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The Mesoproterozoic Husky Creek Formation is an interlayered redbed and basalt package that overlies a ca. 2.5 km thick, regionally extensive basaltic plateau linked to the 1.27 Ga Mackenzie Large Igneous Province. This succession provides an opportunity to study the interaction between contemporaneous fluvial sedimentation and flood basalt volcanism. The Husky Creek Formation is approximately 1900 m thick, consisting predominantly of fluvial channel and subordinate floodplain and eolian strata dominated by lithic detritus intercalated with basalt flows. U-Pb dating of detrital zircon grains collected from four stratigraphic levels in the Husky Creek Formation reveals two main age groupings: (1) a 1270 Ma peak attributed to the Mackenzie Large Igneous Province; and (2) Pre-1.6 Ga detrital zircon ages, which reflect sources from a broad region of northwestern Laurentia and are interpreted to be recycled from underlying sedimentary rocks of the Hornby Bay Basin. An upsection decrease in the proportion of ca. 1270 Ma zircon grains, coupled with increasing sandstone compositional maturity, reflects the expansion of the drainage basin during burial of a volcanic pile, with recycling becoming more dominant as the Husky Creek Formation accumulated. The Husky Creek Formation was deposited in the waning stages of the Mackenzie Igneous Event by west-flowing rivers into a geographically restricted basin above an extensive mafic volcanic plateau. This paper provides insight into fluvial basin development during the aftermath of one of Earth's largest igneous events. Key words: fluvial sedimentology, Mackenzie LIP, Husky Creek Formation, Mesoproterozoic, detrital zircon geochronology, Introduction Large igneous provinces (LIPs), and particularlycontinental flood basalts, have been a subject of substantial research targeting their relationship to mantle plumes and continental breakup (Ernst and Buchan 1997). While [...]

Petrological modeling and geochronology (Lu--Hf garnet, U--Pb monazite, zircon, and titanite) for seven mid-amphibolite to granulite-facies metamorphic rocks in the Thelon tectonic zone (Ttz) provide new insights into the evolution of this orogen. A Grt-Sp-Sil diatexite records 2.01-2.00 Ga garnet and monazite growth during >830 [degrees]C contact metamorphism associated with voluminous convergent margin plutonism. The most widespread, 1.96-1.90 Ga metamorphism is associated with clockwise pressure (P)--temperature (T) paths, indicating it was driven by crustal thickening. Earlier (1.96-1.92 Ga) and lower temperature (630 [degrees]C-730 [degrees]C; 6-8 kbar) metamorphism in the eastern Slave craton contrast with ~860 [degrees]C (7.5 kbar), 1.91-1.90 Ga diatexites in the central, Paleoproterozoic plutonic rock-dominated, core of the Ttz. These differences are interpreted to reflect lower vs. upper plate settings, respectively. A contribution of mantle heat is suggested by the counter-clockwise P-T path and 885 [degrees]C (5.7 kbar) conditions recorded by diatexite associated with c. 1.9 Ga peraluminous leucogranite that dominates a corridor along the Ttz--Rae craton boundary. A tectonic model is proposed wherein the Ttz evolved at an accretionary margin after rifting of Ttz microcontinent (mTtz) of the Rae craton at c. 2.2-2.1 Ga. Voluminous plutonism at 2.01-1.98 Ga formed via east-dipping subduction under mTtz. Following 1.97 Ga collision of the Slave craton and mTtz, west-dipping subduction generated 1.96-1.95 Ga plutonism in the composite mTtz-Slave upper plate. Collision of Rae craton at 1.95-1.94 Ga led to crustal thickening, widespread 1.91-1.90 Ga high-grade metamorphism and extensive crustal melting in the central Ttz. Key words: Thelon tectonic zone, Lu--Hf garnet geochronology, U--Pb accessory mineral geochronology, quantitative metamorphic petrology, thermobarometry, Introduction The Late Paleoproterozoic is marked by pan-continental orogenic belts that stitched together Earth's Archean cratons. Laurentia--one of the largest and longest lived continental collages--was in large part constructed from [...]

