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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 [...]

Geochronological studies in northern Wedel Jarlsberg Land, southwestern Svalbard (Norway), showed that the Tonian (c. 950 Ma) igneous rocks were subjected to metamorphism during the Torellian (c. 640 Ma) and early Caledonian (470-460 Ma) events. Predominant augen gneisses, derived from a Tonian protolith, are intercalated in that area, with schists comprising two distinct metamorphic mineral assemblages. The Ml (Torellian) assemblage containing garnet-I + quartz + plagioclase-I + biotite-I + muscovite-I was formed under amphibolite-facies conditions at c. 550-600 °C and 5-8 kbar (1 kbar = 100 MPa). The M2 (Caledonian) assemblage comprising garnet-II + quartz + plagioclase-II + biotite-II + muscovite-II + zoisite + chlorite crystallized at c. 500-550 °C and 9-12 kbar, corresponding to epidote-amphibolite facies conditions. The M2 mineral assemblage constitutes the pervasive Caledonian fabric of the schists that was subsequently reactivated in a left-lateral strike-slip shear regime. The subsequent c. 70° clockwise rotation of the original structure to its present position was caused by a large-scale passive rotation during the Paleogene Eurekan orogeny. The new pressure-temperature estimates suggest that metamorphic basement in the study area was consolidated during the Torellian middlegrade event and then overprinted by Caledonian moderate- to high-pressure subduction-related metamorphism. A following sinistral shear zone assembled the present structure of basement units. Our results pose a question about the possible extent of Torellian precursor to the Caledonian basement across the High Arctic and the scale of its subsequent involvement in early Caledonian subduction. In conjunction with previous studies, the results suggest a possible correlation between southwestern Spitsbergen and the Pearya Terrane in Ellesmere Island. Des etudes geochronologiques dans le nord du WedelJarlsberg Land, sud-ouest du Svalbard, montrent que les roches ignees du Tonien (~950 Ma) ont subi un metamorphisme durant les evenements du Torellien (~640 Ma) et du Caledonien precoce (470-460 Ma). Des gneiss oeilles predominants, provenant d'un protolithe du Tonien, sont, dans ce secteur, intercales avec des schistes comprenant deux assemblages mineralogiques metamorphiques distincts. L'assemblage M1 (Torellien) contenant du grenat-I + quartz + plagioclase-I + biotite-I + muscovite-I a ete forme sous des conditions du facies des amphibolites a ~550-600 °C et a une pression de 5-8 kbar (1 kbar = 100 MPa). L'assemblage M2 (Caledonien), comprenant du grenat-II + quartz + plagioclase-II + biotite-II + muscovite-II + zoisite + chlorite, a cristallise a ~500-550 °C et a une pression de 9-12 kbar, ce qui correspond a des conditions de facies des amphibolites a epidote. L'assemblage M2 constitue la fabrique envahissante caledonienne des schistes, laquelle a par la suite ete reactivee lors d'un regime de cisaillement de decrochement lateral senestre. La rotation subsequente d'environ 70 ° dans le sens horaire de la structure originale a sa position actuelle a ete causee par une rotation passive a grande echelle durant l'orogene de l'Eureka au Paleogene. Selon les nouvelles estimations de pression-temperature, le socle metamorphique dans le secteur a l'etude a ete consolide durant un metamorphisme intermediaire, au Torellien, et par la suite surimprime au Caledonien par un metamorphisme a pression moderee a elevee relie a une subduction. Une zone de cisaillement senestre a par la suite assemble la structure actuelle d'unites de socle. Nos resultats questionnent l'etendue possible du precurseur du Torellien au socle caledonien a travers le Haut-Arctique et l'echelle de son implication subsequente dans la subduction au Caledonien precoce. En conjonction avec des etudes anterieures, ils suggerent une correlation possible entre le Spitsbergen du sud-ouest et le terrane de Pearya dans l'ile d'Ellesmere. [Traduit par la Redaction], Introduction A classical view on the evolution of crystalline basement in Svalbard (Norway) is that early Paleozoic Caledonian deformation and metamorphism overprint the effects of earlier tectonothermal events dating back [...]

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 [...]

