Résumés
Abstract
The Benton pluton, located in the Eel River area of west-central New Brunswick, Canada, consists of two components—the Caldwell Brook quartz monzonite and Dugan Road monzogranite. Field relations suggest that the two are essentially coeval, the Dugan Road being slightly younger. The Benton pluton intrudes Cambrian to Early Ordovician sedimentary rocks of the Woodstock Group and overlying Early to Middle Ordovician calc-alkaline rhyolitic, andesitic, dacitic, and basaltic rocks of the lower Meductic Group. A new U–Pb (LA-ICP-MS) zircon age of 467 ± 2. Ma indicates that the Dugan Road monzogranite component of the Benton pluton was emplaced during the Middle Ordovician (late Dapingian to early Darriwilian). The Dugan Road monzogranite is ca. 7 million years younger than the nearby arc-related Connell Mountain tonalite and Gibson granodiorite, and ca. 13 million years younger than arc- related volcanic rocks of the Porten Road Formation, the oldest unit of the Meductic Group. The Benton pluton is interpreted to have been emplaced in an active extensional arc setting, coinciding with a shift in the focus of subduction-related volcanism from the Eel River area of New Brunswick to the Greenfield area of adjacent Maine, USA.
Résumé
Le pluton de Benton, situé dans le secteur d’Eel River dans le centre-ouest du Nouveau-Brunswick, au Canada, est constitué de deux éléments : la monzonite de quartz du ruisseau Caldwell et le monzogranite du chemin Dugan. Leurs rapports sur le terrain laissent supposer que les deux éléments sont essentiellement du même âge, celui du chemin Dugan étant légèrement plus récent. Le pluton de Benton pénètre des roches sédimentaires du Cambrien à l’Ordovicien précoce du groupe de Woodstock ainsi que des roches sus-jacentes calco-alcalines rhyolitiques, andésitiques, dacitiques et basaltiques de l’Ordovicien précoce à moyen de la partie inférieure du groupe de Meductic. Une nouvelle datation U–Pb (LA-ICP-MS) sur zircon de 467 ± 2 Ma révèle que l’élément de monzogranite du chemin Dugan du pluton de Benton s’est mis en place durant la période de l’Ordovicien moyen (du Dapingien tardif au Darriwilien précoce). Le monzogranite du chemin Dugan est plus récent d’environ sept millions d’années que la granodiorite de Gibson et la tonalite du mont Connell apparentées à un arc voisines, et plus récent d’environ 13 millions d’années que les roches volcaniques d’un arc de la Formation de Porten Road, l’unité la plus ancienne du groupe de Meductic. Le pluton de Benton est interprété comme un élément s’étant mis en place dans le cadre d’un arc d’extension active coïncidant avec un déplacement du foyer du volcanisme lié à une subduction depuis le secteur d’Eel River au Nouveau-Brunswick au secteur de Greenfield dans l’État voisin du Maine, aux États-Unis.
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