New data and interpretations on geological relationships of igneous rocks at Mokka Fiord, Axel Heiberg Island, Nunavut, provide insight into the timing and nature of magmatism associated with the Sverdrup Basin and High Arctic Large Igneous Province (HALIP). Field relationships indicate that the igneous rocks, previously interpreted to be volcanic flows, are most likely an intrusive unit discordant to regional bedding. An intrusive origin helps resolve chronostratigraphic inconsistencies in previous work. The host rocks are palynologically constrained to be late Barremian to late Aptian in age and are interpreted to be Paterson Island or Walker Island member of the Isachsen Formation. If the igneous body is intrusive, it's previously reported Ar--Ar age (102.5 [+ or -] 2.6 Ma) is no longer in conflict with accepted stratigraphic interpretations and probably reflects the emplacement age of the intrusion. Lingering uncertainties in interpreting the normal and reverse magnetic polarities determined in the previous work remain, and both are considered viable. Although this uncertainty precludes definitive conclusions on the significance of paleomagnetic data at Mokka Fiord, examination of the stratigraphic, paleomagnetic, and geochronologic relationships there highlight potential for the study of excursions, or reversed magnetic polarity subchrons, in the Cretaceous Normal Superchron elsewhere in the HALIP.De nouvelles donnees et interpretations sur les relations geologiques de roches ignees dans le fjord Mokka (ile Axel Heiberg, Nunavut) fournissent de nouveaux renseignements sur la chronologie et la nature du magmatisme associe au bassin de Sverdrup et a la grande province ignee de l'Extreme Arctique (HALIP). Les relations de terrain indiquent que les roches ignees, interpretees precedemment comme etant des coulees volcaniques, constituent tres probablement une unite intrusive discordante par rapport au litage regional. Une origine intrusive aide a resoudre des incoherences chronostratigraphiques dans des travaux anterieurs. Il est determine, du point de vue palynologique, que les roches hotes sont d'age barremien tardif a aptien tardif et sont interpretees comme etant le membre de l'ile Paterson ou de l'ile Walker de la Formation d'Isachsen. Si le corps igne s'avere intrusif, son age Ar--Ar (102,5 [+ or -] 2,6 Ma) deja publie n'entre plus en conflit avec les interpretations stratigraphiques acceptees et reflete probablement l'age de mise en place de l'intrusion. Des incertitudes demeurent concernant l'interpretation des polarites magnetiques normales et inverses determinees dans les etudes anterieures, et les deux sont jugees viables. Si ces incertitudes empechent de tirer des conclusions definitives sur la signification de donnees paleomagnetiques au fjord Mokka, l'examen des relations stratigraphiques, paleomagnetiques et geochronologiques font ressortir un potentiel pour l'etude d'excursions, ou de sous-chrons de polarite magnetique inversee, dans le superchron normal du Cretace ailleurs dans l'HALIP. [Traduit par la Redaction], IntroductionCretaceous siliciclastic and igneous rocks of the Sverdrup Basin near the mouth of Mokka Fiord, Axel Heiberg Island (Fig. 1), were examined to clarify conflicting and apparently irreconcilable published data [...]

Abstract: An occurrence of diagenetic fluorapatite cement is documented within the Cambro-Ordovician Keeseville Formation, Potsdam Group, near Chateaugay in New York State. The fluorapatite cement occurs as stratiform layers within [...]

Abstract: Paleoproterozoic metasedimentary successions of the northwestern Canadian Shield provide records of tectonic events, but the definition of depositional ages has proved elusive. Although previously poorly understood, the Montresor belt [...]

Abstract: The Wopmay orogen is a Paleoproterozoic accretionary belt preserved to the west of the Archean Slave craton, northwest Canada. Reworked Archean crystalline basement occurs in the orogen, and new [...]

