Probable Archean nepheline syenite plutons in the Superior Province adjacent to the Labrador Trough

Abstract

Three nepheline-bearing plutons have recently been discovered in the Superior Province northwest of Schefferville. They are apparently related miaskitic nepheline syenites, varying to leucocratic nepheline syenite, juvite, and rarely ijolite. All three plutons are crudely zoned with an increasing nepheline content towards the centres. The foliation and lineation in these rocks are the same as those in the surrounding country rocks. Together with folding, microscopic comminution, and metamorphic recrystallization, this structure suggests that these plutons were intruded prior to or during the Kenoran Orogeny. This conclusion is consistent with a K/Ar biotite minimum age of 2398 ± 72 Ma (3%) obtained for one sample.