Rubidium-strontium whole-rock ages from the Oxford Lake-Knee Lake Greenstone Belt, northern Manitoba

Abstract

Rubidium-strontium whole rock ages have been determined on rock units from the Oxford Lake-Knee Lake greenstone belt within the Superior Province in northeastern Manitoba. The Magill Lake Pluton, a post-Oxford Lake Group granitic intrusion gave an age of 2455 +/- 35 Ma (a87Rb = 1.42 x 10-11 yr.-1) and an initial 87Sr/86Sr ratio of 0.7078 +/- 0.0043. The Bayly Lake Pluton, believed to be a pre-Oxford Lake Group granodiorite gave an age of 2423 +/- 74 Ma with an initial 87Sr/86Sr ratio of 0.7029 +/- 0.0001. Volcanic rocks, of the Hayes River Group, from Goose Lake (30 km south of Gods Lake Narrows) were dated at 2680 +/- 125 Ma with an initial 87Sr/86Sr ratio of 0.7014 +/- 0.0009. The age for Magill Lake and Bayly Lake Plutons can be interpreted as the minimum ages of granitic intrusion in the area, while the age for the Hayes River Group volcanic rocks is consistent with Rb-Sr ages of volcanic rocks from other Archean greenstone belts within the northwestern Superior Province.