The Paleoproterozoic Hottah terrane is the westernmost exposed bedrock of the Canadian Shield and a critical component for understanding the evolution of the Wopmay Orogen. Thirteen new high-precision U-Pb zircon crystallization ages are presented and support field observations of a volcano-plutonic continuum from Hottah terrane through to the end of the Great Bear magmatism, from >1950 to 1850 Ma. The new crystallization ages, new geochemical data, and newly published detrital zircon U-Pb data are used to challenge hitherto accepted models for the evolution of the Hottah terrane as an exotic arc and microcontinent that arrived over a west-dipping subduction zone and collided with the Slave craton at ca. 1.88 Ga. Although the Hottah terrane does have a tectonic history that is distinct from that of the neighbouring Slave craton, it shares a temporal history with a number of domains to the south and east--domains that were tied to the Slave craton by ca. 1.97 Ga. It is interpreted herein that Hottah terrane began to the south of its current position and evolved in an active margin over an always east-dipping subduction system that began prior to ca. 2.0 Ga and continued to ca. 1.85 Ga, and underwent tectonic switching and migration. The stratigraphy of the ca. 1913-1900 Ma Hottah plutonic complex and Bell Island Bay Group includes a subaerial rifting arc sequence, followed by basinal opening represented by marginal marine quartz arenite and overlying ca. 1893 Ma pillowed basalt flows and lesser rhyodacites. We interpret this stratigraphy to record Hottah terrane rifting off its parental arc crust--in essence the birth of the new Hottah terrane. This model is similar to rapidly rifting arcs in active margins--for example, modern Baja California. These rifts generally occur at the transition between subduction zones (e.g., Cocos-Rivera plates) and transtensional shear zones (e.g., San Andreas fault), and we suggest that extension-driven transtensional shearing, or, more simply, terrane translation, was responsible for the evolution of Bell Island Bay Group stratigraphy and that it transported this newly born Hottah terrane laterally (northward in modern coordinates), arriving adjacent to the Slave craton at ca. 1.88 Ga. Renewed east-dipping subduction led to the Great Bear arc flare-up at ca. 1876 Ma, continuing to ca. 1869 Ma. This was followed by voluminous Great Bear plutonism until ca. 1855 Ma. The model implies that it was the westerly Nahanni terrane and its subducting oceanic crust that collided with this active margin, shutting down the >120 million year old, east-dipping subduction system. Le terrane de Hottah (Paleoproterozoique) est le roc de socle affleurant le plus a l'ouest dans le Bouclier canadien; il est aussi une composante essentielle a la comprehension de l'evolution de l'orogene de Wopmay. Treize nouveaux ages de cristallisation, de haute precision, determines par U-Pb sur des zircons, sont presentes et ils supportent les observations sur le terrain d'un continuum volcano-plutonique pour le terrane de Hottah jusqu';! la fin du magmatisme Great Bear, soit de >1950 a 1850 Ma. Les nouveaux ages de cristallisation, de nouvelles donnees geochimiques et des donnees nouvellement publiees d'ages U-Pb sur des zircons detritiques sont utilises pour contester les modeles jusqu'ici acceptes pour l'evolution de terrane de Hottah en tant qu'un arc exotique et un microcontinent qui est arrive par-dessus une zone de subduction a pendage vers l'ouest et qui est entre en collision avec le craton des Esclaves il y a environ 1,88 Ga. Bien que le terrane de Hottah ait un historique tectonique distinct de celui du craton des Esclaves avoisinant, il partage un historique temporel avec de nombreux autres domaines au sud et a l'est, des domaines qui etaient relies au craton des Esclaves il y a environ 1,97 Ga. Il est interprete ici que le terrane de Hottah a debute au sud de sa position actuelle et qu'il a evolue dans une bordure active par-dessus un systeme de subduction avec un pendage toujours a l'est, commencant avant environ 2,0 Ga et continuant jusqu'a 1,85 Ga, par la suite subissant un echange tectonique et une migration. La stratigraphie du complexe plutonique de Hottah, ~1913 a 1900 Ma, et du Groupe de Bell Island Bay comprend une sequence subaerienne de rifting d'arc, suivie d'une ouverture de bassin, representee par une arenite quartzique de bordure marine, sur lesquels reposent sur des ecoulements de basalte en coussins ~1893 Ma, et des quantites moindres de rhyodacites. Nous interpretons cette stratigraphie comme un enregistrement du rift du terrane de Hottah depuis sa croute d'arc parental, ce qui en essence constitue la naissance du nouveau terrane de Hottah. Ce modele est semblable aux arcs subissant un rifting dans des bordures actives, par exemple, la Basse Californie moderne. Ces rifts se trouvent generalement a la transition entre les zones de subduction (p. ex. les plaques Cocos-Rivera) et les zones de cisaillement de transtension (p. ex. la faille de San Andreas); nous suggerons que le cisaillement de transtension, pousse par l'extension, ou plus simplement la translation du terrane, etait responsable de l'evolution de la stratigraphie du Groupe de Bell Island Bay et que cette transtension a transporte ce terrane de Hottah, nouvellement cree, lateralement (soit vers le nord, selon les coordonnees modernes), arrivant adjacent au craton des Esclaves vers 1,88 Ga. Une reprise de la subduction avec pendage vers l'est a conduit a la poussee active de l'arc de Great Bear vers 1876 Ma et jusqu';! 1869 Ma. Cela a ete suivi par beaucoup de plutonisme Great Bear jusqu';! vers 1855. Selon le modele, c'est le terrane de Nahanni, vers l'ouest, et sa croute oceanique de subduction qui sont entres en collision avec cette bordure active, fermant ainsi le systeme de subduction a pendage est, age de plus de 120 millions d'annees. [Traduit par la Redaction], Introduction In September 2012, NASA's Curiosity rover discovered an outcrop of alluvial-derived conglomerate in Gale Crater, Mars, and it was named Hottah, after Hottah Lake, Northwest Territories, Canada (Williams et [...]

