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.

A regional perspective of the Quetico metasedimentary belt, Superior Province, Canada

“…A second cycle of tholeiitic and calc-alkaline volcanism (''Keewatin' ') and associated plutonism occurred between 2755 and 2702 Ma (Davis et al 1982, with a volumetric peak at 2730-2735 Ma. Major D, deformation preceded intrusion of late plutons at 2695-2685 Ma.…”

Correction for deviations due to magnetic anisotropy of palaeomagnetic directions from the Mulcahy Gabbro, north-west Ontario

“…2) (Davis, Blackburn & Krogh 1982). Davis et al (1982) also dated the host metavolcanics rocks at between 2743 f 1 and 2735 + 41-3 Ma. Thus the Mulcahy Gabbro formed soon after the volcanic activity; and the emplacement of the Atikwa Batholith overlapped with or followed soon after the emplacement of the Mulcahy Gabbro.…”

“…The intrusion is divided into upper, middle and lower main stratigraphic zones based on modes of crystallization (Fig. 2) (Davis, Blackburn & Krogh 1982). Davis et al (1982) also dated the host metavolcanics rocks at between 2743 f 1 and 2735 + 41-3 Ma.…”

Geology of the Palladium-rich Legris Lake Mafic-Ultramafic Complex, Western Wabigoon Subprovince, Northwestern Ontario

“…Granitoid complexes (2732 Ma to 2708 Ma), with Na-rich marginal phases, which are accompanied by rare mafic to ultramafic stocks. These granitoids are associated with comagmatic volcanic rocks (Davis et al, 1982;Edwards and Davis, 1984); and 3. Post-tectonic granitoid stocks (2709 Ma to 2685 Ma), in and marginal to the greenstone belts.…”