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Understanding the development of island arcs that accreted to the North American craton is critical to deciphering the complex geological history of the Canadian Cordillera. In the case of the Hazelton arc (part of the Stikine terrane, or Stikinia) in northwestern British Columbia, understanding arc evolution also bears on the formation of spatially associated porphyry Cu-Au, epithermal, and volcanogenic massive sulfide deposits. The Hazelton Group is a regionally extensive, long-lived, and exceptionally thick Upper Triassic to Middle Jurassic volcano-sedimentary succession considered to record a successor arc that was built upon the Paleozoic and Triassic Stikine and Stuhini arcs. In central Stikinia, near Terrace, British Columbia, the lower Hazelton Group (Telkwa Formation) comprises three volcanic-intrusive complexes (Mt. Henderson, Mt. O'Brien, and Kitselas) that, at their thickest, constitute almost 16 km of volcanic stratigraphy. Basal Telkwa Formation conglomerates and volcanic rocks were deposited unconformably on Triassic and Paleozoic arc-related basement. New U-Pb zircon ages indicate that volcanism initiated by ca. 204 Ma (latest Triassic). Detrital zircon populations from the basal conglomerate contain abundant 205-233 Ma zircons, derived from regional unroofing of older Triassic intrusions. Eleven kilometres higher in the section, ca. 194 Ma, rhyolites show that arc construction continued for >10 million years. Strata of the Nilkitkwa Formation (upper Hazelton Group) with a U-Pb zircon age of 178.90 ± 0.28 Ma represent waning island-arc volcanism. Telkwa Formation volcanic rocks have bimodal silica concentrations ranging from 48.1 to 62.8 wt.% and 72.3 to 79.0 wt.% and display characteristics of subductionrelated magmatism (i.e., calc-alkaline differentiation with low Nb and Ti and high Th concentrations). Mafic to intermediate rocks form a differentiated suite that ranges from high-Al basalt to medium- to high-K andesite. They were derived from hydrous melting of isotopically juvenile spinel lherzolite in the mantle wedge and from subsequent fractional crystallization. Compared to basalts and andesites ([ζ.sub.Nd] = +5 to +5.5), rhyolites have higher positive [ζ.sub.Nd] values (+5.9 to +6.0) and overlapping incompatible element concentrations, indicating that they are not part of the same differentiation suite. Rather, the rhyolites formed from anatexis of arc crust, probably caused by magmatic underplating of the crust. This study documents a temporal and spatial co-occurrence of Hazelton Group volcanic rocks with a belt of economic Cu-Au porphyry deposits (ca. 205-195 Ma) throughout northwestern Stikinia. The coeval relationship is attributed to crustal underplating and intra-arc extension associated with slab rollback during renewed or reconfigured subduction beneath Stikinia, following the demise of the Stuhini arc in the Late Norian. Il est essentiel de comprendre le developpement des arcs insulaires qui se sont accretes au craton de l'Amerique du Nord afin de pouvoir decoder l'historique geologique complexe de la Cordillere canadienne. Dans le cas de l'arc Hazelton (une partie du terrane Stikine ou Stikinia) dans le nord-ouest de la Colombie Britannique, la comprehension de l'evolution de l'arc comporte aussi la formation des gisements de porphyres Cu-Au epithermaux et de gisements de sulfures massifs volcanogenes, associes dans l'espace. Le Groupe de Hazelton est une sequence volcano-sedimentaire de grande etendue regionale, de longue duree et d'une epaisseur exceptionnelle, datant du Trias superieur au Jurassique moyen; cette succession conserverait un arc successeur qui a ete erige sur les arcs Stikine et Stuhini (Paleozoique et Trias). Dans le Stikinia central, a proximite de Terrace, Colombie-Britannique, le Groupe de Hazelton inferieur (Formation de Telkwa) comprend trois complexes volcaniques intrusifs (le mont Henderson, le mont O'Brien et Ktiselas) qui, a l'endroit le plus epais, forment une stratigraphie volcanique de pres de 16 km. Les conglomerats a la base de la Formation de Telkwa et les roches volcaniques ont ete deposes de maniere discordante sur un socle relie aux arcs (Trias et Paleozoique). De nouveaux ages U-Pb sur zircon indiquent