Three trilobites, Hypagnostus aff. clipeus, Cotalagnostus sp. nov., and Pagetidesjohannis sp. nov., not previously recorded in Newfoundland, are associated with Onymagnostus cf. hybridus, H. mammillatus, Peronopsis cf. fallax minor, Paradoxides (P.) davidis davidis, P. (P.) cf. abenacus, Brunswickia (B.) cf. jaculator, B. (Jincella) sp., Agraulos sp., and some hyolithids, stenothecid molluscs and orthid, acrotretid and lingulate brachiopods in a thin limestone within dark grey, slaty mudstones of the Young's Cove Formation on St. John's Island, Fortune Bay. A stratigraphical position within the Cambrian punctuosus Zone in the upper part of the Drumian Stage is indicated. The presence of the oculate eodiscid Pagetides in late mid-Cambrian rocks, within the Avalon Tectonostratigraphical Zone, is highlighted, because the genus was previously only known associated with the much earlier Cambrian olenellid zones of Laurentia. Paradoxides (P.) cf. abenacus and the species of Brunswickia (B.) close to peregrina, respectively, provide a link with the New Brunswick mid-Cambrian and paradoxissimus successions in England and Scandinavia, whereas the specimens of Hypagnostus aff. clipeus indicate a more global significance in common with forms in the punctuosus sequences of Siberia and Australia. The St. John's Island sequence includes lithofacies and fossils typical of the Manuels River Formation preserved elsewhere in southeastern Newfoundland. This is the first recognition of such a sequence in the Young's Cove Formation of Fortune Bay on the western margin of the Avalon Tectonostratigraphical Zone. Resume : Trois trilobites, Hypagnostus aff. clipeus, Cotalagnostus sp. nov. et Pagetides johannis sp. nov., signales pour la premiere fois a Terre-Neuve, sont associes a Onymagnostus cf. hybridus, H. mammillatus, Peronopsis cf. fallax minor, Paradoxides (P.) davidis davidis, P. (P.) cf. abenacus, Brunswickia (B.) cf. jaculator, B. (Jincella) sp., Agraulos sp. et certains hyolithes, mollusques stenothecides et brachiopodes orthides, acrotretides et lingules dans un mince calcaire dans des mudstones a clivage ardoisier gris fonce de la Formation de Young's Cove dans Ule St. John's de la baie de Fortune. Une position stratigraphique dans la Zone cambrienne a punctuosus, dans la partie superieure de l'etage drumien, est indiquee. La presence de l'cediscide ocule Pagetides dans des roches du Cambrien moyen tardif de la zone tectonostratigraphique d'Avalon est a noter, etant donne que ce genre n'etait auparavant connu qu'en association avec les zones a olenellides cambriennes de la Laurentie. Paradoxides (P.) cf. abenacus et l'espece de Brunswickia (B.) proche de peregrina constituent, respectivement, des liens avec les successions neo-brunswickoises du Cambrien moyen et a paradoxissimus en Angleterre et en Scandinavie, alors que les specimens d'Hypagnostus aff. clipeus indiquent une signification plus planetaire en commun avec des formes presentes dans les sequences a punctuosus de Siberie et d'Australie. La sequence de Ule St. John's comprend des lithofacies et fossiles caracteristiques de la Formation de Manuels River preserves en d'autres localites du sud-est de Terre-Neuve. Il s'agit du premier signalement d'une telle sequence dans la Formation de Young's Cove de la baie de Fortune, sur la marge occidentale de la zone tectonostratigraphique d'Avalon. [Traduit par la Redaction], Introduction St. John's Island lies within the Harbour Breton map-area of southeastern Newfoundland, at the entrance to St. John's Bay, midway between the promontories of St. John's and Boxey Point [...]

