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Abstract: Two temporally distinct Neoarchean turbidite packages are known to occur in the Slave craton. The older is a greywacke-mudstone succession that includes the renowned Burwash Formation (ca. 2661 Ma). [...]

Mafic and ultramafic rocks crop out as decimetre- to centimetre-sized bodies of talc-antigorite-olivine (±orthopyroxene) and chlorite-amphibole schists interleaved in the pelitic Kluane Schist of southwestern Yukon. The metamorphic assemblages in ultramafic rocks exposed at Doghead Point overprint two generations of cleavage and are consistent with metamorphism reaching >550°C (talc + olivine) and >750°C (olivine + enstatite) in the contact aureole of the Eocene Ruby Range batholith. The bulk rock major and trace element patterns in the ultramafic schists (>40 wt.% MgO, Mg/(Mg+ Fe) > 0.90) are unlike residual mantle from partial melting (i.e., ophiolite, orogenic massif, abyssal ocean floor) but are similar to peridotite or pyroxenite cumulates from arc magmas. Identical trace element concentrations and patterns are observed in several late Triassic basalts, pyroxenites, and websterites occurring to the southeast in Stikinia (present coordinates). A highly discordant U-Pb zircon date for one antigorite-talc-olivine schist sample (200-210 Ma) is within the range of U-Pb zircon ages for the late Triassic Lewes River - Stuhini arc in northwestern Stikinia (200-208 Ma, 216-220 Ma). When combined with other published age information, the ultramafic rocks in the Kluane Schist are interpreted as fragments of deeper arc-related mafic and ultramafic intrusive rocks introduced to the Kluane forearc basin between 95 and 82 Ma by exhumation along shear zones in northwestern Stikinia, most likely the Wann River or Llewellyn Faults. The Kluane Schist represents a west-facing forearc basin bordered to the east by arc-parallel strike-slip fault(s) that served to exhume and imbricate large knockers into the accretionary prism. Des roches mafiques et ultramafiques affleurent en amas de schistes a talc-antigorite-olivine (± orthopyroxene) et amphibole-chlorite, de taille decimetrique a centimetrique, interstratifies dans le dans le schiste pelitique Kluane du sud-ouest du Yukon. Les assemblages metamorphiques dans les roches ultramafiques affleurant a Doghead Point se superposent a deux generations de clivage et ils concordent avec un metasomatisme atteignant >550°C (talc + olivine) et >750°C (olivine + enstatite) dans l'aureole de metamorphisme du batholite de Ruby Range (Eocene). Les patrons en elements majeurs et traces de la roche en vrac dans les schistes ultramafiques (>40 % poids MgO, Mg/(Mg+Fe) > 0,90) ne ressemblent pas a ceux d'un manteau residuel d'une fusion partielle (c.-a-d. ophiolite, massif orogenique, plancher oceanique abyssal), mais ils sont plutot semblables a ceux de cumulats de peridotite ou de pyroxenite de magmas d'arcs. Des concentrations et des patrons identiques d'elements traces sont observes dans plusieurs basaltes du Trias tardif, dans des pyroxenites et des websterites se trouvant au sud-ouest dans Stikinia (coordonnees presentes). Une date, fortement discordante, U-Pb sur zircon pour un echantillon de schiste a antigorite-talc-olivine (200-210 Ma) est dans la plage des ages U-Pb sur zircon pour l'arc Lewes River--Stuhini (Trias tardif) dans le nord-ouest de Stikinia (200-208 Ma, 216-220 Ma). Lorsque combine avec d'autres informations publiees d'ages, les roches ultramafiques dans le schiste de Kluane sont interpretees en tant que fragments de roches intrusives mafiques et ultramafiques plus profondes, introduites dans le bassin d'avant-arc Kluane entre 95 et 82 Ma par exhumation le long de zones de failles dans le nord-ouest de Stikinia, plus probablement les failles de Wann River ou de Llewellyn. Le schiste de Kluane represente un bassin d'avant-arc de regard ouest limite a l'est par des failles de decrochement paralleles a l'arc qui ont servi a exhumer et imbriquer de grands blocs dans le prisme accretionnaire. [Traduit par la Redaction], Introduction Subduction, subcretion, and collisions that involve volcanic arcs are an underlying theme in the story of nearly all mountain belts. It was these processes that were responsible for construction [...]

