The Acadian plutonic rocks of New Brunswick

Abstract

Extensive bimodal plutonism accompanied and followed the Acadian deformation in New Brunswick. These Acadian plutons define a Central Plutonic Belt, which is largely confined to a terrain with an Acadian trend of 030°, and a Southern Plutonic Belt, which occurs within a structural province with an Acadian and Variscan trend of 060". It has been possible to classify the Acadian plutons north of the Avalonian Platform according to their structures, textures, field relationships, mineralogy, and chemical characteristics; supplemented by radiometric age dates. Plutonic rock types include: A-B a mafic-felsic association; C-syntectonic tonalite and granodiorite; D-muscovite-bearing; F-megacrystic granitoids; H-equigranular biotite granites; and E and G-'transitional' granites. The magmatism, regardless of location, follows a common evolutionary trend and appears to comprise a sequence of intrusions from early Devonian to Carboniferous time with no significant break in the evolution. These characteristics along with the bimodal chemistry and the lack of compositional polarity suggest that the development of these Acadian plutons was not subduction-related. A time-dependent process such as radioactive heating of a thickened crust is a more probable mechanism for their genesis. Au Nouveau-Brunswick, la deformation acadienne fut accompagnee puis suivie d'un plutonisme bimodal tres etendu. Ces plutons acadiens definissent une zone intrusive centrale et une zone intrusive meridionale: la premiere se confine en grande partie dans une region qui presente une orientation acadienne de 030° alors que la seconde se trouve a 1'interieur d'une province structurale marquee par une orientation acadienne et varisque de 060°. Au nord de la plate-forme avalonlenne, les plutons acadiens ont pu etre classifies selon leurs structures, textures, relations de terrain ainsi que leurs caracterisques mineralogiques et chimiques, le tout etant complete par des datatlons radiometriques. Les roches intrusives comprennent: A-B une association mafique et felsique; C-une granodiorite et une tonalite syntectoniques; D-roches intrusives £ muscovite; F-granitoides & biotite equigranulaire; et E et G-granites "de transition". Peu importe l'endroit, on observe une tendance evolutive commune ace magmatisme qui semble comprendre une suite d'intrusions, evoluant sans interruption du Devonien inferieur au CarbonifSre. Ces caracteristiques, en plus de la bimodalite du chlmisme et de 1*absence de polarite de composition, auggerent que ces plutons acadeins ne furent pas formes par subduction. Pour engendrer ceux-cl, un processus IIS au temps, tel que le rechauffement radioactlf d'une croute qui s'est epaissie, est plus probable. [Traduit par le journal] GEOLOGIC SETTING The pre-Carboniferous rocks north of the exposed Avalonian Platform can be divided into four tectonostratigraphic zones (Ruitenberg et at. 1977). These are, from southeast to northwest, the Fredericton Trough, the Miramichi Massif, the Elmtree Inlier and the Matapedia Basin (Fig. 1). The plutonic ...

A Review of Proterozoic to Early Paleozoic Lithotectonic Terranes in New Brunswick, Canada and their Tectonic Evolution during Penobscot, Taconic, Salinic and Acadian Orogenesis

“…2). The highly deformed Cambrian to Ordovician sedimentary and volcanic strata that define this terrane are intruded by numerous plutons of Middle Ordovician and Late Silurian to Middle Devonian age (Fyffe et al , 1981Fyffe and Cormier 1979;Fyffe 1982;Fyffe et al 1988b;Whalen et al 1996bWhalen et al , 1998. The geological characteristics of the Miramichi Highlands as a whole resemble those of both the Gander Zone and Exploits Subzone of Newfoundland Fyffe 1991, 1995).…”

Stratigraphy and eruptive history of the Late Devonian Mount Pleasant Caldera Complex, Canadian Appalachians

“…Interbedded volcanic and sedimentary rocks of the Mascarene Group are variably deformed, with the youngest rocks being the least deformed. A period of granitoid 'Acadian plutonism' overlapped with and followed this volcanism (Fyffe, Pajari & Cherry, 1981). Isotopic and field evidence from these granitoids indicates that Acadian polyphase deformation took place in Silurian to Middle Devonian time (Hubacher & Lux, 1987;Bevier, 1988;MacLellan & Taylor, 1989;McCutcheon & Bevier, 1990).…”

A precise age for the Utopia Granite, southwestern New Brunswick, Canada

“…PrevIoUs dAtING oF tHe UtoPIA GrANIte Fyffe et al (1981) reported a Rb-Sr whole rock age of 406 ± 7 Ma for the Utopia Granite, and Bevier (1990) reported a preliminary U-Pb zircon age of 430 ± 3 Ma. McLeod (1990) pointed out that the latter age contradicts fossil evidence, which indicates an Early Devonian age for the Eastport Formation in the contact aureole of the granite.…”