The western end of the Avalon Zone in southern New Brunswick
DOI:
https://doi.org/10.4138/1661Abstract
The western end of the Avalon zone of southern New Brunswick displays a history extending from middle Proterozoic to Triassic lime. About 620 Ma magmatism above a Late Precambrian subduction zone emplaced volcanic rocks and plutons into an orthogneiss-platformal sequence basement which had been modified by mafic intrusion and thermal metamorphism about 780 Ma. About 565 Ma a bimodal sheeted dyke complex accompanied by bimodal volcanism and high-level granite was emplaced into a major mylonile zone during minor spreading or transtension. Shallow water clastic marine sediments accumulated during Cambro-Ordovician lime. From Silurian to mid-Devonian, die northwestern part of the zone subsided along steep faults which served as conduits for bimodal igneous activity. Strong Carboniferous deformation along the Bay of Fundy affected the interior of the terrane only slightly, if at all. Acadian and Taconic orogenies had little effect on this region, which acted as a relatively stable crystalline block during the Paleozoic. The exposed rocks may form a "welt" on continuous basement of similar character, which disappears north-westward beneath younger formations by down-stepping on faults, and south-eastward beneath overriding allochihons. RÉSUMÉ La terminaison occidental de la zone d' Avalon au sud du Nouveau-Brunswick montre une histoire s'étalant du Protérozoique moyen au Trias. Vers 620 Male magmalisme au-dessus d'une zone de subduction emplaça des roches volcaniques et des plutons dans un socle à orthognesis et séquence de plate-forme qui avail été modifié vers 780 Ma par une intrusion mafique et un métamorphismc thermal. Vers 565 Ma un complexe bimdal de "sheeted dikes", accompagné d'un volcanisme bimodal et d'un granite de niveau élevé, s'emplaça au sein d'une zone importante de mylonite au cours d'une faible expansion ou transtension. L'Ordovicien vit l’accumulaiion de sédiments clastiques d'eau peu profonde. Du Silurien au Dévonien moyen. la portion nord-ouest de la zone s'abaissa le long de failles à forts pendages qui agirent comme conduits pour une activité ignée bimodale. Une forte déformation carbonifère le long de la Baie de Fundy n'eut guère d'effet sur l’intérieur de la lanière. Les orogénèses acadienne et taconique n'eurent qu'un effel quelconque sur cette région qui forma un bloc crislallin relativement stable au couts du Paléozoique. Les affleuremenls peuvent conslituer un "renflemeni" sur un socle continu de même facture qui disparait vers le nord-ouesl sous les formations plus jeunes par abaissemenl sur des failles et vers le sud-est sous les allochtones chevauchanls. [Traduit par le journal]Downloads
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