Petrogenesis and tectonic evolution of the Lake of the Woods greenstone belt, western Wabigoon Subprovince, Ontario, Canada.

• Main Author: Ayer, John Albert.
• Format: Thesis
• Language: unknown
• Published: Université d'Ottawa / University of Ottawa 1999
• Subjects: Geology.; Canada; Don Lake; Keewatin
• Online Access: https://dx.doi.org/10.20381/ruor-16022; http://www.ruor.uottawa.ca/handle/10393/8849

The Neoarchean Lake of the Woods greenstone belt is located immediately south of Kenora, Ontario within the western part of the Wabigoon Subprovince of the Superior Province. The supracrustal rocks have been subdivided into 3 major lithostratigraphic assemblages. The Lower Keewatin is the oldest assemblage with a zircon U-Pb age of 2738 +/- 2.0 Ma. It consists of Mg and Fe tholeiitic metabasalts. The Upper Keewatin Assemblage disconformably overlies the Lower Keewatin Assemblage. Two geochemically distinct volcanic suites are recognised. The dominant suite consists of compositionally diverse calc-alkaline metabasalt to metarhyolite. Felsic volcanic rocks from this suite yield U-Pb zircon ages ranging from 2712--2723 Ma. A coeval suite of mafic to ultramafic volcanic rocks consists of tholeiitic metabasalt, komatiitic metabasalt and metakomatiite. The Electrum assemblage unconformably overlies the Upper Keewatin Assemblage in the northern part of the belt. It consists of metaconglomerates, metasandstones and minor metavolcanic rocks having detrital ages indicating deposition after 2699 Ma. The volcanic rocks consist of shoshonitic meta-andesite and calc-alkaline metarhyolite. The Electrum shoshonites are part of a chemically diverse suite of potassic igneous rocks emplaced at a late stage in the tectonic evolution of the western Wabigoon Subprovince. The suite is also comprised of silica undersaturated ultrapotassic rocks of the Falcon Island pluton (2695 Ma) and silica saturated monzodiotitic intrusions such as the Don Lake stock. The Falcon Island pluton consists of nepheline-bearing, alkali feldspar syenite and alkali feldspar melasyenite with lessor amounts of clinopyroxenite, monzodiorite, and peraluminous alkali feldspar syenite. A genetic linkage of gold mineralization to oxidized alkaline intrusions has been proposed on the basis of mineral chemical studies from the Abitibi Subprovince. Nd isotopic data from a compositional spectrum of representative rocks from the major stratigraphic units of the belt indicates a major change in the isotopic signature of mantle sources at about 2.7 Ga. Comparison of Nd, Pb and Sr isotope data from a number of well documented potassic suites across the southern Superior Province indicates heterogeneity was widespread in the post 2.7 Ga mantle. The correlation of this isotopic data suggests mixing between a juvenile depleted mantle component and an enriched end-member with isotopic characteristics approaching those of the ancient granitic terrain of Winnipeg River Subprovince and the Opatica and Pontiac metasedimentary subprovinces. (Abstract shortened by UMI.)