The Carmanville ophiolitic mélange of northeastern Newfoundland forms an olistostrome within a thick succession of Middle to Upper Ordovician flyschoid shale, siltstone, and grey-wacke. The olistostrome consists of sedimentary, volcanic, and ultramafic olistoliths ranging in size from granules to several kilometres. The matrix appears to have been derived entirely by disaggregation and disintegration of hydroplastic and thixotropic sediments. The matrix was sufficiently fluid for turbulent motion to occur in the lower parts of the olistostrome, yet viscous enough to produce alignment of fragments and a pervasive cleavage, as well as drag folds in the surrounding hydroplastic sediments. The olistoliths have been drawn from a stratigraphic column hundreds, if not thousands, of metres thick, and an area many kilometres across. A small proportion of the olistoliths were deformed and metamorphosed prior to incorporation in the olistostrome.The Carmanville ophiolitic mélange is tentatively correlated with the Dunnage mélange to define the northern margin of a sheet of ocean floor and island arc obducted toward the southeast onto an accreting continental rise in Llanvirnian–Llandeilian time. Olistostrome formation within this unstable pile commenced in post-Arenigian time, and may have continued intermittently until Llandoverian time. The olistostrome and surrounding rocks were further deformed, metamorphosed, and intruded by granitoid plutons during Silurian and Devonian time.
Previous interpretations of the stratigraphic position of a series of volcanic and sedimentary strata along the northern coast of Passamaquoddy Bay, New Brunswick, are somewhat enigmatic. Recent fieldwork has indicated that the sequence is a lithostratigraphic, biostratigraphic, and most probably a chronostratigraphic equivalent to the Eastport Formation (Gedinnian) of Maine, located a few kilometres to the west. It is proposed that henceforth, the succession be termed the Eastport Formation.
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 ...
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