UPb zircon age of the Strange Lake peralkaline complex: implications for Mesoproterozoic peralkaline magmatism in north-central Labrador

Abstract

A fine-grained, exotic-poor granite of the Strange Lake peralkaline complex contains zircons that are dated at 1240 ± 2 Ma. This granite is one of the oldest intrusions of this ring complex and one of only a few that contain primary zircon; others contain abundant alkali zircono-silicates. Mesoproterozoic anorogenic rocks in north-central Labrador form three lithotectonic associations: Association I, anorthosite suite; II, mafic magmatism; and III, peralkaline felsic magmatism. A compilation of precise age data for a large number of these anorogenic rocks indicates that there are two main temporal-spatial episodes of anorogenic magmatism comprising Association I and II intrusions: an interior trend (A) from 1.46 to 1.42 Ga and a coastal trend (B) from 1.34 to 1.27 Ga. Temporal-spatial relationships between Association III and Association I-II intrusions suggest a genetic relationship between the Flowers River peralkaline granite (Association III, 1289 Ma) and the spatially associated Char Lake quartz monzonite (Association I, 1291 Ma). No anorthositic or mafic rocks of comparable age occur near the Strange Lake peralkaline complex (Association III) and the Red Wine Intrusive Suite (Association III). However, the close temporal relationship (1224–1250 Ma vs. 1240 Ma) between the spatially widely separated Seal Lake gabbros (Association II) and the Strange Lake peralkaline granite (∼200 km) may indicate a cotectonic relationship between these intrusions. The three episodes of anorogenic magmatic activity that occurred in north-central Labrador correlate with similar Mesoproterozoic magmatism in the Grenville Province. The Strange Lake peralkaline complex, in particular, was emplaced nearly contemporaneously with several other anorogenic felsic rocks throughout the Grenville Province, suggesting the occurrence of a large-scale event at this time.