Search

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 Roy Group in the Chibougamau area of the Abitibi subprovince, Southeastern Superior craton, Quebec, exemplifies Archean volcanic evolution. The Roy Group formed in two volcanic cycles, with voluminous basal mafic tholeiitic volcanic rocks being capped by a thin succession of calc-alkaline felsic volcanic rocks, banded iron formations, and cherts that represent regional stratigraphic markers. The Gilman Formation is thought to represent the mafic base of the 2nd Roy Group volcanic cycle. Our new mapping reveals that the Gilman Formation (North of the Lac Dore Layered intrusive complex) can be subdivided into a tholeiitic lower part (David member), a calc-alkaline extrusive sequence (Allard member), and a tholeiitic, more mafic upper part (Bruneau Formation, newly defined here). New U-Pb zircon ages on Allard member tuffs (2726.6 ± 0.7 Ma) are within error of those obtained from rhyolites of the Waconichi Formation (2728.2-2728.7 Ma), which underlies the Gilman Formation. These ages, along with geochemical and lithological similarities, imply that the Allard member belongs to the Waconichi Formation and that the David member occupies the same stratigraphic position as the Obatogamau Formation. The upper part of the former Gilman Formation is reassigned to the new Bruneau Formation. A thin transitional calc-alkaline basalt unit at the base of the Allard member is geochemically similar to basalts occurring at the top of the Lemoine member of the Waconichi Formation near the Lemoine mine, suggesting that the Allard member is slightly younger than the Lemoine member, and that its base (also associated with iron formation, breccia, and chert) represents a regional stratigraphic break favourable for volcanogenic-hosted massive sulphide (VHMS) exploration. Le Groupe de Roy dans le secteur de Chibougamau de la sous-province de l'Abitibi, dans le sud-est du craton du Superieur, au Quebec, est un exemple d'evolution de volcaniques archeeennes. Le Groupe de Roy a ete forme; durant deux cycles volcaniques, avec une base volumineuse de roches volcaniques, mafiques et tholeeiitiques, recouvertes par une mince succession de roches volcaniques calco-alcalines felsiques, des formations de fer rubanees et des cherts qui est interpretee commes des marqueurs stratigraphiques regionaux. La Formation de Gilman representerait la base mafique du 2e cycle volcanique du Groupe de Roy. Notre nouvelle cartographie revele que la Formation de Gilman (au nord du complexe intrusif de roches stratifieees du lac Dore) peut etre subdivisee en une partie infeerieure tholeiitique (membre de David), une sequence calco-alcaline extrusive (membre d'Allard) et une partie superieure tholeiitique plus mafique (Formation de Bruneau, nouvellement deefini dans cet article). De nouvelles donnees d'ages U-Pb sur des zircons des tufs du membre d'Allard (2726,6 ± 0,7 Ma) sont a l'inteerieur de la marge d'erreur des ages obtenus sur des rhyolites de la Formation de Waconichi (2728,2 - 2728,7 Ma) qui est sous-jacente a la Formation de Gilman. Selon ces ages et les similitudes geochimiques et lithologiques, le membre d'Allard appartiendrait a la Formation de Waconichi et le membre de David occuperait la meeme position stratigraphique que la Formation d'Obatogamau. La partie superieure de l'ancienne Formation de Gilman est reassigneea la nouvelle Formation de Bruneau. Une mince unite de basalte transitionelle a calco-alcalin a la base du membre d'Allard est geochimiquement similaire aux basaltes qui se retrouvent au sommet du membre de Lemoine de la Formation de Waconichi, a proximite de la mine Lemoine, suggerant que le membre d'Allard soit legerement plus jeune que le membre de Lemoine et que sa base (aussi associeeea une formation de fer, des breches et du chert) represente un marqueur stratigraphique regional favorable a l'exploration pour des sulfures massifs dans des roches volcaniques. [Traduit par la Redaction], Introduction The Abitibi subprovince (Fig. 1), southeastern Superior craton, contains the world's largest preserved Archean greenstone belt (Goodwin and Ridler 1970; Thurston and Fryer 1983; Daigneault et al. 2004). Bimodal [...]

ABSTRACT Mafic-ultramafic bodies of possible ophiolitic origin are widespread within the northern part of the Dashwoods Subzone of the Newfoundland Appalachians. The bodies fall into two types; the first consists [...]

The magnitude of late Mesozoic terrane translation along the western North American continental margin is controversial. Paleomagnetic data suggest more than 3000 km of dextral displacement of the Insular superterrane and associated assemblages between ca. 74 and 50 Ma. Conversely, geologic evidence is more compatible with less than 500 km of offset during this time. Precambrian cratonic rocks older than 2.5 Ga are restricted to northern latitudes (above 40 [degrees] N) in North America, and the presence or absence of Archean zircons within easterly derived Cretaceous strata has been proposed as a 'crucial test' of the major translation hypothesis. There is no plausible source of Archean and Early Proterozoic zircons found in the Queen Charlotte, Nanaimo, and Methow basins other than the Canadian Shield or closely associated Proterozoic strata. The coexistence of Archean-Early Proterozoic, Middle Proterozoic (1.5-1.6 Ga) and Mississippian detrital zircon in these basins indicates deposition in northern latitudes, incompatible with the Baja B.C. hypothesis.

The tectonic history of Dashwoods microcontinent and its associated sediments and arc plutons in the Appalachian mountain belt is studied.

Available geochronological (U-Pb and Ar/Ar) and geological data indicate that the Corner Brook Lake block of the Humber zone in the western Newfoundland Appalachians has unique characteristics. Grenvillian ages (ca. 1.0 Ga), which are typical for the Laurentian Appalachian margin, are absent in the crystalline basement to the Corner Brook Lake block. This makes it unlikely that the block is underlain by true parautochthonous Humber margin basement. However, the lithological makeup of its late Neoproterozoic-Early Cambrian sedimentary cover and detrital zircon populations indicate a Laurentian-type provenance. In addition, there is no geochronological or other geological evidence for a Middle Ordovician tectono-thermal event in the Corner Brook Lake block, suggesting that it escaped the penetrative tectono-thermal effects of the Taconic collision present elsewhere in the Laurentian realm. Instead, the block underwent strong regional deformation and associated peak metamorphism during the Silurian Salinic orogeny. Combined evidence, including the absence of Grenvillian ages, the presence of late Neoproterozoic ca. 600 Ma granitoid plutons, the regionally distinct early Paleozoic tectonic history of the Corner Brook Lake block, and its fault-bounded nature, implies that the block represents an allochthonous terrane. Available data indicate that significant orogen-parallel movement of the block (possibly 400 km or more) could have taken place during the Appalachian orogeny. The possibility of large-scale strike-slip tectonics, in addition to the well-documented convergent motions, has significant implications for the tectonic interpretation of the early Paleozoic evolution of the Newfoundland Appalachians. [ABSTRACT FROM AUTHOR]