock types and field relations suggest that this is not the case. It is likely that the equivalent Malagawatch Formation of the North Mountain area, as well as high-grade metasedimentary rocks of the Melford Formation and Chuggin Road complex in the Creignish Hills and Lime Hill gneiss complex in the North Mountain area, represent the same or stratigraphically equivalent units as the Blues Brook Formation. The minimum ages of all of these units are constrained by cross-cutting syn- and post-tectonic plutons with ages mostly between 565 and 550 Ma, indicating that sediments were deposited, regionally metamorphosed, deformed, and intruded by plutons in less than 40-50 million years. The assemblage of pelitic, psammitic, and carbonate rocks indicates that a passive margin in a tropical climate was quickly changed to an active Andean-type continental margin in which voluminous calcalkaline dioritic to granitic plutons were emplaced. This sedimentary and tectonic history is characteristic of the Bras d'Or terrane and is shared by its likely correlative, the Brookville terrane in southern New Brunswick. Les secteurs des collines Creignish et du mont North dans le sud-ouest de l'ile du Cap-Breton sont principalement constitues de roches neoproterozo'iques typiques du terrane de Ganderian Bras d'Or. Les ages U-Pb sur zircon detritique de la formation de Blues Brook des collines Creignish presentes ici confirment une sedimentation survenue il y a au plus 600 Ma environ. Meme s'il est possible que certains elements de la formation soient beaucoup plus ages, les similarites des lithotypes et les observations sur le terrain laissent supposer que ce n'est pas le cas. Il est probable que la formation equivalente de Malagawatch dans le secteur du mont North de meme que les roches metasedimentaires a forte teneur de la formation de Melford et du complexe du chemin Chuggin dans les collines Creignish et le complexe de gneiss de la colline Lime dans le secteur du mont North representent les memes unites que la formation de Blues Brook ou des unites stratigraphiquement equivalentes. Les ages minimaux de toutes ces unites sont limites par les plutons syntectoniques et post-tectoniques transversaux, ages pour la plupart de 550 a 565 Ma, ce qui revele que les sediments se sont deposes, se sont metamorphises et deformes a lechelle regionale, et ont ete penetres par les plutons au cours dune periode de moins de 40 a 50 millions d'annees. L'assemblage de roches pelitiques, psammitiques et carbonatees signale qu'une marge passive dans un climat tropical s'est rapidement transformee en une marge continentale de type andeen active dans laquelle de volumineux plutons calco-alcalins dioritiques a granitiques se sont mis en place. Un tel passe sedimentaire et tectonique est caracteristique du terrane de Bras d'Or et constitue un trait que le terrane a en commun avec l'unite vraisemblablement correlative du terrane de Brookville dans le sud du Nouveau-Brunswick. [Traduit par la redaction], INTRODUCTION The Creignish Hills and North Mountain areas of western Cape Breton Island (Fig. 1) consist mostly of Neoproterozoic metasedimentary and plutonic rocks typical of the Bras d'Or terrane of [...]

Geological mapping, petrological studies, and U-Pb (zircon) dating were done to better characterize metasedimentary and metaigneous rock units in the northeastern Aspy terrane, Cape Breton Highlands, Nova Scotia. Foliated biotite [...]

The Atlantic Geoscience Society (AGS) undertakes a wide range of communication and educational activities and projects, one of which is the publication of the Geological Highway Map of Nova Scotia. [...]

The Aspy and Bras d'Or terranes in northern Cape Breton Island are both interpreted as part of Ganderia in the northern Appalachian orogen but contrasts in rock types, ages, and [...]