An ash-rich volcaniclastic sandstone immediately underlying dinosaur-rich material from the Danek Bonebed in the Horseshoe Canyon Formation (HCF), Edmonton, Alberta, Canada, contains accessory zircon, which have been dated employing U-Pb geochronology. Both laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and chemical abrasion isotope dilution thermal ionization mass spectrometry (ID-TIMS) U-Pb analyses have been conducted. The zircon age distributions are complex with U-Pb dates ranging from Precambrian to Cretaceous. We consider the youngest ID-TIMS 206Pb/238U date of 71.923 ± 0.068 Ma as the maximum deposition age of the ash-rich sandstone, placing the overlying Danek bonebed in the early Maastrichtian. This age is compatible with the paleontological assemblage from the Danek Bonebed and the regional stratigraphy. The zircon age distribution also implies that the HCF had a complex provenance of the detritus with some Archean and Proterozoic zircons, a group of Mesozoic, and alarge compliment of Cretaceous grains. The results highlight the importance of high precision geochronology in constraining the age of important fossil deposits such as the Danek Bonebed. Un gres volcano-clastique riche en cendres, situe immediatement sous le materiau riche en dinosaures du Danek Bonebed (<< lit d'os Danek >>) dans la Formation de Horseshoe Canyon, a Edmonton, Alberta, Canada, contient des zircons accessoires qui ont ete dates par geochronologie U-Pb. Des analyses U-Pb par spectrometrie de masse a plasma induit couplee a l'ablation laser (LA-ICP-MS) et par abrasion chimique, dilution isotopique et spectrometrie de masse a thermoionisation (ID-TIMS) ont ete effectuees. Les distributions des ages du zircon sont complexes avec des dates U-Pb dans une plage du Precambrien au Cretace. Nous considerons la plus recente date de 71,923 ± 0,068 Ma, determinee par ID-TIMS 206Pb/238U, comme etant l'age maximum de deposition du gres riche en cendres, ce qui place le lit d'os Danek sus-jacent au Maastrichtien precoce. Cet age est compatible avec l'assemblage paleontologique du lit d'os Danek et la stratigraphie regionale. La distribution des ages du zircon signifie aussi que la provenance des detritus de la Formation de Horseshoe Canyon est complexe; en effet, quelques zircons datent de l'Archeen et du Proterozoique et la formation contient ainsi un groupe de grains du Mesozoique et de nombreux grains du Cretace. Les resultats soulignent l'importance d'une geochronologie de grande precision pour bien encadrer l'age des importants depots de fossiles tels que le lit d'os Danek. [Traduit par le Redaction], Introduction The Danek Bonebed (hereafter DBB) in Edmonton, Alberta, is a Late Cretaceous paleontological locality that yielded important information on dinosaur behavior, evolution, and ecology. However, until now an explicit [...]

Tom Krogh revolutionized the field of precise U-Pb geochronology through a series of ground-breaking technical advances in the 1970s and 1980s that changed our investigative approach to understanding geologic processes. Earth scientists around the world have used his dating methods for more than 30 years to produce high-precision ages that have advanced our knowledge of Earth's evolution through time. Tom applied these techniques to investigate the formation of ancient crust in the Superior and Grenville provinces, and other orogens, and the timing of terrestrial impacts. His legacy is built upon these scientific contributions, the many people he trained and inspired, and the global distribution of laboratories that use his methods. Au cours des decennies 1970 et 1980, Tom Krogh a revolutions le domaine de la geochronologie U-Pb precise grace a des perceees novatrices qui ont change notre approche d'examen scientifique pour comprendre les processus geologiques. Les specialistes en sciences de la Terre de partout au monde utilisent ses methodes de datation depuis plus de 30 ans pour obtenir des ages de grande precision qui ont avance notre connaissance de revolution de la Terre dans le temps. Tom a utilise; ces techniques pour etudier la formation de l'ancienne croflte dans les provinces de Grenville et du Supeerieur ainsi que dans d'autres orogenes et pour determiner avec precision l'age et la localisation d'importants impacts de meteorites. Son legs est fonde sur ces contributions scientifiques, les nombreux gens qu'il a formes et inspires ainsi que la distribution mondiale des laboratoires qui utilisent ses methodes. [Traduit par la Redaction], Introduction In this Special Issue we wish to honour the scientific achievements of Thomas Edvard Krogh (1931-2008). Tom's innovations in the field of U-Pb geochronology in the 1970s and 1980s [...]

