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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 ± 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 ± 3.7 Ma and 619.6 ± 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. doi:10.4138/atlgeol.2019.009 ATLANTIC GEOLOGY 55, 265–274 (2019) 0843-5561|18|0265–0274$2.50|0 on Grand Manan Island show similarities in rock types and ages to components in the Islesboro block in Penobscot Bay in coastal Maine (Stewart et al. 2001; Reusch et al. 2018), and hence correlation with that area is also possible. The purpose of this paper is to report U–Pb zircon and 40Ar/39Ar muscovite ages from cobbleto boulder-sized granitic pegmatite clasts in a conglomerate that occurs at the base of the Ross Island Formation on Grand Manan Island (Fig. 2). Muscovite from these clasts previously had yielded K–Ar ages of 640 Ma and 590 Ma (Leech et al. 1963; Lowdon et al. 1963). The provenance of these clasts is unknown, 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 demonstrated that most of these rocks are Late Neoproterozoic to Early Cambrian (Miller et al. 2007; Fyffe et al. 2009; Fyffe 2014), and the range of ages and rock types has led to the interpretation that they correlate with the New River and Mascarene terranes of southern New Brunswick (Miller et al. 2007; Fyffe 2014). However, some units -

atlantic geology

Neoproterozoic U–Pb (zircon) and 40Ar/39Ar (muscovite) ages from granitic pegmatite clasts, basal Ross Island Formation, Grand Manan Island, New Brunswick, Canada