The Coldbrook Group is a unique suite of late Ediacaran volcanic and epiclastic rocks deposited in an extensional setting in the Avalonian Caledonia terrane of southern New Brunswick. It is informally divided into a lower part composed of mainly andesitic to dacitic tuffs and epiclastic sedimentary rocks intruded by bimodal plutons, and an upper part composed mainly of mafic flows and tuffs interlayered with but mainly overlain by rhyolitic flows and tuffs and minor epiclastic sedimentary rocks. Recent U-Pb (zircon) dating of four formations in the Coldbrook Group and a subvolcanic granitic dome led to the proposal that the lower and most of the upper Coldbrook Group and associated plutons were formed within <760 kyr at about 551.5 Ma whereas the uppermost rhyolite (Fundy Trail Parkway rhyolite) and underlying basalt of the Hosford Brook Formation formed in a younger event at about 549.5 Ma. Overlapping dates and chemical data also suggest that the subvolcanic granitic domes are the plutonic counterparts of the ca. 551.5 Ma felsic volcanic rocks whereas the other granitic plutons represent extracted melts that evolved separately. Whole-rock geochemical and isotopic data combined with previous field work and map information and integrated with the geochronological data provide new insights into the genesis of these magmas and their change from intermediate to bimodal magmatism. The data indicate that the volcanic and plutonic rocks are mainly tholeiitic and were derived from varying proportions of juvenile melts and recycled older arc lithosphere. The mafic rocks have chemical similarities to flood basalts which inherited some calc-alkalic signatures from older arc-like rocks. Intermediate magmas that formed much of the lower Coldbrook Group had larger lithospheric inputs and thus have mainly calc-alkalic signatures. The Vernon Mountain, Blackall Lake and Silver Hill area rhyolites represent evolved melts derived from the lower Coldbrook Group magmas, and their chemical differences are interpreted to result from melt extraction and solid-liquid dripping magmatic processes. Enhanced extension and thinning led to formation of less lithosphere-contaminated melts that formed the ca. 549.5 Ma bimodal units of the upper Coldbrook Group. [ABSTRACT FROM AUTHOR]

The Park Spur pluton was emplaced in the Aspy terrane of the central Cape Breton Highlands at 374.2 ± 2.9 Ma (U-Pb zircon). It consists mainly of muscovite-biotite monzogranite with small areas of garnet-bearing muscovite monzogranite and abundant pegmatite and aplite dykes. On its northern margin the pluton intruded metamorphic rocks of the Ordovician-Silurian Cape North Group and associated orthogneiss and on the south it intruded low-grade metamorphic rocks of the Silurian Calumruadh Brook Formation. Deformation along the southern margin of the Park Spur pluton is consistent with emplacement during dextral transpression between the Bras d'Or and Aspy terranes. The Late Devonian age combined with S-type petrological characteristics show that the Park Spur pluton and nearby Canal pluton are related to the ca. 375 Ma Black Brook Granitic Suite, all interpreted to have been emplaced during later stages of the Acadian orogeny in Ganderia as a result of delamination. [ABSTRACT FROM AUTHOR]

New zircon U-Pb, trace element, and Lu-Hf laser ablation inductively coupled mass spectrometry (LA-ICP-MS) data are presented for five Early to Middle Devonian granitic and felsic volcanic rocks from the Cashes Ledge igneous suite, central Gulf of Maine, USA. These samples were previously analyzed by U-Pb LA-ICP-MS and whole-rock geochemical methods and the new data generally corroborate the earlier results. Coarse-grained alkali-feldspar granite from northwest of the Fundy magnetic anomaly, the interpreted fault boundary in the offshore between Gondwanan microcontinents Ganderia to the northwest and Avalonia to the southeast, yielded a crystallization age of 414 ± 2 Ma. Southeast of the inferred fault, crystallization ages are 385 ± 3 Ma and 386 ± 3 Ma for two crystal tuff samples near the fault, 403 ± 3 Ma for an alkali-feldspar granite ~50 km southeast of the fault, and 399 ± 5 Ma for syenogranite ~25 km southeast of the fault, which also yielded inherited grains at ~1.3 Ga and between 613 ± 15 Ma and 558 ± 9 Ma. Lu-Hf LA-ICP-MS data for zircon retaining igneous crystallization ages have εHf(t) between 2.9 and 13.1 and model ages based on felsic sources between 0.52 and 1.04 Ga, reflecting a mix of late Mesoproterozoic (Avalonian?) basement and primitive melt, possibly in an extensional setting. Zircon Nb/ Hf ratios generally greater than 0.001 indicate a predominately within-plate/anorogenic/rifr setting, consistent with their whole-rock chemistry. U/Yb-Nb/Yb and U/Yb-Hf tectonic setting discrimination diagrams show ocean island to continental arc signatures, with a stronger continental arc signature for the syenogranite. Most zircon grains have Eu/Eu* values less than 0.1, indicating a crustal thickness of ~30 km or less at the time of their crystallization. [ABSTRACT FROM AUTHOR]