U-Pb zircon geochronological investigations at Battle Harbour, in the Pinware terrane, eastern Grenville Province show that a cross-bedded psammitic rock from Battle Island was deposited after 1200 Ma and prior to Grenvillian orogenesis, as part of a package of psammitic, semi-pelitic and calc-silicate rocks. This represents a major finding as no previous data had indicated any supracrustal-rock deposition after ca. 1500 Ma in the interior eastern Grenville Province. The age is comparable to that obtained from supracrustal units of minor extent elsewhere in the interior Grenville Province, indicating that change in crustal level in these regions was modest during Grenvillian orogenesis. Grenvillian metamorphism at amphibolite facies occurred at 1030 ± 4 Ma, based on evidence from a concordant mafic rock within the supracrustal assemblage that is interpreted to be a sill. Grenvillian orogenesis at Battle Harbour was accompanied by abundant pegmatite injection over an extended period, as indicated by cross-cutting relationships and various states of deformation displayed by the pegmatites. An amazonite-bearing pegmatite has an age of 1024 ± 3 Ma. An even younger, crosscutting pegmatite contains only inherited zircon grains. Des recherches geeochronologiques U-Pb sur zircon a Battle Harbour, dans le terrane de Pinware, dans l'est de la Province de Grenville, montrent qu'une roche psammitique de Battle Island a ete deposeee plus recemment que 1200 Ma et avant l'orogene de Grenville; elle eetait comprise dans un ensemble de roches psammitiques, semi-peelitiques et calco-silicatees. Ces recherches representent une decouverte importante puisque aucune donneee anteerieure n'avait indiquee une deposition d'une roche supracrustale plus recemment que ~1500 Ma a l'inteerieur de la Province de Grenville orientale. Cet age est comparable a ceux obtenus des unites supracrustales de moindre etendue ailleurs a l'inteerieur de la Province de Grenville, indiquant que le changement dans le niveau de la croflte de ces regions etait modeste durant l'orogene de Grenville. Le metamorphisme grenvillien au facies des amphibolites a eu lieu a 1030 ± 4 Ma, selon des evidences provenant d'une roche mafique concordante a l'interieur de l'assemblage supracrustal, laquelle a ete interpretee en tant qu'un filon couche. A Battle Harbour, l'orogene de Grenville etait accompagne d'une importante injection de pegmatites au cours d'une peeriode prolongeee, tel qu'indique par les relations d'entrecroisement et les divers niveaux de deformation visibles dans les pegmatites. Une pegmatite contenant de l'amazonite a un age de 1024 ± 3 Ma. Une pegmatite encore plus jeune qui recoupe en travers ne contient que des grains de zircon heerites. [Traduit par la Redaction], Introduction Grenvillian orogenesis (used here to define that period of tectonism between 1085-985 Ma; Gower and Krogh 2002) represents a major period of convergence and collision along the southern flank [...]