The mineralogy, petrology, and geochemistry of an igneous-textured clast in the Peace River L6 chondrite meteorite was examined to determine the roles of nebular processes, accretion, and parent-body metamorphism in its origin. The centimetre-scale clast is grey and fine grained and is in sharp contact with the host chondrite. Two sub-millimetre veins cut across both the clast and host, indicating that the clast formed prior to the impact (shock) event(s) that produced the numerous veins present in the Peace River meteorite. The clast and host are indistinguishable in terms of mineral compositions. In contrast, there are differences in modal mineralogy, texture, as well as trace element and oxygen isotope composition between the clast and host. These differences strongly suggest that the clast was formed by impact melting of LL-group chondritic material involving loss of Fe-FeS and phosphate components, followed by relatively rapid cooling and incorporation into the Peace River host meteorite. Subsequent metamorphism on the Peace River parent body caused recrystallization of the clast and homogenization of mineral compositions and thermally labile element abundances between the clast and host. Shock metamorphism, including formation of shock melt veins, occurred post-metamorphism, during fragmentation of the L chondrite parent body. The results suggest that the formation of the Peace River parent asteroid included the incorporation of material from other asteroids and that the pre-metamorphic protolith was a breccia. Accordingly, we propose that the Peace River meteorite be reclassified as a polymict breccia. La mineralogie, la petrologie et la geochimie d'un claste a texture ignee dans la meteorite chondrite Peace River L6 ont ete etudiees afin de determiner les roles des processus nebulaires, d'accretion et de metamorphisme quant a l'origine de l'amas parent. Le claste d'echelle centimetrique est gris et a grain fin; il est de plus en contact net avec la chondrite hote. Deux veines de taille inferieure a un millimetre recoupent le claste et la roche hote, indiquant que le claste s'est forme avant le(s) evenement(s) d'impact qui a(ont) produit les nombreuses veines presentes dans la meteorite Peace River. Le clase et son hote ont exactement les memes compositions minerales. Par contre, il existe des differences dans la mineralogie modale, la texture, les elements traces et la composition des isotopes d'oxygene entre le claste et la roche hote. Ces differences suggerent fortement que le claste ait ete forme par la fusion sous impact du materiel chondritique du groupe LL, impliquant la perte des composantes Fe-FeS et phosphatiques, la fusion a ete suivie d'un refroidissement relativement rapide et de l'incorporation dans la meteorite hote Peace River. Un metamorphisme subsequent sur l'amas parent Peace River a cause la recristallisation du claste et l'homogeneisation des compositions minerales et des abondances des elements labiles thermiques entre le claste et la roche hote. Un metamorphisme de choc, incluant la formation de veines sous le choc de la fusion, a eu lieu apres le metamorphisme, durant la fragmentation de l'amas parent chondrite L. Selon les resultats, la formation de l'astro'ide parent de la meteorite Peace River comprendrait l'incorporation de materiel d'autres astro'ides et le protolithe pre-metamorphique aurait ete une breche. Nous proposons donc que la meteorite Peace River soit reclassifiee en tant que breche polymictique. [Traduit par la Redaction], Introduction The Peace River meteorite fell at approximately 0440 hours local time on March 31st, 1963, near the town of Peace River, Alberta, after a bright fireball that was observed [...]

The eastern Himalayan syntaxis is host to the actively deforming metamorphic massif, Namche Barwa. This massif has experienced a complex history of uplift and deformation, influenced by intense fluvial erosion associated with the Yarlung Tsangpo. Here we present new thermobarometric and geochronologic information on metamorphic rocks from the Namche Barwa--Gyala Peri region. Pressure-temperature data are combined with U-Th-Pb ages of monazite and titanite in an effort to trace the metamorphic evolution of the eastern Himalaya. Metapelitic rocks containing garuet-biotite-plagioclase assemblages yield peak metamorphic pressures and temperatures of 10-14 kbar and 700-900[degrees]C in the structural core of the massif. There is a distinct metamorphic break across the Namula thrust, separating high-grade rocks to the north from lower grade rocks to the south. Ion microprobe monazite and titanite ages of 3-10 Ma indicate that timing of metamorphism is roughly coincident with the age of granitic melt production (

Abstract: The Wyoming Province is a distinctive Archean craton in the northwestern United States that can be subdivided into three subprovinces, namely, from oldest to youngest, the Montana metasedimentary province, [...]

A comparative study of orogenic domains of the Range and Basin province and Variscan belt indicate the presence of extended shear zones in prominent metamorphic core complexes. The shear zones develop from heterogeneous deep-seated ductile deformation and evolutes from noncoaxial flow. The deformations influence the hot crust layers and indicate that orogenic extensions depend on contractional tectonics.

SHRIMP U-Pb zircon dating on representative rocks of the Huai'an Complex, a key area in the northern part of the Trans-North China Orogen (TNCO), is carried out where high-pressure mafic granulites and retrograded eclogites were first discovered in the North China Craton.