The Partridge Island block is a newly identified tectonic element in the Saint John area of southern New Brunswick, located south of and in faulted contact with Proterozoic and Cambrian rocks of the Ganderian Brookville and Avalonian Caledonia terranes. It includes the Lorneville Group and Tiner Point complex. The Lorneville Group consists of interbedded volcanic and sedimentary rocks, subdivided into the Taylors Island Formation west of Saint John Harbour and West Beach Formation east of Saint John Harbour. A sample from thin rhyolite layers interbedded with basaltic flows of the Taylors Island Formation at Sheldon Point yielded a Late Devonian - Early Carboniferous U-Pb (zircon) age of 358.9 +6/-5 Ma. Petrological similarities indicate that all of the basaltic rocks of the Taylors Island and West Beach formations are of similar age and formed in a continental within-plate tectonic setting. West of Saint John Harbour, basaltic and sedimentary rocks of the Taylors Island Formation are increasingly deformed and mylonitic to the south, and in part tectonically interlayered with mylonitic granitoid rocks and minor metasedimentary rocks of the Tiner Point complex. Based on magnetic signatures, the deformed rocks of the Tiner Point complex can be traced through Partridge Island to the eastern side of Saint John Harbour, where together with the West Beach Formation, they occupy a thrust sheet above a redbed sequence of the mid-Carboniferous Balls Lake Formation. The Tiner Point complex includes leucotonalite and aegirine-bearing alkali-feldspar granite with A-type chemical affinity and Early Carboniferous U-Pb (zircon) ages of 353.6 ± 5.7 and 346.4 [+ or -] 0.7 Ma, respectively. Based on similarities in age, petrological characteristics, alteration, iron oxide--copper-gold (IOCG)-type mineralization, and deformation style, the Partridge Island block is correlated with Late Devonian--Early Carboniferous volcanic- sedimentaryplutonic rocks of the Cobequid Highlands in northern mainland Nova Scotia. Deformation was likely a result of dextral transpression along the Cobequid-Chedabucto fault zone during juxtaposition of the Meguma terrane. Le bloc de Partridge Island est un element tectonique nouvellement identifie dans la region de Saint John du sud du Nouveau-Brunswick; il est situe au sud et dans un contact de faille avec des roches datant du Proterozoique et du Cambrien des terranes de Brookville (Ganderien) et de Caldonia (Avalonien). Le bloc comprend le Groupe de Lorneville et le complexe de Tiner Point. Le Groupe de Lorneville est forme de roches volcaniques et sedimentaires interlitees, subdivisees entre la Formation de Taylors Island a l'ouest du port de Saint John et la Formation de West Beach a l'est. Un echantillon de minces couches de rhyolite interlitees avec des ecoulements basaltiques de la Formation de Taylors Island a la pointe Sheldon a donne un age Devonien tardif - Carbonifere precoce de 358,9 +6/-5 Ma, determine par U-Pb sur zircon. Des similitudes petrologiques indiquent que toutes les roches basaltiques des formations de Taylors Island et de West Beach ont un age similaire et qu'elles ont ete formees dans un environnement continental a l'interieur d'une plaque tectonique. A l'ouest du port de Saint John, des roches basaltiques et sedimentaires de la Formation de Taylors Island sont de plus en plus deformees et mylonitiques vers le sud; elles sont aussi en partie interlitees tectoniquement avec des roches granitoides mylonitiques et des roches metasedimentaires accessoires du complexe de Tiner Point. En se basant sur les signatures magnetiques, les roches deformees du complexe de Tiner Point peuvent etre retracees a travers l'lle Partridge, jusqu'au cote est du port de Saint John ou, avec la Formation de West Beach, elles forment une nappe de charriage au-dessus d'une sequence de lits rouges de la Formation de Balls Lake (Carbonifere moyen). Le complexe de Tiner Point comprend des granites alcalins feldspathiques avec une tonalite leucocrate et de l'aegyrine qui ont une affinite chimique de type A; ils datent du Carbonifere precoce et ont des ages respectifs de 353,6 ± 5,7 et 346,4 ± 0,7 Ma determines par datation U-Pb sur zircons. En se basant sur les similitudes d'age, les caracteristiques petrologiques, l'alteration, la mineralisation de type IOCG (oxyde de fer, cuivre, or) et le style de deformation, le bloc de Partridge Island est correle avec les roches volcaniques sedimentaires plutoniques (Devonien tardif - Carbonifere precoce) des hautes terres de Cobequid dans le nord de la partie continentale de la Nouvelle-Ecosse. La deformation proviendrait d'une transpression dextre le long de la zone de failles Cobequid-Chedabucto durant la juxtaposition du terrane de Meguma. [Traduit par la Redaction], Introduction Southern New Brunswick consists of a collage of inferred peri-Gondwanan terranes and terrane fragments (Fig. 1), some of which may have been part of the microcontinent of Ganderia and [...]