The Boothia mainland region of the north-central Rae domain is underlain by remnants of a Neoarchean volcano sedimentary sequence dismembered by two regionally extensive Neoarchean high-potassium granitoid suites with rare occurrences of a structurally interleaved, Paleoproterozoic sedimentary cover sequence. The granitoids and their gneissic equivalents are dominated by variably deformed and metamorphosed I-type, metaluminous, polyphase, commonly porphyritic to augen, biotite ± hornblende monzogranite, and subordinate granodiorite, with rare tonalite. New geochronological results, the first for this area, demonstrate that the widespread Neoarchean granitoid plutonism is dominantly 2.61-2.59 Ga, with a less prominent 2.66 Ga plutonic event. The age of zircon recrystallization suggests that ca. 2.60 Ga Archean metamorphism and fabric development ([S.sub.1]) affected the 2.66 Ga plutons prior to or contemporaneously with intrusion of the voluminous ca. 2.6 Ga suite. ζ[Nd.sub.(t)] for the ca. 2.61-2.59 Ga suite range from 1.4 to -1.9, overlapping with the ca. 2.66 Ga suite that range from 1.4 to 1.5. The Nd isotopic data, coupled with the presence of inherited ca. 2.65, 2.70, and 2.85-2.90 Ga zircon, suggests recycling of older, Neoarchean to Mesoarchean crust in the formation of these suites. Metaplutonic rocks preserve Paleoproterozoic deformation ([F.sub.4] and [F.sub.5]) and amphibolite-facies metamorphism, sporadically recorded in zircon rims that formed at 1.81 Ga. This event strongly reoriented the Neoarchean fabrics in metaplutonic rocks, generally without the development of a new coaxial Paleoproterozoic fabric, and we attribute this strain and metamorphism to the Hudsonian orogeny. La region terrestre Boothia du domaine Rae centre-nord repose sur des vestiges d'une sequence volcano-sedimentaire datant du Neoarcheen; cette sequence est demembree par deux suites granitoldes d'echelle regionale, a teneur elevee en potassium et posseedant de rares occurrences d'une sequence structurellement intercalee d'une couverture sedimentaire datant du Paleoproterozoique. Les granitoldes et leurs equivalents gneissiques sont domines par un monzogranite a deformation variable, metamorphise, de type I, metalumineux, polyphase;, souvent porphyrique a oeille et a biotite ± hornblende avec une granodiorite subordonnee et une rare tonalite. De nouveaux resultats geochronologiques, les premiers pour ce secteur, demontrent que le plutonisme granitoide neoarcheen etendu date surtout de 2,61 a 2,59 Ga, avec un evenement plutonique moins important vers 2,66 Ga. L'age de la recristallisation du zircon suggere que, vers 2,60 Ga, le meetamorphisme archeeen et le deeveloppement de la fabrique ([S.sub.1]) aient affecte les plutons agees de 2,66 Ga avant ou en meme temps que l'intrusion de la volumineuse suite vers 2,6 Ga. Les valeurs ζ[Nd.sub.(t)] pour la suite datant de ~2,61 a 2,59 Ga varient de 1,4 a -1,9, chevauchant la suite datant ~2,66 Ga, dont les valeurs ζ[Nd.sub.(t)] varient de 1,4 a 1,5. Les donnees d'isotopes Nd, jumelees a la presence de zircons heerites dont les ages sont ~2,65, 2,70 et 2,85-2,90 Ga, suggerent un recyclage de l'ancienne croflte neeoarcheenne a meesoarcheenne pour la formation de ces suites. Des roches meetaplutoniques ont preserve: la deformation paleeoproteerozolque ([F.sub.4] et [F.sub.5]) ainsi que le meetamorphisme au faciees des amphibolites, retrouve sporadiquement dans les bordures des zircons qui se sont formees a 1,81 Ga. Cet evenement a grandement reorientee les fabriques neoarcheeennes dans les roches meetaplutoniques, geeneralement sans le deeveloppement d'une nouvelle fabrique coaxiale paleoproteerozolque; nous attribuons cette deformation et ce metamorphisme a l'orogenese hudsonienne. [Traduit par la Redaction], Introduction The occurrence and abundance of potassic granites is well documented for many Archean cratons (Sylvester 1994) and understanding their genesis is important to developing models for processes of craton [...]

