The Topsails igneous suite, western Newfoundland: an Early Silurian subduction-related magmatic suite?

Abstract

The Topsails igneous suite contains several Late Ordovician to Early Silurian volcanic and intrusive sequences, which overlie and intrude Early to Middle Ordovician oceanic and arc rocks. The oldest components of this suite may represent calcalkaline, continental-arc magmatism. The younger components are bimodal, with felsic compositions vastly predominating, and include a major ( > 2200 km2) alkaline (A-type) granite complex. These felsic components have similarities to peralkaline suites formed in unusual subduction-related settings. Younger mafic components resemble within-plate basalts emplaced in a continental setting.Silurian magmatic activity in the Canadian Appalachians is widespread, includes diverse magmatic types, and has contrasting metamorphic and tectonic overprinting, even in contiguous areas. These features and the probability of major postSilurian displacements in the orogen render correlation and interpretation difficult. Tectonic models that consider basin closure and major plate movements to be complete by Middle Ordovician time fail to adequately explain the Silurian activity. Available data best fit a model that relates Late Ordovician to Silurian magmatic activity to the opening and closing of small, discontinuous basins, portions of which may have been floored by oceanic crust. L'ensemble de roches ignkes de Topsails inclut plusieurs skquences volcaniques et intrusives d'lge ordovicien tardif B silurien moyen; elles recouvrent et recoupent des roches octaniques et d'arcs d'lge ordovicien moyen 2 pkcoce. Les roches les plus anciennes dans cet ensemble correspondent probablement 2 une activitk magmatique calco-alcaline de type arc continental. Les roches les plus jeunes sont bimodales, caract6risCes par des compositions felsitiques largement dominantes, et incluent un important (> 2200 km2) complexe granitique alcalin (type-A). Ces roches felsitiques montrent des similitudes avec les stquences peralcalines qui ont kt6 formkes dans des contextes, plut6t inhabituels, associks B une subduction. Les roches mafiques les plus jeunes ressemblent 2 des basaltes intra-plaques mis en place en milieu continental.L'activitt magmatique silurienne dans les Appalaches canadiennes est largement kpandue; elle inclut divers types magmatiques marquks par des contrastes nets de surimpression mttamorphique et tectonique, m2me dans les kgions contiguks. Ces particularitks et la probabilitk de dkplacements majeurs postsiluriens durant l'orogenkse rendent difficiles les corrklations et l'interpktation. Les modkles tectoniques qui considkrent une fermeture de bassin et des mouvements de plaques importants complktks 2 l'ordovicien moyen ne peuvent expliquer adkquatement l'activitk magmatique silurienne. Les enseignements disponibles sont en accord avec un modkle qui relie l'activitk magmatique, de l'ordovicien tardif au Silurien, B l'ouverture et B la fermeture de petits bassins, discontinus, dont certaines portions auraient pu Etre formkes d'un plancher ce croiite ockanique.[Traduit par la revue]Can.

The origin of mafic-ultramafic bodies within the northern Dashwoods Subzone, Newfoundland Appalachians

“…This magmatic episode has been attributed to slab break-off of the oceanic part of the Ganderian plate following its collision with the composite Laurentian margin (van Staal et al 2003;Whalen et al 2003). Silurian magmatism is dominated volumetrically by granite and rhyolite (Whalen 1989), but some mafi c plutons have been described within the region (the Main Gut and Boogie Lake suites ;Carew 1979;Currie and van Berkel 1989;Dunning et al 1990). These have been dated at 431±2 and 435 +6/-3 Ma, respectively (Dunning et al 1990), in agreement with the ages presented herein.…”

“…Both subzones are dominantly composed of the Late Cambrian to Lower Silurian Notre Dame Arc (Whalen et al 1997;van Staal et al 2003), paragneiss, arc-back arc complexes, and ophiolites (e.g., Swinden et al 1997;Lissenberg et al 2005 b). Post-tectonic late Lower to Upper Silurian magmatism is widespread, and is dominated by granite with subordinate mafi c rocks (Currie and van Berkel 1989;Whalen 1989;Dunning et al 1990;Whalen et al 1996Whalen et al , 2003. Geochemical and isotopic data, inherited Proterozoic zircon grains, and tectonic relationships indicate that the Notre Dame Arc was formed on a rifted piece of the Laurentian margin, referred to as the Dashwoods microcontinent, which was separated from Laurentia by the Humber seaway in the Cambrian-Early Ordovician (Whalen et al 1997;Waldron and van Staal 2001).…”

Geological development of eastern Humber and western Dunnage zones: Corner Brook–Glover Island region, Newfoundland

“…rather than a stratigraphic contact between the Grand Lake Complex and Glover Formation largely invalidates the basis for these correlations. The Glover Island Granodiorite has been included within the Hungry Mountain Complex, which outcrops largely to the east and north of Grand Lake (Whalen 1989); however, a UIPb zircon date of 440 Ma for the granodiorite indicates that it is significantly younger than the Early to Middle Ordovician age of the complex (e.g., Dunning et al 1987;Whalen et al 1987). The age of the Glover Island Granodiorite is similar to that of the eastern portion of the Burlington Granodiorite (G.R.…”

Time-Transgressive Salinic and Acadian Orogenesis, Magmatism and Old Red Sandstone Sedimentation in Newfoundland

“…These zones contain brickred felsic (Fig. 6B) and green mafic amoeboid inclusions, suggesting that the intermediate zones may represent hybridized mafic-felsic magma, similar to hybridized magmas common in the adjacent Topsails Igneous Suite (Whalen and Currie 1984;Whalen 1989). …”