Pinwarian (1.50 Ga) volcanism and hydrothermal activity at the eastern margin of the Wakeham Group, Grenville Province, Quebec

Abstract

Volcanic belts developed along the southeastern continental margin of Laurentia between 1.70 and 1.30 Ga and subsequently metamorphosed at high grade are today largely concealed among gneiss complexes of the Grenville Province. At the eastern end of the Wakeham Group and in the La Romaine Supracrustal Belt to the east, four 1.50 Ga volcanic centres were found among gneissic synvolcanic intrusions typical of the 1.52–1.46 Ga Pinwarian continental magmatic arc. Upper amphibolite- to granulite-facies rhyolitic to dacitic lavas and coarse lapillistone overlie or are intimately associated with arenites typical of the Wakeham Group. Garnetite, ironstone, carbonate rock, calc-silicate rock, and sillimanite-bearing nodules, veins, and gneiss, locally preserving lapilli, are also present. The distribution, paragenesis, and modes of most of these latter units differ from those of normal metasediments but are diagnostic of metamorphosed exhalites and hydrothermal alteration zones. In the La Romaine Supracrustal Belt, they are associated with pyroclastic horizons and a mineralized composite amphibolite unit. Volcanic textures include flow banding, wispy lapilli moulding fragmented lapilli and rounded lapilli with quartz-feldspar mosaics (filled vesicles), and in situ shattering of lapilli. These textures and the presence of advanced argillic alteration point to vesicular volcanism and hydrothermal activity in a subaerial to shallow submarine environment. Rare mafic lapilli attest to coeval mafic magmatism. The pervasive calc-alkaline signature of the eruptive and intrusive felsic to mafic rocks and their distribution are compatible with the development of 1.50 Ga intra-arc volcano-sedimentary belts stemming from the Wakeham Group basin and extending eastward within the Pinwarian continental magmatic arc.

Tectonic Setting and Evolution of the Grenville Orogen: An Assessment of Progress Over the Last 40 Years

“…This reevaluation, which suggests a tectonic setting comparable to the modern Japan Sea (Easton 1992), led to its renaming as the Composite Arc Belt (CAB) by Carr et al (2000). In addition, the discovery of metavolcanic rocks that formed in the upper parts of the Mesoproterozoic continental margin arc (Ratcliffe et al 1991;Wodicka et al 2004;Corriveau and Bonnet 2005) implies that both shallow and deep levels of the arc are preserved. These interpretations exemplify the profound changes in perception of both the pre-Grenvillian history of SE Laurentia and the origin of the arcderived Grenvillian gneiss complexes, formerly regarded as 'basement'.…”

Southern continuation of the Wakeham Group and Robe-Noire mafic suite (eastern Grenville Province) from hydrocarbon-targeted seismic reflection data on Anticosti Island, Quebec, Canada

“…The Abbé Huard shear zone recorded early NW-directed thrusting and late SE-directed transtensional motions (Martignole et al 1994;Gobeil et al 2003). The Wakeham Group is several kilometers in thickness and is composed of mainly arenaceous sedimentary rocks deposited at ca 1.5 Ga (van Breemen and with minor conglomerate, mudrock, marble and volcanic flows (Gobeil et al, 2003;Corriveau and Bonnet 2005). At 1.17 Ga the supracrustal sequence was intruded by a series of tholeiitic gabbroic sills up to several hundreds of meters in thickness and tens of kilometers in length (Robe noire mafic suite) that form about 30% of the outcrop area of the Davy Trough ( Fig.…”

Origine et développement de litages dans des roches de composition granitique /

“…Cette production de magma peut être expliquée par les précurseurs de l'orogénie grenvillienne comme le début de l'amincissement crustal par exemple (Windley, 1989;Windley, 1993). De plus de 1,5 à 1,45 Ga, l'orogénie pinwarienne pourrait jouer un rôle important dans la partie nord-est de la province (Gower, 1996;Wasteneys et al, 1997;Corriveau & Bonnet, 2005). Cette orogénie serait marquée par une zone de subduction à pendage sud associée à du magmatisme d'arc.…”

“…Ces âges à environ 1,5 Ga ne correspondent pas à un événement bien défini dans la région centrale de la province du Grenville. Dans la région nord-est du Grenville ainsi qu'au Labrador, les roches datées à 1,5 Ga sont généralement reliées à l'orogénie pinwarienne (Gower, 1996;Wasteneys et al, 1997;Corriveau & Bonnet, 2005). Cette orogénie a été délimitée dans le temps entre 1520 et 1460 Ma par Gower & Krogh (2002).…”