U-Pb geochronologic constraints on the crustal evolution of the Long Range Inlier, Newfoundland

The Long Range Mountains of Newfoundland expose the northeastern most basement inlier of the Appalachian Orogen. U-Pb results for two samples of basement gneiss reveal crustal formation ages of 1466 +/- 10 Ma (Western Brook Pond chamockite) and 1530 +/- 8 Ma (Cat Arm Road gneiss), indicating an affinity with Pinwarian magmatism (1510-1450 Ma) in Labrador. A third sample of basement gneiss from the Cat Arm Road dam site yielded a minimum formation age of 1631 Ma. These basement gneisses were intruded by granite plutons during two periods of Grenvillian magmatism; Group I at 1032-1022 Ma and Group II at 993-985 Ma. Group I intrusions include the 1032.0 +/- 1.5 Ma Lomond River granite and the 1022.0 +/- 2.0 Ma Lake Michel igneous suite; Group II intrusions include the 999 +/- 4 Ma Potato Hill charnockite, 993 +/- 7 Ma Horse Chops granite, 984.9 +/- 1.6 Ma Cloud River granite, and may include the Apsy granite. The metamorphic history of the Long Range Inlier is complex and three discrete Proterozoic metamorphic events can be delineated on the basis of field relationships and U-Pb dates for metamorphic minerals. M, metamorphism is a regional high-grade event that occurred prior to 1032 Ma, the emplacement age for the unmetamorphosed Lomond River granite. M-2 and M-3 occurred at 1022 and 989 Ma, respectively; coinciding with the two main periods of Grenvillian magmatism. The Precambrian crustal evolution of the Long Range Inlier is very similar to the Pinware terrane of Labrador, consistent with a single contiguous terrane presently separated by the Gulf of St. Lawrence. A surprising discovery from this study is identification of the first known occurrence of Silurian mafic magmatism in the Long Range Inlier, the 430.5 +/- 2.5 Ma Taylor Brook gabbro.