ABSTRACT The relationship between low-grade metasedimentary and high-grade paragneissic Precambrian rock units in the Bras d'Or terrane of central Cape Breton Island is a long-standing geological problem. Whole-rock geochemical and [...]

In their article 'Reply to the discussion by J.W.F. Waldron and C.E. White on 'Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf', R.L. Romer and U. Kroner reinterpret geochronological data presented by J.W.F. Waldron, D.I. Schofield, C.E. White, and S.M. Barr to imply an Ordovician, not a Cambrian, depositional age for the succession of the Harlech Dome, North Wales, and Meguma Supergroup, Nova Scotia. However, an extensive history of biostratigraphic and geological survey data refutes this interpretation and shows that the rocks are unequivocally Cambrian. Waldron et al. used the U-Pb zircon laser-ablation--multicollector--inductively coupled plasma--mass spectrometry technique primarily to provide information on sediment provenance and not depositional age. Investigation of anomalously young [sup.206]Pb/[sup.238]U ages showed evidence of Pb loss. These data provide little constraint on depositional age and cannot be used to infer that the Harlech Grits Group is Ordovician. Dans leur article << Reply to the discussion by J.W.F. Waldron and C.E. White on 'Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf >>, R.L. Romer et U. Kroner reinterpretent les donnees geochronologiques presentees par J.W.F. Waldron, D.I. Schofield, C.E. White et S.M. Barr, pour signifier un age de deposition Ordovicien et non Cambrien, pour la succession du dome Harlech, dans le Nord du Pays de Galles, et du Supergroupe Meguma en Nouvelle-Ecosse. Cependant, un historique elabore des donnees biostratigraphiques et des releves geologiques refutent cette interpretation et demontrent que les roches datent categoriquement du Cambrien. Waldron et al. ont utilise la technique U-Pb sur zircon, ablation par laser--spectrometrie de masse a plasma inductif et collecteurs multiples, surtout pour fournir de l'information concernant la provenance des sediments et non pas l'age de deposition. L'investigation des ages [sup.206]Pb/[sup.238]U anormalement jeunes a revele des evidences de perte de plomb. Ces donnees restreignent peu l'age de deposition et elles ne peuvent etre utilisees pour conclure que le Groupe Harlech Grits date de l'Ordovicien. [Traduit par la Redaction], Introduction In a recent article entitled 'Reply to the discussion by J. W. F. Waldron and C.E. White (2012) on 'Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian [...]

Appalachian-Caledonide orogen development has been traditionally illustrated using cross-sections showing terrane accretion and collision over time. This approach is valuable but leads to implicit assumptions: subduction was initiated at passive [...]

ABSTRACT The Late Silurian Landry Brook and Dickie Brook plutons and Charlo plutonic suite underlie a combined area of approximately 80 [km.sup.2] in the northeastern part of the Ganderian Tobique-Chaleur [...]

The ca. 620 Ma Huntington Mountain pluton and East Bay Hills Group, which comprise part of the Avalonian Mira terrane, Cape Breton Island, Nova Scotia, Canada, are characterized by pervasive [...]

A quartz sandstone bed in a dominantly conglomeratic section in the central part of the Lower Carboniferous Horton Group on Petit-de-Grat Island, offshore southern Cape Breton Island, Nova Scotia, contains [...]

