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Zircon grains from a granitic pegmatite clast from conglomerate at the base of the Ross Island Formation on Grand Manan Island indicate an igneous crystallization age of 664.1 [+ or -] 4.6 Ma. The clast also contains abundant older inherited grains back to the Archean. Muscovite in the same clast and an additional similar clast yielded cooling ages of 607.0 [+ or -] 3.7 Ma and 619.6 [+ or -] 4.1 Ma, respectively, providing a maximum depositional age for the host conglomerate of the Ross Island Formation. The Seven Hundred Acre Island Formation in the Islesboro block in Penobscot Bay, Maine, contains a granitic pegmatite dyke of similar age, suggesting that it was close to the site of deposition of the Ross Island Formation of Grand Manan Island in the late Ediacaran. This suggestion is supported further by similarity in rock types and detrital zircon spectra between the Seven Hundred Acre Island Formation and The Thoroughfare and Kent Island formations on Grand Manan Island. Des grains de zircon provenant d'un ciaste de pegmatite granitique du conglomerat a la base de la Formation de Ross Island sur l'ile Grand Manan signalent une cristallisation ignee survenue il y a 664,1 [+ or -] 4,6 Ma. Le ciaste renferme egalement une abondance de grains herites plus ages remontant a l'Archeen. La muscovite dans le meme ciaste et un ciaste similaire supplementaire a accuse des ages de refroidissement de 607,0 [+ or -] 3,7 Ma et de 619,6 [+ or -]4,1 Ma, respectivement, ce qui definit l'age maximal de la sedimentation du conglomerat hote de la Formation de Ross Island. La Formation de Seven Hundred Acre Island dans le bloc d'Islesboro a l'interieur de la baie de Penobscot, dans le Maine, abrite un dyke de pegmatite granitique d'age similaire, ce qui laisse supposer qu'il se trouvait pres de l'emplacement de la sedimentation de la Formation de Ross Island sur l'ile Grand Manan au cours de l'Ediacarien tardif. La similarite des types rocheux et des spectres de zircons detritiques entre la Formation de Seven Hundred Acre Island et les formations de Thoroughfare et de Kent Island sur l'ile Grand Manan appuient une telle supposition. [Traduit par la redaction], INTRODUCTION Pre-Mesozoic rocks are exposed on the southeastern third of Grand Manan Island and adjacent offshore islands in the Bay of Fundy (Figs. 1, 2). Published U-Pb (zircon) ages have [...]

Abstract: Pre-Mesozoic rocks are exposed on the southeastern third of Grand Manan Island and adjacent offshore islands in the Bay of Fundy. U-Pb (zircon) ages reported here demonstrate that most [...]

Southeastern Grand Manan Island consists of explosive and effusive volcanic rocks of the Ross Island and Ingalls Head formations that include syn-eruptive sediments and hyaloclastites. Lavas are commonly amygdaloidal and/or [...]