Zircon U–Pb ages from the Wabigoon–Manitou Lakes region, Wabigoon Subprovince, northwest Ontario

Abstract

Three distinct stratigraphic units have been recognized in the Crow Lake – Savant Lake belt. These are a basal unit consisting of high magnesium tholeiitic flows, a middle unit consisting mostly of tholeiitic to calc-alkaline pyroclastic rocks and flows, and an upper unit of high iron tholeiitic flows.A zircon U–Pb study has been carried out on seven rocks from the Wabigoon–Manitou Lakes region of this belt. In the Manitou Lakes area, a minimum age of 2755 Ma on a porphyry pluton intruded into the Wapageisi Volcanics gives a minimum age for the high magnesium tholeiitic sequence.A trondhjemite phase of the Atikwa batholith near Wabigoon Lake that is dated at 2732.2 ± 2.9 Ma has the same age within experimental error as a rhyolite flow from the Lower Wabigoon Volcanics in the same area that is dated at [Formula: see text]. However, a trondhjemite phase of the Atikwa batholith at Eagle Lake that is dated at [Formula: see text] is distinctly younger than a dacite flow collected nearby from the Lower Wabigoon Volcanics that is dated at [Formula: see text]. Both these volcanic rocks are from the middle mixed sequence.A rhyolite tuff from the Boyer Lake Volcanics, from the upper high iron tholeiitic sequence, gives a relatively young age of [Formula: see text]. An age of 2695 ± 3.6 Ma on the post-tectonic Taylor Lake stock gives a minimum age for the end of deformation.Several new techniques such as air abrasion with pyrite, crushing and abrasion, and high gradient magnetic separation have been employed to reduce the discordance of zircons. Of these, the air abrasion technique has proven to be the most effective.