A review of the ages determined for mantle material (xenoliths and xenocrysts entrained in kimberlite) derived from the Slave Province continental lithospheric mantle (CLM) indicates that a portion of the central Slave lithosphere may be ancient (3.5-3.3 Ga) harzburgite, but the majority of this lithosphere is much younger (2.9-2.0 Ga). Relying on the most robust chronometers, the majority of Slave lithosphere peridotite formed in the Neoarchean (peak at 2.75 Ga), whereas the majority of eclogite formed in the Paleoproterozoic (2.2-2.0 Ga). The northern Slave lithosphere contains evidence of peridotite xenolith ages that young with depth. The Paleoproterozoic eclogites may have multiple origins including remnants of subducted oceanic crust and mafic--ultramafic magmas that crystallized at great depth (100-200 km). Re--Os studies of sulfide inclusions in diamond indicate that some diamonds currently mined are ancient (~3.5 Ga), but many Slave diamonds could be considerably younger. Most eclogitic diamonds recovered from the Slave craton are interpreted to be related to the formation of Paleoproterozoic eclogite. There is abundant evidence for Mesoproterozoic modification of the Slave lithosphere (e.g., heating by magma emplacement at great depth and metasomatism) and possible new addition to the lithosphere at that time. The Canadian Slave and African Kaapvaal lithospheres have similar peaks in cratonic peridotite formation ages at about 2.8 Ga, indicating that a large portion of the CLM in these two cratons formed and stabilized in the Neoarchean. One difference is that the Slave peridotites are much less enriched in Si[O.sub.2], possibly reflecting the more metasomatized nature of the Kaapvaal CLM. The dominance of Paleoproterozoic formation ages for Slave mantle eclogites contrasts with the dominance of Neoarchean formation ages for Kaapvaal mantle eclogites. Une revision des ages determines sur des materiaux du manteau provenant du manteau lithospherique continental de la Province des Esclaves (des xenolites et des xenocristaux entraines dans de la kimberlite) indique qu'une portion de la lithosphere centrale des Esclaves pourrait etre une ancienne harzburgite (3,5-3,3 Ga) mais que la plus grande partie de cette lithosphere est beaucoup plus jeune (2,9-2,0 Ga). En se basant sur les chronometres les plus robustes, la plus grande partie de la peridotite de la lithosphere des Esclaves s'est formeeeau Neeoarcheeen (crete a 2,75 Ga) alors que la plus grande partie de l'eclogite s'est formeee au Paleeoproteerozoique (2,2-2,0 Ga). La lithosphere nord des Esclaves contient des evidences d'ages de peridotite xenolite qui rajeunissent en profondeur. Les eclogites datant du Paleeoproteerozoique peuvent avoir de multiples origines, incluant des lambeaux de croflte subductee et des magmas mafiques-ultramafiques qui se sont cristalliseesa de grandes profondeurs (100-200 km). Des etudes Re--Os des inclusions de sulfures dans les diamants indiquent que quelques diamants actuellement exploiters sont anciens (~3,5 Ga) mais que plusieurs des diamants provenant de la Province des Esclaves pourraient etre beaucoup plus jeunes. La plupart des diamants de paragenese eclogitique provenant du craton des Esclaves sont interprets comme etant reliesa la formation de l'eclogite paleoproterozoique. Il existe beaucoup de preuves de modifications, au Mesoproteerozoique, de la lithosphere des Esclaves (p. ex. un reechauffement par la mise en place de magma a grande profondeur et du metasomatisme) et l'ajout possible de nouvelle lithosphere a ce moment. Les lithospheres des Esclaves et de Kaapvaal ont des cretes similaires dans la formation de la peeridotite cratonique vers environ 2,8 Ga, indiquant qu'une grande portion du manteau lithospherique cratonique dans ces deux cratons s'est formee et s'est stabilize;ea ce moment. Une difference est que les peeridotites des Esclaves sont beaucoup moins enrichies en Si[O.sub.2], refleetant possiblement la nature plus metasomatiseee du manteau lithospherique cratonique Kaapvaal. La dominance des ages de formation paleeoproteerozoiques pour les eclogites du manteau des Esclaves contraste avec la dominance des ages de formation neoarcheeens pour les eclogites du manteau du Kaapvaal. [Traduit par la Redaction], Introduction The continental lithospheric mantle (CLM) is the rigid part of the upper mantle extending from the Moho to depths of as much as 250 km beneath ancient cratons. Much [...]