[1] The Changgo culmination, one of the North Himalayan domes in south central Tibet, consists of a multiphase granite core surrounded by a deformed metasedimentary carapace. The granitic core records general non-coaxial shear with a top-to-the-south sense shear component. The contact between the core and the carapace is a shear zone, characterized by general non-coaxial shear with a top-to-the-north shear sense, interpreted to be the northern continuation of the South Tibetan detachment system (STDS). The shear zone contains lenses of leucogranite dated at 35.4 Ma. This is interpreted to reflect Eocene crustal thickening, coeval with the earliest shortening event recorded in the carapace. The main phase of the Changgo granite crystallized at 23.5 Ma, while undeformed aplite dikes, the youngest phase observed in the granite, were intruded at 22.1 Ma. Aplite dikes crosscut the main deformation fabric within the Changgo granite; therefore, that deformation and associated south directed shearing must have ended between 23.5 Ma and 22.1 Ma. The dikes are strained within the STDS, indicating that final displacement along the STDS must post-date 22 Ma, yet be older than 18.4 Ma, the cooling age of muscovite in the shear zone. It is proposed that the exhumation of the Changgo culmination is related to tectonically driven erosion in response to crustal thickening and rebuilding of the orogenic critical taper wedge. Subsequently, deformation in the wedge migrated toward the foreland, expanding the orogenic wedge laterally and moving the locus of displacement from the Main Central thrust structurally downward to the Main Boundary thrust. Citation: Larson, K. P., L. Godin, W. J. Davis, and D. W. Davis (2010), Out-of-sequence deformation and expansion of the Himalayan orogenic wedge: insight from the Changgo culmination, south central Tibet, Tectonics, 29, TC4013, doi: 10.1029/2008TC002393.