que le volcanisme a ete initie vers 204 Ma (Trias sommital). Les populations de zircons detritiques provenant du conglomerat de base contiennent d'abondants zircons de 205-233 Ma provenant du retrait regional du toit d'anciennes intrusions triasiques. A onze kilometres plus haut dans la section, des rhyolites, vers 194 Ma, montrent que la construction des arcs a continue durant plus de 10 Ma. Les strates de la Formation de Nilkitkwa (Groupe de Hazelton superieur), avec un age U-Pb sur zircon de 178.90 ± 0.28 Ma, representent une diminution du volcanisme d'arc. Les roches volcaniques de la Formation de Telkwa ont des concentrations de silice bimodales, variant de 48,1 a 62,8 et de 72,3 a 79,0 (% poids), et presentent des caracteristiques de magmatisme relie a la subduction (c.-a-d. une differentiation calco-alcaline avec des concentrations faibles en Nb et Ti et elevees en Th). Des roches mafiques a intermediaires forment une suite differentiee qui varie de basalte a haute teneur en Al a andesite a haute a moyenne teneur en K. Ces roches ont ete derivees d'une fusion hydratee d'une lherzolite a spinelle isotopiquement jeune dans un biseau de manteau et d'une cristallisation fractionnelle subsequente. Comparees aux basaltes et aux andesites ([ζ.sub.Nd] = +5 a +5,5), les rhyolites ont des valeurs [ζ.sub.Nd] positives plus elevees (+5,9 a +6,0) et des concentrations d'elements incompatibles qui se chevauchent, indiquant qu'ils ne font pas partie d'une meme suite de differenciation. Plutot, les rhyolites se sont formees a partir de l'anatexie d'une croute d'arc, probablement causee par un sous-placage magmatique de la croute. La presente etude documente une cooccurrence temporale et spatiale des roches du Groupe de Hazelton avec une ceinture de gisements de Cu-Au porphyriques rentables (vers 204 a 195 Ma) a travers le nord-ouest de Stikinia. La relation contemporaine est attribuee a un sous placage de la croute et d'une extension intra-arc associes a un repositionnement de la dalle durant un renouvellement ou une reconfiguration de la subduction sous Stikinia a la suite de l'effondrement de l'arc Stuhini au Norien tardif. [Traduit par la Redaction], Introduction The Late Triassic--Early Jurassic was a peak period for the formation of porphyry and related mineral deposits in the exceptionally well-endowed Stikine terrane (Stikinia) of the Canadian Cordillera (Fig. [...]

The Lower to Middle Jurassic Hazelton Group represents the final stage of magmatic arc activity in the intraoceanic Stikine terrane, which was followed by accretion within the Cordilleran terrane collage. The Hazelton Group is exposed in the following areas: (i) on the periphery of the Bowser Basin, where arc and back-arc strata are overlain by mainly sedimentary strata of the upper Hazelton Group and then by the clastic basin fill of the Bowser Lake Group; and (ii) within a 300 km long rift system, the Eskay rift, west of the Bowser basin, where a predominantly bimodal volcanic succession contains significant mineral deposits. Examination of representative stratigraphic sections throughout the regional extent of the upper Hazelton Group has suggested significant revisions and clarification of its stratigraphy and include the following: (i) informal division of the Hazelton Group into upper and lower parts and recognition of a diachronous unconformity or unconformities at the boundary between them; (ii) establishment of a type section for the sandstone-dominated Smithers Formation; (iii) establishment of separate Quock and revised Spatsizi formations in the north and extension of the Quock Formation to include all lithostratigraphically equivalent units of blocky, thinly bedded siliceous mudstone and tuff around the periphery of the Bowser basin; and (iv) introduction of the Iskut River Formation for rift-related and volcanic facies in the Eskay rift area. Two independent rifting events occurred during deposition of the Hazelton Group: a Late Sinemurian to Early Pliensbachian phase in the northwest-trending Hazelton trough and a more restricted Aalenian to Bajocian extensional event in the Eskay rift. Le Groupe de Hazelton (Jurassique inferieur a moyen) represente l'etape finale d'activite d'arc magmatique dans le terrane intra-oceanique Stikine, laquelle fut