We report a diverse assemblage of trace fossils from the Lower(?) Cambrian High Head member of the Church Point Formation near Yarmouth, Nova Scotia. Based on the presence of sharp-based beds, load casts, and flute casts, along with other sedimentological criteria, the strata are interpreted to have a turbidite origin. Other characteristics, including wrinkle structures and high fidelity of trace-fossil preservation, suggest that the inter-episode biotope was influenced by the presence of biomats. The trace-fossil assemblage includes (in approximate order of abundance) Planolites, Helminthopsis, Oldhamia, Chondrites, Gordia, Cladichnus, Psammichnites gigas, Treptichnus, Phycodes, Lorenzinia, Palaeophycus, and Teichichnus. Trace fossils are increasingly abundant upwards in the section, but they are ultimately mitigated by an increase in (inferred) sedimentation rates. The trace-fossil assemblage, which bears many similarities to other Lower Cambrian locales (e.g., Puncoviscana Formation of northwest Argentina, Chapel Island Formation of southeastern Newfoundland), and the distribution of ichnofossils strongly support an earliest Cambrian age for the studied strata. More importantly, evolutionary trends can be interpreted from the trace-fossil assemblage, namely (1) an increase in size and diversity of animals in deep water; (2) an expansion of motile strategies used to coexist with biomats; and, (3) increasingly complex mining strategies below the sediment-biomat interface. Nous signalons l'existence d'un assemblage varie; d'ichnofossiles dans le membre cambrien infeerieur (?) de High Head de la Formation de Church Point, pres de Yarmouth, en Nouvelle-Ecosse. A la lumiere de la presence de lits dont la base est nettement definie, d'empreintes de charge et de flutes, ainsi que d'autres criteres sedimentologiques, les strates sont interpretees comme etant d'origine turbiditique. D'autres caracteeristiques, dont la presence de rides et le degre eleve de detail preserve des ichnofossiles, suggerent que le biotope inter-episode etait influence par la presence de tapis biologiques. L'assemblage d'ichnofossiles comprend (en ordre approximatif d'abondance) Planolites, Helminthopsis, Oldhamia, Chondrites, Gordia, Cladichnus, Psammichnites gigas, Treptichnus, Phycodes, Lorenzinia, Palaeophycus et Teichichnus. L'abondance des ichnofossiles augmente vers le haut de la section, bien que cette augmentation soit ultimement contrecarree par une augmentation des taux de sedimentation (presumes). L'assemblage, qui ressemble a plusieurs egards aux assemblages d'ichnofossiles d'autres localues du Cambrien inferieur (p. ex. la Formation de Puncoviscana, du nordouest de l'Argentine, la Formation de Chapel Island du sud-est de Terre-Neuve), et la distribution des ichnofossiles appuient fortement la these d'un age du tout debut du Cambrien pour les strates etudieees. Fait encore plus important, l'assemblage d'ichnofossiles permet de deduire diffeerentes tendances evolutionnaires, a savoir : (1) l'augmentation de la taille et de la diversite des animaux en eau profonde, (2) la mise au point de nouvelles strategies motiles permettant de coexister avec les tapis biologiques et (3) l'augmentation de la complexite des strategies de forage sous l'interface sediments- tapis biologique., Introduction Because of the paucity of body fossils in the Lower Cambrian, the biostratigraphic indicator of the start of the Lower Cambrian System is placed at the base of the [...]

ABSTRACT Machias Seal Island in the northern Gulf of Maine consists of fine- to medium-grained weakly foliated quartz monzodiorite. Although previously inferred to be as young as Devonian, the quartz [...]

ABSTRACT Late Neoproterozoic (680 Ma to 560 Ma) Avalonian rocks in the Mira terrane of southeastern Cape Breton Island have been metamorphosed inhomogeneously, at very low grade to low grade, [...]

