Early Devonian bimodal volcanic rocks of Southwestern New Brunswick: petrography, stratigraphy, and depositional setting

Abstract

The coastal volcanic belt of the northeastern United States and New Brunswick consists of a bimodal sequence of marine to subaerial Silurian and Early Devonian volcanic and associated sedimentary rocks. The Mascarene lithostratigraphic terrane of New Brunswick is probably the northern extension of this belt. This paper describes the volcanic stratigraphy, eruptive and depositional styles, paleogeography and tectonic setting of a 125 km2 area of the Mascarene terrane located along the coast of Passamaquoddy Bay. The area mapped includes a ~ 3.5 km thick bimodal and subalkaline volcanic sequence of interbedded rhyolitic and basaltic flows and pyroclastic rocks and tenigeneous shale and sandstone. These rocks were intruded by the St. George Batholith and overlain unconformably by the Late Devonian Perry Formation. The area is divided into 53 lithologic units which are mappable at a scale of 1:10,000. Rhyolitic rocks are volumetrically most important.Hawaiian, Strombolian, Plinian and Vulcanian eruptive systems are represented. The mafic units form flow, scoria cone, phreatomagmatic tuff cone, and peperitic breccia deposits. The felsic units were emplaced as welded and nonwelded air-fall, ash cloud, ground and base surge, and pyroclastic flow deposits, as well as lava flows and domes. There are three cycles of mafic/ felsic volcanism. The shale, sandstone and mudstone units in the lower part of the section are littoral deposits. The uppermost sedimentary rock unit is a fluvial deposit. The volcaniclastic units primarily contain air-fall volcanic fragments within the littoral sediments. Reworked volcanic rocks are rare. All the sedimentary units contain well-preserved cuspate and scoriaceous basaltic and rhyolitic glass shards, indicating deposition in a low-energy environment with rapid sedimentation rates. Sedimentation was concomittant with volcanism and there were no marked periods of volcanic quiescence. Facies analysis and unit morphology indicate eruptions from multiple small volcanic centres. The basaltic flows, however, consistently flowed from the north and northeast to the south suggesting eruption from a single rift system. Several depositional settings were considered, but considering constraints based on (1) composition of the volcanic rocks, (2) nature of volcanic cycles, (3) thickness of the sequence and the subsidence history, (4) rates of sedimentation, (5) facies relationships, and (6) synvolcanic structures, the most likely setting is a volcanic plateau lacking large calderas located within a continental rift.La ceinture volcanique cohere du Nouveau-Brunswick et du nord-ouest des Etats-Unis comprend une serie bimodale de volcanites marines a subaeriennes, d 'age silurien a eodevonien, et les roches sedimentaires qui leur sont associees. La Laniere lithostratigraphique de Mascarene represente probablement l'extension septentrionale de cette ceinture au Nouveau-Brunswick. Cet article decrit la stratigraphie volcanique, les styles eruptifs et de depot, la pal6ogeographie et l 'environnement tectoniqu...

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

“…Gently south-dipping strata of the Mascarene Group lie along the southern margin of Saint George Batholith and north of the St. George Fault. They comprise an interbedded sequence of subaerial mafic and felsic flows, and red sandstone and siltstone of the Middle to Upper Silurian (Wenlockian to Ludlovian) Eastport Formation (Pickerill and Pajari 1976;Van Wagoner and Fay 1988;Van Wagoner et al 1994). The southerly dipping Eastport volcanic sequence, which yielded a U-Pb zircon date of 423 ± 1 Ma (Van Wagoner et al 2001), may well be conformable with the Waweig Formation (Fig.…”

Geological setting and petrochemistry of early Middle Devonian volcanic and gabbroic rocks in the Guysborough area, Nova Scotia

“…1). All appear to have formed in a continental, within-plate setting (this study and Blanchard et al, 1984;Bradley, 1982Bradley, , 1983Pe-Piper etal., 1989;Baldwin, 1991;Van Wagoner et al, 1989;Dostal et al, 1989Dostal et al, , 1994Doig et al, 1991;Hon et al, 1992). Thus the Sunnyville Formation is part of a continuum of extensional magmatism which extended from the Silurian in northwestern New Brunswick into the Carboniferous in the Magdalen Basin, Cape Breton Island and locally else where (e.g., Barr et al, 1994;Fyffe and Barr, 1986).…”

Geochronology of the Letete and Waweig formations, Mascarene Group, southwestern New Brunswick

“…Pickerill and Pajari (1976) correlated these intertidal to fl uvial sedimentary and associated volcanic rocks with the Eastport Formation of coastal Maine. The Eastport Formation in New Brunswick comprises amygdaloidal mafi c fl ows and agglomerate, massive to fl ow-banded felsic fl ows, welded and non-welded lapilli tuff, pisolitic tuff, peperitic breccia, and grey to maroon sandstone and conglomerate totalling ~ 4000 m (Hay 1967;Pickerill and Pajari 1976;Pickerill et al 1978;Van Wagoner et al 1988, 1994Dadd and Van Wagoner 2001). Ostracodes from both the Hersey and the Eastport formations of coastal Maine are indicative of an Early Devonian age (Berdan 1971).…”