Glacial erratics collected on Melville Island, western Canadian Arctic Archipelago, were analyzed to determine their mainland provenance, thereby constraining their long-distance transport by the Laurentide Ice Sheet. These erratics can be broadly subdivided into three main lithologies: granite (n = 15), quartzite (n = 7), and diabase-diorite (n = 3). The granite erratics are most distinctive from a provenance perspective and can be further subdivided into three geochemical groups based on their potassium content: (1) a high-[K.sub.2]O group ([K.sub.2]O > 4.0 wt.%), (2) an intermediate-[K.sub.2]O group ([K.sub.2]O between 2.0 and 4.0 wt.%), and (3) a low-[K.sub.2]O group ([K.sub.2]O < 2.0 wt.%). In situ thin section laser ablation inductively coupled plasma mass spectrometer U-Pb zircon ages obtained for eight granite erratics yielded both Archean (2575 Ma) and a range of Paleoproterozoic (2472-1778 Ma) crystallization ages. In addition, three overprint ages were identified at 1.90, 1.84, and ~1.0 Ga. The most compelling constraint for a northward regional ice flow originating on the mainland are two high-precision conventional U-Pb zircon ages of 1969.5 ± 1.0 and 2472.3 ± 0.5 Ma, indicating that these granite erratics must have been derived from the 2.0-1.9 Ga Taltson-Thelon Orogen and the nearby 2.5-2.4 Ga Queen Maud Block, respectively. These granite-dominated terranes are located 600 km due south and southeast of the collection area on Melville Island. Although it is unknown whether the final deposition of these erratics on Melville Island involved transport by one or more glaciations, it is apparent that this ice flow cannot be accommodated by the proposed north-south axis of the M'Clintock Ice Divide, the primary topographic feature of the northwestern Laurentide Ice Sheet during the last glacial maximum. The transport of erratics reported here would have required a former ice divide oriented east-west over the mainland, close to that proposed for the Ancestral Keewatin Divide. An east-west ice divide in this region is consistent with previously reported ice-flow indicators that document northward flow from the mainland and recent thermomechanically coupled ice-sheet numerical modeling that indicates former maximum ice thickness on the mainland immediately south of Melville Island. Des blocs erratiques recueillis sur l'ile Melville, dans l'archipel arctique canadien, ont ete analyses afin de determiner leur provenance des regions continentales, encadrant ainsi leur transport sur de longues distances par l'Inlandsis laurentidien. Ces blocs erratiques peuvent etre subdivises selon trois principales lithologies : granite (n = 15), quartzite (n = 7) et diabase-diorite (n = 3). Les erratiques de granite sont les plus distinctifs du point de vue de la provenance et ils peuvent etre subdivises de nouveau en trois groupes geochimiques bases sur leur contenu en potassium : (1) un groupe a teneur elevee en [K.sub.2]O ([K.sub.2]O > 4,0 % poids), (2) un groupe a teneur intermediaire en [K.sub.2]O ([K.sub.2]O entre 4,0 et 2,0 % poids) et (3) un groupe a faible teneur en [K.sub.2]O ([K.sub.2]O < 2,0 % poids). Des ages U-Pb in situ determines sur des zircons en lame mince par analyse a couplage inductif et spectrometrie de masse avec ablation au laser (LA-ICP-MS) de huit blocs erratiques de granite ont donne des ages de cristallisation archeens (2575 Ma) et paleoproterozoiques (2472-1778 Ma). De plus, trois ages de surimpression ont ete identifies a 1,90, 1,84, et ~1,0 Ga. La contrainte la plus convaincante pour un ecoulement regional de la glace vers le nord a partir du continent a ete la determination de deux ages conventionnels U-Pb de grande precision sur des zircons, soit 1969,5 ± 1,0 et 2472,3 ± 0,5 Ma, indiquant que ces blocs erratiques de granite doivent provenir respectivement de l'orogene Taltson-Thelon (2,0-1,9 Ga) et du bloc Queen Maud (2,5-2,4 Ga) avoisinant. Ces terrains domines par des granites sont situes a 600 km franc sud et sud-est du secteur de collecte sur l'ile Melville. Bien que l'on ne sache pas si la deposition finale de ces blocs erratiques sur l'Ole Melville impliquait un transport par une ou plusieurs glaciations, il est evident que cet ecoulement glaciaire ne peut etre aide par l'axe N-S propose de la ligne de partage glaciaire M'Clintock, l'element topographique principal de l'Inlandsis laurentidien durant le dernier maximum glaciaire. Le transport des blocs erratiques dont il est question dans le present article aurait requis une ancienne ligne de partage glaciaire orientee E-O sur le continent, a proximite de la ligne proposee pour la ligne ancestrale de partage des glaces du Keewatin. Une ligne de partage E-O dans cette region concorde avec les anciens indicateurs d'ecoulement glaciaire qui documentent un ecoulement vers le nord a partir du continent et concorde avec une modelisation numerique recente jumelee thermique-mecanique de l'inlandsis qui indique que l'ancienne epaisseur maximale de la glace sur le continent se situait tout juste au sud de l'ile Melville. [Traduit par la Redaction], Introduction Crystalline erratics have long been recognized in the southern part of the Canadian Arctic Archipelago (CAA), resting on Paleozoic sedimentary rocks of the Arctic Platform and Franklinian mobile belt [...]