We report single-grain ages for detrital muscovite separated from sandstone samples from five localities in southern New Brunswick and southeastern Cape Breton Island, Nova Scotia, and from two quartzite clasts from a quartzitepebble conglomerate that underlies the sampled sandstone units in New Brunswick. The oldest detrital grains were found in one of the quartzite clasts; their age range, ca. 650-630 Ma, is defined not only by the single-grain analyses but also by spot dating (using a UV laser) within a single large grain, suggesting that these grains came from a single source. The second quartzite clast has a blastomylonitic fabric with muscovite 'fish,' and most of the muscovite ages have been partially reset (at ca. 550 Ma) from the original ca. 650-630 Ma ages. The age distribution plots obtained for the sandstone samples suggest the presence of muscovite that still retains the original source age, but most of the grains have been partially reset by the same ca. 550 Ma event that reset muscovite ages in the second quartzite clast. We suggest that the quartzite source that produced the two clasts was also the source of muscovite in the Avalonian Cambrian rocks of Maritime Canada. The original source rock was likely a metamorphic or perhaps granitic rock unit situated relatively proximal to the site of deposition of the quartzite protolith, but the actual source is not known, and locally, no potential candidates are exposed. The resetting event at ca. 550 Ma may be linked to initial stages of regional transtension associated with rifting of Avalonia from Gondwana. Nous rapportons des ages determines sur des grains uniques de muscovite detritique provenant d'echantillons de gres de cinq localites du sud du Nouveau-Brunswick et du sud-est de l'ile du Cap Breton, en Nouvelle-E cosse, ainsi que de deux clastes de quartzite d'un conglomerat de galets-quartzite qui se retrouve sous les unites de gres echantillonnees au Nouveau-Brunswick. Les plus anciens grains detritiques ont ete retrouves dans l'un des clastes de quartzite; leur plage d'age, d'environ 650-630 Ma, est definie non seulement par des analyses sur grains uniques mais aussi par une datation ponctuelle (au moyen d'un laser UV) a l'interieur d'un seul gros grain, suggerant que ces grains proviennent d'une seule source. Le second claste de quartzite avait une texture blastomylonitique avec des grains lenticulaires << mica fish >> et la plupart des ages pour la muscovite avaient ete partialement reinitialises a ~550 Ma a partir des ages originaux ~650-630 Ma. Les courbes de distribution de l'age, obtenues pour les echantillons de gres, suggerent la presence de muscovite ayant conserve l'age original de la source; cependant, la plupart des grains ont ete reinitialises par le meme evenement survenu a ~550 Ma qui a reinitialise les ages de la muscovite dans le second claste de quartzite. Selon nous, la source de quartzite qui a produit les deux clastes serait aussi la source de la muscovite dans les roches avaloniennes, datant du Cambrien, des provinces maritimes canadiennes. La roche source originale etait probablement une unite de roche granitique ou metamorphique situee relativement pres du site de deposition du quartzite protolithe, mais la source reelle est inconnue et aucun << candidat >> potentiel n'affleure localement. L'evenement de reinitialisation survenu il y a ~550 Ma pourrait etre relie aux stades initiaux de transtension regionale associee a la creation du rift entre l'Avalonie et le Gondwana. [Traduit par la Redaction], Introduction For many years, U-Pb ages of detrital zircon grains have been used to infer the provenance of sedimentary units. More recently, Haines et al. (2004), among others, also have [...]

ABSTRACT Detrital zircon ages were determined for conglomerate and sandstone samples from six fault-bounded belts in New Brunswick and coastal Maine. Formations sampled included the Martinon (Brookville belt), Flagg Cove [...]

Detrital zircon ages from the lower part of the Late Proterozoic(?) to Middle Cambrian Goldenville Group in the Meguma terrane of Nova Scotia suggest derivation from local sources in the Avalonian and Pan-African orogens on the margins of Early Cambrian Gondwana. Samples from near the top of the group show a broader distribution, including ages back to Archean. The [ζ.sub.Nd] data show a corresponding trend, from slightly positive in the lower Goldenville Group to highly negative in the upper Goldenville Group and overlying Upper Cambrian to Lower Ordovician Halifax Group. The trends are consistent with deposition of the lower part of the Meguma succession in a rift, in which uplifted rift-flanks were the main source of the early basin fill, whereas subsequent thermal subsidence of rift margins allowed for more widespread sediment sourcing in younger units. The rift was possibly located between Gondwana and Avalonia, and may have been the locus for separation of Avalonia from Gondwana to form part of the Rheic Ocean. Les ages des zircons detritiques du Groupe de Goldenville (Proterozoique tardif(?) a Cambrien moyen) dans le terrane de Meguma de la Nouvelle-Ecosse suggerent une provenance de sources locales dans les orogenes avalonien et pan-africain sur les bordures du continent de Gondwana au Cambrien precoce. Des echantillons preleves pres du sommet du groupe montrent une distribution plus vaste, incluant des ages archeens. Les donnees [ζ.sub.Nd] montrent une tendance correspondante, de legerement positive dans le Groupe de Goldenville inferieur a hautement negative dans le Groupe de Goldenville superieur et dans le Groupe de Halifax sus-jacent (Cambrien superieur a Ordovicien inferieur). Les tendances concordent avec la deposition de la partie inferieure de la succession de Meguma dans une fosse d'effondrement; les flancs souleves de cette fosse auraient constitue la source principale de materiel de remplissage du bassin primitif alors qu'une subsidence thermique subsequente des bordures de la fosse aurait conduit a une source de sediments plus etendue pour les unites plus jeunes. La fosse d'effondrement etait possiblement situee entre le Gondwana et l'Avalonie et elle constitue possiblement le lieu de la separation de l'Avalonie du Gondwana pour la formation d'une partie de l'ocean Rheique. [Traduit par la Redaction], Introduction Meguma, the most outboard terrane of the Canadian Appalachians (Fig. 1a), has no clear correlative elsewhere in the Appalachian-Caledonide orogen. Although generally regarded as a peri-Gondwanan terrane, Meguma shows [...]

