New U-Pb baddeleyite ages for Neoarchean and Paleoproterozoic mafic dyke swarms of the southern Nain Province, Labrador: Implications for possible plate reconstructions involving the North Atlantic craton

Abstract

We present ten new ID-TIMS U-Pb baddeleyite ages for late Neoarchean to Paleoproterozoic dyke swarms cutting Archean gneisses of the Hopedale block (North Atlantic craton, NAC). An age of 2505 ± 4 Ma for a NNE-trending pyroxenite dyke represents the first date for extension-related mafic magmatism of this antiquity in the Labrador portion of the NAC. Four samples of N-S to NNE-trending Kikkertavak dykes yield ages between 2238 ± 6 Ma and 2216 ± 2 Ma, defining a minimum age range and distribution for this extensive swarm. A single NNE-trending dyke is dated at 2169 ± 13 Ma, representing a new magmatic event at this age in Nain Province, but is equivalent in timing to the well-known Biscotasing dykes in the southern Superior craton. Three NW-trending dykes (termed Ellen Island dykes) yield ages of 2051 ± 6 Ma, 2051 ± 1 Ma and 2050 ± 2 Ma, and represent part of a newly-recognized but important swarm in southern Nain craton. The 2.05 Ga dykes better define a vast radiating fan of dykes that include Kangâmiut and MD3 dykes of southern West and South-West Greenland, respectively. A U-Pb baddeleyite age of 1800 ± 4 Ma has been obtained for a fourth, NW-trending (“Ussiranniak Lake”) dyke, which also represents a newly-revealed mafic magmatic event, both in the Labrador and Greenland portions of the NAC. The results presented here are unique for Labrador, but invite comparison with other Neoarchean and Paleoproterozoic mafic dykes elsewhere in the North Atlantic craton and other Archean cratons (e.g., Superior, Kola-Karelia, Zimbabwe). Multiple precise age matches, dyke geochemistry, and dyke geometries for several swarms allow a preliminary level testing of possible reconstructions involving the North Atlantic and eastern Superior cratons.