Secondary-ion mass spectrometry (SIMS) U-Pb and trace element data are reported for zircon to address the controversial geochronology of eclogite-facies metamorphism in the Lindas nappe, Bergen Arcs, Caledonides of W Norway. Caledonian eclogite-facies overprint in the nappe was controlled by fracturing and introduction of fluid in the Proterozoic--Sveconorwegian--granulite-facies meta-anorthosite-norite protolith. Zircon grains in one massive eclogite display a core-rim structure. Sveconorwegian cores have trace element signatures identical with those of zircon in the granulite protolith, i.e. 0.31 [less than or equal to] Th/U [less than or equal to] 0.89, heavy rare earth element (HREE) enrichment, and negative Eu anomaly. Weakly-zoned to euhedral oscillatory-zoned Caledonian rims are characterized by Th/U [less than or equal to] 0.13, low LREE content (minimum normalized abundance for Pr or Nd), variable enrichment in HREE, and no Eu anomaly. A decrease of REE towards the outermost rim, especially HREE, is documented. This signature reflects co-precipitation of zircon with garnet and clinozoisite in a feldspar-absent assemblage, and consequently links zircon to the eclogite-facies overprint. The rims provide a mean [sup.206]Pb/[sup.238]U crystallization age of 423 [+ or -] 4 Ma. This age reflects eclogite-forming reactions and fluid-rock interaction. This age indicates that eclogite-facies overprint in the Lindas nappe took place at the onset of the Scandian (Silurian) collision between Laurentia and Baltica.

The presence of newly formed crust introduced from mantle sources and the occurrence of crustal melting and intrusion characterized the tectonic formation of the late Archean crust in the Slave Province, Canada. Supracrustal and granitoid rock samples were studied using samarium-neodymium isotopic analysis. The results showed that the samples obtained from the central and eastern regions contained higher Nd concentrations than those from the west. This indicated that the western magma samples had been contaminated by older extrusions which confirmed the mid to early Archean crustal exposure of the western region.

The Proterozoic crystalline Lindas nappe of the Bergen arc, Caledonides of western Norway, displays local Caledonian eclogite facies overprint along fractures and shear zones. The overprint results from fluid infiltration in a dry granulite facies protolith under eclogite facies conditions. Formation of a low Th/U zircon overgrowth in eclogites is interpreted to be coeval with crystallization of the eclogite facies assemblage. A lower intercept age of 456 [+ or -] 7 Ma obtained from combined zircon U-Pb data for an eclogite and an associated granulite are believed to reflect the eclogite facies fluid infiltration event. An alternative minimum age of 419 [+ or -] 4 Ma can be extracted from the data. A charnockite and a mafic granulite yield Proterozoic intrusion ages of 1237 +43/-35 and 951 [+ or -] 2 Ma, and a garnet-bearing granulite provides an age of 929 [+ or -] 1 Ma for the late Sveconorwegian granulite facies metamorphism. The Proterozoic ages are compatible with a correlation between the Lindas and Jotun nappes and an origin of the Lindas nappe in the Sveconorwegian province of Baltica. We propose a possible model featuring subduction of the Lindas nappe at 456 [+ or -] 7 Ma attached to the Baltica plate during a Late Ordovician (Caradoc) collision between Baltica and an outboard island arc in the Iapetus Ocean. Accretion of some of the ophiolite-bearing terranes preserved in the Caledonides of western Norway may have taken place during this event. Keywords: Caledonian orogeny, eclogite facies, granulite facies, Grenvillian orogeny, U/Pb, zircon.

