Geochemistry of Ordovician volcanic rocks of the Tetagouche Group of southwestern New Brunswick

Abstract

The Lower to Middle Ordovician volcanic suite of the Tetagouche Group from the southwestern part of the Miramichi Terrane in the Woodstock-Meductic area in southwestern New Brunswick is composed of a bimodal basalt-rhyolite association. The basalts have calc-alkalic characteristics and were emplaced on the continental crust in a volcanic arc or back-arc environment. The rhyolites were probably derived by melting of an amphibolite-facies crust. The basalts differ from those of the Tetagouche Group from the Bathurst area which include within-plate basalts and MORB. However, they both may be part of a single Ordovician arc-back-arc system.Le cortege volcanique du Groupe de Tetagouche (Ordovicien median a inferieur) dans la portion sud-ouest de la Laniere de Miramichi (region de Woodstock-Meductic, sud-ouest du Nouveau-Brunswick) se compose d'une association bimodale de basalte et rhyolite. Les basaltes presentent des caracteres calco-alcalins et ils se sont mis en place sur la croute continentale dans un milieu d 'arc insulaire ou de retro-arc. Les rhyolites proviennent probablement de la fonte d 'une croute de facies a amphibolites. Les basaltes different de ceux du Groupe de Tetagouche dans la region de Bathurst, qui comprennent des basaltes intra-plaques et des MORB, quoique tous deux puissent faire partie d 'un systeme arc:retro-arc ordovicien unique.[Traduit par le journal]

Stratigraphy and geochemistry of Ordovician volcanic rocks of the Eel River area, west-central New Brunswick

“…Both porphyritic facies plot in the continental margin (extensional) arc field on Fig. 9, corroborating the tectonic setting proposed by Dostal (1989).…”

“…1, 2) is underlain by Ordovician volcanic rocks that provide important constraints on the Paleozoic tectonic history of the Appalachian orogen (van Staal and Fyffe 1995a). These volcanic rocks have been previously interpreted on the basis of limited geochemistry as a bimodal assemblage generated in a supra-subduction zone setting (Dostal 1989). However, additional data reported here, indicate that rocks of intermediate composition form a significant proportion of the volcanic pile, a feature characteristic of many modem volcanic arcs.…”

“…Volcanic rocks are classified chemically on the basis of silica content following Gill (1981); basalt is defined as containing less than 53%, low-silica andesite from 53 to 57%, high-silica andesite from 57 to 63%, dacite from 63 to 70%, and rhyolite greater than 70% silica. Dostal (1989) has previously shown that basalt from the Oak Mountain Formation and rhyolite from the Porten Road Formation of the Meductic Group (as defined herein) were generated at a destructive plate boundary. His conclusions are confirmed and augmented by the present regional study, which includes samples with a much wider areal distribution.…”

“…Volcanic rocks in the upper part of the Porten Road Formation are an interlayered sequence of quartz-rich rhyolite and quartz-poor dacite. Dostal (1989) has proposed that the rhyolite were generated by partial melting of amphibolitefacies continental crust. In this scenario, rising basaltic magma provides the additional heat required to melt the lower crust.…”

A Review of Proterozoic to Early Paleozoic Lithotectonic Terranes in New Brunswick, Canada and their Tectonic Evolution during Penobscot, Taconic, Salinic and Acadian Orogenesis

“…The Meductic volcanic rocks possess geochemical characteristics consistent with an arc setting; therefore, they are interpreted to represent an arc that formed above a subduction zone dipping to the southeast beneath the leading edge of Ganderia (Dostal 1989;Fyffe and Swinden 1991;Fyffe 1991, 1995;Fyffe 2001). The disconformity at the base of the Belle Lake Formation (Fig.…”