Petrochemistry of contrasting late Precambrian volcanic and plutonic associations, Caledonian Highlands, Southern New Brunswick

Sandra M. Barr, Chris E. White
1988 Atlantic geology  
The eastern Caledonian Highlands of southern New Brunswick consist mainly of greenschist-facies or subgreenschistfacies volcanic, sedimentary, and plutonic rocks generally considered to be typical of Late Precambrian sequences in the Avalon T errane of the northern Appalachian Orogen. As aresult of regional mapping combined with petrological studies and radiometric dating, these rocks in the eastern Caledonian Highlands have been divided into two contrasting groups. The older group, apparently
more » ... group, apparently ranging in age from about 600 to 630 Ma, consists of metatuff aceous rocks ranging from mafic to felsic in composition, fine-grained volcanogenic metasedimentary rocks (slate and phyllite), arkosic metasedimentary rocks, and dioritic to granitic plutons. The volcanic rocks appear to be calc-alkalic, and both the volcanic and plutonic rocks were formed in a subductionrelated tectonic setting. In contrast, the other group of rocks appears to be about 550 Ma in age and consists of arkosic sedimentary rocks, subaerial rhyolite and basalt flows, laminated siltstone, felsic lapilli tuff, volcaniclastic conglomerate, and plutons of mainly gabbroic and syenogranitic composition. These units typically are much less deformed and metamorphosed than the older group of units. The volcanic and plutonic rocks appear to be cogenetic bimodal suites, with petrochemical characteristics suggesting that they formed in a rifting environment within an older volcanic arc. Les Monts Caledoniens orientaux (Nouveau-Brunswick meridional) sont constitues surtout de roches volcaniques, sedimentaires et plutoniques metamorphisees dans le facies des schistes verts (ou presque), generalement considerees comme typiques des series tardiprecambriennes de la Laniere d'Avalon de l'Orogene appalachien septentrional. A la suite d 'un lever regional combine a des etudes petrologiques et des datations radiometriques, on a divise ces roches des Monts Caledoniens orientaux en deux groupes distincts. Le plus ancien groupe, qui s'echelonne vraisemblablement d 'environ 600 a 630 Ma, comprend des roches a metatufs de composition mafique a felsique, des roches metasedimentaires volcanogeniques a grain fin (ardoise et phyllade), des roches metasedimentaires arkosiques et des plutons dioritiques a granitiques. Les volcanites semblent etre calco alcalines. Les volcanites comme les plutonites furent engendrees dans un contexte tectonique lie a une subduction. Par contre, l 'autre groupe de roches semble dater d 'environ 550 Ma et comprend des roches sedimentaires arkosiques, des epanchements subaeriens de basalte et de rhyolite, des siltstones lamines, des tufs a lapilli felsiques, des pouaingues volcaniclastiques, ainsi que des plutons a composition principalement gabbroi'que et syenogranitique. Ces unites sont typiquement beaucoup moins deformees et metamorphisees que l 'est le groupe d 'unites plus ancien. Les volcanites et les plutonites semblent appartenir a des lignees cogenetiques bimodales; leurs caracteres petrochimiques suggerent une genese au sein d 'un arc volcanique en contexte de rift. [Traduit par le journal]
doi:10.4138/1662 fatcat:bpu2vwogxzg6hogus7nnlxm2ei