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

摘要

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.