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 [...]

Early Paleozoic sandstones in the Southern Uplands terrane of Scotland were deposited during closure of the Iapetus Ocean between Laurentia and Avalonia. Their tectonic setting and sources are controversial, and different authors have supported subduction-accretion, extensional continental-margin development, or back-arc basin settings. We report new U-Pb detrital zircon ages from five Late Ordovician sandstones from the Northern Belt of the Southern Uplands and test models of their tectonic setting. The U-Pb zircon age distributions are dominated by peaks characteristic of sources in Laurentia and include grains as old as 3.6 Ga, older than any previously recorded in the British Caledonides SE of the Laurentian foreland. Discordant grains in one sample suggest derivation via erosion of metasedimentary rocks incorporated in the Grampian-Taconian orogen. Rare Neoproterozoic grains, previously interpreted as originating from a peri-Gondwanan terrane, may be derived from igneous rocks associated with Iapetan rifting. Only rare zircons are contemporary with the depositional ages. The results are difficult to reconcile with extensional continental-margin and back-arc models, but they support an active continental-margin subduction-accretion model. Close similarities with distributions from the Newfoundland Appalachians are consistent with sinistral transpression during closing of the Iapetus Ocean. Keywords: tectonics, Caledonides, Southern Uplands, detrital zircon geochronology, provenance.

Abstract: Kimberlite-sourced bentonite layers have been discovered in Late Cretaceous sedimentary drill cores located within the Buffalo Head Hills kimberlite field, north-central Alberta. Two bentonites are unambiguously differentiated from 'common' [...]

Abstract: New Rb-Sr phlogopite and U-Pb perovskite age determinations for 12 of 38 known ultramafic bodies in the Buffalo Head Hills area of north-central Alberta show that kimberlitic magmatism occurred [...]

ABSTRACT The Copper Lake area of mainland Nova Scotia is one of several vein-controlled mineralized (Cu-Au-Co) systems associated with widespread carbonate and iron-oxide alteration proximal to the east-trending Cobequid-Chedabucto Fault [...]

Abstract: The 950 m thick Sibley Group is a relatively flat-lying assemblage of siliciclastic and chemical sedimentary rocks exposed from the northwest shore of Lake Superior to the Lake Nipigon [...]

ABSTRACT The Brazil Lake pegmatite of southwestern Nova Scotia is a rare example of Li-Cs-Ta (LCT) -type pegmatite in the Meguma terrane of Nova Scotia. This spodumene-rich pegmatite is hosted [...]

An unusual suite of zircon- and rutile-bearing eclogite xenoliths from the 172 Ma Jericho kimberlite, Northwest Territories, Canada, displays a peculiar geochemistry highlighted by extreme enrichment of high field strength elements. Most profound are the large positive Nb and Zr anomalies that are linked to a high modal abundance of niobian ruffle and zircon. This peculiar geochemistry, combined with results from U-Pb geochronology, requires a complex origin involving east-dipping Paleoproterozoic subduction and partial melting of oceanic crust beneath the Slave craton, one or more metasomatic overprints prior to kimberlite entrainment, and a Mesoproterozoic thermal disturbance in the Slave lithospheric mantle possibly linked to Mackenzie igneous events. Keywords: rutile, geochronology, zircon, eclogite, geochemistry.

