40Ar/39Ar mineral age record of variably superimposed Proterozoic tectonothermal events in the Grenville Orogen, central Labrador
Penetratively cleaved slate–phyllite within supracrustal sequences (Seal Lake and Letitia Lake groups) in northernmost portions of the Grenville parauthochthon in central Labrador record 1018 ± 15 and 985 ± 14 Ma whole-rock 40Ar/39Ar plateau ages, which are interpreted as closely dating deformation and a concomitant low-grade metamorphism. The 40Ar/39Ar signature of Grenvillian tectonothermal effects is variably recorded in more southerly portions of the parautochthon. Locally within the extensive North Pole Brook igneous suite, there is no significant metamorphic retrogression. In these areas, igneous hornblendes record ca. 1650 Ma plateau ages similar to those suggested for emplacement of most of the suite by previously reported Rb–Sr whole-rock isochron and U–Pb zircon analyses. Low-temperature retrogression of igneous assemblages is observed throughout most of the North Pole Brook igneous terrane. Hornblende concentrates from five relatively undeformed samples are characterized by internally discordan...