Late Devonian – Early Carboniferous volcanism in western Cape Breton Island, Nova Scotia

Abstract

The Fisset Brook Formation of western Cape Breton Island and its equivalents at MacMillan Mountain and the north Baddeck River are examples of Late Devonian and Early Carboniferous volcanic sequences associated with the formation of post-Acadian successor basins in the northeastern Appalachians. They consist of bimodal basalt-rhyolite suites interbedded with alluvial fan, lacustrine, and rare fluvial sediments. The earliest volcanic products are rhyolites and somewhat evolved basalts associated with coarse sediments, followed by tholeiitic to transitional basalt flows interlayered with lacustrine-type deposits. Geochemical studies on the Fisset Brook Formation indicate extensive remobilization of alkalies, Ca, Rb, and Sr, making these elements inappropriate for determining tectonic setting or magmatic affinity. Use of less mobile elements (Ti, Nb, Y, and Zr) suggests that the basalts are tholeiitic and that the apparent alkalinity of the type section lavas is a result of alteration. We conclude that volcanism in western Cape Breton Island started at MacMillan Mountain and migrated westwards, probably towards the centre of the deepening Magdalen Basin.La formation de Fisset Brook et les sequences volcano-skdimentaires de MacMillan Mountain et North Baddeck River dans I'ouest de l'ile du Cap Breton sont des exemples de volcanisme du DCvonien superieur -Carbonifkre inferieur reliC au stage anorogtnique post-Acadien dans le nord-ouest des Appalaches. Les roches sedimentaires associees aux coulees de basalte et rhyolite suggerent un environnement propice a la formation de c8nes de dejection et de dtp8ts de type lacustre ou fluvial. Les premikres sequences de laves contiennent surtout des rhyolites et andesites basaltiques associees a des faciks proximaux; les sequences plus jeunes sont formees de basaltes tholeiitiques ou de transition interstratifies avec des dCp8ts lacustres. Nos etudes gtochimiques revelent que I'alteration des laves de la formation de Fisset Brook mobilise de preference les elements alcalins, Ca, Rb et Sr. L'utilisation d' C1Cments relativement "immobiles" (Ti, Nb, Y et Zr) indique que les basaltes sont tholeiitiques et que leur caractkre apparemment alcalin est dQ aux processus secondaires. La gtochronologie et stratigraphie des laves suggkrent I'amorce du v~lcanisme~dans la region de MacMillan Mountain, suivie d'une migration des centres Cruptifs vers I'ouest ou le centre du bassin des Iles-de-la-Madeleine.

Carboniferous volcanic rocks of the Magdalen Islands, Gulf of St. Lawrence

“…The original chemical character of the basalts in the sequence is ambiguous because of the unusual and extreme alteration that has modified the chemistry. However, the continental "within-plate" tectonic setting indicated by the data is consistent with the interpreted tectonic setting of the region during the Devono-Carboniferous (e.g., Bradley 1982;Mann et al 1983), and other basalts formed in the region during that time also appear to be tholeiitic to transitional to alkalic (e.g., Keppie and Dostal 1980;Blanchard et al 1984;Barr and Fyffe 1985). Continuing studies of the stratigraphic position and geochemistry of these volcanic rocks may lead to clarification of patterns of changing tholeiitic and alkalic character with time and place in the Fundy Epieugeosyncline, which may in turn result in a better understanding of the original chemical affinities of the basalts in the Magdalen Islands.…”

“…Localized volcanism in the Fundy Epieugeosyncline during this time was diachronous but widespread (e.g., Blanchard et al 1984), with volcanic rocks in the Magdalen Islands being some of the youngest.…”

“…In the Atlantic Canada region, these basins have been collectively referred to as the Fundy Epieugeosyncline (Howie and Barss 1975). They were the main sites of upper Paleozoic sedimentation, but volcanism was also typically part of their evolution, for example, in the Magdalen Islands (Sanschagrin 1964;Brisebois 198 l), Newfoundland (Chorlton 1980), Cape Breton Island (Kelley and MacKasey 1963;Blanchard et al 1984), northern mainland Nova Scotia (Keppie and Dostal 1980;Donohoe andWallace 1982), New Brunswick (MacKenzie 1964;Ruitenberg and McCutcheon 1980), and Maine (Schluger 1963). Most of these volcanic rock suites are bimodal, and the basaltic components are generally tholeiitic or tholeiitic transitional to alkalic (e.g., Keppie and Dostal 1980;Blanchard et al 1984).…”

The Appledore Island pluton of the Rye Complex, coastal New Hampshire and Maine, USA: geochronological and chemical evidence for the affinity of an enigmatic terrane

“…The Appledore Island pluton of the Rye Complex, coastal New Hampshire and Maine, USA Copyright © Atlantic Geology, 2014 sor basins (Blanchard et al 1984;Durling and Marillier 1993;Pe-Piper and Piper 2002). These include the ~ 340 Ma basalts of Cape Breton Island (Blanchard et al 1984;Barr et al 1994), Carboniferous basalts of New Brunswick (Fyffe and Barr 1986;Park et al 2014), 385 Ma rocks of the Guysborough area, Nova Scotia (Cormier et al 1995), 355-362 Ma basalts of the Magdalen Basin (Barr et al 1985;PePiper andPiper 1998, La Flèche et al 1998), 330 to 375 Ma Fountain Lake Group basalts of Nova Scotia (Dessureau et al 2000), and ~ 370 Ma Wamsutta Formation in the Narragansett Basin of southern New England (Thompson and Hermes 2003).…”

Late Palaeozoic sedimentation along the Appalachian orogen

“…The section consists mainly of volcanic and coarse-grained red siliciclastic rocks. In the Mabou basin the volcanics are of bimodal basalt-rhyolite suites which are apparently tholeiitic (Blanchard et al 1984). The sedimentary environments have been interpreted primarily as alluvial fans, as well as fluvial and some lacustrine systems (Schluger 1973, Fralick & Schenk 1981.…”