Radiometric dating, including numerous high-precision U-Pb baddeleyite and zircon ages, of Paleoproterozoic flood basalts, dike swarms, and layered mafic intrusions worldwide, indicates that a substantial volume of mafic magma was produced on Earth ca. 2.45 Ga. New U-Pb data presented here for the 2473 Ma Matachewan and 2446 Ma Hearst diabase dike swarms in North America establish a critical temporal link with ancient flood-basalt volcanism in Karelia and constrain the timing of a very ancient magnetic field reversal on Earth. The potential volume, magnitude, and extent of this magmatism may approach many of the better-known Mesozoic flood-basalt provinces and represent the oldest recognized large igneous province. The initiation and subsequent proliferation of flood-basalt and associated magmatism near the Archean-Proterozoic boundary may reflect a fundamental change in heat flux at the core-mantle boundary that heralded the breakup of a Late Archean supercontinent.

Neoproterozoic fluvial quartzarenites from the Shaler Group on Victoria Island in the western Canadian Arctic yield a diverse suite of detrital zircons. U-Pb ages from single zircons fall into three modes: Archean (3.01-2.62 Ga), Paleoproterozoic (1.97-1.84 Ga), and Mesoproterozoic (1.64-1.03 Ga). Particularly intriguing is the unusually high proportion (50%) of the Mesoproterozoic mode, as the nearest exposed source is the Grenville structural province, 3000 km southeast of Victoria Island. Unimodal northwest paleocurrents, obtained from cross-bedding, are compatible with a southeasterly provenance. These data, supported by sedimentological evidence from the Shaler Group and from correlative strata in the northwestern Canadian Cordillera, imply the existence of a large, perennial river system flowing northwestward from the Grenville orogen. An analogy with the Llanos drainage basin in Venezuela and Colombia is proposed on the basis of similar geography, climate, and sedimentation. These data also provide a maximum age for the Shaler Group (basal Reynolds Point Formation) of about 1.11 Ga.

The tectonic evolution of the Hurwitz Group, a widespread succession of predominantly metasedimentary rock up to 7 km thick in the Hearne province of the Canadian Shield, has not been fully evaluated due to a lack of absolute geochronologic data. The Hurwitz Group has been interpreted previously as either a passive-margin foredeep sequence associated with the 1.9-1.77 Ga Trans-Hudson orogen, or correlative with the Snowy Pass and 2.45 Ga Huronian Supergroups, located on the Wyoming and Superior cratons, respectively. U-Pb baddeleyite-zircon analyses from a gabbro sill yield a minimum age of 2094 + 26/-17 Ma for the lower parts of the Hurwitz Group, which could be as old as ca. 2400 Ma, depending on the time of metamorphism. It is clear that the mafic magmatism and sedimentation documented in the lower Hurwitz Group are not linked temporally to the Trans-Hudson orogen, but rather are related to an earlier episode of crustal destabilization and extension, possibly the opening of the Manikewan Sea.

New U-Pb geochronological and Sm-Nd isotopic results across the northwestern margin of the Superior Province in Manitoba, Canada, require a major reinterpretation of the nature, structure, and location of the Superior--Trans-Hudson boundary in the area. A significant finding of this study is that an area northwest of Assean Lake, previously interpreted to be dominantly Early Proterozoic, contains ancient crust. Detrital zircon U-Pb results from two metagraywacke samples in this ancient crustal segment reveal [is greater than or equal to] 3.75 Ga source material, consistent with crustal residence Nd model ages ([T.sub.CR]) of 3.85 and 3.76 Ga, and the U-Pb zircon age for one tonalite gneiss sample is ca. 3.54 Ga ([T.sub.CR] of 3.63 Ga). This newly discovered pre-3.5 Ga crust provides the first evidence for the possible preservation of some very old rocks (pre-3.8 Ga) in this region, older than any known Superior Province crust. Keywords: Superior Province, ancient crust, Early Archean, Manitoba, U-Pb zircon, Sm-Nd.