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...
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