In the Yathkyed Lake area the Tyrrell shear zone (TSZ) marks the boundary between the northwestern and central Hearne subdomains of the Western Churchill Province. The TSZ is dominated by Proterozoic dextral strain, but in areas of low dextral strain, older shear fabrics are consistent with an earlier thrusting event. Four syntectonic granite sheets from within low-dextral-strain zones in the TSZ and contiguous shear zones at the base of the Yathkyed belt have ages of 2636–2629, 2652 ± 8, 2665–2639, and 2644 ± 3 Ma. The Yathkyed belt occurs in the hanging wall of these shear zones and comprises a greenschist- to amphibolite-grade, overturned panel that is overlain by an upper amphibolite-grade polydeformed panel. The geometry is consistent with a thrust-imbricated stack. Two episodes of deformation in the hanging wall are bracket between ca. 2660 and 2616 +6–4 Ma and between 2616 +6–4 Ma and ca. 2.60 Ga. The Yathkyed belt is interpreted to have initially been emplaced as a thick-skinned, thrust nappe along the TSZ, during 2.66–2.62 Ga tectonism, and reactivated at ca. 2.62–2.60 Ga, causing further crustal thickening. In the Upper Panel, protracted upper amphibolite-grade metamorphism and associated anatectic melting are recorded by zircon, titanite, and monazite ages ranging from ca. 2561 to 2492 Ma. This thermal event is in part attributed to burial in response to ca. 2.62–2.60 Ga thrust reactivation. The timing and means of emplacement of the Upper Panel on top of the Lower Panel is uncertain; however, ca. 2.50 Ga thrusting elsewhere in the northwestern Hearne subdomain provides one possible mechanism. [ABSTRACT FROM AUTHOR]

The Central Hearne supracrustal belt, one of the largest Neoarchean “greenstone” terranes in the Canadian Shield, occurs in the Hearne domain of the Western Churchill Province, one of the largest, poorly known fragments of Archean crust on Earth. The belt contains two isotopically juvenile volcano–plutonic assemblages (I: ∼2710–2690 Ma, and II: ∼2685–2680 Ma), separated in time by localised, ∼2690 Ma, greenschist-facies deformation (D1), and overlain by ∼2680 Ma Archean siliciclastic and chemical sedimentary rocks. Extensive, penetrative, greenschist-facies regional deformation (D2) occurred at ∼2680 Ma, with amphibolite-facies metamorphism localised in the aureoles of isotopically juvenile synkinematic plutons. In many respects, the Central Hearne supracrustal belt is similar to other Neoarchean “greenstone” belts that have been interpreted in terms of arc-subduction systems, e.g. the Abitibi greenstone belt of the Superior Province. However, the principal tectonic characteristics of the Central Hearne supracrustal belt include: (i) location in an anomalously wide (>225 km) swath of penecontemporaneous juvenile crust that extends across much of the Hearne domain; (ii) close, primary intercalation of contemporaneous volcanic rocks of MORB-like and arc-like geochemical signatures, coupled with highly discontinuous volcanic map units; (iii) abundant intermediate to felsic volcanic rocks that do not represent a localised, laterally extensive volcanic arc edifice; and (iv) the development of isolated, independent, felsic volcanic centres throughout the magmatic history of the belt. These features are incompatible with oceanic arc or plateau models. We propose that the early history (assemblage I) of the Central Hearne supracrustal belt may be analogous with a modified extensional, suprasubduction “infant arc” model, such as that described for the earliest (Eocene) phase of construction of the Izu–Marianas–Bonin and Tonga arc-trench systems of the Southwest Pacific Ocean. The later history (assemblage II) may reflect attempted initiation of classical subduction and arc construction. [Copyright &y& Elsevier]