suivie par son accretion dans le collage de terranes de la Cordillere. Le Groupe de Hazelton affleure : (i) a la peripherie du bassin Bowser, ou des strates d'arc et d'arriere-arc sont recouvertes par des strates surtout sedimentaires du Groupe de Hazelton superieur et ensuite par le remplissage clastique de bassin du Groupe de Bowser Lake et (ii) dans un systeme de rifts d'une longueur de 300 km, le rift Eskay, a l'ouest du bassin Bowser, ou une succession volcanique principalement bimodale contient des gites mineraux significatifs. Un examen de sections stratigraphiques representatives a travers l'etendue regionale du Groupe de Hazelton superieur suggere d'importantes revisions et precisions de sa stratigraphie dont : (i) une division informelle du Groupe de Hazelton en parties inferieure et superieure et la reconnaissance d'une ou de plusieurs discordances diachroniques a la limite entre les parties; (ii) l'etablissement d'une section-type pour la Formation de Smithers, dominee par des gres; (iii) l'etablissement, au nord, d'une Formation de Quock distincte ainsi qu'une revision de la Formation de Spatsizi et l'extension de la Formation de Quock pour inclure toutes les unites a equivalence lithostratigraphique de mudstone et de tufs siliceux, a blocs et a lits minces, autour du bassin Bowser et (iv) l'introduction de la Formation d'Iskut River pour les facies volcaniques et ceux relies au rift dans la region du rift Eskay. Deux evenements independants de distension ont eu lieu durant la deposition du Groupe de Hazelton : une phase (Sinemurien tardif a Pliensbachien precoce) a tendance nord-ouest dans la fosse Hazelton et un evenement d'extension plus restreint (Aalenien a Bajocien) dans le rift Eskay. [Traduit par la Redaction], Introduction The Jurassic Period marks a key transition in the tectonics of the Canadian Cordillera. During this time, the western margin of North America was changing rapidly from a complex [...]

In 2000, the first outbreak of hantavirus pulmonary syndrome was recognized in the Brazilian Amazon (Maranhão State). An epidemiologic study identified a 13.3% prevalence of hantavirus-specific immunoglobulin G. The analysis of risk factors suggests that persons are occupationally exposed to infected rodents in the crop fields.

Beef carcasses (n = 150) of A-maturity were selected randomly to determine baseline shear force and sensory panel ratings, assess variation in tenderness, and evaluate mean value differences between Certified Angus Beef (CAB), commodity Choice, and Select steaks. Three steaks were removed from the triceps brachii (TB), longissimus lumborum (LL), gluteus medius (GM) semimembranosus (SM), biceps femoris (BF), and quadriceps femoris complex (QF), and assigned to Warner-Bratzler shear (WBSF) and sensory panel analyses. As anticipated, marbling score and measured percentage of i.m. fat were greatest (P < 0.05) for CAB, intermediate (P < 0.05) for Choice, and least (P < 0.05) for Select carcasses. A muscle x quality level interaction (P < 0.05) was observed for WBSF values and sensory panel tenderness ratings. The TB, LL, GM, and BF steaks from CAB carcasses had lower (P < 0.05) WBSF than Select steaks from the same muscles. Even though WBSF values did not differ (P > 0.05) between CAB and Choice QF and TB steaks, the LL and GM steaks from CAB carcasses were more tender (P < 0.05) than Choice-grade LL and GM steaks. The TB from Select carcasses had higher (P < 0.05) WBSF values than TB steaks from CAB or Choice carcasses, but sensory panel ratings indicated that quality level showed little consistency among the GM, SM, BF, and QF. Trained sensory panelists rated CAB LL steaks more tender (P < 0.05) than LL steaks from Choice and Select carcasses, and Choice LL steaks were evaluated as more (P < 0.05) tender than those from Select carcasses. These results demonstrate that the influence of marbling on tenderness was more evident in muscles of middle meats than in end cuts, particularly in muscles of the round. Key Words: Beef, Marbling, Quality Grade, Tenderness

In 2000, the first outbreak of hantavirus pulmonary syndrome was recognized in the Brazilian Amazon (Maranhao State). An epidemiologic study identified a 13.3% prevalence of hantavirus-specific immunoglobulin G. The analysis [...]