Geochronology of Wabigoon belt granitoids, northwestern Ontario: Rb/Sr isochrons for seven late-tectonic plutons

Abstract

Whole-rock Rb/Sr isochrons are presented for seven late-tectonic granitoid plutons intruded into supracrustal rocks of the Wabigoon volcanic–plutonic belt. Age estimates range from 2461 ± 78 Ma (Ottertail Lake stock) to 2645 ± 158 Ma (Bears Passage stock). A mean age estimate by weighted pooling of the isochrons gives 2555 ± 41 Ma, while pooling 39 samples into one regression gives 2568 ± 35 Ma. These ages concur with estimates for the duration of the Kenoran orogeny.Error limits on our isochrons incorporate the duration of polydiapirism, aplitic dyking, and deuteric metasomatism. Available ages indicate that syntectonic and late-tectonic granitoid plutonism spanned a geologically short time interval (centered at 2565 ± 62 Ma) that cannot be differentiated by the Rb/Sr technique. Consistently low initial Sr ratios of 0.7008 ± 0.0006 indicate a mantle or low Rb/Sr source.