Early Devonian bimodal volcanic rocks of Southwestern New Brunswick: petrography, stratigraphy, and depositional setting
DOI :
https://doi.org/10.4138/1659Résumé
to subaenastal volcanic belt of the northeastern United States and New Brunswick consists of a bimodal sequence of marine of New Brutfurian and Early Devonian volcanic and assocUted sedimentary rocks. The Mascarene lithostratigraphic terrane depositional styletf probably the northern extension of this belt. This paper describes the volcanic stratigraphy, eruptive and Passamaquoddy Bay geography and tectonic setting of a 125 km2 area of the Mascarene terrane located along the coast of rhyolitic and basaltic flo^a mapped includes a - 3.5 km thick bimodal and subalkaline volcanic sequence of ""^ded GeorgeBathoUthandoverlain'fiyroclastic rocks and terrigeneous shale and sandstone. These rocks were intruded by the St. which aremappable at ascale of iformablyby the Late DevonianPerry Formation. The area is divided into 53 hthologic units Hawaiian, StromboIian,Piiniana39 • Rhyolitic rc>cks are volumetrically most irnportanL phreatomagmatic tuff cone, and peperitic *«*» <™Ptive **— « represented. The mafic units form flow, scona cone. ashcloud^undandbasesurge.^yroclastic^^ felsicvokanism. The shale, sLdston^L mudsto^P08^ ^ ^ sedimentaryrockum^isafluvialdeposit Thevolca^ sedimenrReworkcdvolcamcrocrarerare A^Z^ a k r*i i i. _i ■ j- . ™.n^ units contain well-preserved cuspate and sconaceousbasaluc andrhyobticglasssha^mdi^^ concomittant with volcanism and there were no marked periods ^o]canic quiescence. Fades analysis and unit morphology indicate eruptions from multmle small volcanic centres. The basai,, flowSi ^^ ^i^y flowed from the north and northeast to the south suggesting eruption from a single rift syste, Several depositional seltings were considered, but cor^idermg consists ba^ and the subsidence history. (4) rates of sedimentation. (5) fades relations.-^ ^ (6) synvolcanic structures, the most likely setting is a volcanic plateau lacking large calderas located within a continent.! jifL RESUME La ceinture volcanique cotiere du Nouveau-Bmnswick et du nord-ouest des Etau-Uajs comprend une serie bimodale de volcanites marines a subaeriennes, d'age silurien a eodfivonien, et les roches seetimentaiies q>i leur sont associees. La Laniere lithostratigraphique de Mascarene reprfisente probablement l'extension septentrionale de c\tte cebuure au Nouveau-Brunswick. Cet article decrit la stratigraphie volcanique, les styles 6ruptifs et de de'pdt, la paleogeograpfye et l'environnement tectonique d'une region de 125 km2 au sein de la Laniere de Mascarene, sise le long du littoral de la baie de Passamaquoddy. La region levee renferme une seiie volcanique bimodale et subalcaline d'environ 3.5 km d'epaisseur forme" d*un interlitage d'epanchements rhyolitiques et basaltiques, de pyroclastites, shales et gres. Ccs roches furent recoupees par le Batholite de St. George et recouvertes en discordance par la Formation de Perry (DeVonien lardif). On divise la region en 53 unites lithologiques qui sont cartographiques a une fichelle de 1:10,000. Les roches rhyolitiques dominent en terme de volume. I,es systemes firuptifs hawai'en. strombolien, plinien et vulcanien sont presents. Les uniuSs mafiques comprennent des depots de coulee, de cone de scories, de cone de tufs phr£atomagmatique et de breche de pfiperite. Les unites felsiques se sont mises en place sous forme de retombees a^riennes (soudees ou non), de nudes cin6ritiques, de deTerlantes basales et de coulees pyroclastiques, avec aussi des coulees et des domes laviques. On reconnait trois cycles volcaniques mafiques a felsiques. Les unites de shale, gres et mudstone presentes dans la partie interieure de la section sont des depots littoraux. L'unite setlimenlairc sommittale est un d£pot fluvial. Les unites volcaniclasuqucs renferment surtout des retombces acriennes dc fragments sur les s&liments littoraux. Les volcanites remaniees sont rares. Toutes les unites sedimentaires conticnnent des eclats de vcrre rhyolitique et basall ique cuspid^s et scoriaces bien preserves, tcmoins d'un d£pot en contexte de faible energie et fori taux de sedimentation. La sedimentation £tait synchrone du volcanisme et il n'y a aucune periode prononcce dc quiescence volcanique. Une analyse des faciesetde la morphologie des unites indique des eruptions £manant deplusieurscenticsd'cmission volcaniqucs punctiformes. Par contre, les coulees basaltiques s'epancherent de facon consistente du nord el du nord-est vers le sud, ce qui suggere une Eruption a partir d'un systeme de rift unique. On a envisage plusieurs environnements de d6pot, ccpendant le plus probable est un plateau volcanique depourvu de grandes caldeiras et sitae1 au scui d 'un rift continental, vu les con train tcs imposces par (1) la composition des volcanites, (2) la nature des cycles volcaniques, (3) re'paisseurdel'assiseet This to irede la subsidence, (4) les taux de sedimentation, (5) les relations de fades et (6) les structures synvolcaniques.Téléchargements
Publié-e
1988-12-01
Comment citer
van Wagner, N. A., McNeil, W., & Fay, V. (1988). Early Devonian bimodal volcanic rocks of Southwestern New Brunswick: petrography, stratigraphy, and depositional setting. Atlantic Geoscience, 24(3). https://doi.org/10.4138/1659
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