Distinct [sup.18]O depletion is characteristic of a large majority of the 620-550 Ma felsic igneous rocks of Avalonia in the northern Appalachian orogen. Neoproterozoic rocks in the Boston Avalon terrane have the lowest δ[sup.18][O.sub.WR] values (≥-3.1‰), followed by the Mira terrane in Cape Breton Island and the Caledonia terrane in New Brunswick (≥-1.2‰), the Avalon terrane in Newfoundland (≥+2.8‰), and the Antigonish Highlands in Nova Scotia (≥+5.3‰). In contrast, this depletion of [sup.18]O is observed in very few of the Paleozoic felsic igneous rocks from these Avalonian terranes, and also in very few of the Neoproterozoic and Paleozoic felsic igneous rocks from the inboard Ganderian terranes. The low-[sup.18]O character of the Neoproterozoic igneous rocks is related to regional pervasive, post-magmatic alteration by predominantly meteoric-hydrothermal fluids (δ[.sup.18][O.sub.H2O] ~ -6‰ to -4‰) at 200-450 °C. The alteration likely occurred during late Neoproterozoic transtensional extension of Avalonia. Large-scale fluid infiltration and circulation within the Avalonian crust accompanied this extension with development of pull-apart sedimentary basins and extension-related magmatism that were the prelude to Cambrian submergence of Avalonia. This regional [sup.18]O depletion provides a geochemical fingerprint by which Avalonia can be distinguished from other peri-Gondwanan terranes. These data suggest that Avalonia existed as a composite terrane on the Gondwanan margin in the Neoproterozoic, separate from Ganderia. Un appauvrissement en [sup.18]O est caracteristique d'une grande partie des roches ignees felsiques, 620-550 Ma, de l'Avalonia dans le nord de l'orogene appalachien. Les roches neoproterozoiques du terrane Boston Avalon ont les valeurs δ[sup.18][O.sub.WR] les plus faibles (≥-3,1 ‰), suivies du terrane Mira dans l'Ele du Cap Breton et le terrane Caledonia au Nouveau-Brunswick (≥-1,2 ‰), du terrane Avalon a Terre-Neuve (≥+2,8 ‰) et dans les terres hautes de l'Antigonish en Nouvelle-Ecosse (≥+5,3 ‰). Par contre, cet appauvrissement en [sup.18]O est observe dans tres peu de roches ignees felsiques paleozoiques de ces terranes d'Avalon et aussi dans tres peu de roches felsiques ignees neoproterozoiques et paleozoiques des terranes interieurs de Gander. La faible teneur en [sup.18]O des roches ignees neoproterozoiques est liee a une alteration postmagmatique regionale penetrante par des fluides hydrothermaux principalement meteoriques (δ[.sup.18][O.sub.H2O] ~ -6 a -4 ‰) a 200-450 °C. L'alteration est probablement survenue au cours de l'extension de tension transverse d'Avalonia au cours du Neoproterozoique tardif. Une infiltration et une circulation de fluides a grande echelle a l'interieur de la croite avalonienne a accompagne cette extension avec le developpement de bassins sedimentaires d'etirement et d'un magmatisme relie a l'extension qui forment le prelude a la submersion d'Avalonia au Cambrien. Cet appauvrissement regional en [sup.18]O fournit une signature geochimique par laquelle le terrane d'Avalonia peut etre distingue d'autres terranes peri-Gondwana. Selon ces donnees, Avalonia aurait existe en tant que terrane composite sur la bordure gondwanienne au Neoproterozoique, separe de Ganderia., [Traduit par la Redaction] Introduction The comparative tectonostratigraphic histories and relationships among the peri-Gondwanan composite terranes comprising Avalonia and Ganderia in the northern Appalachian orogen have been the subject of [...]

ABSTRACT A major ductile high-strain zone up to 5 km in width can be traced for at least 70 km diagonally across the Avalonian Caledonia terrane of southern New Brunswick. [...]

ABSTRACT The Mechanic Settlement Pluton, southern New Brunswick, is a high-level mafic-ultramafic pluton of Late Neoproterozoic age (ca. 557 Ma). Based on surface-outcrop and drill-core samples, the pluton includes six [...]